ALBERT

Description: Publication year: 2012 Source: Geoscience Frontiers Jinyang Zhang, Changqian Ma, Zhenbing She The Erlangmiao granite intrusion is located in the eastern part of the East Qinling Orogen. The granite contains almost 99 vol.% felsic minerals with accessory garnet, muscovite, biotite, zircon, and Fe-Ti oxide. Garnet is the dominant accessory mineral, shows zoned texture, and is rich in w (FeO) (14.13%–16.09%) and w (MnO) (24.21%–27.44%). The rocks have high SiO 2 , alkalis, FeO t /MgO, TiO 2 /MgO and low Al 2 O 3 , CaO with w (Na 2 O)/ w (K 2 O)〉 1. Their Rb, Ga, Ta, Nb, Y, and Yb contents are high and Sr, Ba, Eu, Zr, P, and Ti contents are low. These features indicate that the Erlangmiao granite is a highly evolved metaluminous A-type. Garnet crystallized at the expense of biotite from the MnO-rich evolved melt after fractionation of biotite, plagioclase, K-feldspar, zircon, apatite, and ilmenite. The relatively high initial 87 Sr/ 86 Sr ratios (0.706–0.708), low and negative ɛ Nd (120 Ma) values (−6.6 to −9.0), and old Nd model ages (1.5–1.7 Ga) suggest that the rocks were probably formed by partial melting of the Paleoproterozoic granitic gneisses from the basement, with participation of depleted mantle in an extensional setting. Graphical Abstract Highlights ► FeO-, MnO-rich garnet crystallized at the expense of biotite from MnO-rich granitic magma. ► Granite formed from a highly evolved metaluminous A-type magma. ► Granite magma derived through the melting of Paleoproterozoic granitic gneisses.

Description: Publication year: 2012 Source: Geoscience Frontiers Sanghoon Kwon, Gautam Mitra The map expression of “abrupt” changes in lateral stratigraphic level of a thrust fault has been traditionally interpreted to be a result of the presence of (1) a lateral (or oblique) thrust-ramp, or (2) a frontal ramp with displacement gradient, and/or (3) a combination of these geometries. These geometries have been used to interpret the structures near transverse zones in fold-thrust belts (FTB). This contribution outlines an alternative explanation that can result in the same map pattern by lateral variations in stratigraphy along the strike of a low angle thrust fault. We describe the natural example of the Leamington transverse zone, which marks the southern margin of the Pennsylvanian–Permian Oquirrh basin with genetically related lateral stratigraphic variations in the North American Sevier FTB. Thus, the observed map pattern at this zone is closely related to lateral stratigraphic variations along the strike of a horizontal fault. Even though the present-day erosional level shows the map pattern that could be interpreted as a lateral ramp, the observed structures along the Leamington zone most likely share the effects of the presence of a lateral (or oblique) ramp, lateral stratigraphic variations along the fault trace, and the displacement gradient. Graphical Abstract Highlights ► Map expression of “abrupt” changes in lateral stratigraphic level of a thrust fault. ► New interpretation along a frontal-ramp without vertical-axis rotations. ► “Abrupt” changes controlled by lateral (or oblique) ramp, stratigraphy along a fault, and displacement gradients on a frontal ramp.

Description: Publication year: 2012 Source: Geoscience Frontiers Y. Srinivas, A. Stanley Raj, D.Hudson Oliver, D. Muthuraj, N. Chandrasekar The applications of intelligent techniques have increased exponentially in recent days to study most of the non-linear parameters. In particular, the behavior of earth resembles the non-linearity applications. An efficient tool is needed for the interpretation of geophysical parameters to study the subsurface of the earth. Artificial Neural Networks (ANN) perform certain tasks if the structure of the network is modified accordingly for the purpose it has been used. The three most robust networks were taken and comparatively analyzed for their performance to choose the appropriate network. The single-layer feed-forward neural network with the back propagation algorithm is chosen as one of the well-suited networks after comparing the results. Initially, certain synthetic data sets of all three-layer curves have been taken for training the network, and the network is validated by the field datasets collected from Tuticorin Coastal Region (78°7'30"E and 8°48'45"N), Tamil Nadu, India. The interpretation has been done successfully using the corresponding learning algorithm in the present study. With proper training of back propagation networks, it tends to give the resistivity and thickness of the subsurface layer model of the field resistivity data concerning the synthetic data trained earlier in the appropriate network. The network is trained with more Vertical Electrical Sounding (VES) data, and this trained network is demonstrated by the field data. Groundwater table depth also has been modeled. Graphical Abstract Highlights ► Vertical Electrical Sounding data in the Tuticorin region has been modeled for ground water occurrence and saline water intrusion. ► Artificial Neural Network program using Feed forward back propagation algorithm gains more advantage over conventional methods. ► Error percentage on comparing with the conventional method makes the program to extend on different type of field data. ► Synthetic Memory driven model forms the frame work of the algorithm to support any kind of rough field data. ► Saline water intrusion and ground water occurrence can be very well studied with well defined sub surface structural modeling.

