ALBERT

Description: 〈p〉Publication date: 1 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 181〈/p〉 〈p〉Author(s): Ponnusamy Saravanan, Anil K. Gupta, Hongbo Zheng, Mruganka K. Panigrahi, Muthusamy Prakasam〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Multi-proxy record of benthic and planktic foraminifera, total organic carbon and carbon and oxygen isotope ratios from Core SK291/GC15, off the coast of Goa, eastern Arabian Sea reveals significant paleoceanographic and paleoclimatic turnovers during ~6000 to 1700 calibrated years before the Present (cal yr BP). Benthic foraminiferal census data was analyzed with multivariate techniques including factor and cluster analyses of highest ranked species from the studied core that enabled to identify seven biofacies. The record suggests centennial to millennial-scale changes in the surface conditions driven by monsoon-linked upwelling in the eastern Arabian Sea during the studied interval. Various benthic biofacies combined with isotope and planktic foraminiferal data suggest that depletion of dissolved oxygen and increase in organic productivity in the study area was caused by intense monsoonal upwelling since the middle Holocene. The results suggest that during 5400–4700 and 3000–2500 cal yr BP the southwest (SW) monsoon was strong leading to intense upwelling in the study area as reflected by increased 〈em〉Globigerina bulloides〈/em〉 percentages. These were generally warmer intervals in the northern hemisphere. The SW monsoon significantly weakened (abrupt decrease in 〈em〉G. bulloides〈/em〉 population) during 4700–3400 cal yr BP roughly coinciding with a long arid phase in the Indian subcontinent and a cold interval in Europe. Our record suggests an abrupt increase in SW monsoon intensity during ~3000 to 2500 cal yr BP, when a pronounced change in benthic biofacies is also noted that suggests a major shift in the sub-surface conditions. Our data document a prolong weak SW monsoon phase beginning at ~4600 cal yr BP, little earlier than 4.2 ka event, in the eastern Arabian Sea.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019302676-ga1.jpg" width="307" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 181〈/p〉 〈p〉Author(s): Jinxia Chen, Qingyun Nan, Tiegang Li, Rongtao Sun, Hanjie Sun, Jian Lu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Changes in paleoenvironments from 3500 to 1300 cal. yr BP have been documented by a high-resolution grain-size and organic carbon isotope record in core Z8 from the Shandong mud wedge in the southern Yellow Sea (YS). The sensitive grain-size component, sorting coefficients and 〈em〉δ〈sup〉13〈/sup〉〈/em〉C〈em〉〈sub〉org〈/sub〉〈/em〉 values were used to identify the paleohydrologic variations and the intensity of the East Asian winter monsoon (EAWM). The coarse fraction of sediment, together with organic isotope and sea surface temperature (SST) data, shows a weak EAWM during 3500–2300 cal. yr BP, a gradual increase in the EAWM from 2300 to 1700 cal. yr BP and an enhanced EAWM since 1700 cal. yr BP. Superimposed on this general trend, several prominent short-lived strong EAWM episodes peaked at approximately 3300, 3100, 2900, 2750, 2620, 2220, 1900, 1700 and 1400 cal. yr BP. The paleoenvironmental record matches ancient Chinese historical climate records as well as socioeconomic changes, with lower economic levels occurring during stronger EAWM episodes. The results show that prosperous stages of ancient Chinese dynasties mainly occurred in weak EAWM periods, while collapses and/or changes in ancient Chinese dynasties generally occurred during cold periods with a strong EAWM. We suggest that the persistent short-lived strengthening of the EAWM could have exerted a remarkable influence on ancient agricultural societies through decreases in both winter temperature and monsoonal precipitation.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019302640-ga1.jpg" width="270" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 183〈/p〉 〈p〉Author(s): Alp Ünal, Şafak Altunkaynak, Ömer Kamacı, Istvan Dunkl, Jeffrey A. Benowitz〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Post-collisional magmatism in western Anatolia produced several granitic bodies represented by shallow level intrusions. In this study, we present field, geochronology and geothermo-barometry results of the Solarya Pluton (SP, NW Turkey) in order to better understand its emplacement into the different levels of the crust. The SP consists of three main plutonic members showing different textural properties; the northern part of the plutonic body is represented by K-feldspar megacrystalline granodiorite (KFMG) with distinct porphyritic texture and southern part is made up of microgranite-granodiorite (MGG) displaying microgranular texture whereas haplogranite, which displays graphic/granophyric textures, is represented by a thin aureole between the SP and basement rocks.〈/p〉 〈p〉Field relations, petrography and geothermo-barometry studies combined with 〈sup〉40〈/sup〉Ar/〈sup〉39〈/sup〉Ar and U-Pb zircon dating results suggest that different members of the SP were emplaced into different levels of crust with different mechanisms. The KFMG (〈sup〉40〈/sup〉Ar/〈sup〉39〈/sup〉Ar − 23.2 Ma, U-Pb – 21.8 Ma) began its emplacement forcefully in the relatively deeper levels in the crust (av. 1.65 kbar; av. 797 °C; 6.1 km depth). After this stage, MGG (〈sup〉40〈/sup〉Ar/〈sup〉39〈/sup〉Ar – 22.6 Ma, U-Pb – 21.2 Ma) was passively emplaced into the shallow levels (av. 0.69 kbar; av. 745 °C; 2.4 km depth) via cauldron subsidence and in the latter stages the sheet intrusive rocks (haplogranite 〈sup〉40〈/sup〉Ar/〈sup〉39〈/sup〉Ar – 21.6 Ma and hypabyssal association) were emplaced into the ring faults at 1.5 km depth. Forceful to passive emplacement of the SP into the upper crust occurred under Aegean extensional tectonics. Our study contributes to examination of the granite ascent and emplacement within other extensional provinces worldwide.〈/p〉 〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303311-ga1.jpg" width="500" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 29 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Juye Shi, Zhijun Jin, Quanyou Liu, Zhenkai Huang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉There are multiple sets of lacustrine source rocks in the Paleogene of the Jiyang Depression, Bohai Bay Basin, Eastern China, which are main targets in the terrestrial shale oil exploration. Compared with marine shales, lacustrine fine-grained rocks are more complex in their mineralogical compositions, sedimentary structures and vertical stacking patterns. Therefore, it is of great theoretical and practical significance to carry out petrological characterization and lithofacies classification in lacustrine fine-grained rocks. Based on observations in cores and thin sections as well as elemental and organic geochemical analyses, this study systematically analyzes petrological characteristics of Eocene lacustrine fine-grained sedimentary rocks in the Jiyang Depression from perspectives of mineralogical compositions, sedimentary structures and organic matter abundance. Three end members (carbonate minerals, clay minerals and terrigenous clastic minerals), together with organic matter abundance and sedimentary structure, are employed to establish a lithofacies classification scheme that is suitable for fine-grained rocks in the Jiyang Depression, Eastern China. A total of 7 lithofacies types are recognized, such as the organic matter-rich laminated calcareous mudstone lithofacies and the moderately organic matter-rich layered calcareous mudstone lithofacies. Through analysis of lithofacies from the bottom to the top of the drilling well, sixth-order sequence units are found to have good correspondence to lithofacies assemblages. Based on consideration of magnetic susceptibility, mineral content, and geochemical proxies, these sixth-order sequence units are divided into three types of lithofacies assemblages, namely the Type A lithofacies assemblage corresponding to the dominantly rising base level, Type B lithofacies assemblage corresponding to the dominantly falling base level, and Type C lithofacies assemblage with the isostatic base level. Among them, the Type C lithofacies assemblage is the most favorable for shale oil exploration and development. Results of this study are expected to not only deepen understanding of lithofacies and its genesis and origin of lacustrine fine-grained rocks, but also provide a theoretical basis for shale oil exploration and development.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303542-ga1.jpg" width="363" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 20 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Jian-Bo Zhou, Wei Han, Ming-Chun Song, Long Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Laiyang Basin is located in the northern margin of the Sulu high-pressure and ultrahigh-pressure (HP-UHP) metamorphic belt. The sediment source and depositional time of the Laiyang Basin can provide important insights into the exhumation mechanism of the Sulu Orogen and the formation of the Tancheng-Lujiang (Tan-Lu) Fault, but have not been well constrained. In this study, seven samples were collected from typical sections of the Laiyang and Qingshan groups in the southern margin of the Laiyang Basin in the Sulu Orogen. LA-ICPMS U-Pb dating of detrital zircon from these samples yielded ages from 3145 Ma to 115 Ma and can be divided into four groups: (1) 3145–1728 Ma, which indicate a provenance from the Precambrian basement rocks of the North China Craton; (2) 908–522 Ma, which are consistent with the ages of the protolith of the Sulu HP-UHP rocks; (3) 240–220 Ma, which are identical to the ages of the HP-UHP metamorphism. This suggests that the HP-UHP rocks of the Sulu Orogen had been exposed to the surface and contributed to the deposition of the Laiyang Group by the Early Cretaceous; (4) 148–115 Ma (weighted mean age: 125 ± 0.5 Ma; MSWD = 1.2), which, as the main group, suggests that the major source of the sediments in the Laiyang Group was from Early Cretaceous igneous rocks. These young ages, combined with the ages of 119 ± 1 (MSWD = 0.7) Ma determined from the overlain Qingshan Group, confine the depositional age of the Laiyang Group to 119–125 Ma. Further comparison of detrital zircon U-Pb age spectrum between the Laiyang Basin and the Hefei Basin indicates that these two basins were developed independently, rather than developed from single basin and then truncated by the Tan-Lu Fault as suggested by previous studies. Based on the formation age of the Laiyang Basin and other age constraints, we further suggest that the Tan-Lu Fault was formed during the Late Triassic to Early Jurassic. The Mesozoic geological settings in the Sulu Orogen, including the sediments of the Laiyang Basin, Early Cretaceous magmatic intrusive and detachment activities of the Wulian Fault, imply that the Cretaceous exhumation of the Sulu HP-UHP belt was consistent with a metamorphic core complex model.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303086-ga1.jpg" width="500" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 183〈/p〉 〈p〉Author(s): Yu Zhu, Shao-cong Lai, Jiang-feng Qin, Ren-zhi Zhu, Fang-yi Zhang, Ze-zhong Zhang, Bao-ping Gan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The occurrence of A-type granites following adakitic granites can provide unique insights into the tectonic evolution of subduction zone. This paper presents a comprehensive study of zircon U-Pb-Hf isotopes and whole-rock geochemistry on the Neoproterozoic gabbro-diorites, biotite granites, and K-feldspar granites in the southwestern margin of the Yangtze Block, South China. Zircon U-Pb dating of three distinctive intrusions yield concordant ages of 810.4 ± 2.0 Ma for gabbro-diorites, 800.3 ± 2.1 Ma for biotite granites, and 749.1 ± 2.0 Ma for K-feldspar granites. The gabbro-diorites are sodic and calc-alkaline rocks with low SiO〈sub〉2〈/sub〉 (52.62–53.87 wt%), medium MgO (2.67–3.41 wt%), high Fe〈sub〉2〈/sub〉O〈sub〉3〈/sub〉T (7.18–7.49 wt%) and CaO (5.68–7.50 wt%) contents. They display high Th/Zr and Rb/Y ratios but low Nb/Zr and Nb/Y ratios. Together with their positive whole-rock εNd(t) (+1.0 to +1.5) and zircon εHf(t) values (+3.66 to +8.18), we suggest that these gabbro-diorites were derived from the partial melting of depleted lithospheric mantle modified by subduction-related fluids. The biotite granites display relatively high Sr contents (335–395 ppm), Sr/Y ratios (38.9–54.3), low Y (7.04–9.71 ppm) and Yb contents (0.78–1.08 ppm), resembling the adakitic granites. Their low Mg〈sup〉#〈/sup〉 (36–41) values, Cr (2.94–3.59 ppm) and Ni (1.32–1.55 ppm) contents as well as positive εNd(t) (+0.5 to +0.6) and εHf(t) values (+1.62 to +8.07) indicate that they were formed by partial melting of thickened juvenile mafic lower crust, probably within the existence of garnet. The K-feldspar granites have high SiO〈sub〉2〈/sub〉 (76.61–77.14 wt%) and alkalis (Na〈sub〉2〈/sub〉O + K〈sub〉2〈/sub〉O = 8.55–9.69 wt%) contents, high 10,000 * Ga/Al (2.56–2.80) ratios and differentiation index (95.3–96.9), indicating the affinity to highly fractionated A-type granites. We suggest that these A-type granites were mainly generated by the partial melting of felsic crustal rocks under low pressure condition and subsequently extensive fractional crystallization is significant. Taking into account previous studies from the western Yangtze Block, South China, we propose that the gabbro-diorites, adakitic granites and A-type granites in this study were formed in persistent subduction process during the Neoproterozoic.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303293-ga1.jpg" width="278" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 20 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Nozomi Hatano, Kohki Yoshida, Yoshiko Adachi, Eiji Sasao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Bulk chemical composition and mineral composition of the Pliocene sediments in southwest Japan reveal the effects of source rock compositions and grain sizes, as well as the relationship between sedimentary environments and the degree of chemical weathering in the Pliocene warm period. A wide variation in the degree of chemical weathering, source rock compositions and grain sizes was observed with vertical and spatial changes in the sedimentary environment. Coarse-grained sediments, deposited in sandy channels and their floodplains, indicate a lower but wide range of CIA values. This result suggests that the degree of chemical weathering can be modified by changes in grain size due to hydrologic processes. In contrast, stagnant water sediments, composed of homogeneous fine-grained sediments, display a wide variety of REE compositions and Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉/SiO〈sub〉2〈/sub〉 ratios mainly caused by variation in source rock compositions and grain sizes. However, the CIA values of the stagnant water sediments are over 90, such that these sediments display a tight cluster near the Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 apex on the Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉-(CaO + Na〈sub〉2〈/sub〉O)-K〈sub〉2〈/sub〉O ternary diagram. This study demonstrates CIA values are generally above 90, which is due to the increased leaching of Ca, Na, and K with exposure to under intense chemical weathering conditions even if the source rocks and grain sizes are variable. Regardless of the wide variety of source rock compositions and grain sizes, REE and kaolinite-rich clay mineral concentrations in these sediments are indicative of the intense weathering conditions that prevailed in the Pliocene period (3–4 Ma) in southwest Japan.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 183〈/p〉 〈p〉Author(s): Wei Qu, Yuan Gao, Qin Zhang, Ming Hao, Qingliang Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉North China is located on the N–S seismic belt of mainland China and is characterized by dense faults and intense seismicity. We analyzed the current regional crustal deformation using GPS observations from 1999 to 2007 and 2011–2017. We then established a dynamic finite element model based on the geological structure, geophysical parameters, and GPS velocity constraints to analyze the strain-stress features. Finally, we discuss the rationality of the simulation results, the variations in crustal activity, which may have been caused by the post-earthquake impact of the 2011 Mw 9.0 Tohoku and 2008 Mw 7.9 Wenchuan earthquakes, and the geodynamics of North China. Most parts of North China exhibited extensional stress in an approximately NW–SE direction during 2011–2017. In the two study periods, the maximum shear strain rates predominantly occurred in western North China; the central and eastern parts had relatively smaller values in 2011–2017. These characteristics indicate that the post-earthquake impact of the Tohoku earthquake significantly influenced most parts (central and eastern) of North China, whereas the Wenchuan earthquake mainly affected the western part. Our work quantitatively described the variations in current crustal movement velocities, stress-strain fields, and fault activity rates in North China. These characteristics indicate that the unique tectonic environment, intense crustal activity, and earthquake-prone nature of North China require continuous research attention. The results obtained in this study not only portray the current tectonic activity deformations but also reveal recent geodynamic processes in North China.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303116-ga1.jpg" width="500" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 183〈/p〉 〈p〉Author(s): Rui Bao, Guodong Jia, Chuanlun Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We performed an extensive survey of total organic carbon (OC) and stable OC composition of in the deep South China Sea sediments from the International Ocean Discovery Program (IODP) Expedition 349 Sites U1431, U1433 and Ocean Drilling Program (ODP) Leg 184 Site 1148. Our results reveal dramatic spatial and temporal variations in organic geochemical characteristics among the three Sites. Before ~8 Ma, OC deposited at Site U1431 may be predominantly terrigenous, whereas OC deposited at Sites U1433 and 1148 is mainly of marine origin. After ~8 Ma, OC accumulation at the three Sites progressively increases, mainly due to enhancement of marine primary productivity and input of terrestrial organic matter; the three sites receive mainly marine OC, whereas Sites U1433 and 1148 receive relatively more terrestrial OC compared with Site 1431. Additionally, methane concentrations vary from ~20 to ~100,000 ppmv at Site U1433 and from ~10 to ~600 ppmv at Site 1148 with higher geothermal gradients (78 and 84 °C/km, respectively). In contrast, methane concentrations are 〈5 ppmv at Site U1431 with lower geothermal gradient (14.8 °C/km). Such high methane concentrations and ratios of methane to ethane at Site U1433 suggest that the gaseous hydrocarbons in the southwestern sub-basin (deep water depth, 〉4000 km) are primarily sourced from microbial production. Our findings suggest that the sources, trajectories, and fates of OC buried in the deep South China Sea since the mid-Miocene are spatially and temporally variable, controlled by sedimentological processes in the sub-basins, and regional tectonic evolution and long-term paleoenvironmental changes.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S136791201930313X-ga1.jpg" width="384" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 183〈/p〉 〈p〉Author(s): Kang Li, Eric Kirby, Xiwei Xu, Guihua Chen, Junjie Ren, Duo Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Crustal extension along north-south graben characterizes active deformation within the central Tibetan Plateau. However, the geodynamic significance of these fault systems remains uncertain, in part reflecting sparse data regarding the onset of extension, rate(s) of slip, and paleoseismic histories along these faults. The Dong Co fault is located to the north of the dextral Beng Co fault in central Tibet. Based on the interpretation of satellite images, we use unmanned aerial vehicle (UAV) topographic surveying and 〈sup〉14〈/sup〉C dating of two offset fluvial terraces to characterized active slip along the Dong Co fault of 1.2 +0.3/−0.3 m and 3.7 +0.5/−0.4 m during the past 550–1060 yr BP and 3880–6290 yr BP, respectively. These results indicate that the slip rate of the Dong Co fault during the latter half of the Holocene has been 0.7 +0.3/−0.2 mm/yr. Fault displacement and scaling relationships imply that the most recent earthquake was approximately Mw ~ 7.0. Together with the dextral Beng Co fault system, the Dong Co fault appears to record stretching of a wedge-shaped domain bounded by conjugate strike-slip faults. Our study supports models in which extension along normal faults can accommodate differential stretching between conjugate strike-slip faults.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303141-ga1.jpg" width="391" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 183〈/p〉 〈p〉Author(s): Gaokui Wu, Changsong Lin, Haijun Yang, Jingyan Liu, Yongfu Liu, Hao Li, Xianzhang Yang, Jun Jiang, Qiaolin He, Dengkuan Gao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Investigation of major unconformities and large-scale palaeo-uplifts that developed during basin deformation is key in determining the geodynamic setting and hydrocarbon accumulation. Based on the integral analysis of seismic, logging, and outcrop data, the distribution and erosion amounts of Mesozoic major unconformities, the uplifts of the Tabei Uplift and the geodynamic setting in the Kuqa–Tabei region of the Tarim Basin are documented in this study. The Tabei Uplift underwent four stages of uplifts, resulting in four regional angular unconformities and significant changes in palaeo-geomorphology. The deformation occurring at the end of the Permian is characterised by the uplift in the Midwest and the development of an angular unconformity (TT) with maximum erosion thickness of 1200 m. Another deformation occurred at the end of the Triassic, leading to significant uplift of the palaeo-uplift and producing an extensive angular unconformity (TJ) with maximum denudation thickness of 400 m. The end-Jurassic deformation resulted in another uplifting along the palaeo-uplift and generated a regional unconformity (TK) with maximum erosion thickness of 500 m. The Late Cretaceous deformation is characterised mainly by the development of the Wensu Palaeo-uplift in the western margin of the study area. The associated angular unconformity (TE) has a limited distribution mainly along the palaeo-uplift with maximum erosion thickness of 300 m. Four stages of uplifts are attributed to the Palaeo–Tethys oceanic closure; the Qiangtang collision; the Lhasa collision; and the Kohistan collision, respectively. Triangular unconformity belts in the paleo-uplift slope area are favourable for petroleum accumulation.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303098-ga1.jpg" width="500" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 183〈/p〉 〈p〉Author(s): Martin R. Gillespie, Rhian S. Kendall, A. Graham Leslie, Ian L. Millar, Thomas J.H. Dodd, Timothy I. Kearsey, Thomas P. Bide, Kathryn M. Goodenough, Marcus R. Dobbs, Michael Kim Woon Lee, Kiefer Chiam〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Six plutons of granitic to gabbroic rocks have been recognised in the poorly exposed ground of north and east Singapore using new data from borehole cores and field observations. Five of the plutons were emplaced sequentially during the period 285–230 Ma, and these have been grouped within a single parent unit (〈em〉Bukit Timah Centre〈/em〉) in a new lithodemic framework for Singapore. These plutons record the development of early Permian to Triassic arc-related magmatism towards the southern end of the Sukhothai Arc system of Thailand, Peninsular Malaysia and Indonesia. Compositional trends in the plutons record decreasing crustal contribution as the arc matured. The volcanosedimentary succession underlying southwest Singapore records contemporaneous deposition in the forearc basin, and includes pyroclastic units of sufficient thickness and extent to be assigned ‘member’ status in a new lithostratigraphical framework for Singapore. The largest pyroclastic unit, which is 〉150 m thick, developed as volcanic activity peaked at 〈em〉c.〈/em〉 242 Ma and is correlated with a large (probably caldera-forming) eruption of one of the Permo-Triassic plutons. The composition, typology and age of the Bukit Timah Centre plutons confirm their affinity with Eastern Belt intrusions of the Eastern Province (one of three granitoid provinces in Southeast Asia), and support a widely accepted model that Eastern Province granitoids formed in an Andean-type setting as Palaeo-Tethys crust descended beneath the Indochina–East Malaya block. Widespread development of hydrothermal-tuffisite in the Permo-Triassic intrusions is correlated tentatively with rapid uplift following slab breakoff, when arc activity ceased in the Singapore region in the interval 〈em〉c.〈/em〉 230–205 Ma. A sixth pluton, much younger than (and unrelated to) the Bukit Timah Centre, was emplaced in northeast Singapore in the Upper Cretaceous.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019302925-ga1.jpg" width="217" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 183〈/p〉 〈p〉Author(s): Ying Xiong, Xiucheng Tan, Zhifeng Zuo, Guoliang Zou, Mingjie Liu, Yun Liu, Ling Liu, Di Xiao, Jie Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Palaeokarsts contain important information about subaerial exposures due to sea-level regression, which has been considered as a dominant genesis of reservoirs. Herein we describe a typical sedimentary core section of the Middle Ordovician Majiagou Formation that records multi-stage penecontemporaneous karstification in North China. Petrographic observations and stable isotopic data reveal high-frequency penecontemporaneous subaerial exposure and resulting karstification. Evidence for this includes erosional surfaces, gypsum breccias, facies-controlled dissolution vugs and vadose infillings, fabric-selective dissolution, and negative carbon and oxygen isotopic excursions. Karstification generally occurred in the middle and upper parts of an upward-shallowing sequence within a single depositional cycle, leading to meteoric water dissolution of shoals and mounds. This significantly enlarged the primary pores and generated new reservoir space. As such, high-quality hydrocarbon reservoirs became well developed, which are regularly and cyclically stacked at locations a few meters below the multiple exposure surfaces. Reservoir porosity also varies systematically with the high-frequency sedimentary cycles, and is generally at a maximum in the middle and upper parts of a cycle. The multi-stage penecontemporaneous subaerial exposure and resulting karstification reflect high-frequency changes in relative sea level in North China at this time, thereby providing a framework for identifying thin carbonate reservoirs in and around the Ordos Basin.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303219-ga1.jpg" width="409" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 12 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Gege Hui, Sanzhong Li, Pengcheng Wang, Yanhui Suo, I.D. Somerville〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Earthquake geohazards that occur throughout the Borneo Block, especially in SW Borneo, cannot be reconciled within the classical earthquake mechanism and a uniform stress field, and unfulfilled earthquake forecast for many years. In this paper, we present a new inventory of 37 Borneo earthquakes, and focal mechanisms show that in NE Borneo earthquakes and aftershocks are dominated by NW-trending normal faults, in East Borneo earthquakes are controlled by the reactivation of NW-trending sinistral strike-slip faults, and the NE-trending thrusts acted as the main seismogenic faults in the SE Borneo seismicity zone. We calculated the Coulomb stress and observed the shallow faults exhibiting a high coefficient response to the Coulomb stress change and all these earthquakes under the Coulomb failure regime have decreased by the stress shadows or are triggered by dynamic stress increase and propagation. We performed a research using the horizontal GPS velocity displacements and vertical seismic sections and found that the micro-blocks convergence occurred here corresponding to the Coulomb stress distribution, and can best explain the earthquake mechanism within the “Borneo Block”. Additionally, the earthquakes in SW Borneo showing a concordant focal mechanism along the Red-River Fault-Tinjar Fault- Sumatra Trench, are deduced to have formed along the “Sunda Block” boundary. Finally, the micro-block boundaries determined from the heatflux map can be effective in describing the main and aftershocks distribution in SE Asia, and the deep-shallow coupling dynamic model is proposed to solve the stress loading for these crustal-scale earthquakes and the responses to plate convergence in SE Asia.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉 〈p〉A simplified micro-blocks convergence model and seismogenic zone of the SE Asia〈/p〉 〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303074-ga1.jpg" width="281" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 10 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Mengyan Shi, Quanlin Hou, Chunming Wu, Quanren Yan, Hao Y.C. Wang, Nannan Cheng, Qian W.L. Zhang, Zhen M.G. Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Dunhuang region is located to the south of the Central Asian Orogenic Belt and connecting the Tarim Craton westerly and North China Craton easterly, respectively. It is an important position for understanding the geodynamics and tectonic framework of Central Asia. However, the issue about whether it is a Phanerozoic orogen or a Precambrian block is still controversial. Magmatic arcs are the most prominent and laterally persistent structural elements of orogenic belts and used to reconstruct now-disrupted orogenic belts. This paper concerns the petrogenesis and tectonic setting of andesitic-dacitic-rhyolitic volcaniclastic rocks and dacitic porphyries in the Sanweishan area, northern Dunhuang region. Volcaniclastic rocks overlie the metasedimentary rocks by fault and dacitic porphyries intrude into the metasedimentary rocks. The calc-alkaline signature and relative enrichment of large-ion lithophile elements of volcaniclastic rocks and dacitic porphyries seemingly favor a subduction setting. Zircon U-Pb dating results reveal the deposition at 424-414 Ma for volcaniclastic rocks and emplacement at ca. 364 Ma for dacitic porphyries. The coeval granitoid plutons in the Sanweishan area show arc geochemical signature and are originated from partial melting of the subducted sediments based on the available data. Paleozoic volcanic-subvolcanic rocks and plutons in this area probably represent a magmatic arc developed on the accretionary complex, resembling the arc magmatic rocks formed in the Nankai complex, SW Japanese Island arc. Our results provide constraints on the existence of the Paleozoic magmatic arc in the northern Dunhuang region and suggest the so-called “Dunhuang block” is virtually a Phanerozoic orogen rather than a Precambrian block.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303062-ga1.jpg" width="166" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 182〈/p〉 〈p〉Author(s): Jing-Yuan Chen, Jin-Hui Yang, Ji-Heng Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The major elemental and oxygen isotopic features of Cretaceous granitoids in the coastal area of southeastern China cannot be adequately explained by existing Sr-Nd isotopic models of two-component crust-mantle mixing. In this paper, we report the whole-rock elemental, and Sr-, Nd-, and Hf-isotopes, and the zircon U-Pb age and Hf-O isotopic compositions for the Puqian, Danyang, Qingliangshan, Nanyu, and Qishan plutons in northeastern Fujian of this area to further investigate their petrogenesis. The examined rocks included pyroxene diorite, monzodiorite, granodioritic enclave, monzogranite and alkali-feldspar granite. Zircon U-Pb dating gave crystallization ages of 115 Ma for the Puqian monzogranite and granodioritic enclave, 97–109 Ma for the Danyang monzogranite, 99 Ma for the Nanyu pyroxene diorite, 97 Ma for the Qishan alkali-feldspar granite, and 97–103 Ma for the Qingliangshan alkali-feldspar granite. Our new Sr-Nd-Hf-O isotopic and petrogenetic studies of these granitoids showed that, aside from the ancient crustal component (δ〈sup〉18〈/sup〉O = 7.5‰, ε〈sub〉Hf〈/sub〉(t) = −10) and the mantle-derived magma (δ〈sup〉18〈/sup〉O = 5.3‰, ε〈sub〉Hf〈/sub〉(t) = 2), a separate juvenile low δ〈sup〉18〈/sup〉O crustal source (δ〈sup〉18〈/sup〉O = 4.2‰, ε〈sub〉Hf〈/sub〉(t) = 2) must be involved. Since the emplacement of the diorite-monzodiorite-granodiorite-monzogranite suite and the A-type granite was coeval with pull-apart basins and bimodal volcanic rocks, the Cretaceous granitoids in northeastern Fujian, coastal area of southeastern China, were emplaced in an extensional setting, possibly due to the backarc extension and the changing drifting direction of the paleo-Pacific plate.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019302913-ga1.jpg" width="386" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 183〈/p〉 〈p〉Author(s): Hongxu Mu, Dan-Ping Yan, Liang Qiu, Wen-Xin Yang, Ruo-Yan Kong, Ling-Xiao Gong, Shubing Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Upper Triassic Xujiahe Formation is a succession of continental clastic rocks in the western Sichuan Basin, China. This formation has previously been regarded as deposited in a foreland basin linked to the NE-SW-striking Longmen Shan Thrust Belt. However, this hypothesis is questionable due to the presence of faults within the Longmen Shan Thrust Belt. Focusing on the Late Triassic proto-basin, we obtained new data from both outcrops and boreholes, which provide information on the sedimentary facies and provenance in the basin. The results show that the basin was originally striking E-W and that the depocentre migrated southward during the Late Triassic. Palaeocurrent indicators and detrital zircon age data reveal that the Upper Triassic strata were derived mainly from the Qinling Orogenic Belt, with a minor component of detritus derived from the South China Block. Detrital zircon U-Pb ages of ~228 Ma, from the bottom of the Xujiahe Formation, constrain the timing of onset of clastic deposition. Our results suggest that the Late Triassic western Sichuan Basin was a foreland basin at the southern front of the Qinling Orogenic Belt.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019302901-ga1.jpg" width="330" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 182〈/p〉 〈p〉Author(s): Ling Tang, Xiongqi Pang, Yan Song, Zhenxue Jiang, Shu Jiang, Qianwen Li, Hongan Zhang, Youdong Yang, Xiaohui Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉With the increasing demand for hydrocarbons, exploration tends to be deeper and unconventional resources. However, whether there are the lower limits for exploration depth or thermal maturity (R〈sub〉o〈/sub〉) appears to be particularly essential. It is of considerable significance to determine the lower limit of hydrocarbon generation (LLHG) since this limit can provide guidelines for hydrocarbon potential estimation. According to the mechanisms of hydrocarbon generation and expulsion, five methods are combined to determine and verify the LLHG, whose values can be expressed by LLHG〈sub〉(Ro)〈/sub〉 and LLHG〈sub〉(H)〈/sub〉. Source rock samples from the Paleogene Shahejie Formation (Es) in the Dongpu Depression were taken as an example to determine the LLHG, and then controlling factors of the LLHG were discussed. LLHG〈sub〉(Ro)〈/sub〉 values for Es range from 3.23% to 3.97% (average 3.71%) and LLHG〈sub〉(H)〈/sub〉 values range from 5244 m to 5525 m (average 5433 m). Regionally, LLHG values display obvious differences between the northern and southern of depression. LLHG values in the north are roughly larger than those in the south. In the northern depression, the LLHG〈sub〉(Ro)〈/sub〉 values are ranging from 3.61% to 3.97% (average 3.81%) and LLHG〈sub〉(H)〈/sub〉 values are ranging from 5415 m to 5545 m (average 5488 m). However, in the southern part, the LLHG〈sub〉(Ro)〈/sub〉 values range from 3.20% to 3.74% (average 3.48%) and the LLHG〈sub〉(H)〈/sub〉 values range from 5265 m to 5375 m (average 5278 m). The main controlling factors for LLHG diversity between the north and the south of depression are organic matter (OM) type and abundance, formation temperature and pressure.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉 〈p〉Based on the definition and theoretical model of the LLHG (a), four methods including hydrocarbon generation potential (b〈sub〉1〈/sub〉), residual hydrocarbon amount (b〈sub〉2〈/sub〉), organic element variation (b〈sub〉3〈/sub〉) and expulsed hydrocarbon amount (b〈sub〉4〈/sub〉) are used to calculate the value of LLHG, the results are verified by the thermal simulation experiment (c).〈/p〉 〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019302809-ga1.jpg" width="478" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 182〈/p〉 〈p〉Author(s): Dongdong Liu, Zhuo Li, Zhenxue Jiang, Chen Zhang, Ziya Zhang, Jianbo Wang, Dongxu Yang, Yan Song, Qun Luo〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Evaluating the influences of laminae on shale pore structures is vital to understand the enrichment mechanism of lacustrine shale gas. This study investigates lacustrine shales from the lower Cretaceous Shahezi Formation in the Changling Sag, southern Songliao Basin, NE China, using mineralogical and geochemical analyses, CO〈sub〉2〈/sub〉 & N〈sub〉2〈/sub〉 adsorption, and high-pressure mercury intrusion porosimetry (MIP), to compare pore structure characteristics between laminated and massive shales, and elucidate their main controlling factors. Our results show that, laminae in lacustrine shales from the Shahezi Formation include those clay-rich, organic-rich, and silty ones, and minor carbonate-rich ones. Micropores in both laminated and massive shales show tri-modal distributions with main peaks at 0.47–0.54 nm, 0.57–0.63 nm, and 0.80–0.85 nm, respectively; however, the laminated shales exhibit great variations in micropore volumes among different samples. Mesopores within the laminated shales are smaller than those in the massive shales, and their pore volumes (PV) are about 1/3 less than those of the massive shales. This is due to that the laminated shales are rich in slit-like pores whereas the massive shales have more plate-like and ink-bottle pores. Thermal maturity (R〈sub〉o〈/sub〉) and total organic carbon (TOC) contents are the essential factors controlling the development of micropores and mesopores in the laminated shales, however they show weak effects on macropore development in this formation; this may be related to that shales from the Shahezi Formation generally have low TOC contents and type III kerogen. Clay minerals and quartz both have weak relevance to pore development in this formation.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019302871-ga1.jpg" width="482" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 182〈/p〉 〈p〉Author(s): Xiaohua Teng, Xiaomin Fang, Alan J. Kaufman, Chenglin Liu, Jiuyi Wang, Jinbo Zan, Yibo Yang, Chunlian Wang, Haiming Xu, Ruth F. Schulte, Nadine M. Piatak〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Jianghan Basin, Central China, contains a thick, continuous sequence of early Cenozoic evaporite-bearing deposits that provide a wealth of information about early Cenozoic climate change and evaporites accumulation in East Asia. However, the paleoclimatic history of the basin and its effect on the evaporites are largely unknown. We obtained a deep drill core (SKD1, 2346.5 m long) from the late Cretaceous to early Eocene evaporite-bearing deposits in the Jianghan Basin. Detailed analyses of the lithofacies, mineralogy and geochemistry of the core indicate that salinization and deepening of the lake occurred (corresponding to the Yuyang Formation to the lower Xingouzui Formation), followed by desalting and shallowing (corresponding to the upper Xingouzui Formation). Reconstruction of the spatiotemporal evolution of the evaporites in the Jiangling depression suggests a transition from semi-arid conditions in the late Cretaceous to extremely arid conditions in the initial stage of the Eocene. The climate then became semi-humid during the deposition of the upper Xingouzui Formation, indicating a monsoon or monsoon-like climate in East Asia during the early Eocene. The southward migration of the depocenter of the Jiangling depression, coupled with a warm and extremely arid climate, resulted in the precipitation of evaporites during the accumulation of the upper Shashi Formation and the lower Xingouzui Formation. These results indicate great potential for identifying potash resources within the subsag in the southern Jiangling depression.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019302883-ga1.jpg" width="500" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 182〈/p〉 〈p〉Author(s): Hakim Saibi, Mohamed Amrouche, Abdel-Rahman Fowler〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Sinkholes and subsurface cavities can pose a real challenge to the stability of engineering constructions due to the risk of ground collapse and subsidence. The city of Al-Ain (UAE) is known to have several geo-hazards related to shallow sinkholes and karst cavities that have been reported in the locally outcropping formations. In this study, a micro-gravimetric survey was carried out around Al-Ain city in order to explore the subsurface density distribution of the karstified formations. A total number of 452 gravity measurements, covering an area of approximatively 1600 km〈sup〉2〈/sup〉 were used to invert the 3D density distribution to a depth of 1500 m. From this inversion, we have distinguished seven abnormally low density bodies ranging in size from 75 m to 750 m within the cavernous limestone Asmari Formation, consistent with a complex deep cavity system. The discovered cavities follow the local structural trend along the NW-SE direction, and lie within the high-risk areas of the geohazard map of Al-Ain city, in zones considered unstable in former geotechnical studies. The likely origin of the cavity systems is the dissolution of bedrock in water circulating in the limestone formations, along a connected shallow and deep fracture network. Further geophysical studies will be required to adequately map and investigate each deep cavity system, and to distinguish between the deep cavities and the shallow cavities reported in the area.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019302895-ga1.jpg" width="493" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 183〈/p〉 〈p〉Author(s): Han-Ao Li, Jin-Gen Dai, Shi-Ying Xu, Bo-Rong Liu, Xu Han, Ya-Nan Wang, Cheng-Shan Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We report new apatite fission track (AFT) ages and thermal modeling results from the central Songpan-Ganzi, central and easternmost Lhasa, and eastern Qiangtang blocks to provide robust constraints on the extent and expansion of the Proto-Tibetan Plateau. Our results reveal two main stages of rapid cooling events in different geological units. The central Songpan-Ganzi, central Lhasa and eastern Qiangtang blocks underwent a phase of rapid cooling event during the Paleocene-Early Eocene (~62–40 Ma) followed by extremely slow cooling since then. Such a sharp transition from relatively rapid to very slow cooling in approximately 40 Ma in a large area, suggest the eastern part of the Proto-Tibetan Plateau had formed since 40 Ma. The easternmost Lhasa block experienced a stage of rapid cooling during the Late Eocene-Oligocene (~40–24 Ma). This stage of rapid cooling event was coeval with the first stage of rapid cooling event in the Longmen Shan thrust belt, suggestive of the eastward expansion of the eastern part of the Proto-Tibetan Plateau. Our Paleogene AFT ages and their corresponding rapid exhumation, synthesized with other thermochronological and paleoaltimetry data, are not consistent with those of the predictions from the channel flow model. Instead, these observations favor the outward extrusion model. The eastward expansion of the Proto-Tibetan Plateau improved the previous northward and southward growth model.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S136791201930327X-ga1.jpg" width="488" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 184〈/p〉 〈p〉Author(s): Guangbao Du, Qingju Wu, Xuemei Zhang, Jing He, Liye Zou, Yangyang Feng, Jie Liu, Fabio Romanelli〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We present a Pn wave velocity and anisotropy model of the central segment of the North-South Seismic Belt in China, where there are numerous stable basins and active faults, making this segment attractive for extensive studies. The model was obtained by a tomographic analysis of 49,973 Pn wave phase readings collected by the China Earthquake Networks Center and temporary stations in Yunnan and Sichuan. The tomographic velocity model shows that the average Pn wave velocity is 8.06 km/s; prominent high-velocity (high-V) anomalies are visible under the Sichuan Basin, the Zoige Basin and the Ordos block, which clearly outline their tectonic margins. A pronounced low-velocity (low-V) zone is observed from the Songpan-Ganzi block to the Chuan-Dian and Daliangshan blocks, suggesting the presence of hot material upwelling. The station delay data show a gradual variation from negative to positive values, possibly reflecting a crustal thickness variation from the southwest to the northeast of the study area. A correlation between the Pn wave anisotropy and the distribution of velocity anomalies is observed: anisotropy is relatively weaker in the high-V anomaly zones beneath stable basins, while it is stronger in the low-V anomaly zones and the high-to-low-V anomaly transition zones. The high-resolution velocity and anisotropy tomographic model that we obtained could also provide a better understanding of the study area seismicity, since the occurrence of strong earthquakes seems to be related to the presence and strength of lateral heterogeneities at the uppermost mantle level.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019302937-ga1.jpg" width="228" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 183〈/p〉 〈p〉Author(s): Heng Peng, Jianqiang Wang, Chiyang Liu, Shaohua Zhang, Massimiliano Zattin, Nan Wu, Qi Feng〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Cenozoic outward growth of the Tibetan Plateau is traditionally considered to be responsible for the arcuate structures in the northeastern Tibetan Plateau. However, it is still unclear how pre-Cenozoic tectonics contributed to this unique geomorphic setting. To decipher the Meso-Cenozoic tectonic evolution, we systematically summarize the published thermochronological data and perform a low-temperature thermochronology study on Paleozoic-Mesozoic samples from the Haiyuan-Liupanshan region. Apatite fission-track ages from the new samples vary widely, ranging from 158.4 Ma to 34.4 Ma. Apatite fission-track and (U-Th-Sm)/He thermal history modeling, constrained by zircon fission-track data and geological evidence, indicate that this area experienced multiple stages of cooling from the Late Triassic to the Cenozoic. These cooling events include (i) Late Triassic-Early Jurassic, (ii) Late Jurassic-Early Cretaceous, (iii) Late Cretaceous-Early Cenozoic, and (iv) Late Cenozoic (~7 Ma). Late Triassic-Early Jurassic cooling was driven by the collision of the Nouth China Plate and the Sorth China Plate. The Late Jurassic-Early Cretaceous tectonothermal event is interpreted as a record of the intracontinental orogeny in East Asia. It is possible that Late Cretaceous-Early Cenozoic exhumation was the far-field response to the Neo-Tethyan subduction under the Lhasa terrane. In addition, Late Cenozoic (~7 Ma) rapid cooling in the Yueliangshan Range (southern part of the Haiyuan-Liupanshan region) was a result of the intense activation of the easternmost Haiyuan fault, in response to the outward growth of the Tibetan Plateau. These findings suggest that pre-Cenozoic tectonics played an important role in the growth of the present-day northeastern Tibetan Plateau edifice.