Description: Publication year: 2012 Source: Geoscience Frontiers Dedong Li, Yuwang Wang, Jingbin Wang, Zhaohua Luo, Jiulong Zhou, Zongfeng Yang, Cui Liu According to the metallogenic theory by transmagmatic fluid (TMF), one magmatic intrusion is a channel of ore-bearing fluids, but not their source. Therefore, it is possible to use TMF’s ability for injection into and for escaping from the magmatic intrusion to evaluate its ore-forming potential. As the ore-bearing fluids cannot effectively inject into the magmatic intrusion when the magma fully crystallized, the cooling time and rates viscosity varied can be used to estimate the minimum critical thickness of the intrusion. One dimensional heat transfer model is used to determine the cooling time for three representative dikes of different composition (granite porphyry, quartz diorite and diabase) in the Shihu gold deposit. It is also estimated the rates viscosity varied in these time interval. We took the thickness of dike at the intersection of the cooling time – thickness curve and the rates viscosity varied versus thickness curve as the minimum critical thickness. For the ore-bearing fluids effectively injecting into the magma, the minimum critical thicknesses for the three representative dikes are 33.45 m for granite porphyry, 8.22 m for quartz diorite and 1.02 m for diabase, indicating that ore-bearing dikes must be thicker than each value. These results are consistent with the occurrence of ore bodies, and thus they could be applied in practice. Based on the statistical relationship between the length and the width of dikes, these critical thicknesses are used to compute critical areas: 0.0003–0.0016 km 2 for diabase, 0.014–0.068 km 2 for quartz diorite and 0.011–0.034 km 2 for granite porphyry. This implies that ore-bearing minor intrusions have varied areas corresponding to their composition. The numerical simulation has provided the theoretical threshold of exposed thickness and area of the ore-bearing intrusion. These values can be used to determine the ore-forming potentials of dikes. Graphical Abstract Highlights ► Heat transfer and viscosity models are used to determine cooling time and viscosity variation for dikes, respectively. ► Minimum critical thicknesses of three representative dikes for ore-bearing fluid injection are computed. ► Minimum critical areas of ore-bearing dikes are estimated in view of their ratios of length/ width.

Description: Publication year: 2011 Source: Geoscience Frontiers Wei Ju, Guiting Hou, Le Li, Fangfeng Xiao This paper presents the end Late Paleozoic tectonic stress field in the southern edge of Junggar Basin by interpreting stress-response structures (dykes, folds, faults with slickenside and conjugate joints). The direction of the maximum principal stress axes is interpreted to be NW–SE (about 325°), and the accommodated motion among plates is assigned as the driving force of this tectonic stress field. The average value of the stress index R ′ is about 2.09, which indicates a variation from strike-slip to compressive tectonic stress regime in the study area during the end Late Paleozoic period. The reconstruction of the tectonic field in the southern edge of Junggar Basin provides insights into the tectonic deformation processes around the southern Junggar Basin and contributes to the further understanding of basin evolution and tectonic settings during the culmination of the Paleozoic. Graphical Abstract Highlights ► The direction of the maximum principal stress axes is interpreted to be NW–SE. ► The stress regime is a variation from strike-slip to compressive. ► The accommodated motion among plates may be the cause of this stress field.

Description: Publication year: 2011 Source: Geoscience Frontiers Liu He, Chuanlun L. Zhang, Hailiang Dong, Bin Fang, Genhou Wang Isoprenoidal glycerol dialkyl glycerol tetraethers (iGDGTs) from the Gulu hot springs (23–83.6 °C, pH 〉 7) and Yangbajing hot springs (80–128 °C, pH 〉 7) were analyzed in order to investigate the distribution of archaeal lipids among different hot springs in Tibet. A soil sample from Gulu was incubated at different temperatures and analyzed for changes in iGDGTs to help evaluate whether surrounding soil may contribute to the iGDGTs in hot springs. The sources of bacterial GDGTs (bGDGTs) in these hot springs were also investigated. The results revealed different profiles of iGDGTs between Gulu and Yangbajing hot springs. Core iGDGTs and polar iGDGTs also presented different patterns in each hot spring. The PCA analysis showed that the structure of polar iGDGTs can be explained by three factors and suggested multiple sources of these compounds. Bivariate correlation analysis showed significant positive correlations between polar and core bGDGTs, suggesting the in situ production of bGDGTs in the hot springs. Furthermore, in the soil incubation experiment, temperature had the most significant influence on concentration of bGDGTs rather than iGDGTs, and polar bGDGTs had greater variability than core bGDGTs with changing temperature. Our results indicated that soil input had little influence on the composition of GDGTs in Tibetan hot springs. On the other hand, ring index and TEX 86 values were both positively correlated with incubation temperature, suggesting that the structure of archaeal lipids changed in response to varying temperature during incubation. Graphical Abstract Highlights ► Glycerol dialkyl glycerol tetraethers (GDGTs) are determined from Tibetan hot springs and soil. ► Archaeal and bacterial GDGTs are produced in situ in the hot spring. ► Soil incubation experiments show a positive correlation between ring index or TEX 86 and incubation temperature.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 2, March 2012, Pages I-II [No author name available]

Description: Publication year: 2012 Source: Geoscience Frontiers, Available online 11 February 2012 Huatian Zhang, Jianghai Li, Shoujie Liu, Wenshan Li, M. Santosh, ... The Khondalite Belt within the Inner Mongolia Suture Zone (IMSZ) in the North China Craton is a classic example for Paleoproterozoic ultrahigh-temperature (UHT) metamorphism. Here we report new spinel-bearing metapelitic granulites from a new locality at Xumayao within the southern domain of the IMSZ. Petrological studies and thermodynamic modeling of the spinel + quartz bearing assemblage shows that these rocks experienced extreme metamorphism at UHT conditions. Spinel occurs in two textural settings: 1) high XZn(Zn/(Mg+Fe+Zn) = 0.071-0.232) spinel with perthitic K-feldspar, sillimanite and quartz in the rock matrix; and 2) low XZn(0.045-0.070) spinel as inclusions within garnet porphyroblasts in association with quartz and sillimanite.Our phase equilibria modeling indicates two main stages during the metamorphic evolution of these rocks: 1) near-isobaric cooling from 975°C to 875°C around 8 kbar, represented by the formation of garnet porphyroblasts from spinel and quartz; and 2) cooling and decompression from 850°C, 8 kbar to below 750°C, 6.5 kbar, represented by the break-down of garnet. The spinel + quartz assemblage is considered to have been stable at peak metamorphism, formed through the break-down of cordierite, indicating a near-isothermal compression process. Our study confirms the regional extent of UHT metamorphism within the IMSZ associated with the Paleoproterozoic subduction-collision process. Highlights ► Ultra-high temperature (UHT) granulites reported from a new locality in the North China Craton. ► Peak P-T condition of T〉950°C and P〉7.5kbar defined by the stability of spinel + quartz. ► Regional UHT metamorphism and anti-clockwise P-T path