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303189-ga1.jpg" width="287" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 183〈/p〉 〈p〉Author(s): Wei Zhang, Jinqiang Liang, Jiangong Wei, Pibo Su, Lin Lin, Wei Huang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Geochemical data for hydrate gases acquired from the GMGS3 and GMGS4 gas hydrate drilling expeditions conducted by the Guangzhou Marine Geological Survey (GMGS) are used to explore the origin of hydrate gases and their relationship to deep hydrocarbon reservoirs, and to evaluate the contribution of different genetic types of gases to the formation and accumulation of gas hydrates in the Shenhu area of the northern part of the South China Sea (SCS). Compositionally, methane is the dominant gas (〉90%) in the void gas and pressure core gas. In addition, as much as ~3% of the gas is composed of C〈sub〉2+〈/sub〉 hydrocarbons, including ethane, propane, iso-butane, butane, iso-pentane, and n-pentane. The δ〈sup〉13〈/sup〉C-CH〈sub〉4〈/sub〉 and δD-CH〈sub〉4〈/sub〉 values indicate a mixed biogenic-thermogenic origin for the hydrate-forming gas. The methane isotope correlation indicates that the source of the hydrate gas is closely related to the deep conventional gas reservoirs discovered in the Baiyun Sag-Panyu Low Uplift area. Both the hydrate gases and the deep reservoir gases are sourced from the hydrocarbon kitchens in the Baiyun Sag, revealing a paragenetic relationship within the same petroleum system. The composition of the hydrocarbons and the isotopic variation of methane with depth suggest that the thermogenic gas was likely affected by compositional and isotopic fractionation during the long-distance migration from the deep source rocks to the shallow gas hydrate stability zone (GHSZ). The impact of biodegradation on a solely thermogenic gas could also affect the final composition of the hydrate-forming gas. Analysis of the GHSZ based on gas hydrate compositions suggests that the occurrence of thermogenic gas could also indicate the coexistence of structure I (S〈sub〉I〈/sub〉) and structure II (S〈sub〉II〈/sub〉) gas hydrates in the Shenhu area, with the S〈sub〉II〈/sub〉 hydrates accumulating in or below the lower part of the S〈sub〉I〈/sub〉 GHSZ. The confirmed presence of S〈sub〉II〈/sub〉 hydrates in the Shenhu area relocated the base of the GHSZ deeper than was indicated by the bottom simulating reflector, which warrants further study in future explorations for gas hydrates in the Shenhu area.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303050-ga1.jpg" width="262" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 183〈/p〉 〈p〉Author(s): Samurdhika Rathnayake, Robert Tenzer〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Global geoidal undulations are often used as the constraining parameter to model the mantle convection pattern, while gravity data are typically applied to interpret the lithospheric structure. In more recent studies, especially after launching the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite gravity-gradiometry mission, gravity gradient measurements have also been used in various geoscience applications. The main motivation of using gravity gradients is to provide a more conclusive information about a spatial localization of investigated phenomena. In geophysical studies, such implications are particularly related to a probably better detection of investigated lithospheric structures, such as active tectonic margins. In this study, we address this aspect by comparing interpretational characteristics from gravity and gravity gradient information. The Bouguer and mantle gravity gradients are used for this purpose to interpret the lithospheric structure beneath the Indian Ocean as well as the (adjacent) continental lithospheric structures (such as the East African Rift System). Our results confirm that gravity gradient more closely reproduces some tectonic and volcanic features, such as oceanic subductions, volcanic island arcs, and convergent continental tectonic margins. Similarly, mid-oceanic spreading ridges are localized slightly better in the gravity gradient map. Our findings also indicate that the interpretational quality cannot be improved by using directly observed gravity gradients. The reason is that these interpretations require applying gravimetric forward modelling techniques in order to enhance a particular lithospheric structure.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S136791201930286X-ga1.jpg" width="500" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 181〈/p〉 〈p〉Author(s): 〈/p〉

Description: 〈p〉Publication date: Available online 30 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Dibyashakti Panda, Bhaskar Kundu, Vineet K. Gahalaut, Claude Rangin〈/p〉

Description: 〈p〉Publication date: Available online 29 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Yang Wang, Ping Wang, Weipeng Ge, Renjie Zhou, Lindsay M Schoenbohm, Bo Zhang, Jinjiang zhang, Zhaode Yuan, Xiaofeng Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Cona-Oiga rift (COR) is the easternmost member of a series of ∼N-S trending Cenozoic rifts in the southern Tibetan Plateau. The Yarlung River flows from west to east, across the COR and exhibits diverse river morphology along strike. We analyze tributary fluvial longitudinal profiles in the Yarlung drainage and the published strain rate field on both sides of the rift in order to gain knowledge about its development and crustal deformation patterns within the plateau interior. Tributaries on the western side of the rift have relatively low normalized steepness index (〈em〉k〈sub〉sn〈/sub〉〈/em〉). Concave curves in χ-elevation plots and cross-divide contrasts in χ, mean relief, and mean gradient, indicate ongoing river reorganization in this region. In contrast, high topographic relief and steep stream channels developed on the eastern side. In addition, spatial variations in negative dilatational strain rates indicate diverse crustal shortening and regional uplift across the COR. We suggest that the Cona-Oiga rift plays an important role in accommodating deformation associated with the continuing indentation of the eastern Himalayan syntaxis. Tectonic forcing might be the dominant factor controlling landscape evolution across the COR.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019301361-ga1.jpg" width="386" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 25 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Peter Lunt〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉This review outlines how SE Asian tectonic and stratigraphic studies could be more closely linked. Many tectonic papers on the region include comments on stratigraphic evidence, and stratigraphic papers often allude to tectonic events, but this paper highlights the benefits of a more detailed integration of the two fields of study into a single geological model, by using inductive sequence stratigraphic methods supported by geohistory plots. The South China Sea and North Borneo region has been traditionally been divided into Provinces, each with its own distinct stratigraphy. A handicap in merging all the Provinces into one geological model has been the inconsistent application of basic biostratigraphy, and some examples are given that illustrate that more careful documentation of a complex data set is required in future work.〈/p〉 〈p〉The inductive stratigraphic method requires increased analytical work to calibrate seismic data, but even on current data an episodic stratigraphic history is indicated, and a single tectono-stratigraphic framework for the whole region is emerging, with a greatly simplified and consistent terminology. This review examines the impact of these methods on one important period of transition around the Oligo-Miocene boundary.〈/p〉 〈p〉The summary given for the Oligo-Miocene transition questions the viability of the commonly cited slab-pull tectonic model, as both the historical order of geological events and geographic spread of effects does not fit that model as currently understood.〈/p〉 〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S136791201930121X-ga1.jpg" width="264" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 26 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Caineng Zou, Keyu Liu, Rukai Zhu〈/p〉

Description: 〈p〉Publication date: Available online 29 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Dan Wang, Xiang-Kun Zhu, Nina Zhao, Bin Yan, Xian-Hua Li, Fuqiang Shi, Feifei Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Radiometric calibration of the Cryogenian glaciations is critical in understanding the nature of the climatic, geochemical and biological events in the Cryogenian period. However, the timing of termination of the Sturtian glaciation remains unsettled. Here we carried out new SIMS U-Pb zircon dating from two tuff layers at the non-glacial Datangpo Formation at the Jiangjunshan section in Guizhou, South China. The SIMS U-Pb zircon analyses yield U-Pb concordia ages of 659.3 ± 2.4 Ma and 657.3 ± 3.2 Ma for the two tuff layers, respectively. The age of 659.3 ± 2.4 Ma obtained from the tuff layer occurring at the boundary between Sturtian diamictites and the non-glacial Datangpo Formation is regarded as the best age estimate for the termination of Sturtian glaciation in South China. This new U-Pb age is well consistent with those from the previous studies, suggesting a globally synchronous termination of the Sturtian glaciation at ca. 659 Ma. The onset of the Marinoan glaciation has been estimated to occur at ca. 649 Ma, based on the radiometric age obtained in this study and previous cyclostratigraphic results. Thus it is argued that the Marinoan glaciation was a long-lived glaciation and spanned approximately 14 million years.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019301282-ga1.jpg" width="273" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 28 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): K. Vijaya Kumar, W.G. Ernst, C. Leelanandam, J.L. Wooden〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We determined SHRIMP U-Pb ages of zircons from three mafic granulite samples of the polymetamorphosed, multiply-deformed Kondapalli-Ongole domain of the Eastern Ghats Belt (EGB), SE India. Our goals are: 1) to evaluate the origin of zircons in the high-grade mafic granulites; and 2) to clarify the petrotectonic evolution of magmatic and metamorphic rocks along the SE margin of India. The zircons record three distinct Paleoproterozoic U-Pb age groups: igneous protoliths of the mafic granulites apparently crystallized at ∼1715 Ma, and underwent granulite-facies high-temperature metamorphism at ∼1676 Ma, with a subsequent fabric-defining garnet-granulite grade metamorphic overprint at ∼1610 Ma. Based on textures, cathodoluminescence images, and geochemistry, we identified three zircon types among the ∼1610 Ma zircons: Type I and II zircon grains recrystallized or newly grown in equilibrium with feldspar and garnet, respectively; Type III zircons crystallized from aqueous anatectic melt in quartzofeldspathic veins. Some zircons of all the three types show alteration effects. The ∼1715 Ma event likely represents formation of the Kondapalli-Ongole magmatic arc crust, whereas the ∼1610 Ma high-grade metamorphic event reflects suturing of the arc to proto-India and cratonization of the EGB. The interval between the formation of U-poor, low Th/Yb zircons (〈em〉equilibrated with garnet〈/em〉) and U-rich, high Th/Yb zircons (〈em〉equilibrated with fluid-rich melt〈/em〉) is geologically insignificant, suggesting that tectonic accretion of the EGB, its final suturing, and orogenic collapse took place rapidly.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019301336-ga1.jpg" width="180" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 29 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Tianjian Yang, Xiaoming Sun, Guiyong Shi, Yang Lu, Yu Fu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Ailaoshan-Red River shear zone (ASRR) in SE Tibet accommodated about 20% convergence of the Cenozoic India-Asia continental collision which resulted in complicated thermal history during Paleocene to Miocene. The Ailaoshan massif, in the middle part of ASRR, is characterized by extensive mylonitization and migmatization, but the exact timing of the large scale left lateral shearing and whether the crustal partial melting occurred prior to or coeval with the left lateral shearing remain controversial. The detailed structural observation suggests the pre-kinematic nature of the Ailaoshan corundum with respect to the left lateral shearing. LA-ICP-MS U-Pb dating of metamorphic zircon and monazite inclusions in the pre-kinematic Ailaoshan corundum obtained a weighted 〈sup〉206〈/sup〉Pb-〈sup〉238〈/sup〉U ages of 28.0 ± 0.5 Ma (MSWD = 3.3; N = 27) and 28.3 ± 0.3 Ma (MSWD = 1.8; N = 18), respectively, which gave an upper limit on the initiation of the left lateral shearing in the Ailaoshan massif. Moreover, the presence of protogenetic siliceous melt inclusions in the pre-kinematic corundum indicates that the Cenozoic crustal anatexis of the Ailaoshan massif has occurred before the left lateral shearing. Along with available geochronological data, the crustal partial melting of the Ailaoshan massif was attributed to joint results, which at least include the Neoproterozoic convergence, the Triassic Indosinian Orogeny, and the Cenozoic evolution as a response to the India-Asia continental collision.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019301300-ga1.jpg" width="365" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 177〈/p〉 〈p〉Author(s): Mohamad Ramdhan, Sri Widiyantoro, Andri D. Nugraha, Jean-Philippe Métaxian, Nicholas Rawlinson, Asep Saepuloh, Said Kristyawan, Andry S. Sembiring, Agus Budi-Santoso, Antoine Laurin, Ahmad A. Fahmi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Mt. Merapi, located in central Java, Indonesia, is one of the most active volcanoes in the world. It has been subjected to numerous studies using a variety of methods, including tomographic imaging, in an attempt to understand the structure and dynamics of its magmatic plumbing system. Results of previous seismic tomographic studies that include Mt. Merapi poorly constrain the location of its underlying magma source due to limited data coverage. In order to comprehensively understand the internal structure and magmatism of Mt. Merapi, a project called DOMERAPI was conducted, in which 53 broadband seismic stations were deployed around Mt. Merapi and its neighbourhood for approximately 18 months, from October 2013 to April 2015. In this study, we compare Vp, Vs, and Vp/Vs tomograms constructed using data obtained from local (DOMERAPI) and regional seismic networks with those obtained without DOMERAPI data. We demonstrate that the data from the DOMERAPI seismic network are crucial for resolving key features beneath the volcano, such as high Vp/Vs ratios beneath the Merapi summit at ∼5 km and ∼15 km depths, which we interpret as shallow and intermediate magma bodies, respectively. Furthermore, west-east vertical sections across Mt. Merapi, and a “dormant” (less active) volcano, Mt. Merbabu, exhibit high Vp/Vs and low Vp/Vs ratios, respectively, directly beneath their summits. This observation likely reflects the presence (for Mt. Merapi) and absence (for Mt. Merbabu) of shallow magma bodies near the surface.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019301312-ga1.jpg" width="500" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 27 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Huan Li, Zhe-Kai Zhou, Thomas J. Algeo, Jing-Hua Wu, Wei-Cheng Jiang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Neoproterozoic tectonic evolution of South China is important for understanding the tectonic assembly of modern East Asia. As a key sedimentary-volcanic sequence, the Banxi Group in South China contains a wealth of information on the genesis of the Nanhua rift basin, which is linked to the assembly and breakup of the Rodinia supercontinent. However, the geochronological and tectonic signatures of the Banxi Group in the Jiangnan orogenic belt are still controversial. In this study, the tuffaceous rocks in the Banxi area were analyzed with regard to their whole-rock major- and trace-element concentrations, and zircons in the tuffaceous rocks were analyzed for LA-(MC)-ICPMS U–Pb ages, trace elements and Hf isotopic compositions. These rocks are well preserved and show high concentrations of SiO〈sub〉2〈/sub〉 (61.7–72.3%), K〈sub〉2〈/sub〉O (1.7–4.5%), Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 (8.4–18.9%), Rb (55–195 ppm) and Th (4.3–12.4 ppm), low concentrations of TiO〈sub〉2〈/sub〉 (0.24–0.95%), Sr (54–128 ppm), Nb (5.6–12.1 ppm) and Ta (0.4–0.9 ppm), LREE enrichment (La〈sub〉N〈/sub〉/Yb〈sub〉N〈/sub〉 = 6.6–14.7), and negative Eu anomalies (Eu/Eu* = 0.45–0.85). They have chemical affinities with high-K calc-alkaline S-type granites and exhibit continental volcanic-arc characteristics. The zircons are magmatic in origin and yield a U-Pb age distribution with three peaks: Neoproterozoic (597–949 Ma, mostly 761–788 Ma), 2) Mesoproterozoic (1122–1387 Ma), and 3) Paleoproterozoic (1952–2605 Ma). The Neoproterozoic zircons yield slightly different, but overlapping, mean ages as a function of lithology: 770.2 ± 3.7 Ma for tuffaceous siltstones, 768.2 ± 6.7 Ma for tuffs, and 766.4 ± 5.2 Ma for tuffaceous slates. All zircons in the study units exhibit high U/Yb ratios (0.1–0.6) and low Hf (7106–12554 ppm) and Y (305–6617 ppm) contents, suggesting continental crustal derivation. Some of the zircons have larger LREE contents and smaller Ce anomalies relative to typical magmatic zircons, suggesting later fluid modification. The Neoproterozoic zircons have εHf(t) values ranging from –16.5 to 16.7 (mostly –8 to 10), corresponding to crustal model ages (T〈sub〉DM〈/sub〉〈sup〉C〈/sup〉) of 0.97 to 2.73 Ga. These ages imply a mixture of juvenile (i.e., Neoproterozoic) arc-derived material and Paleoproterozoic heterogeneous crust as magmatic sources for the tuffaceous sequences. Based on our integrated dataset, we infer that the Banxi tuffaceous rocks were extrusive equivalents of S-type granitoids that show volcanic-arc affinities but that were nonetheless deposited in a post-collisional and subsequent rifting-related extensional setting within the newly amalgamated South China Block. We account for this apparent contradiction by proposing that, following collision of the Yangtze and Cathaysia blocks, a rapid breakup of the continental arc caused by deep mantle upwelling led to initiation of post-collisional extension and rifting in the Nanhua Basin.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S136791201930135X-ga1.jpg" width="279" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 177〈/p〉 〈p〉Author(s): Endra Gunawan, Sri Widiyantoro, Zulfakriza, Irwan Meilano, Cecep Pratama〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉GPS data after the 2 July 2013 〈em〉M〈sub〉w〈/sub〉〈/em〉 6.1 Aceh earthquake provide valuable information for understanding the postseismic behavior of a strike-slip fault in northern Sumatra, Indonesia. The analysis of postseismic deformation following the 2004 Sumatra-Andaman earthquake and the 2012 Indian Ocean earthquake suggest that the ongoing deformation affected northern Sumatra between July and December 2013. The postseismic deformation of the 2013 Aceh earthquake is herein investigated, with the contribution of poroelastic rebound and viscoelastic relaxation evaluated. The results suggest that the model displacement of those two mechanisms failed to estimate the data. The afterslip analysis of the 2013 Aceh earthquake, on the contrary, fits the data very well with a seismic slip occurring at multiple fault segments of the Sumatran fault in northern Sumatra, Indonesia.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019301348-ga1.jpg" width="247" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 177〈/p〉 〈p〉Author(s): Dibyashakti Panda, Amit Mondal, Bhaskar Kundu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We propose that topography can be used as a proxy for the eastward lateral “glacier-like flow” of the Tibetan crust in the Himalayan-Tibetan orogenic system. Geodetic observations across the Tibetan plateau indicate ∼22 mm/yr of crustal motion with respect to stable Eurasia by considering Newtonian channel flow model. Further, correlation between regional strain rate (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mover accent="true"〉〈mi〉e〈/mi〉〈mo〉̇〈/mo〉〈/mover〉〈/mrow〉〈/math〉) and topographic elevation (h) is found to be statistically robust, with stress exponent (n) of 3.03 ± 0.1. Therefore, we suggest that the Tibetan crust follows well defined power-law relation that is consistent with the nonlinear deformation associated with dislocation-creep. Moreover, the predicted viscosity range of the Tibetan crust is consistent with the channel flow model proposed by previous investigators using different approaches in different time scales.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019301324-ga1.jpg" width="487" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 19 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Huan Xu, Yongqing Liu, Hongwei Kuang, Nan Peng〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Eolian systems were widespread in China in the Cretaceous. However, the reports of pre-Cretaceous eolian and its related systems are scarce, which prohibits studying the construction, accumulation and preservation of eolian systems as well as its allogenic and autogenic controlling factors. In this paper, we report on fluvial–eolian successions from the Late Jurassic Tianchihe Formation in the Ningwu–Jingle Basin. These successions represent the oldest reported inland fluvial–eolian systems in China. Fourteen lithofacies types are recognized in the Tianchihe Formation and have been grouped into six facies associations, including meandering fluvial channel, levee and overbank in the lower part, and eolian sandsheet, eolian dune, ephemeral fluvial channel and floodplain in the upper part. The fluvial system comprises a series of wetting upward cycles, which indicate humid climate culminating in high precipitation and shallow water table level. Eolian dune deposits composed of grainflow, grainfall, wind ripple strata and pin stripe laminations currently implies that all deposits types are internally bounded by reactivation surface and superimposition surface, suggesting compound dunes or draas. Eolian sandsheet deposits consist dominantly of subcritical climbing translatent strata and pin stripe lamination. The association of eolian dune and eolian sandsheet is development of a dry eolian system. Twelve drying upward cycles mainly composed of eolian sandsheet–eolian dune successions and four wetting upward cycles consisting of eolian sandsheet/dune–ephemeral fluvial channel/floodplain successions occur in the eolian system. These repeated cycles likely reflect an evolving erg system directly controlled by sediment supply, sediment availability and relative water table. The vertical transition from fluvial to eolian systems indicate a local climatic oscillation from relatively humid to arid conditions, which may be related with the uplift of the East China Plateau in the Late Jurassic.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912018305121-ga1.jpg" width="185" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 27 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Murat Şahin, Cenk Yaltırak, Zekiye Karacık〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The Nallıhan and Çayırhan regions in western Anatolia host the stratigraphically and tectonically important features of Nallıhan Wedge. The stratigraphic relationships and structural architecture of the wedge are not well understood, which are essential for better understanding of the timing and tectonic evolution of western Anatolia. Today, the Nallıhan Wedge is bounded by the North Anatolian Fault and the Thrace-Eskişehir Fault in the northwest and southwest, respectively. The existence of Dağküplü Mélange within the wedge represents the closure of the İzmir-Ankara Ocean. The occurrence of the Lower Jurassic shelf, slope, reef and deep sea successions transitioning upward into the Cretaceous shelf and slope successions represent the opening and closing cycles of the Intra-Pontide Ocean. The tight and asymmetric folds (steep in the west, gentle in the east) within this stratigraphic sequence and the development of the Eocene units reflect the closure of the Intra-Pontide and İzmir-Ankara oceans. The geometric structure and evolution of the Nallıhan Wedge is directly related to the final continental collision. W-E and SW-NE striking large-scale oblique thrusts also exhibit notable strike-slip components within the study area. The principal direction of the fold axes are W-E and WNW-ESE oriented for the Eocene and Neogene units. During the Eocene, the depositional environment of the study area was a ramp basin mainly dominated by a braided river, when a portion of the Intra-Pontide Ocean was situated on the northern side of the study area. The compressional tectonic regime continued to the end of the Oligocene, which is followed by a new tectonic regime during the Miocene, when the triangular shape region between the Thrace-Eskişehir Fault and the North Anatolian Fault developed as an intermontane basin. The evolution of this basin can be compared with the Tercan Wedge, bordered by the North Eastern Anatolian Fault and the North Anatolian Fault.〈/p〉 〈p〉In the Nallıhan and Çayırhan regions the N-S-trending compressional regime started during the Upper Cretaceous and continued until the final continental collisional during the Upper Eocene. The compressional structures in the area became reactivated during the post-collisional escape tectonic phase in western Anatolia, leading to the development of the prominent Isparta Angle during the Miocene. During this period, the Thrace-Eskişehir Fault and Burdur-Fethiye Shear Zone also formed as intracontinental transform fault zones in western Anatolia. The Nallıhan Wedge started to form in a wedge-shaped area between the Thrace-Eskişehir Fault and the zone of strike-slip faults with thrust component that later developed into the North Anatolian Fault. Thus, Eocene and pre-Eocene structures obtain strike-slip component by an inversion during the Miocene. During and post Pliocene, the Thrace-Eskişehir Fault lost its tectonic activity as the North Anatolian Fault propagated westward into the region previously controlled by the Thrace-Eskişehir Fault. During this interval the Nallıhan Wedge entered a new stage of deformation, which is also observed today.〈/p〉 〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912018305224-ga1.jpg" width="277" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 27 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Jian Li, Lianbo Zeng, Weilian Li, Yongshu Zhang, Zhihong Cai〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Himalayan deformation substantially impacts the hydrocarbon migration and accumulation in the western Qaidam Basin. In order to investigate how the Himalayan deformation influences the hydrocarbon migration and accumulation in fracture type reservoir, we took Shizigou oil field in the western Qaidam Basin as an example and studied the Himalayan deformation history based on the results from the balanced cross-section restoration of 2 sections across the Shizigou oil filed at first. Then we simulated the fluid potential of one particular section at different tectonic episodes by the numerical method to investigate how the Himalayan deformation effects on it. We conclude that the Himalayan deformation influences the hydrocarbon migration and accumulation in three aspects. Firstly, the faults which form during the structural evolution and communicate with the source rock can act as the primary pathways for the hydrocarbon migration. Secondly, the fracturing of rocks occurs during structural evolution owing to significant compression, which prefer occurring near the faults especially in hanging wall and the hinge zone of folds. These fractures significantly improve the permeability of the rock and result in good pathways for hydrocarbon migration and high-quality reservoirs for hydrocarbon accumulation. Thirdly, influenced by tectonic deformation, compaction of rock bulk volume generates the rising of fluid potential in the soft formation where fracturing is restricted, in contrast, expansion of rock bulk volume generates the dropping of fluid potential in the position where fracturing is enhanced. The change of fluid potential allows the hydrocarbon to migrate and accumulate rapidly along the faults where low fluid potential occurs attributed to fracturing. The impact of tectonic deformation on the hydrocarbon migration and accumulation results in that the hydrocarbon accumulates in fracture type reservoirs near the faults.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912018305212-ga1.jpg" width="292" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 185〈/p〉 〈p〉Author(s): Yuanku Meng, Walter D. Mooney, Yuan Ma, Han Xu, Rongzhen Tang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Sedimentary rocks in the Gangdese magmatic arc document a long but poorly constrained series of tectonic events that led to basin formation. We investigate one of these events by using detrital zircon grains from Mesozoic sedimentary rocks from the Linbuzong Formation located within the Gangdese magmatic arc. Our aims are to determine the provenance of the rocks in this back-arc basin and to document the paleo-topographical uplift of the Gangdese region in southern Tibet. Detrital zircons from the Linbuzong Formation, located in the middle-eastern segment of the southern Lhasa sub-terrane, have ages in four dominant populations: 140–300 Ma, 480–700 Ma, 1000–1250 Ma, and 1400–1700 Ma. The youngest detrital zircon cluster has a weighted age of ca. 149 Ma which, in conjunction with previously published data, indicates that sedimentary rocks in the Linbuzong Formation were deposited after 149 Ma. The youngest detrital zircon grains have low 〈sup〉176〈/sup〉Hf/〈sup〉177〈/sup〉Hf isotopic ratios and negative ε〈sub〉Hf〈/sub〉(t) values, similar to igneous zircons from the central Lhasa sub-terrane which is considered to be the predominant source for sediments. However, few zircon grains from the youngest age cluster have high 〈sup〉176〈/sup〉Hf/〈sup〉177〈/sup〉Hf ratios with significantly positive ε〈sub〉Hf〈/sub〉 (t) values, suggesting derivation of some sediments from the southern Lhasa sub-terrane, primarily the Gangdese magmatic arc. Combined with the evidence for two conspicuous age populations (480–700 Ma and 1000–1250 Ma) and the Hf isotopic characteristics of the Linbuzong Formation, we propose that the Carboniferous-Permian metasedimentary rocks from the central Lhasa sub-terrane serve as the main source of sediments for the Linbuzong Formation. We conclude that the central Lhasa sub-terrane was exhumed to the surface and attained a high relief, whereas the Gangdese magmatic arc had a relatively low relief (near sea-level) during the Late Jurassic to the Early Cretaceous.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303785-ga1.jpg" width="300" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 185〈/p〉 〈p〉Author(s): Xingfan Wang, Hui Zhao, Hongyu Yang, Keqi Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Badain Jaran Desert (BJD) in NW China is well known for its unique landscape of megadunes coexisting with permanent lakes. The megadunes are already the tallest sand dunes on earth, and some of them are up to 400 m high. However, it is unclear whether or not the height of the megadunes is continuing to increase under present climatic and environmental conditions. In order to determine the growth status of the megadunes, we collected 26 samples from the windward slopes of two megadunes for optically stimulated and infrared stimulated luminescence dating. The results show that the thickness of the modern eolian sand layers increases from the lower part of the windward slopes, with a thickness of less than 1 m, to more than 2 m in the middle, and to 9 m in the upper part. This indicates that the height of the megadunes is continuing to increase under modern conditions. The surface sediments from the base of the windward slope and the adjacent lake basin have relatively old ages of 6–7 ka, indicating that these areas are eroding. The recent eolian sands of the upper part of the megadunes likely originated from the base of the dunes or from the lake basin. The megadunes in the BJD are currently becoming increasingly high and steep due to the upward migration and accumulation of sand particles. Increased humidity and a weakened wind regime in northern China, related to ongoing climatic warming, are likely the main factors in maintaining the growth of the megadunes.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303773-ga1.jpg" width="429" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 185〈/p〉 〈p〉Author(s): Zhengfan Lin, Chao Yuan, Yunying Zhang, Min Sun, Xiaoping Long, Xinyu Wang, Zongying Huang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Whole-rock geochemical and Sr–Nd–Pb–Hf isotopic analyses were conducted on the Triassic Ashele post-orogenic basalts from the Chinese Altai. The tholeiitic Ashele basalts possess moderate Na〈sub〉2〈/sub〉O (2.46–4.52 wt%) but extremely low K〈sub〉2〈/sub〉O (≤0.06 wt%) contents, and are depleted in light rare earth elements (LREE). Their (La/Sm)〈sub〉N〈/sub〉 and (La/Yb)〈sub〉N〈/sub〉 ratios range from 0.78 to 0.88 and from 0.72 to 0.84, respectively, which, together with their low initial 〈sup〉87〈/sup〉Sr/〈sup〉86〈/sup〉Sr (0.7048–0.7052), high εNd(t) (+4.9 to +5.6) and εHf(t) (+14.3 to +16.3) values, indicate that the magmas were derived from a depleted mantle source. Their 〈sup〉206〈/sup〉Pb/〈sup〉204〈/sup〉Pb and 〈sup〉207〈/sup〉Pb/〈sup〉204〈/sup〉Pb ratios (17.919–18.125 and 15.507–15.522, respectively) also support this interpretation. On the other hand, the Ashele basalts are enriched in Cs, Th and U, but depleted in Rb, Ba, Nb and Ta, possibly due to slight mantle metasomatism by subduction-related fluids. Because there was no record for large-scale thermal activity in the deep mantle during the Triassic, and geological evidence demonstrates reactivation of the Erqis fault, we propose that such a tectonic reactivation affected the lithospheric mantle and resulted in its partial melting and subsequent generation of the Ashele basalts. This study shows that a depleted lithospheric mantle, not an ancient continental lithosphere, was underneath the Chinese Altai in the Triassic, which was possibly accreted during the Paleozoic orogeny. Therefore, the lithospheric mantle in this area today was possibly evolved from such a depleted mantle modified by consecutive partial melting after the Paleozoic orogeny.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303736-ga1.jpg" width="362" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: December 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 186〈/p〉 〈p〉Author(s): Tian Yang, Yingchang Cao, Keyu Liu, Lingli Zhou, Jiehua Jin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Understanding the sediment dynamics responsible for the deposition of fine-grained sediments is essential for studying fine-grained sediment origin and its distribution, which is of a great significance for unconventional oil and gas exploration and development. Fine-grained sediments from a Lower Cretaceous rift-basin sequence in the Lingshan Island, the middle of the Dengta section in the Lingshandao Formation were studied. On the basis of detailed outcrop investigation, thin section observation, and laboratory measurements, seven types of lithofacies and three lithofacies associations were identified in the fine-grained sediment sequence. The sediment dynamics were deduced from a comprehensive examination and interpretcation of the sedimentary structures and lithofacies associations. The fine-grained sediments in the research area belong to a silt dominated subclass, which is composed mainly of thin-bedded siltstones with normal grading and mudstones with horizontal lamination. Suspension settling is responsible for the development of horizontal lamination in some mudstone. The Bouma-like lithofacies associations are developed by downslope fine-grained turbidity currents. The hybrid event bed-like lithofacies associations are formed by hybrid flow, while turbidity currents transformed to muddy debris flows downslope. The interbedded thin sandstone and mudstone banded lithofacies associations may be resulted from a downslope transitional flow between a turbidity current and a muddy debris flow. The vertical facies stacking patterns of the fine-grained sediment sequence indicatec that the fine-grained gravity flow may have been evolved from a transitional flow to a debris flow then to a low-density turbidity flow and finally to a hybrid flow. Lithofacies associations deposited by hybrid flow and transitional flow are potential sweet spots for unconventional oil and gas exploration in such fine-grained sediment formation.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019304171-ga1.jpg" width="231" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: December 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 186〈/p〉 〈p〉Author(s): Murat Özkaptan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The Turkish Pontide orogenic belt belongs to the former Eurasian margin, which is the result of two major successive processes of the closure of the Tethyan oceans: subduction followed by collision. This almost E-W trending large mountain range shows an arc-shaped geometric structure in the northern Turkey. According to previous studies based on geological and paleomagnetic data, oroclinal deformation was proposed as a result of the geodynamic evolution due to the Africa-Eurasia convergence in the region. The aim of study is to determine how this important evolution is expressed in the lithosphere beneath the region by gravity modelling.〈/p〉 〈p〉A Bouguer gravity anomaly map was constructed and from this a gravity model is presented that reveals the general crustal structure underneath the northern Turkey. The results present a significant crustal thickness change that occurs in the N-S and as well as in the E-W directions. From S to N, a significant sharp crustal thickness decrease (~20 km) was found, while from E to W the crustal thickness beneath the Pontides increases by approximately 7 km.〈/p〉 〈p〉While an average thickness of 37 km was calculated in the East, it reached a maximum value of ~44 km in the West. Although the reason for the increase in crustal thickness from north to south is logical in terms of the geodynamic evolution, the increase from east to west is probably caused by the nature of the continental collision. The most plausible explanation is an (oblique) NW indentation of the Kırşehir Block into the Pontides.〈/p〉 〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019304109-ga1.jpg" width="326" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: December 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 186〈/p〉 〈p〉Author(s): ChangHao Xiao, GongJian Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The recently discovered Xiyi Pb–Zn deposit in Yunnan Province, SW China, contains 1.2 Mt of Pb and Zn metal. It is located within the Baoshan Block, in the Sanjiang Tethys orogenic belt and is hosted along fractures within carbonates of the Lower Carboniferous Xiangshan Formation. The deposit is hosted by veins within NE–SW trending strike-slip and steeply dipping NW–SE trending normal fault zones. The formation of the deposit involved sedimentary, hydrothermal, and supergene oxidation stages. The hydrothermal stage associated with mineralization include three sub-stages (i) a steeply-dipping quartz–calcite-rich sphalerite sub-stage; (ii) a polymetallic sulfide sub-stage; and (iii) a vein-host calcite–pyrite sub-stage. The deposit is enriched in Pb, Zn, Sb, Cd, Ag, and U, and depleted in Ni, Se, Ti, and Co. The ores have total rare-earth element (REE) concentrations of 17.4–186 ppm and are enriched in the light REE (LREE) with (La/Yb)〈sub〉N〈/sub〉 ratios of 3.75–9.23 and strongly positive Eu (Eu/Eu* = 1.42–4.60) and slightly negative Ce (Ce/Ce* = 0.70–0.88) anomalies. The positive Eu anomalies and LREE enrichment suggest that the ore-forming fluids were exsolved from a concealed intrusion during magmatic degassing. The S isotopic compositions of sulfides and sulfates indicate that S within the deposit was derived from both magmatic sources and barite within the hosting carbonates via thermochemical sulfate reduction. 〈em〉In-situ〈/em〉 LA–ICP–MS analysis indicates that sphalerite within the deposit is texturally and chemically variable, with elevated Fe, Mn, Cd, Cu, Ag, Sb, Sn, Pb, and Tl contents. In comparison, galena within the deposit is enriched in Sb, Ag, Cd, Sn, and Tl, and pyrite has elevated Ag, As, Sb, and Pb contents. The trace element compositions of sphalerite and galena indicate that the Xiyi deposit may be the product of a distal hydrothermal event although the direct genetic relationship is not clear. The fracture-hosted nature, mineral assemblages, geochemistry, and mineral S isotopic and trace-element compositions of the Xiyi Pb–Zn deposit indicate that it is an epigenetic carbonate-hosted Pb–Zn deposit. This study also indicates that sphalerite is a more useful mineral than galena in terms of using mineral trace-element geochemistry to discriminate different deposit types.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019304080-ga1.jpg" width="269" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: February 2020〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 188〈/p〉 〈p〉Author(s): Sara Nasri, Ali Nejati Kalate, Amin Roshandel Kahoo, Mehrdad Soleimani Monfared〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Geological modeling by geophysical data in the Makran subduction zone is a challenging task which comes from its extreme structural and geological complexity. Different geological models were presented for this zone in previous studies by the use of various sources of information. Among these studies, numerous geophysical models were introduced to illustrate depth, geometry and location of the subduction zone and definition boundaries with adjacent zones. However, structural complexity of the media and high degree of variation in geological units reduce accuracy of geophysical model derivation. In this study, an integrated strategy via model fusion for geological model building of the Makran subduction zone was presented using gravity and magnetic data. In the presented strategy, gravity and magnetic models were integrated through fusing procedure. Herewith airborne magnetic and gravity data were inverted by fine gridding and solving large scale problems for each set of potential field data. While magnetic model inherently was able to reveal near surface structures, gravity data modeled large depth anomalies. Afterwards, a discrete wavelet transform rule was used for fusion magnetic and gravity models to derive a unique model containing advantage of both sets of data. The fused model revealed more detail of the Makran zone structure, location of the subduction zone and steep dip faults. The final models proposed depth of 40 km for the top of the oceanic crust with variation in thickness from 5 to 8 km, basin ward. The subduction zone located 200 km in the onshore and it shows a very low dip.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 177〈/p〉 〈p〉Author(s): Ulrich Knittel, Monika Walia, Shigeyuki Suzuki, Yuan-Hsi Lee〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Within the Sanbagawa metamorphic belt, the timing of high-pressure and retrograde metamorphism is controversial. Recently, an area in the Asemi River region (central Shikoku, Japan) was delineated that had been subjected to ecologite facies metamorphism prior to retrograde metamorphism in the epidote-amphibolite facies which provides a new opportunity to constrain the age of high-pressure metamorphism. Detrital zircon from this area yields ages as young as 84 ± 4 Ma. Hence, the protoliths were deposited not earlier than ca. 88 Ma and thus, eclogite facies and retrograde metamorphism occurred after 88 Ma, probably at 86–82 Ma as indicated by the age of metamorphic zircon and K-Ar and Ar-Ar ages for white mica.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 177〈/p〉 〈p〉Author(s): Chao Cheng, Shengsi Sun, Yunpeng Dong〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Taibai ductile shear zone affecting the northern margin of the Taibai granitic pluton which emplaced in the North Qinling Orogenic Belt, is crucial to understand the amalgamation and post-collision history between the North China Block and the South China Block. The shear sense indicators and the kinematic vorticity numbers (0.42–0.59) suggest that the Taibai shear zone is an elongating general shear zone involving both sinistral shear and pure shear components. The quartz lattice preferred orientations mainly indicate the activation of prism 〈a〉 slip system combined with rhomb 〈a〉 slip to prism 〈a〉 slip system. The dynamic recrystallization of quartz is accommodated by sub-grain rotation and bulging recrystallization while plagioclase mainly displays bulging recrystallization. These characteristics suggest that the mylonites have experienced ductile shear deformation under greenschist facies conditions at temperatures of ∼400–550 °C. Zircons from granitic mylonite yield upper and lower intercept ages of 425 ± 4 Ma and 144 ± 1 Ma, respectively, suggesting the protolith of the mylonite crystallized at ca. 425 Ma and was involved into a hydrothermal activity at ca. 144 Ma. Muscovite 〈sup〉40〈/sup〉Ar/〈sup〉39〈/sup〉Ar dating of the mylonite sample yield a plateau age of 346 ± 5 Ma and an inverse isochron age of 344 ± 4 Ma, constraining the ductile shear deformation occurring during the Early Carboniferous time. We suggest that the Taibai shear zone was formed by NE-SW oblique compression with top-to-the-NW shear sense during the Early Carboniferous time, following the N-S shortening caused by collision between the North China Block and South China Block along the Shangdan suture at ca. 400 Ma.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019301142-ga1.jpg" width="354" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 6 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Yu Zou, Dongna Liu, Fenghua Zhao, Hongwei Kuang, Yuxiang Sun, Jianbo Cheng〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The relatively low Mesoproterozoic oxygen concentrations in atmospheric and marine environments remained controversial because the marine chemical evolution has not been sufficiently researched. To provide a better understanding of the secular redox conditions of shallow-water sedimentary environments and to perform global isotopic comparisons, we present new data of rare earth elements and yttrium (REE+Y), redox-sensitive elements (RSEs), and carbonate carbon-oxygen isotopes from Mesoproterozoic marine succession in the Shennongjia Group of the Yangtze Shennongjia area. Seawater-like REE+Y distribution patterns with significantly negative Ce anomalies, which had previously been screened to avoid detrital effects in the leached carbonates, illustrate the oxidation of shallow seawaters during the deposition of this group. Although the Ce/Ce* and (Pr/Yb)〈sub〉SN〈/sub〉 values remain relatively low in carbonate samples throughout the Mesoproterozoic, these values are higher than those of the modern oxygenated ocean, indicating less intense oxygenation. This conclusion is supported by the high enrichment factors of the RSEs in screened samples resulting from a considerable marine reservoir for dissolved RSEs in a constantly oxidized environment. Under these circumstances, the δ〈sup〉13〈/sup〉C〈sub〉carb〈/sub〉 chemostratigraphy is moderately varied, with values near +3.5‰ and lower than +5‰, and more dynamic variability is observed over time, which is related to progressively smaller marine dissolved inorganic carbon (DIC) reservoirs. In addition, the significant negative excursion of δ〈sup〉13〈/sup〉C〈sub〉carb〈/sub〉 near to or less than 0‰ in this lower subgroup is globally matched in different blocks and may correspond to the oxidation of isotopically light organic matter in oceans. A worldwide comparison indicates that the δ〈sup〉13〈/sup〉C〈sub〉carb〈/sub〉 chemostratigraphies combined with limited geochronological data may constrain this extended negative excursion to ca. 1.3–1.2 Ga and the Shennongjia Group to ca. 1.3–1.1Ga.