Description: Publication year: 2012 Source: Geoscience Frontiers, Available online 6 February 2012 N.S. Magesh, N. Chandrasekar, John Prince Soundranayagam Integration of remote sensing data and the geographical information system (GIS) for the exploration of groundwater resources has become a breakthrough in the field of groundwater research, which assists in assessing, monitoring, and conserving groundwater resources. In the present paper, various groundwater potential zones for the assessment of groundwater availability in Theni district have been delineated using remote sensing and GIS techniques. Survey of India toposheets and IRS-1C satellite imageries are used to prepare various thematic layers viz. lithology, slope, land-use, lineament, drainage, soil, and rainfall were transformed to raster data using feature to raster converter tool in ArcGIS. The raster maps of these factors are allocated a fixed score and weight computed from multi influencing factor (MIF) technique. Moreover, each weighted thematic layer is statistically computed to get the groundwater potential zones. The groundwater potential zones thus obtained were divided into four categories, viz., very poor, poor, good, and very good zones. The result depicts the groundwater potential zones in the study area and found to be helpful in better planning and management of groundwater resources.

Description: Publication year: 2012 Source: Geoscience Frontiers, Available online 13 January 2012 Xiang Gao, Pingkang Wang, Dairong Li, Qiang Peng, Chengshan Wang, ... The well SK-I in the Songliao Basin is the first scientific borehole targeting the continental Cretaceous strata in China. Oval concretions, thin laminae and beds of dolostone are found intercalated within mudstone and organic rich black shale in the Nenjiang Formation of Campanian age. Low ordered ferruginous dolomite is composed of euhedral-subhedral rhombs with cloudy nucleus and light rims formed during the diagenesis, which are typical features of replacement. The heavy carbon isotopes (δCPDB–1.16∼16.0) are results of both the fermentation of organic matter by microbes and degassing of carbon dioxide during the period of diagenesis, and the presence of light oxygen isotopes (δOPDB–18.53∼–5.1) is a characteristic feature of fresh water influence which means the carbonate may have been altered by ground water or rainwater in the late diagenesis. Marine water incursions into the normally lacustrine basin have been proved by both the salinity of Z value and the occurrence of foraminifera in the same strata where dolomite occurs. Pyrite framboids observed by SEM are usually enclosed in the dolomite crystals or in the mudstones, supporting the sulphate reducing bacteria (SRB). The formation of both dolomite and pyrite are associated with marine water incursions, which not only supply magnesium ion for dolomite, but also result in limited carbonate precipitation in the basin. The presence of pyrite framboids indicates the development of an anoxic environment associated with salinity stratification in the lake. The dolomite in the Nenjiang Formation is the results of marine water incursions, diagenetic replacement of calcareous carbonate and sulphate reducing bacteria (SRB). ▪ Highlights ► Dolomite shows rhombs, with replacement structure of cloudy nucleus and light rims. ► δ C PDB values suggest fermentation of organic matter by microbes. ► Salinity of Z value and occurrence of foraminifera proved marine water incursions. ► Pyrite framboids in the dolomite crystals suggest sulphate reducing bacteria (SRB).

Description: Publication year: 2012 Source: Geoscience Frontiers, Available online 10 February 2012 Dilip Saha, Vikash Tripathy A first report on tuff beds from the Owk Shale in the Proterozoic Kurnool sub-basin in southern India is presented. The rhyolitic to rhodacitic tuffs, overlying shelfal limestones formed at depths below storm wave base, have rheomorphic features indicative of viscoplastic flow, and geochemical signatures of rhyolitic to rhyodacitic unwelded to welded tuffs, similar to those described from other Proterozoic intracratonic basins like Vindhyan and Chhattisgarh basins in India. Fragmentary nature of altered glass with perlitic cracks and local admixture with intrabasinal sediments suggest phreatomagmatic reactions. The widespread and repeated occurrences of felsic tuffs in these basins, possibly derived from low degree melting of continental crust, suggest intermittent tectonothermal instability which likely influenced basinal topography and cyclic development of the carbonate platforms.