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019301129-ga1.jpg" width="243" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 21 April 2017〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Dongliang Guan, Xiaoping Ke, Yong Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The effective elastic thickness (Te) of the lithosphere, which reflects lithospheric strength, is a useful parameter in the investigation of the characteristics of the oceanic lithosphere. Instead of the conventional spectral method, we used a space-domain convolution method to estimate Te, which involves the convolution of the crustal load with a set of point-loaded response functions in order to get a set of model flexures. The best Te estimate is obtained from the best agreement between the model flexures and the observed flexure derived from the inversion of the gravity data. Compared with the spectral method, this method eliminates the instability problem when the topography is small and increases the spatial resolution of Te. Based on this convolution method, for the first time, we determined Te for the lithosphere in the East and South China Seas and the adjacent area. The result shows that the Bohai Sea, the northern part of the Yellow Sea, the northwestern part of the East China Sea, and the Yinggehai Basin have the strongest lithosphere with a Te reaching 30 km. The central part of the South China Sea and the Okinawa Trough Basin have the weakest lithosphere with a Te of less than 6 km. In addition, we investigate the relationship between Te and the distribution of the crustal load and the relationship between Te and the undulations of the Crust Mantle Interface (CMI). We conclude that the lithospheric strength, Te, decreases with an increase in the sufficient old load. Meanwhile, a positive correlation is found between Te and the CMI. When the CMI becomes deeper or shallower, the corresponding Te becomes larger or smaller, respectively.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S136791201730189X-fx1.jpg" width="500" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 19 January 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Hui Jiang, Tao Su, William Oki Wong, Feixiang Wu, Jian Huang, Gongle Shi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Fossils are critical for understanding the uplift history of the Tibetan Plateau and its impact on the diversity and diversification of living organisms in Eurasia. However, well-preserved fossils, especially plant megafossils are rare in the plateau. In this paper, we describe two species of 〈em〉Koelreuteria〈/em〉, namely 〈em〉K. lunpolaensis〈/em〉 sp. nov. and 〈em〉K. miointegrifoliola〈/em〉, based on exquisitely preserved capsular valves from the late Oligocene of the Lunpola Basin, central Tibet. 〈em〉Koelreuteria lunpolaensis〈/em〉 is distinguishable from all extant and fossil species of the genus in the strongly asymmetric form of the capsular valves, the emarginate or lobed apex of the valves, and zigzag lateral veins that are tapering towards the margin of the valves, and is considered to represent an extinct lineage of the genus. 〈em〉Koelreuteria miointegrifoliola〈/em〉 is most similar to 〈em〉K. bipinnata〈/em〉-type group of extant 〈em〉Koelreuteria〈/em〉. The diverse 〈em〉Koelreuteria〈/em〉 confirms a warm and humid environment with a low elevation in central Tibet during the late Oligocene based on their modern distributions. Fossil evidence indicates that the Tibetan Plateau was a center for diversity and diversification of 〈em〉Koelreuteria〈/em〉 in the Oligocene/Miocene. It also suggests that Tibet might also serve as a refugium for the 〈em〉K. bipinnata〈/em〉-type group in the late Oligocene.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912018300142-fx1.jpg" width="283" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 176〈/p〉 〈p〉Author(s): Jian Lu, Anchun Li, Jin Zhang, Peng Huang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The southwestern South Yellow Sea (SYS) is influenced by tremendous sediment loads derived from the Yellow River (Huanghe) and the Yangtze River (Changjiang). However, the influence of Yangtze River sediments and their transport mechanism in this area remain unresolved. In this study, we present the grain size, clay minerals, and elemental compositions of surface sediments from the southwestern SYS, together with an analysis of field observation seawater salinity and suspended sediment data, to investigate the provenance and transport mechanism of the sediments. Discrimination diagrams of clay minerals, Cr/Th vs. Sc/Al, and rare earth elements (REEs) indicate that the southwestern SYS sediments are mainly derived from the old Yellow River subaqueous delta and the Yangtze River. Interestingly, Yangtze sediments enter the SYS in ways that differ seasonally. In summer, Yangtze sediments may be transported into the central SYS by the dispersion of Changjiang Diluted Water (CDW) and may also be transported northwestward by the Subei Coastal Current (SCC) to the area off the Jiangsu coast. In winter, the Yangtze-derived sediments deposited off the Jiangsu coast in summer are transported into the central and/or even north SYS under the combined effects of the SCC, Yellow Sea Coastal Current (YSCC), and Yellow Sea Warm Current (YSWC). Throughout the transport processes, there is an alternation between a source and sink of Yangtze sediments off the Jiangsu coast; the coast serves as a sink of Yangtze sediments in summer but as a source of SYS sedimentation in winter. The depositional and transport mechanisms of Yangtze-derived sediments are closely associated with seasonal variations in the circulation system of the SYS.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S136791201930118X-ga1.jpg" width="417" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 8 December 2017〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Chenyang Cai, Diying Huang, Feixiang Wu, Min Zhao, Ning Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The semi-aquatic hemipteran family Gerridae (water striders), similar to other gerromorphan bugs, is a distinct group noted for their ability to walk on the surface of water, especially with respect to their locomotion, feeding, and behaviour. The three principal Holarctic gerrine genera, 〈em〉Aquarius〈/em〉 Schellenberg, 〈em〉Gerris〈/em〉 Fabricius and 〈em〉Limnoporus〈/em〉 Stål, are important organisms for studies of biogeography, evolutionary trends and ecological adaptations of the Gerridae. Fossil gerrids are comparatively sparse, and direct fossil evidence elucidating the early diversification and biogeography of the extant widespread genus 〈em〉Aquarius〈/em〉 remains elusive. Here we redescribe and reinterpret the extinct species 〈em〉Aquarius lunpolaensis〈/em〉 (Lin, 1981) based on new well-preserved conspecific specimens from contemporaneous localities in the Lunpola and Nima basins of central Tibet, China. The new fossils confirm the placement of these fossils in 〈em〉Aquarius〈/em〉 as evidenced by their large body size, first antennal segment longer than the following two segments combined, and well-developed abdominal connexival spines. The new discovery of a series of larval instars at different developmental stages confirms that “〈em〉Halobates bagonensis〈/em〉” should be interpreted as an exuvium of the dominant species 〈em〉Aquarius lunpolaensis〈/em〉 and demonstrates that the extant western Palaearctic 〈em〉najas〈/em〉-group had a much wider distribution in the late Oligocene (Chattian). The occurrence of an 〈em〉Aquarius〈/em〉 water skater supports the hypothesis that the elevation of central Tibet was comparatively low, some 25 million years ago.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912017306880-fx1.jpg" width="500" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 177〈/p〉 〈p〉Author(s): Tianjian Yang, Xiaoming Sun, Guiyong Shi, Dongsheng Li, Haoyang Zhou〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Yuanjiang marble-hosted ruby deposit in the middle Ailao Shan-Red River (ASRR) shear zone, is the only economic ruby deposit in China. This deposit is hosted in Paleoproterozoic sillimanite gneisses and the ores are found in metamorphosed platform carbonates. Rubies are unevenly distributed within calcite-rich marble layers and mainly associated with phlogopite, scapolite, graphite, pyrite. Rubies contain zircon, rutile, apatite, calcite inclusions. The genesis of the Yuanjiang ruby deposit and its genetic link to the ASRR shear zone remain poorly understood. In this contribution, its formation age has been indirectly constrained by the in-situ LA-ICP-MS U-Pb dating of zircon inclusions in rubies and 〈sup〉40〈/sup〉Ar/〈sup〉39〈/sup〉Ar dating of syngenetic phlogopite from the ruby-phlogopite bearing marble, which yielded the ages of 36.2 ± 1.1 Ma (MSWD = 1.4, 2σ, n = 4) and 22.2–22.5 Ma, respectively. The 36.2 Ma U-Pb age of metamorphic zircon inclusions falls within the range of local crustal thickening related subduction-collision and coupled with the spatial distribution in which ruby deposits were not restricted in the shear zone, we propose that ruby mineralization was triggered by the local continental subduction-collision rather than the large-scale left-lateral shearing. Due to the estimated closure temperature of the 〈sup〉40〈/sup〉Ar-〈sup〉39〈/sup〉Ar system is lower than the ore-forming temperature, the obtained phlogopite 〈sup〉40〈/sup〉Ar/〈sup〉39〈/sup〉Ar ages of 22.2–22.5 Ma represent the minimum ore-forming age of the Yuanjiang ruby deposit. These phlogopite ages reveal a slower cooling rate of ruby deposits within the shear zone (including the Yuanjiang and the Yen Bai ruby deposits) than outside of the shear zone (the Luc Yen deposit), which can be attributed to the additional heat from the left-lateral shearing movement. Therefore, we propose that the left-lateral shearing plays an important role in transporting marble-hosted ruby deposits in the Ailao Shan-Red River shear zone to the subsurface.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019301233-ga1.jpg" width="371" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 177〈/p〉 〈p〉Author(s): Julien Morin, Marc Jolivet, Laurie Barrier, Amandine Laborde, Haibing Li, Olivier Dauteuil〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In Central Asia, numerous fragments of planation surfaces are visible within the present day topography. However, their precise timing of formations is still poorly constrained and it is not clear if they are remnants of a single extensive planation surface or if they represent different planation episodes. By reconstructing the landscape evolution of the Tian Shan region and by analyzing the relations between the planation surfaces preserved within the eastern Tarim Basin and the sedimentary record, we demonstrate that the numerous erosional surfaces preserved within the Tian Shan Range represent different episodes of surfaces genesis. These erosion events span from the late Paleozoic to the Early Cenozoic. The widespread preservation of large fragments of these surfaces within the Tian Shan Range implies that this region did not undergo strong relief building during most of its Mesozoic evolution but was dominated by plains associated to small hills along episodically active discrete tectonic structures. Finally, the preservation of these surfaces within the active Tian Shan Range implies a long-term, strong non-equilibrium state of the topography during its Cenozoic evolution. This was probably promoted by the arid to semi-arid climate prevailing since the Late Paleogene onset of relief building.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019301221-ga1.jpg" width="286" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 3 February 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Yi-chun Zhang, Shu-zhong Shen, Yu-jie Zhang, Tong-xing Zhu, Xian-yin An, Bo-xin Huang, Chun-lin Ye, Feng Qiao, Hai-peng Xu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Two new Middle Permian foraminifer faunas are described from the Xiala Formation in the Zhabuye and Xiadong sections in the central Lhasa Block. The presence of some significant taxa in paleobiogeography such as 〈em〉Shanita〈/em〉, 〈em〉Lysites biconcavus〈/em〉, 〈em〉Hemigordiopsis subglobosa〈/em〉, indicates that the Lhasa Block was in the Cimmerian Province in paleobiogeography during the Middle Permian. Furthermore, the 〈em〉Nankinella-Chusenella〈/em〉 fusuline assemblage that occurs in the upper part of the Xiala Formation in the Xiadong section resembles contemporaneous fusuline faunas from the Xainza and Bashor areas in the Lhasa Block and the northern part of the Tengchong Block. The endemism of the 〈em〉Nankinella-Chusenella〈/em〉 assemblage in the Lhasa and Tengchong blocks indicates that these two blocks were isolated from both the South Qiangtang Block and the northern Gondwanan margin during the Middle Permian. It further suggests that both the Bangong-Nujiang Ocean and the Neotethys Ocean would have opened before the Middle Permian. A new species 〈em〉Chusenella tsochenensis〈/em〉 sp.nov. was described.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912018300087-fx1.jpg" width="500" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 11 March 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Zhengjian Xu, Luofu Liu, Benjieming Liu, Tieguan Wang, Zhihuan Zhang, Kangjun Wu, Chenyang Feng, Wenchao Dou, Yang Wang, Yun Shu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The fact that high-quality lacustrine source rocks (generally shale and mudstone) control the formation and distribution of conventional and unconventional oil and gas reservoirs in lacustrine basins has been well-accepted in petroleum exploration and exploitation. Taking the Chang 7 lacustrine source rocks in the Ordos Basin as an example, several points having been reached are as follows. (1) The Chang 7 source rocks possess an excellent source rock potential, and the shales hold a better potential than the mudstones. (2) The paleoenvironments of the Chang 7 source rocks were sub-reducing to sub-oxidizing conditions and fresh- and brackish-water depositional environments with a maximum water depth of 150 m. The organic matter origins of the source rocks are mainly plankton, algae, bacteria and other aquatic microorganisms. (3) The beginning time of the oil generation of the Chang 7 source rocks is at 165 Ma, and the peak oil generation occurred during 115–95 Ma. The cumulative amounts of oil generation are up to 4711 × 10〈sup〉3〈/sup〉 t/km〈sup〉2〈/sup〉 and the ratios of peak generation amounts to cumulative generation amounts are 〉50%. The beginning timing and peak generation timing of the shales are earlier than those of the mudstones, respectively, and the cumulative oil generation amount of the shales is higher than that of the mudstones, indicating a better oil generation potential of the shales. (4) Due to the more remained oil possessed in the shales, the hydrocarbon expulsion threshold of the Chang 7 shales (2560 m) is deeper than that of the Chang 7 mudstones (2080 m). (5) The occurrences of the Chang 8–6 tight oils are predominantly controlled by the outer boundary of the Chang 7 source rocks distribution, while the transition areas between thickness, TOC, and R〈sub〉O〈/sub〉 high value centers are the accumulation and enrichment zones. The Chang 7 shales controlled the occurrence of the Chang 8 tight oil reservoirs and the Chang 7 mudstones controlled the occurrence of the Chang 7 and Chang 6 tight oil reservoirs.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 181〈/p〉 〈p〉Author(s): Nguyen Hoang, Ryuichi Shinjo, La The Phuc, Le Duc Anh, Tran Thi Huong, Zoltán Pécskay, Dao Thai Bac〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Basaltic and related- pyroclastic products aged 0.67, 0.46 and 0.2 Ma produced by eruption of Chư B'luk (Buon Choah), Phu Son (Pass 52, Quang Phu) volcanoes in the Krông Nô district, and Ea T’ling and Nam Dong volcanoes in the Cu Jut district covers an area of 120 km〈sup〉2〈/sup〉 with a thickness of a few meters to about 80 m. The volcanoes are aligned along a sub-meridian oriented extensional fault, from Phu Son in the south via Chư B'luk, Ea T’ling in the middle to Nam Dong in the north. The basalts are divided into geochemically alkaline and tholeiitic groups. Ne-normative alkaline basalts include samples from the upper layer of Phu Son volcano, those in the Trinh Nu waterfall area (Ea T’ling volcano) and cored samples conducted near the Dray Sap waterfall. Q-normative tholeiitic basalts include all the samples from Chư B'luk and Nam Dong volcanoes, and massive basalts in the lower layer of Phu Son volcano. Geochemically the tholeiitic basalts are vastly different from the alkaline basalts in that they have higher SiO〈sub〉2〈/sub〉 (50–55 wt% compared to 〈47 wt% in alkaline basalt), Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 (〉14–16 wt% compared to 〈14 wt%), lower K〈sub〉2〈/sub〉O (〈1.5 wt% compared to 〉1.5–2.5 wt%) and lower TiO〈sub〉2〈/sub〉 (〈1.8 wt% as compared to 〉2 wt% in alkaline basalt). Melting temperature and pressure calculations based on computing primitive melt compositions showed that the tholeiitic basalts may be produced in a narrow temperature range of 1365–1385 °C, corresponding to pressure of 1.2–1.6 GPa. The alkaline basalts may be produced in a temperature range between 1400 and 1440 °C and pressure varying from 3.1 to 3.35 GPa. Both the tholeiitic and alkaline basalts are free of crustal contamination. They show geochemically similar characteristics to those of continental intraplate basalts although the alkaline basalt show much more enrichment in incompatible elements. The 〈sup〉87〈/sup〉Sr/〈sup〉86〈/sup〉Sr and 〈sup〉143〈/sup〉Nd/〈sup〉144〈/sup〉Nd ratios of the two basaltic groups are quite similar, varying within narrow ranges of, respectively, 0.7038–0.7041, 0.5129–0.51286 but their 〈sup〉206〈/sup〉Pb/〈sup〉204〈/sup〉Pb isotopic ratios vary widely relative to 〈sup〉207〈/sup〉Pb/〈sup〉204〈/sup〉Pb and 〈sup〉208〈/sup〉Pb/〈sup〉204〈/sup〉Pb suggesting their interaction with different isotopic components and/or isotopic evolution history. Isotopic modeling relative to major mantle isotopic components suggests that the alkaline basalts may be generated by interaction between an N-MORB-like and an enriched mantle type 1 (EM1) at deep levels. The isotopic component is usually known as DUPAL-like regional mantle isotopic anomaly believed to be widespread in SE Asian mantle. The isotopic compositions of tholeiitic basalt may be generated by mixing between the DUPAL-like component with an enriched mantle type 2 (EM2)-like at higher levels in the lithospheric mantle.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S136791201930255X-ga1.jpg" width="246" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 181〈/p〉 〈p〉Author(s): Jiadai Li, Xiaofeng Li, Rong Xiao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Jiepai deposit, located in the northeastern part of the Miao’ershan-Yuechengling batholith, South China, is characterized by predominant skarn mineralization that formed near the contact between the Silurian biotite granites and the Upper Cambrian carbonate rocks. Jiepai scheelites are recognized as two main generations based on their occurrences, cathodoluminescence (CL) signatures, and REE systematics. Prograde skarn-hosted scheelite I has uniformly dark CL characteristics and LREE-enriched patterns. Retrograde skarn-hosted scheelite IIa is homogeneously dark under CL, and has a slightly MREE-enriched pattern, whereas quartz vein-hosted scheelite IIb is delineated by fine oscillatory CL zones and a relatively flat REE pattern. Additionally, the CL images reveal that both scheelite I and II were modified by later-stage hydrothermal overprints, which occur as ubiquitous overgrowth rims and cutting veins with bright CL signatures, low REE, but similar REE patterns to their precursors. The compositional variations and fluid inclusions in Jiepai scheelites identify episodic pulses of hydrothermal fluids with different properties. The ore-forming fluids with high Nb/Ta, but low Nb, Ta and REY in the early retrograde stage are featured by moderate to high temperature and low to moderate salinity. Under relatively oxidizing conditions, they interacted with the host rock and underwent boiling to precipitate scheelite I. By contrast, the fluids with higher Nb, Ta and REY, but lower Nb/Ta in the late retrograde stage have slightly lower temperature and higher salinity. We therefore speculate that scheelite II may deposit from later magmatic fluids that have experienced continued boiling in more reducing environment.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019302500-ga1.jpg" width="286" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 177〈/p〉 〈p〉Author(s): Massimiliano Zattin, Xiuxi Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This study presents new apatite fission-track data collected from intrusive and sedimentary rocks of the western Qinling mountain range. Results show a large range of data, with ages spanning from Upper Jurassic to Oligocene. No particular age-elevation relationships have been detected. Thermal modelling shows clearly that the region was affected by a nearly steady-state slow cooling starting from the Jurassic. This is particularly true for samples collected north of the West Qinling Fault whereas samples collected to the south show a re-heating event, followed by enhanced exhumation. As a whole, these data testify that the studied part of the western Qinling region was relatively stable for a long period and relatively insensitive to the tectonics related to the growth of the Tibetan Plateau. The present-day relief is mainly the result of transtensional tectonics that occurred in the Eocene.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019301518-ga1.jpg" width="348" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 177〈/p〉 〈p〉Author(s): D. Konopelko, Yu.S. Biske, K. Kullerud, I. Ganiev, R. Seltmann, W. Brownscombe, R. Mirkamalov, B. Wang, I. Safonova, P. Kotler, V. Shatov, M. Sun, J. Wong〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Paleozoic evolution of the western Tien Shan, which is built up on the basement of the Karakum continent, is poorly constrained compared to the better investigated Tien Shan terranes along the margin of the Tarim Craton. We present magmatic, metamorphic and detrital zircon ages for the regionally metamorphosed Baisun block and the metasediments comprising the Karakum basement in the westernmost parts of the South Tien Shan terrane. Age spectra of detrital zircon from metasediments of the Baisun metamorphic block and the western South Tien Shan show remarkable similarities over the vast area extending for ca. 500 km and are characterized by major Neoproterozoic peak at 1200–600 Ma and smaller peaks at 2300–1700 and 2700–2400 Ma. The 570–540 Ma ages of the youngest grains define late Neoproterozoic (Ediacaran) – early Cambrian maximum depositional ages of the metasediments. Comparison of the obtained age spectra with those published for the adjacent Tien Shan terranes indicate that the detrital zircon grains in the studied Ediacaran sediments were derived from the southern Precambrian continents of Karakum and Tarim while transport from the Northern Tien Shan was limited. The age of the Barrovian metamorphism in the Baisun block is constrained by ages of anatectic granites in the range 352–340 Ma, corresponding to early Carboniferous. These ages well match the 340–330 Ma ages, established for the adjacent Lolabulak and Garm metamorphic blocks. Based on the regional distribution of suture zones we suggest that during the Carboniferous the relatively small tectonic blocks of the South Gissar comprised an archipelago, located between the larger continents of Karakum and Tarim and possibly connected with the Paleotethys Ocean. The archipelago scenario can explain hot and rapid metamorphic and tectonic processes, documented in the South Gissar, similar to the ongoing collision along the Australia – SE Asia junction.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019301476-ga1.jpg" width="349" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 26 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Qisong Xu, Jian Wang, Yingchang Cao, Xintong Wang, Jie Xiao, Kashif Muhammad〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Many studies have focused on the tectonic evolution and sedimentary processes of the Beisantai Uplift, NW China during the late Permian. However, the sedimentary characteristics of the area are still not well documented due to a complex tectonic evolution of the uplift and the limited distribution of core data. To understand the sedimentary evolution of this study area, a “source-to-sink” system research is adopted. First, the research redefines the sequence stratigraphic framework of the late Permian, which corresponds to a complete third-order sequence that can be further divided into a transgressive system tract (TST) and a regressive system tract (RST). Then, the integration of three-dimensional (3D) seismic reflection data, well logs, mud logs and core data provides new insights into the transportation and sedimentary processes within the “source-to-sink” system. The different characteristics of the source area, transfer system and sedimentary paleogeomorphology between the TST stage and RST stage ultimately led to significantly different sedimentary characteristics in the two stages.〈/p〉 〈p〉In the TST stage, the “source-to-sink” system exhibited a continued transgressive depositional characteristic that matched the sediment discharge evolution. The steeper sedimentary paleogeomorphology enabled the development of large-scale fan deltas with few beach bars. During the RST stage, the “source-to-sink” system had low sediment discharge and a smooth sedimentary paleogeomorphology. The “source-to-sink” system was predominantly characterized by small-scale beach bars with few fan deltas. With the decreasing level of sediment discharge and continued smoothing of the sedimentary paleogeomorphology, the beach bars expanded.〈/p〉 〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉 〈p〉During the TST stage, the source area atrophies and produces a continued transgressive depositional characteristic of the “source-to-sink” system. Fan deltas dominate the system in the steep paleogeomorphological setting. During the RST stage, the source area expands and make the system expand. Beach bars dominate the system in the gentle paleogeomorphological setting.〈/p〉 〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019302597-ga1.jpg" width="500" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 181〈/p〉 〈p〉Author(s): Xiaoqi Wu, Quanyou Liu, Guangxiang Liu, Chunhua Ni〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The chemical compositions and stable carbon and hydrogen isotopic compositions of natural gases in different strata of the Yuanba gas field in the Sichuan Basin were analyzed to investigate their genetic types and source. Natural gases from the Permian Changxing and Triassic Feixianguan formations have dryness coefficients higher than 0.995 and contain H〈sub〉2〈/sub〉S in most gas samples, having a positive correlation between the H〈sub〉2〈/sub〉S and CO〈sub〉2〈/sub〉 contents. The identification of gas origin and gas-source correlation from this study indicate that natural gas in the Ziliujing Formation and most gas samples from the Xujiahe Formation are coal-type gas produced from primary cracking of kerogen, and they are self-sourced reservoirs in relatively independent systems. The natural gases in the 1st and 2nd members of the Xujiahe Formation were mixed with minor amounts of oil-type gas from argillaceous carbonate rocks in the Leikoupo Formation. In addition to the self-accumulated oil-type gas in the Leikoupo Formation, natural gas mainly came from the overlying or lateral source rocks in the Xujiahe Formation. The H〈sub〉2〈/sub〉S-bearing natural gases in the Changxing and Feixianguan formations were produced by the cracking of crude oil from source rocks in the underlying Wujiaping Formation, with partial contributions from certain local source rocks in the Permian Dalong Formation. The H〈sub〉2〈/sub〉S-bearing natural gas has undergone the thermochemical sulfate reduction (TSR) which were dominated by heavy hydrocarbons. The high δ〈sup〉13〈/sup〉C values of CO〈sub〉2〈/sub〉 in these gas reservoirs mainly result from the interaction between acidic fluids and carbonate rocks in the reservoirs.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019302585-ga1.jpg" width="500" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 19 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): A. Graham Leslie, Thomas J.H. Dodd, Martin R. Gillespie, Rhian S. Kendall, Thomas P. Bide, Timothy I. Kearsey, Marcus R. Dobbs, Michael Kim Woon Lee, Kiefer Chiam〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Singapore bedrock geology is dominated by late Permian to Triassic arc magmatism and a genetically related, essentially Middle to Upper Triassic, marine to fluvial volcano-sedimentary inner forearc succession. These Mesozoic strata are deformed into a pattern of NE-translated ductile–brittle deformation structures during the latest Triassic to earliest Jurassic collision and amalgamation of the Sibumasu continental block with the southern part of the Sukhothai Arc. The subduction-related magmatic complex represented in Singapore by the granitic to gabbroic plutons of the Bukit Timah Centre likely acted as a backstop to thrusting at this time. Collisional tectonics drove progressive shortening and steepened earlier-formed inclined asymmetrical folds, culminating in the regional-scale development of a non-coaxial, NE-vergent and NE-facing, fold and thrust system. In Singapore, the Murai Thrust and Pasir Laba Thrust are identified as major elements of this system; both are associated with SW-dipping thrust-imbricate duplex slices. Two distinct early Cretaceous (Berriasian and Barremian) sedimentary successions overstep these collisional tectonic structures. An array of mostly NE–SW and ENE–WSW trending faults and fractures acts as important control on bedrock unit distribution across Singapore and are most likely generated by Cenomanian dextral shear stress. That stress locally reactivated faults initiated during orogeny, or even earlier. Knowledge of the geotechnical impact of these structural features is critical to both future development and ongoing management of the subsurface in Singapore.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019302421-ga1.jpg" width="483" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 26 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Mukteshwar Nath Mishra〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The Shillong plateau in northeast India constitutes an actively deforming anticlinal basement uplift in the foreland of the Himalayas in the north and the Indo-Burman ranges in the east. The study aims to document zones of active crustal deformation in the Shillong plateau through the interpretation of the geometry and the quantitative analysis of stream profiles derived from 30-m SRTM DEM.〈/p〉 〈p〉Longitudinal profiles of the streams draining the plateau exhibit conspicuous convex upward reaches, mainly to the upstream of faults and in areas of deep river incision. Analysis of river profiles using Hack’s stream-gradient index (〈em〉SL〈/em〉-index) reveals perturbations in profiles and steep channel-gradients in the middle reaches of the streams.〈/p〉 〈p〉Spatial distribution of the 〈em〉SL〈/em〉-index brings out extensive zones of anomalously high stream-gradients along the monoclinal flexure at the southern margin of the plateau adjacent to the Dauki fault and along the northern margin, where multiple en echelon faults define step-like topography. In the western part of the plateau, spatial association of zones of high stream-gradients with well-defined fault-scarps is suggestive of active crustal deformation by differential vertical movement along faults.〈/p〉 〈p〉The observed spatial distribution of anomalously high stream-gradients is uncorrelated with the lithological variations and hence, perturbations in river profiles and abrupt changes in stream-gradients are suggestive of differential tectonic uplift of the plateau. The study suggests that the rate of active tectonic deformation in the plateau decreases from the east to the west.〈/p〉 〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019302561-ga1.jpg" width="382" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 25 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Jianwei Zeng, Kai Liu, Ren Jiang, Junjie Yu, Changbo Li, Ling Zhao, Bo Peng, Jinxiu Lao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Drilling cores from the Hangjiahu Coastal plain in the southwestern corner of the Southern Yangtze River deltaic plain, East China, contain a variety of soft-sediment deformation structures in the Late Pleistocene lacustrine and tidal sediments. They include load-flame structures, ball-and-pillow structures, diapir structures, liquefied sand veins, liquefied breccias, syn-sedimentary fault, seismo-cracks and brittle breccias. Sedimentary facies assessment of host deposits and development features rule out an exogenic origin of the soft-sediment deformation structures, such as gravity-flow, storm activity, wave action or flood. These soft-sediment deformation structures in the study area are interpreted as seismites, their spatial distribution suggest that the earthquakes were sourced from the intersection of the Majin-Wuzhen Fault and the Huzhou-Jiashan Fault. Seismites recognized in cores indicate three episodes of short and sudden seismicity (magnitude〉5), which are interpreted as a response to syn-depositional tectonic activity and differential subsidence of the Taihu block during the Late Pleistocene period. Systematic study of spatial and temporal distribution of these seismites improves the understanding of the tectonic context and evolutionary history of sedimentary basement.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019302494-ga1.jpg" width="467" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 25 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Xuemei Li, Huiping Zhang, Qi Su〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Cenozoic tectonic deformation in the Madong Shan, especially since the Holocene, is the key to understand stress transfer at the southeastern terminus of the Haiyuan Fault, northeastern Tibetan Plateau. In this work, we explored the uplift pattern of the Madong Shan by combining the form of bedrock channel and river incision rate. The normalizd channel steepness (〈em〉k〈sub〉sn〈/sub〉〈/em〉) and wideness (〈em〉k〈sub〉wn〈/sub〉〈/em〉) indices provided two comparable channel morphologic parameters. To evaluate the differences among the rock uplift, river incision rates were determined by optical stimulated luminescence (OSL) dating of the strath terraces along two rivers. The results show that channels in the northern Madong Shan are relatively steeper and narrower, and have the higher shear stress to incise than those in the south. The incision rates in the northern channels were two times higher than those in the southern channels since the late Holocene. The major changes of channel morphometry and incision rates are coinciding spatially with the stress transfer direction along the Haiyuan Fault, rather than the lithologic variations. Therefore, we speculate that the differential bedrock channel form and river incision were mainly controlled by variable tectonic uplift across the Madong Shan with secondary contribution of the lithology. Deformation of the Madong Shan has been continuously driven by the strain transfer along the Haiyuan Fault.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019302482-ga1.jpg" width="479" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 25 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Sung-Ping Chang, SN Fathiyah Jamaludin, Manuel Pubellier, Nabilah M. Zainuddin, Chee-Meng Choong〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Attention has been given to the relevance of chaotic rock units including tectonic, sedimentary, and diapiric mélanges in the evolution of subduction-related accretionary complexes but they have often been perceived as relicts in suture zones. Northwest Borneo (West Sabah) was evidently a subduction complex which experienced collision caused by the Proto-South China Sea, and a consequence of post-collision intrusion currently expressed as a 4000-metre high mountain, together with gravity tectonics offshore of Palawan and Borneo. The continuous deformation of the accretionary wedge from the collision to the post-collision stages is, however, a matter of contention, along with the timing as subduction ceased. This study integrates the seismic profiles, field observation and topographic interpretation to show that the backstop is composed of ultramafic rocks and a vast amount of severely sheared pillow basalts and radiolarite. Wide shear-bands also exhibit metric phacoid-shaped blocks of basalt and radiolarite. Successor basins cover these collision features to the west, and through a system of circular basins overlying a shale matrix, engulfing metric blocks of basalts, radiolarite and sandstone. The chaotic rock unit was occasionally brought to the surface and the overlying strata are deformed as circular synclines and anticlines. We, therefore, suspect that the mechanism of exposing the mélange involved a diapiric process that pushed this low viscosity material upward. Accordingly, the entire process illustrates a tectonic evolution involving gravity tectonics from the end of the collision to the post-collision setting of northern Borneo.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019302470-ga1.jpg" width="427" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 21 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Ömer Kamacı, Şafak Altunkaynak〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Mineral chemistry, petrography and crystal size distributions of Early Miocene mafic and intermediate lavas from the Kepsut Volcanic Complex (KVC) have been studied to decipher magma chamber processes and dynamics beneath northwestern Anatolia. KVC which is a part of the Western Anatolian Volcanic Province comprises lavas represented by various compositions ranging from basaltic andesite to rhyodacite and associated pyroclastics. Basaltic andesite and andesite lavas of the KVC, the focus of this study, present distinct petrographical features such as three plagioclase generations, patchy zoning, oscillatory reverse zoning, sieve textured crystals and clinopyroxene-mantled amphibole that are clear indicators of disequilibrium conditions in magma chamber(s). Petrography, mineral chemistry and crystal size distribution studies of andesite and basaltic andesite lavas of the KVC indicate that magma evolution occurred in four stages: I) Near-Equilibrium Stage, II) Mafic Input Stage, III) Mixing/Mingling Stage and IV) Pre-eruption Stage. Thermobarometry calculations indicate that crystallization of andesite and basaltic lavas occurred at similar pressure (mid-to-deep crustal depths, 5-7 kbar) but distinct temperature conditions (920-952 〈sup〉o〈/sup〉C and 921-1069 〈sup〉o〈/sup〉C, respectively) suggesting that KVC magmas evolved either in the same or different magma chambers at similar depths and experienced open-system processes. Both of these hypotheses are compatible with multistage evolution of the KVC. Combined petrography, mineral chemistry and geothermometry studies on KVC rocks indicate that mixing/mingling processes and subsequent decompression-driven crystallization were the principal mechanisms for the origin of the textural and mineralogical diversity that is characteristic of KVC lavas. Disequilibrium crystallization was probably caused by the influx of a hotter basaltic magma into crustal magma chambers during the first major period of north-south extension in western Anatolia.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S136791201930241X-ga1.jpg" width="380" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 26 April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Abhijit Gogoi, Dilip Majumdar, John Cottle, Pankhi Dutta〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Extensive Mesoproterozoic magmatism occurred in the Karbi Hills Massif, NE India, providing a key to understanding the early geodynamic evolution of Karbi Craton during the Columbia (Nuna) supercontinent cycle. We present here LA-ICP-MS zircon U–Pb ages, Lu–Hf isotopic and geochemical data of Panbari-Geleki-Dallamara and Kuthori granitoids in the Kaziranga area in northern Karbi Craton. These granitoids occur as stock like bodies intruded into the Late Archean-Paleoproterozoic Basement Gneissic Complex, supracrustals and previously emplaced mafic magmatics. Due to subsequent tectono-thermal activities, the older magmato-sedimentary sequences suffered variable degrees of metamorphism and deformations. The U/Pb zircon geochronology indicates that these granitoids were emplaced over a span of about 94 m.y., subsequent to the emplacement of mafic dykes, sills and stocks in a post collision rift basin, now represented by the ‘Shillong Basin’. The Karbi Hills granitoids are younger (1644±33-1550±25 Ma) than the Meghalaya felsic magmatics (1778±37-1620±9.2). Basin formation and sedimentation began in the Shillong Basin (Shillong Group) as early as 1900 Ma and continued till 1400 Ma, coinciding with the assembly and dismantling of Columbia supercontinent. Early Proterozoic psammopelitic sedimentation prior to and/or after the mafic-felsic intrusions is now represented by the ‘Shillong Group’. The mafic magmatics occur in the craton, present a continental flood basalt character. The chemical makes up state that the granitoids bear mostly metaluminous but weakly peraluminous, A-type, within plate characters. The granitoids are highly potassic and silica saturated (up to 74.3 wt% SiO〈sub〉2〈/sub〉), REE deficient, K, Rb and Ba enriched but Nb, Ti and P depleted. The zircon ɛ〈sub〉Hf(t)〈/sub〉 for granitoids show a variation up to 7 εHf units (+1.5 to +9.9), however, 13% grains possess negative ɛHf(t) values. This is particularly ascribed to minor mixing of magmas sourced from depleted mantle and metasomatised continental crust. There is, however, no record of any vestige of ophiolite preserved in the craton that would support an active subduction mechanism responsible for this part of early Mesoproterozoic magmatic episode.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019301701-ga1.jpg" width="500" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 176〈/p〉 〈p〉Author(s): Jiaoyang Zhang, Jie Li, Yao Yan, Jingjing Li, Xiaoqiao Wan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉To examine possible relationships between regional changes in vegetation and climate and fluctuations in solar activity, we obtained a high-resolution 1000-year pollen record from the Sanjiaolongwan Maar Lake (SJML) in northeastern China. An age model was established using analyses of 〈sup〉210〈/sup〉Pb, 〈sup〉137〈/sup〉Cs and AMS 〈sup〉14〈/sup〉C. The pollen assemblages indicate that during the last millennium the vegetation of the study area was temperate coniferous and deciduous broadleaved mixed forest. Although 〈em〉Pinus〈/em〉 is the most abundant pollen type in the record, various lines of evidence suggest that it is not especially temperature-sensitive. However, the analysis of the changes in pollen assemblages over the past 1000 years, and a comparison with pollen records from other lakes in the region, indicate that the 〈em〉Quercus〈/em〉 frequencies can be used as a relatively sensitive temperature index for the study area. Several notable cold periods, with lower 〈em〉Quercus〈/em〉 frequencies, occurred at approximately 1200 AD, 1410 AD, 1580 AD, 1770 AD and 1870 AD. These centennial-scale cold periods basically correspond to major minima in solar activity, suggesting that variations in solar activity may have been an important driver of climate and vegetation change in the study area during the last millennium.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019300781-ga1.jpg" width="462" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 27 April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Fuat Erkül, Cihan Çolak, Sibel Tatar Erkül, Elif Varol〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Alkaline and ultrapotassic volcanic rocks in the Afyon Volcanic Complex are regarded as the first products with asthenospheric signature after post-orogenic magmatism in western Turkey. The Yağcıköy Volcanic Complex (YVC), a key locality in the western off-axis of the Afyon Volcanic Complex, comprises three units consisting of domes, dykes, lava flows and associated volcaniclastic rocks intercalated with Middle Miocene fluvial/lacustrine deposits. Emplacement of the domes and dykes appears to have been controlled by NE-trending faults in a rift environment. The YVC is alkaline and shoshonitic in character, and all the volcanic units in the complex have similar geochemical patterns (enriched in LILE and LREE and depleted in Nb, Ta and Ti). The 〈sup〉87〈/sup〉Sr/〈sup〉86〈/sup〉Sr and 〈sup〉143〈/sup〉Nd/〈sup〉144〈/sup〉Nd ratios range from 0.704989 to 0.706662 and 0.512492 to 0.512595, respectively. The geochemical and isotopic data suggest that fractionation of parental basaltic trachyandesite magmas generated a magma chamber with chemically normal zonation. The geochemical data and modeling results suggest that the YVC originated from a spinel peridotite-bearing lithospheric mantle source that had been metasomatized by subduction components. The rifting environment that hosts the volcanic products is thought to have resulted from slab tear that caused the rise of fertile asthenospheric material to relatively shallow depths. The upwelling of hot asthenospheric melts through a tear subsequently melted the spinel peridotite-bearing lithospheric mantle source.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019301725-ga1.jpg" width="270" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 26 April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Guangyu Fu, Xiaoning Su, Yawen She, Tai Liu, Jun Li, Shanghua Gao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Longquan Shan fault zone (LQSF) locates in the Sichuan Basin of China, parallel to the well-known Longmen Shan fault zone. Different models for the LQSF indicate different understanding of the geological evolution of the Tibetan Plateau. In this paper, we provide evidences which demonstrate that the LQSF is a normal and deep-buried fault zone. Firstly, we find distinct extensional strains around the LQSF based on Global Positioning System (GPS) observations. We also find that the downward GPS velocities across the LQSF decrease suddenly from 4-5 mm/yr at the west to roughly zero at the east. Secondly, we collate focal mechanism solutions to earthquakes of M≥3.0 in the Sichuan Basin and find that 12 out of 21 earthquakes are normal earthquakes. The surrounding extensional strains and the high proportion of normal earthquakes indicate that the shallow part of the LQSF is normal at present. Thirdly, based on the migration section obtained from deep seismic reflection profiling, we outline the geometric structure of the LQSF. It is a deep-buried fault zone that reaches the Moho, with two branches at the top. Such a fault model corresponds with the realities of the low seismic activities around the Longquan Shan anticline, and the scattered earthquakes beneath the Chengdu plain. Finally, we propose a three-stage evolutional model about the Longquan Shan fault system, which includes the formation of anticline in Late Triassic, the uplift of the Mountain in Oligence, and the stage of normal characteristics of the fault zone from Late Miocene.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019301610-ga1.jpg" width="232" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 179〈/p〉 〈p〉Author(s): Pham Nhu Sang, Zhifei Liu, Karl Stattegger〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Clay mineralogy and elemental geochemistry of Core SO18401 on the Vietnam Shelf are used to reconstruct the history of weathering and erosion in central Vietnam over the past 13.2 ka. The variability of the clay species across the 13.2 ka BP together with the age model allows a subdivision into four temporal stages. Provenance analysis based on clay mineralogy indicates that small mountainous rivers in southern-central Vietnam are the major sources of terrigenous sediments on the central Vietnam Shelf. Smectite and kaolinite originated from the chemical weathering of Mesozoic and Neogene-Quaternary basaltic rocks and Paleo-Mesozoic felsic intrusive rocks, respectively, under warm and humid climate conditions; whereas illite and chlorite were mainly derived from physical weathering of Paleo-Mesozoic felsic intrusive rocks and Precambrian metamorphic rocks in central Vietnam. Accordingly, smectite/(illite + chlorite) ratio, together with elemental ratios of Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉/K〈sub〉2〈/sub〉O, TiO〈sub〉2〈/sub〉/Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉, and SiO〈sub〉2〈/sub〉/Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉, can be utilized to reflect the relative importance between chemical weathering and physical weathering/erosion of the parent rocks in southern-central Vietnam. Higher smectite/(illite + chlorite) and Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉/K〈sub〉2〈/sub〉O ratios indicate a more important role of chemical weathering, and higher TiO〈sub〉2〈/sub〉/Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 and SiO〈sub〉2〈/sub〉/Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 ratios suggest enhanced contribution of physical weathering and erosion. A combination of these mineralogical and elemental proxies allows the distinction of four stages of weathering and erosion evolution in southern-central Vietnam over the Holocene and Younger Dryas periods. Enhanced physical weathering and erosion took place during the periods ∼13.2–11.0 ka BP (Stage I) and ∼3.9–2.0 ka BP (Stage III), associated with relatively arid conditions. By contrast, strengthened chemical weathering occurred during the periods ∼11.0–3.9 ka BP (Stage II) and 2.0 ka BP to present (Stage IV), corresponding to more warm and humid climatic conditions. Our study suggests that the weathering and erosion history of southern-central Vietnam over the Holocene is mainly controlled by the East Asian monsoon climate.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019301658-ga1.jpg" width="187" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 179〈/p〉 〈p〉Author(s): Han Zheng, Xiaomeng Sun, Pujun Wang, Wei Chen, Junpei Yue〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Proto-South China Sea (PSCS) represents the lithosphere that formerly occupied the region southeast of South China where the present-day South China Sea is located. The subduction and demise of the PSCS have attracted wide attention, whereas the pre-subduction history (particular the Mesozoic) of the region remains relatively neglected. In this paper, the radiolarian paleobiogeography of the region is analyzed to identify the paleobiogeographic affinity and paleo-connectivity of the PSCS with the Pacific and Tethys oceans during the Mesozoic. Then the continent–ocean configuration and tectonic evolution of the PSCS and adjacent areas are discussed through the integration of paleobiogeographical results and associated paleomagnetic, stratigraphic, and petrologic data. The main conclusions are as follows: (1) During the Triassic, the PSCS was situated in the transition zone between the Pacific and Tethys oceans, and its paleobiogeography was influenced by both oceans. The PSCS was characterized by complex tectonic overprinting by the Pacific and Tethyan tectonic regimes. (2) In the Early–Middle Jurassic, the PSCS was well connected to the Pacific Ocean but poorly connected to the Tethys Ocean, consistent with the paleobiogeography of the PSCS being mainly constrained by the Pacific Ocean. The PSCS was part of the Paleo-Pacific slab. (3) During the Late Jurassic–Cretaceous, the PSCS was in a semi-closed environment. The Late Jurassic–early Late Cretaceous PSCS was part of a west-facing Andean-type subduction zone, and the late Late Cretaceous PSCS was situated in an extensional tectonic setting.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S136791201930166X-ga1.jpg" width="324" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 14 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): LuTong Zhao, JingBin Wang, YuWang Wang, RuFu Ding, LingLi Long, Yu Shi, ZhiYuan Sun〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The Suoerkuduke Cu–Mo skarn deposit is located in Fuyun County, Xinjiang Uygur Autonomous Region in NW China, within the northern margin of the East Junggar block. Comprehensive studies of ore deposits demonstrate that the deposit features two episodes of skarn mineralization: the first (Episode A) skarn is stratiform or lenticular and is characterized by predominantly disseminated Fe–Cu–Mo ores, whereas the second (Episode B) skarn occurs as veins or stockworks and contains predominantly Cu–Mo–Zn ores.〈/p〉 〈p〉Episode A mineralization formed in the Late Devonian (379.2 ± 2.8 Ma), whereas Episode B mineralization formed in the Early Permian (296.6 ± 1.9 Ma). Episode A skarn was genetically linked to dacite/syenite porphyries and may have occurred in an island arc setting, whereas Episode B skarn was genetically linked to granite porphyry (295.3 ± 3.8 Ma) and may have developed in a postcollisional setting.〈/p〉 〈p〉Based on mineral paragenesis and crosscutting relationships, the hydrothermal mineralizing event of Episode A is further divided into three stages, i.e., the prograde (A1), oxide (A2), and retrograde (A3) stages, while that of Episode B is divided into four stages, i.e., the prograde (B1), retrograde (B2), quartz-sulfides (B3) and quartz-carbonate (B4) stages. Three types and seven subtypes of fluid inclusions (L-, V- and S1- to S5-types) are distinguished based on fluid compositions and phase assemblages.〈/p〉 〈p〉Episode A ore-forming fluid (H〈sub〉2〈/sub〉O–NaCl) system involved two major mineralizing events: (1) the first fluid boiling (stage A1) at 530–560 °C and lithostatic pressures of 550–800 bar and (2) the second fluid boiling (stage A3) at 370–420 °C and hydrostatic pressures of 200–300 bar. Episode B ore-forming fluid (H〈sub〉2〈/sub〉O–NaCl–KCl) system involved four major mineralizing events: (1) the first fluid boiling (stage B1) at 530–580 °C and lithostatic pressures of 600–850 bar, (2) the second fluid boiling (stage B3) at 320–360 °C and hydrostatic pressures of 100–200 bar, (3) overpressure trapping; brine inclusions homogenized by halite dissolution can be explained as a result of entrapment under overpressure condition, and (4) mixing with meteoric water (stage B4). Fluid boiling was the predominant ore-forming mechanism, while mixing between magmatic and meteoric fluids may also have contributed to ore mineral precipitation (mainly for sphalerite) in Episode B to a lesser extent.〈/p〉 〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019300938-ga1.jpg" width="206" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 15 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Guoming Gao, Jing Hou, Guofa Kang, Chunhua Bai, Limin Wen, Hong Zhao, Lan Shi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this paper, data of gravimetry, aeromagnetic survey, and surface heat flow are utilized in a combined manner to investigate the crustal thickness, Curie surface, and lithospheric thermal state beneath the Junggar Basin and adjacent Mountain Ranges. The Moho depth, Curie depth, and thermal lithospheric thickness are found to be 38–52 km, 32–50 km, and 120–260 km, respectively. The Moho and Curie surface present a rough inverse correspondence between each other. In the Tianshan and Altai Mountain Ranges, Moho interface is deep but Curie surface is shallow. In the Junggar Basin, Turpan Basin, and Yili Basin, the situation is in reverse. The uppermost mantle in the Central Depression and Eastern Uplift of the Junggar Basin, the Turpan Basin, the Yili Basin, as well as the north-west area off Fuhai is investigated to have been magnetized. The aeromagnetic anomalies and the Curie surface in the Junggar Basin surprisingly reveal that the northward subduction of the north Tarim block/slab under the Junggar Basin accompanied by the uplift of the Tianshan Mountain Range. Also, in response to the northward movement, the rigid Central Depression of the Junggar Basin extruded from its east and west sides. The westward extrusion is manifested by the West Uplift of the western Junggar Mountain Range.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019300926-ga1.jpg" width="311" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 177〈/p〉 〈p〉Author(s): Peng Fang, Guiting Hou〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Ms 8.0 Wenchuan earthquake occurred in the Longmenshan fault zone (LFZ) of the eastern margin of the Tibetan Plateau (TP). The tectonic activities in this region have been a focus of extensive studies in the past two decades. Two different models involving oblique stepwise rise and channel flow, respectively, are proposed and can be used to explain the generation of earthquakes. The oblique stepwise rise model emphasizes more about the fault of the upper crust, whereas the channel flow model concerns more about the different crustal rheological structures. Currently, because of the confirmation of geophysical data on the rheological structure of the TP, more researchers agree with the channel flow model. To investigate the generation of earthquakes in the LFZ, this study establishes a three-dimensional viscoelastic model based on the heterogeneity of the lithospheric structure and the segmentation of faults. Using ANSYS finite element software to simulate the evolution of stress and strain, the calculated results are consistent with focal mechanism solutions, fault striations, and topography. The best-fit stress field suggests that stress localization in the Longmenshan range is mainly controlled by the channel flow and fault segmentation. The differing viscosities and relative movement between the channel flow and the Sichuan Basin induce a concentration of stress in the LFZ. The stress was most concentrated in segment II, closest to the leading edge of the channel flow, and wherein the Wenchuan earthquake occurred. Additionally, the higher locking degree of segment II found before the Wenchuan earthquake induced higher stress levels at shallow depths, corresponding to higher seismic activity in segment II. Thus, the combined action of the channel flow and fault segmentation controls the distribution of stress and causes the generation of earthquakes in the LFZ.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉 〈p〉The combined action of the channel flow and fault segmentation controls the distribution of stress and causes the generation of earthquakes in the Longmenshan fault zone.〈/p〉 〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019301245-ga1.jpg" width="484" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 177〈/p〉 〈p〉Author(s): Yingqiang Li, Renqi Lu, Dengfa He, Xiaoshan Wang, Yiduo Liu, Xiwei Xu, Xibin Tan, Mingang Cai〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Increasingly frequent earthquakes in the Longmenshan (LMS) tectonic belt are linked to the ongoing eastward growth of the Tibetan Plateau during the Late Cenozoic. Following the devastating 2008 Ms 8.0 Wenchuan earthquake in the central LMS and the 2013 Ms 7.0 Lushan earthquake in the southern segment, an unexpected Ms 5.4 Qingchuan earthquake occurred on September 30, 2017 in the northern LMS. We synthesize focal mechanism solutions, relocated aftershocks, regional geology, and seismic reflection profiles in order to determine the pre-existing faults and active fault system in the northern LMS, thus to better assess potential seismic hazards. At a seismically resolvable scale, we identify a large structural wedge at the basement that is cross-cut by numerous multiphase and multi-behavior active faults. Our seismotectonic model indicates that the seismogenic fault responsible for the 2017 Ms 5.4 Qingchuan earthquake is a pre-existing thrust fault with a dip of ∼34° in the frontal thrust ramp. Reactivation of this fault then triggered the activity of the co-seismic strike-slip fault that was formed in the 2008 Wenchuan event. The seismic interpretation, focal mechanism solutions, and aftershock distribution indicate that two sub-segment faults with different geometries are distinguished along the northern LMS. Accordingly, a transformation of the coseismic fault with different geometry and kinematics is formed. With the constraints that the mainshock and aftershocks occurred on two different faults, we propose that both the frontal ramp thrust fault and the recently-formed strike-slip fault are tectonically active. This study highlights the importance of the influence of the pre-existing fault system on the evolution of the northern LMS during the Late Cenozoic. The rapid uplift of the eastern Tibetan Plateau and the complex fault system indicate the potential for seismic risks in the northern LMS.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019301257-ga1.jpg" width="500" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 177〈/p〉 〈p〉Author(s): Shao-Cong Lai, Ren-Zhi Zhu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉High-Mg# (molar Mg/[Mg + Fe]) intermediate to felsic rocks, such as high-Mg andesitic rocks (HMA) and Mg andesites (MA), are usually produced by melting of mantle-derived peridotites and/or interaction with mantle-derived peridotites. Both are crucial in tracking mantle-crust interaction processes in the deep crust. We present LA-ICP-MS in-situ zircon U-Pb isotopic data, whole-rock geochemistry and whole-rock Sr-Nd-Pb-Hf isotopic data for the Basu granodiorites which are exposed between the Jiali fault and the Bangong-Nujiang suture, SE Tibet. The LA-ICP-MS zircon U-Pb data show that the granodiorites were formed at ca. 122.1 ± 1.0 Ma, coeval with other granitoids in this region. The granodiorites belong to the high-K calc-alkaline and high-Mg# (49.7–53.7) series, similar to typical MA. The decreasing A/CNK from 0.97 to 0.87 and increasing FM (molar Fe + Mg) from 0.08 to 0.16 indicate a clinopyroxene entrainment and I-type trend. The rocks also display enriched Rb, Th, U and Pb, but depleted P, Ti and obvious negative Eu anomalies. Evolved whole-rock isotopic compositions of Basu granodiorites include high initial 〈sup〉87〈/sup〉Sr/〈sup〉86〈/sup〉Sr (0.7097–0.7114), negative 〈em〉ε〈/em〉Nd(〈em〉t〈/em〉) (−12.0 to −7.2) and 〈em〉ε〈/em〉Hf(〈em〉t〈/em〉) values (−9.6 to −7.9), and lower to upper crustal affinity of Pb isotopes which imply that they were derived from an ancient and evolved lower crust source. Therefore, we suggest that these granodiorites were products of interaction between partial melting of ancient basaltic lower crust and mantle-derived peridotites. Together with a geochronology dataset from the literature, we suggest that there was intensive granitic magmatism occurred in the Early Cretaceous range from 133 to 113 Ma in the northeastern Lhasa terrane, similar to those in the central and northern Lhasa terrane. Furthermore, we have compared with the dataset of in-situ zircon Lu-Hf isotopes, whole-rock Sr-Nd from the literatures and the relationship with zircon U-Pb ages in the northeastern Lhasa terrane, all of which indicate the importance of evolved and ancient continental crust source in the Early Cretaceous magmatism in the northeastern Lhasa terrane, but also that the mantle-derived materials play a necessary role in the generation. In addition, the amount of enriched and evolved isotopic component gradually decreased from ca.140 to 100 Ma.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019300896-ga1.jpg" width="500" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 177〈/p〉 〈p〉Author(s): Jing Yuan, Guoding Yu, Mingshui Song, Jianhui Zhong, Daotao Dong, Wei Wang, Yali Liu, Lichi Ma〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Deep-water sandstones related to sediment gravity flows are becoming an increasingly important exploration domain in continental rift basins in China. However, ambiguities remain regarding the initiation, evolution, and deposition of sediment gravity flows on faulted slopes, where step faults are commonly developed. To address the uncertainties related to these processes, grain size analysis, lithofacies analysis, logging interpretation, and seismic interpretation were employed to study Paleogene sediment gravity flow deposits from well cores on a faulted slope in the Zhanhua Sag of the Bohai Bay Basin. Twelve lithofacies related to sediment gravity flows were recognized and attributed to intrabasinal sediment gravity flows (ISGFs) induced by slope failures and extrabasinal sediment gravity flows (ESGFs) generated by floods. Active faults were important triggers for ISGFs on the faulted slope in the Zhanhua Sag. The fault activity rate had a prominent role in determining the volume of re-transported sediments, which further influenced the evolution of the resulting flows. Travelling across multiple faults downslope, ISGFs generally underwent considerable velocity losses, with the result that almost all sediments were deposited in shallow water. Moreover, unconsolidated ISGF deposits could be transported again to generate sediment gravity flows, obscuring the depositional characteristics of ISGFs. ESGFs originated from rivers during floods and involved the transformation of cohesive into turbulent hyperpycnal flows. In humid and warm climates, active sag-border faults favoured the generation of long-lived ESGFs. These flows usually travelled along intra-sag faults and therefore considerable volume of sediments could be transferred into deep water. The resulting thick-bedded hyperpycnites contributed substantially to the reservoirs of Bonan Oilfield. Meanwhile, short-lived ESGFs usually generated in the regions where sag-border faults were extinct. They generally travelled down the faulted slope and deposited sediments in shallow water. These features suggest that the initiation, evolution, and deposition of sediment gravity flows on the faulted slope are mainly controlled by faults and climate. Hyperpycnites can serve as excellent reservoirs for hydrocarbon accumulation and they are probably common in other sags of the Bohai Bay Basin.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019301178-ga1.jpg" width="257" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 182〈/p〉 〈p〉Author(s): Xiaohu He, Shucheng Tan, Jiaxi Zhou, Zheng Liu, John Caulfield, Siqi Yang, Huiquan Tian〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We report for the first time the occurrence of leucogranite bodies that intruded the Ailaoshan metamorphic complex along the Ailao Shan-Red River (ASRR) shear zone. Leucogranites in Yuanyang, Southeast Yunnan province, are composed of quartz (~30%), alkali feldspar (~45%), plagioclase (~5%), muscovite (~13%) and biotite (~3%) and other minor silicate minerals (~3%, garnet, tourmaline). U–Pb dating of zircon from leucogranites yields a weighted mean age of 27.4 ± 0.5 Ma, suggesting a late Oligocene anatexis event. These leucogranites are strongly peraluminous with A/CNK values of 1.01–1.19 and have high SiO〈sub〉2〈/sub〉 (73.3–77.0 wt%) and K〈sub〉2〈/sub〉O + Na〈sub〉2〈/sub〉O (7.87–10.08 wt%), and low CaO (0.41–0.99 wt%), MgO (0.04–0.21 wt%), TiO〈sub〉2〈/sub〉 (0.01–0.06 wt%) and Fe〈sub〉2〈/sub〉O〈sub〉3〈/sub〉〈sup〉T〈/sup〉 (0.44–0.86 wt%) contents. They are geochemically similar to Himalayan leucogranites and are enriched in large-ion lithophile elements (e.g. Rb), and depleted in high-field-strength elements (e.g. Nb, Zr, and Hf). They have low Zr/Hf (12.3–22.5) and Nb/Ta (2.54–12.73) with negative Eu anomalies (Eu/Eu〈sup〉*〈/sup〉 = 0.05–0.45), indicative of extensive fractional crystallization of plagioclase and zircon. In addition, these rocks have low 〈sup〉87〈/sup〉Sr/〈sup〉86〈/sup〉Sr (t) (0.7072–0.7111), high ε〈sub〉Nd〈/sub〉(t) (−1.53 to −3.61). They contain zircon grains with ε〈sub〉Hf〈/sub〉 (−5 to +1.8) and old two-stage Hf model ages of 1.24–1.02 Ga, implying that they were probably derived from partial melting of amphibolite (old crustal material) within the lower crust. In combination with previous studies of metamorphism of the ASRR shear zone, our study demonstrates that the leucogranites may have been generated in a highly dynamic setting involving both extrusion and extension that defined the beginning of left-lateral slip-strike movement of the ASRR shear zone at 27 Ma.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 20 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Gang Rao, Chuanqi He, Peng Chen, Zhonghai Wu, Jianmin Hu, Qi Yao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Although rotation of fault blocks during seismic and long-term periods has long been recognized in extensional tectonic regimes, the geometry and kinematic behaviors of normal faults at outcrop scale have scarcely been investigated in sufficient detail. In this study, combining with the analysis of high-resolution topography acquired by small unmanned aerial vehicle (sUAV) using the structure-from-motion (SfM) technique, we present the results of our field observations on the structural characteristics of the Seertengshan Piedmont Fault (SPF), a major active normal fault bounding the northern margin of the Hetao Graben, North China. Although previous studies have reported the recent tectonic activity of this fault including timing of most recent earthquake, average slip rate and repeat time of paleo-earthquakes, few of them have focused on geometric patterns of the outcropping fault zones, which provide excellent outcrop-scale examples to investigating geometry and kinematics of active normal faults. Besides the observed prominent fault scarps indicative of recent tectonic activity along the SPF, outcrop observations indicate that in some cases both planar and curved normal faults are developed, forming complex fault zones. Sequential development of normal faults may have rotated the early-formed fault blocks, resulting in shallowly dipping faults and highly tilted strata. Collectively, structural similarities probably exit among normal faults at multiple spatial scales. We suggest that the results of this study are also helpful for a better understanding of structural development and evolution in other actively extending areas.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303281-ga1.jpg" width="434" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 17 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Soichi Osozawa, Tadashi Usuki, Masako Usuki, John Wakabayashi, Bor-ming Jahn〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We conducted major, trace element, Sr-Nd-Hf isotopic, and U-Pb geochronologic analyses of early Cretaceous Kitakami granitic plutons, northeast Japan. We suggest that these plutons include rocks of adakitic affinity, which indicate partial melting of an eclogitic slab. The Kitakami adakites were mostly derived from juvenile oceanic crustal sources, but include inherited zircons with Archean to Neoproterozoic Hf model ages. Rather than being directly derived from crustal rocks of these ages, zircons may have been detrital in the voluminous trench fill sandstone within the Jurassic northern Kitakami accretionary prism. The exhumation of older basement that served as the detrital zircon source may have been triggered by ridge subduction. Although the plutons show a general southward younging from northern Kitakami (120-130 Ma), southern Kitakami (115-125 Ma), and Abukuma (100-115 Ma), restoration of post-crystallization left-slip faults inverts this spatial pattern and results in a northward-younging pattern. This suggests northward migration of a trench-ridge-transform triple junction that included the Izanagi–Farallon ridge. The Sambagawa eclogite may be genetically related to the Kitakami adakite in time and space if the transform duplexing is restored.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303207-ga1.jpg" width="276" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 184〈/p〉 〈p〉Author(s): Tetsuya Tokiwa, Yusuke Shimura, Makoto Takeuchi, Shinji Shimosato, Koshi Yamamoto, Hiroshi Mori〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This study constrains the provenance of the trench-fill turbidite sandstones of the Jurassic accretionary complex (Chichibu accretionary complex) in Southwest Japan using detrital zircon U–Pb ages data. Zircons from all sites (six sites) yielded mainly Precambrian and Permian–Jurassic ages. The Precambrian zircons were derived from the North China Block, whereas the Permian–Jurassic zircons were derived from igneous rocks in and around the Korean Peninsula. The percentage of Precambrian zircons ranged from 39.9% to 52.9% (average 45.5%) of the total, and that of the Permian–Jurassic zircons ranged from 46.5% to 57.6 (average 52.6%). Thus, during the Jurassic, an equal number of zircons was continuously supplied from in and around the Korean Peninsula and the North China Block into a trench on the eastern margin of the Asian continent. The percentage of Permian and Triassic zircons gradually decreased over time, whereas the percentage of Jurassic zircons gradually increased. These changes likely reflected the igneous activity in and around the Korean Peninsula during the Jurassic. These results indicate that the turbidite sandstones of the Jurassic accretionary complex in Southwest Japan comprise detritus from not only the North China Block but also the igneous activity in and around the Korean Peninsula. Therefore, the Jurassic accretionary complex in Southwest Japan was likely formed near the North China Block.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303220-ga1.jpg" width="500" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 183〈/p〉 〈p〉Author(s): Lorenzo Consorti, Fatih Köroğlu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Maastrichtian to Paleocene shallow-water carbonate rocks are common in many parts of Turkey. The occurrence of the Şahinkaya Member limestones in the Çayırbağı-Çalköy (Düzköy/Trabzon) district of the Sakarya Zone represents the neritic expression in marginal areas of a more extensive back-arc deposition, dominated by the hemipelagic sediments of the Tonya Formation. In this contribution, the larger Foraminifera biostratigraphy of the Şahinkaya Member is revisited in order to define the presence of hiatuses associated with the Eastern Pontides arc-continent collision. The study presented here allows for the definition of an upper Maastrichtian and an overlying Paleocene sequence. They are separated from each other by an unconformity of regional meaning extending between the uppermost Maastrichtian to the lower Danian. Shallow Benthic Zones 1–3 (upper Danian to lower Thanetian) have been recognized. The stratigraphy of the Şahinkaya Member and the paleoenvironmental distribution of some larger Foraminifera suggest that, unlike other areas of the Eastern Pontides, the Paleocene deposition was ongoing but still influenced by regional tectonism.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303177-ga1.jpg" width="500" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 17 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Zhaofu Gao, Xiangkun Zhu, Chuang Bao, Jianxiong Ma, Jian Sun〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Langshan-Zhaertai ore belt in northern China includes a dozen sediment-hosted Zn-Pb-Cu deposits, which are traditionally considered to have been formed during sedimentary exhalative (SEDEX) activities in different subbasins in the same Proterozoic marginal rift system. However, this assumption has never been systematically tested. Herein, we re-evaluate the regional metallogeny by the analysis and comparison of Pb isotope data obtained in this study and published in literatures. The Pb isotope signatures of several representative deposits from this ore belt are heterogeneous and do not lie along similar secondary or anomalous lead evolution lines, suggesting that these deposits belong to different metallogenic systems. The Pb isotope ratios of the bulk of the sulfide ores in south ore belt are characterized by unradiogenic isotope compositions and Proterozoic Pb-Pb model ages, whereas the various types of sulfides from the Huogeqi deposit in north ore belt show a very radiogenic lead signature (〈sup〉206〈/sup〉Pb/〈sup〉204〈/sup〉Pb 〉 17.000), which is broadly consistent with common lead of associated Indosinian magmatic rocks, indicating an magmatic-hydrothermal origin. The Dongshengmiao and Tanyaokou massive-type ore sulfides have similar and exceedingly unradiogenic isotope compositions grouped around 15.200 (〈sup〉206〈/sup〉Pb/〈sup〉204〈/sup〉Pb). Their vein-type sulfides show scattered Pb isotope signatures that fall along a well-correlated linear trend towards the right of the massive-sulfide array, indicating some modification during metamorphism. The similarity of lead isotope compositions of the Jiashengpan vein-type sulfides to the common lead of Hercynian igneous rocks indicates that the proximal source of the ore metals in its epigenetic hydrothermal system was Hercynian igneous activity.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303256-ga1.jpg" width="500" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 183〈/p〉 〈p〉Author(s): Song He, Xiang-Hui Li, Hua-Feng Zhang, Shuang-Qing Li, Fukun Chen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The North China Craton underwent exceptional lithospheric thinning. A debate remains as to the mechanism and timing of this thinning partly as a result of the lack of information on the crustal uplift. Mantle-derived mafic rocks can carry key messages of lithospheric thinning and facilitate the determination of the time and mechanism. Gabbroic rocks from the Jinan area in eastern North China were emplaced in the peak period of the thinning and, for this reason, were chosen as the study object. Isotopic ages and P-T conditions of the Jinan gabbro pluton were measured to examine the uplifting and cooling history of the magma. Jinan gabbros were enriched in large ion lithophile elements and large rare earth elements but depleted in high field strength elements without a significant Eu anomaly. Their Sr-Nd-Pb isotopic features suggest that the magma was derived from the partial melting of an enriched lithospheric mantle (EMI). This pluton was emplaced at ~130 Ma, and crystallization temperatures of pyroxene and biotite were 909–1116 °C and 828–952 °C, respectively. The core and rim crystallization pressures of clinopyroxene and plagioclase are ~4.45 kbar and ~2.56–3.91 kbar, respectively. These might record the pressure changes during the uplift process from ~16.5 to 9.5 km. The Rb-Sr isotopic system of biotite was closed at ~121–117 Ma, constrained by the single–grain biotite Rb-Sr ages. This shows that the cooling depth of pluton is ~8.4 ± 2.4 km. Consequently, the pluton was rapidly uplifted from the ~16.5 km to ~8.4 km, at an uplift rate of 0.81 ± 0.24 km/Ma and/or a cooling rate of approximately 50 °C/Ma during 130–120 Ma. This fast uplift was related to the delamination and thinning of the lithosphere that caused activities associated with magmatism and mineralization in eastern North China during the late Mesozoic.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303244-ga1.jpg" width="408" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 183〈/p〉 〈p〉Author(s): Xiaoli Shen, Qingxiang Du, Zuozhen Han, Zhigang Song, Chao Han, Wenjian Zhong, Xiang Ren〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The mixture of the Cathaysian and Angaran floras signifies the evolution of the Paleo-Asian Ocean (PAO). In this study, we present new zircon U-Pb-Hf isotope analyses from the Jiefangcun Formation, Sidonggou Formation, Kedao Group, and Kaishantun Formation in the Yanbian area, NE China. The Kaishantun Formation contains the Kaishantun flora, which is dominated by the Cathaysian flora with a few Angaran elements. The Jiefangcun Formation is characterized by the Jiefangcun flora, which is dominated by the Angaran taxa and contains some Cathaysian elements. The ages of these strata are widely accepted as Permian. However, in this study, the youngest zircon ages of the rock samples from the Jiefangcun Formation, Kedao Group and Sidonggou Formation are 243–245 Ma. Only the Kaishantun Formation is assigned to the Late Permian. The Kaishantun Formation has age peaks at 758, 934, 1856, and 2493 Ma with negative ε〈sub〉Hf〈/sub〉(t) values, and this formation is therefore mainly derived from the North China Craton (NCC). In contrast, the Kedao Group and Jiefangcun Formation have zircon age peaks at ~260, 338 and ~460 Ma with positive and negative ε〈sub〉Hf〈/sub〉(t) values, at 800–1000 Ma with mostly positive ε〈sub〉Hf〈/sub〉(t) values, and at ~1800 Ma with positive and negative ε〈sub〉Hf〈/sub〉(t) values, which suggest bidirectional provenances, including the Jiamusi-Mongolia Block and the NCC. Thus, the mixing between the Angaran and Cathaysian floras occurred during the Late Permian-Middle Triassic, suggesting a scissor-like closure model of the PAO, and the Solonker suture zone extends eastward to the Yanbian area with bidirectional subduction of the PAO.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303165-ga1.jpg" width="351" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 183〈/p〉 〈p〉Author(s): Zheng Gong, Yan Jing, Haibing Li, Li Li, Xiaoyong Fan, Zheng Liu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The 2016 M6.2 Hutubi Earthquake is an event occurred on a reverse fault located in the northern Chinese Tien Shan, but it is debatable whether the seismogenic fault is a low-angle thrust fault. The coseismic strain responses have been recorded by nine 4-component RZB borehole strainmeters, locating 11–320 km away from the epicenter. The nearest four stations have recorded resolvable static strain responses. The authors used the theoretic tide to calibrate the strains, and relocated the 10.31 km by 6.85 km fault plane through a grid-search method. Two groups of fault parameters 279°/70°/87° and 103°/28°/85° were obtained, and the predictions for 24/26 channels for both groups are consistent with the offsets observed in the near stations by correcting the azimuths. The seismogenic fault is more likely the high-angle backthrust fault based on the comparison with the selected aftershocks. Furthermore, all strainmeters have recorded the dynamic strain waves. The dynamic strains are sensitive to the seismic wave propagation direction, and the peak dynamic strains decay faster in the N-S direction than that in the E-W direction due to the regional structure features. The absolute static strains are comparable to the dynamic strains in the near field, but the ratios between them decrease remarkably in the intermediate and far field. The difference in the dependence on distance was found to be useful to differentiate static strains from dynamic strains.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303104-ga1.jpg" width="500" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 183〈/p〉 〈p〉Author(s): Lixing Lü, Jimin Sun, Zhiliang Zhang, Yingying Jia, Tao Li, Chunhong Li, Shengchen Tian, Mengmeng Cao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Investigations of geometry and kinematics of foreland fold-and-thrust belts provide key information for understanding how convergence is accommodated in deformed forelands of orogenic belts. Here, we present the structural styles, deformation ages and shortening rates of three en echelon anticlines located at the west end of the Baicheng-Kuqa foreland fold-and-thrust belt. The results indicate that the three anticlines developed above the Eocene evaporites of the Kumugeliemu Group which constitute the décollement level in this typical thin-skinned tectonics. The initial growth of the East Awate and North Kalayuergun anticlines, as indicated by the syn-tectonic growth strata accumulations, occurred at ~5.3 Ma with shortening rates of ~0.70–0.77 mm/yr and ~0.40–0.43 mm/yr, respectively. Whereas, the initial folding time of the Middle Kalayuergun anticline is ~2.6–1.7 Ma, resulting in a shortening rate of ~0.35–0.65 mm/yr. The shortening rates are lower when compared with foreland deformation in the middle and eastern parts of the Baicheng-Kuqa fold-and-thrust belt. Such differences are mostly related to the strain partitioning caused by the NW-SE dextral strike-slip Kalayuergun fault as well as the influence of a dextral wrenching component in the west end of the Baicheng-Kuqa fold-and-thrust belt. Our study suggests that episodic tectonic deformation in the southern foreland of Tian Shan has been a response to the ongoing India-Asia convergence since the latest Miocene, and the spatial variability of crustal shortening rates has depended on regional tectonic differences.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphic abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303128-ga1.jpg" width="250" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 13 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Ruigang Ma, Chuanlian Liu, Qianyu Li, Xiaobo Jin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Numerous models have been proposed to constrain the process of the South China Sea formation, yet the Paleogene paleoenvironmental researches are hindered by the paucity of long, continuous, well-dated geological records. In this work, Eocene to Oligocene nannofossil biostratigraphy and assemblage changes in a sediment section from the northern South China Sea were studied to shed light on these issues. We established an age model to confine the studied section between ∼40 and 22 Ma based on 17 calcareous nannofossil datum levels. The age model enabled to date the most prominent seismic reflector T〈sub〉60〈/sub〉 centered at ∼26.8 Ma, a regional tectonic event interpreted as corresponding to the “Ridge Jump Event” in the early phase of South China Sea spreading. Changes in nannofossil abundance and assemblage compositions imply continuous transgression and deepening of water depth from the Late Eocene to Early Miocene. During the Late Eocene, the studied area was a neritic sea with relatively eutrophic conditions supporting abundant 〈em〉R. lockeri〈/em〉 group and 〈em〉C. pelagicus.〈/em〉 From ∼34 Ma to ∼27 Ma, during the Oligocene, the earlier neritic environment was replaced by relative warm and oligotrophic conditions in a shallow sea, as indicated by higher concentration of 〈em〉C. floridanus〈/em〉, 〈em〉Sphenolithus〈/em〉 spp. and 〈em〉Helicosphaera〈/em〉 spp. Since ∼26 Ma, pelagic conditions prevailed, small 〈em〉Reticulofenestra〈/em〉 (〈5μm) became dominant, and 〈em〉Discoaster〈/em〉 spp. also increased in response to the deepened water depth.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉 〈p〉Based on calcareous nannofossil biostratigraphic research for the Late Eocene to Early Miocene sediment section at IODP Site U1501, the regional seismic reflector T〈sub〉60〈/sub〉 at ∼26.8 Ma were dated, corresponding to the final stage of the Ridge Jump Event, which marked the onset of accelerated seafloor spreading of the SCS at ∼27.14-26.77 Ma. The paleoenvironmental conditions and the nannofossil assemblages also stepwise changed in response to tectonic events.〈/p〉 〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019303153-ga1.jpg" width="442" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 15 July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences〈/p〉 〈p〉Author(s): Yunxin Fang, Jiangong Wei, Hailong Lu, Jinqiang Liang, Jing'an Lu, Juan Fu, Ju Cao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Crystalline structure, cage occupancy, and gas composition are important gas hydrate characteristics, which can be used to calculate the gas hydrate’s stability and to estimate the energy potential. In May and October of 2015, a Guangzhou Marine Geological Survey team investigated two sites in the Haima cold seeps in the Qiongdongnan Basin, northern South China Sea. They recovered massive gas hydrate samples by conventional gravity coring. After the Shenhu Sea area and Dongsha Sea area, the Qiongdongnan Basin became a new area on the northern slope of the South China Sea where gas hydrates have been found. In order to reveal the structural and geochemical characteristics of the natural gas hydrates, samples were analyzed by micro-Raman spectroscopy and X-ray diffraction under ambient pressure and low-temperature conditions. The results indicate that the gas hydrate samples from the Haima cold seeps are typical structure I hydrates with a hydration number of 6.12−6.19. In addition, trace amounts of H〈sub〉2〈/sub〉S trapped in the hydrate were identified based on its characteristic vibrational signature. The gas composition and δ〈sup〉13〈/sup〉C-CH〈sub〉4〈/sub〉 of the hydrate-bound gas samples were analyzed for gas-source correlation. All of the gas samples are dominated by methane with small amounts of ethane and propane and had relatively light δ〈sup〉13〈/sup〉C-CH〈sub〉4〈/sub〉, indicating that all of the hydrate-bound gases are mixtures of biogenic and thermogenic gas. The thermogenic gas is inferred to be mainly derived from the coal layers of the Late Miocene-Pliocene Yacheng Formation in the northern Lingshui sag.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphic abstract〈/h5〉 〈div〉 〈p〉The Qiongdongnan Basin became a new area in the South China Sea where gas hydrates were discovered. The data shows that gas hydrate from the Haima cold seeps are structure I hydrates. For the first time that H〈sub〉2〈/sub〉S is discovered to be trapped in the gas hydrate in the South China Sea. The hydrate-bound gas are dominated by light δ〈sup〉13〈/sup〉C methane with small amounts of ethane and propane, indicating a mixture of biogenic and thermogenic gas.〈/p〉 〈p〉Raman characteristics of the gas hydrates from the Haima cold seep. (HM1=Haima-1; HM2=Haima-2).〈/p〉 〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019302767-ga1.jpg" width="216" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 181〈/p〉 〈p〉Author(s): Dhanushka Devendra, Rong Xiang, Fuchang Zhong, Yiping Yang, Linggang Tang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Here we present the first detailed planktonic and benthic δ〈sup〉13〈/sup〉C records and benthic foraminiferal assemblage records from the north-eastern Indian Ocean to decipher the palaeoceanographic changes during the last 56 kyr. We identified three different palaeoceanographic stages, clearly differentiated by significant variations in the benthic foraminiferal assemblages and δ〈sup〉13〈/sup〉C records. The results of this study indicate that productivity was generally higher during the glacial periods than during the Holocene. Comparison of the benthic foraminiferal assemblage distributions and planktonic and benthic δ〈sup〉13〈/sup〉C records show a significant correlation between productivity and the bottom water oxygenation on glacial-interglacial timescales. Productivity gradually increased during the period between 56 and 27.5 kyr. During this period, the dominance of 〈em〉Melonis〈/em〉 spp. and 〈em〉Oridosalis umbonatus〈/em〉 were correlated with conditions of intermediate to high surface productivity and moderate bottom water oxygenation. Increased higher equatorial productivity and low bottom water oxygenation during the period between 27.5 and 15 kyr are supported by planktonic δ〈sup〉13〈/sup〉C and faunal records. During this period, the dominance of benthic foraminifera assemblages characterised by 〈em〉Uvigerina peregrina〈/em〉 indicates sustained continuous phytodetritus flux to the seafloor from enhanced surface water productivity and relatively low bottom water oxygenation. The absence or minimal occurrences of high productivity indicating 〈em〉U. peregrina〈/em〉, the dominance of intermediate to low productivity indicating fauna, and relatively low planktonic δ〈sup〉13〈/sup〉C records suggest low productivity and active deep-water oxygenation after 15 kyr. Concurrent river discharge and rising sea levels during this period are indicated by negative δ〈sup〉18〈/sup〉O of 〈em〉G. ruber〈/em〉 at the site.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019302652-ga1.jpg" width="254" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 180〈/p〉 〈p〉Author(s): 〈/p〉

Description: 〈p〉Publication date: 15 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 180〈/p〉 〈p〉Author(s): 〈/p〉

Description: 〈p〉Publication date: 1 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 181〈/p〉 〈p〉Author(s): Lei Fu, Xiaojun Li, Wang Fang, Su Chen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this study, more than 1600 seismic recordings from 88 small-to-moderate earthquakes during 2009 and 2013, which were recorded at 36 seismic stations, were used to calculate the high-frequency attenuation parameter (〈em〉κ〈/em〉〈sub〉0〈/sub〉). By comparing the 〈em〉κ〈/em〉〈sub〉0〈/sub〉 of six seismic stations with neighboring strong motion stations, we observed that the surficial soil layers have aggravated the high-frequency attenuation phenomenon. Besides, we found that stations located in crustal low-velocity anomaly areas maintained higher 〈em〉κ〈/em〉〈sub〉0〈/sub〉 and those located in high-velocity anomaly areas tended to have lower 〈em〉κ〈/em〉〈sub〉0〈/sub〉. The correlation between 〈em〉κ〈/em〉〈sub〉0〈/sub〉 and S-wave velocity anomaly showed that, at the 0–10 km depth range, the 〈em〉κ〈/em〉〈sub〉0〈/sub〉 values clearly decrease as the velocity anomaly increases. The generalized inversion technique (GIT) was adopted to estimate the 〈em〉Q〈/em〉(〈em〉f〈/em〉) model of the Sichuan Basin (SB) and Songpan-Garzê Orogen (SGO), in accompaniment with the site responses of 28 seismic stations. The derived 〈em〉Q〈/em〉(〈em〉f〈/em〉) model were similar to those obtained from previous studies. Analyses of site responses revealed that the amplification curves and levels of SB and SGO were significantly different. Then, Site responses estimated from the genetic algorithm and GIT were compared. The site response curves of most stations are similar. For stations having significantly different site responses, we investigated by comparing with the results obtained from accelerograms recorded at nearby strong motion stations by applying the horizontal-to-vertical spectral ratio (HVSR) method. The results showed that site responses obtained from the GIT were closer to those of HVSR than those of the genetic algorithm.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Asian Earth Sciences, Volume 181〈/p〉 〈p〉Author(s): Mehmet Ali Gücer, Mehmet Arslan, Okay Çimen, Sarah C. Sherlock〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Devrekani Massif in the northern part of the Central Pontides (Northern Turkey) provides important clues to the regional tectonics and geodynamic processes associated with Jurassic high grade metamorphic conditions. This study reports new paragenetic assemblages, mineral compositions, whole-rock geochemistry and 〈sup〉40〈/sup〉Ar-〈sup〉39〈/sup〉Ar geochronological data from the paragneisses in the massif, and, discusses the 〈em〉P–T〈/em〉 conditions and geodynamic implications of the Jurassic metamorphism during continental extension in the Central Pontides. Upper amphibolite to lower granulite facies paragneisses form one of the main lithological units in the massif. Within these, there are five different mineral parageneses with diagnostic mineral assemblages of: quartz, K-feldspar (An〈sub〉0-1〈/sub〉Ab〈sub〉4-26〈/sub〉Or〈sub〉73-96〈/sub〉), plagioclase (An〈sub〉18-35〈/sub〉), biotite [〈em〉X〈/em〉〈sub〉Phl〈/sub〉: 0.28–0.57; Mg/(Mg + Fe〈sup〉2+〈/sup〉): 0.33–0.61], sillimanite, cordierite [Mg/(Mg + Fe〈sup〉2+〈/sup〉): 0.48–0.71] and garnet (Alm〈sub〉43-80〈/sub〉Grs〈sub〉0-18〈/sub〉Prp〈sub〉5-23〈/sub〉And〈sub〉0-4〈/sub〉Sps〈sub〉10-33〈/sub〉) with minor hercynite. Based on Na-in-Crd thermometry and GASP barometry results, the peak metamorphic conditions are 775 ± 25 〈strong〉°〈/strong〉C and 6 ± 1 kbar in the massif. The field relations, petrography and bulk chemical data suggest that the paragneisses, derived from shale-wackestone and pelitic sedimentary protoliths, are typical rock lithologies of an active continental margin. They display enrichments in LILE over HFSE, coupled with negative Nb and Ti anomalies, which are geochemical signatures of subduction-related sources. It is likely that the peak metamorphism took place during the Middle–Upper Jurassic period (〈em〉ca.〈/em〉 174–156 Ma), suggesting that the metamorphic rocks cooled to 300–350 °C at 〈em〉ca.〈/em〉 156 Ma. The mineral assemblages reveal that the prograde history passed from sillimanite zone conditions up to the cordierite-garnet-K-feldspar zone. The petrological and geochronological data indicate that the protoliths are related to multiple sources such as volcano-sedimentary successions. We conclude that the Devrekani Massif represents the products of pre-Jurassic sedimentation, and Permo-Carboniferous continental arc magmatism, overprinted by Jurassic metamorphism.〈/p〉〈/div〉 〈/div〉 〈div xml:lang="en"〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1367912019302408-ga1.jpg" width="351" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉 〈/div〉