Description: Publication year: 2011 Source: Geoscience Frontiers, Available online 30 December 2011 Linqi Xia, Xueyi Xu, Xiangmin Li, Zhongping Ma, Zuchun Xia The Carboniferous−Early Permian rift-related volcanic successions, covering large areas in the Chinese Tianshan and its adjacent areas, make up a newly recognized important Phanerozoic large igneous province in the world, which can be further divided into two sub-provinces: Tianshan and Tarim. The regional unconformity of Lower Carboniferous upon basement or pre-Carboniferous rocks, the ages (360–351 Ma) of the youngest ophiolite and the peak of subduction metamorphism of high pressure–low temperature metamorphic belt and the occurrence of Ni-Cu-bearing mafic-ultramafic intrusion with age of ∼352 Ma and A-type granite with age of ∼358 Ma reveal that the final closure of the Paleo-Asian Ocean might take place in the Early Mississippian. Our summation shows that at least four criteria, being normally used to identify ancient asthenosphere upwelling (or mantle plumes), are met for this large igneous provin (1) surface uplift prior to magmatism; (2) being associated with continental rifting and breakup events; (3) chemical characteristics of asthenosphere (or plume) derived basalts; (4) close links to large-scale mineralization and the uncontaminated basalts, being analogous to those of many “ore-bearing” large igneous provinces, display Sr-Nd isotopic variations between plume and EM1 geochemical signatures. These suggest that a Carboniferous asthenosphere upwelling and an Early-Permian plume played the central role in the generation of the Tianshan–Tarim (central Asia) large igneous province. Highlights ► The Tianshan-Tarim Carboniferous–Early Permian volcanics constitute a large igneous province. ► The final closure of the Paleo-Asian Ocean occurred in the Early Mississippian. ► The large igneous province (LIP) correlated to asthenosphere upwelling or mantle plume.

Description: Publication year: 2012 Source: Geoscience Frontiers, Available online 10 February 2012 Mohamed K. Salah Seismic anisotropy and its main features along the convergent boundary between Africa and Iberia are detected through the analysis of teleseismic shear-wave splitting. Waveform data generated by 95 teleseismic events recorded at 17 broadband stations deployed in the western Mediterranean region are used in the present study. Although the station coverage is not uniform in the Iberian Peninsula and northwest Africa, significant variations in the fast polarization directions and delay times are observed at stations located at different tectonic domains. Fast polarization directions are oriented predominantly NW-SE at most stations which are close to the plate boundary and in central Iberia; being consistent with the absolute plate motion in the region. In the northern part of the Iberian Peninsula, fast velocity directions are oriented nearly E-W; coincident with previous results. Few stations located slightly north of the plate boundary and to the southeast of Iberia show E-W to NE-SW fast velocity directions, which may be related to the Alpine Orogeny and the extension direction in Iberia. Delay times vary significantly between 0.2 and 1.9 s for individual measurements, reflecting a highly anisotropic structure beneath the recording stations. The relative motion between Africa and Iberia represents the main reason for the observed NW-SE orientations of the fast velocity directions. However, different causes of anisotropy have also to be considered to explain the wide range of the splitting pattern observed in the western Mediterranean region. Many geophysical observations such as the lowPnvelocity, lower lithosphericQvalues, higher heat flow and the presence of high conductive features support the mantle flow in the western Mediterranean, which may contribute and even modify the splitting pattern beneath the studied region.

Description: Publication year: 2011 Source: Geoscience Frontiers, Available online 24 December 2011 Xun Sun, Chunyan Sun, Jiangyun Xiang, Jihui Jia, Panfeng Li, ... To study on the significance and basis of acidolysis index to China marine gas hydrate exploring, since 2006, 111 samples derived from Leg 164 and 204 of the Ocean Drilling Program (ODP) were analyzed in the experiment center of China Petroleum Exploration Research Institute to obtain data on acidolysis hydrocarbon index and methane carbon isotopes by the gas chromatography of PE AutoSystem XL and isotope mass spectrometer (IRMS) of Finnigan MAT251. Through these, we study the reliability of the acidolysis method and characterize the gas hydrate potential. The results show that the acidolysis hydrocarbon index has a stable correspondence with the Gas Hydrate Stability Zone (GHSZ) in the ODP, and that there are clear abnormal signs in shallow samples that might reliably reflect the existence of authigenic carbonate caused by hydrocarbon migration from bottom hydrate. We therefore propose that the ability to characterize the acidolysis hydrocarbon is crucial to submarine gas hydrate exploration in China. Highlights ► Acidolysis index and methane carbon isotope data of ODP drilling samples. ► Acidolysis index abnormality has stable correspondence with GHSZ. ► Distribution of acidolysis methane isotope differs with organic geochemical genesis.

Description: Publication year: 2011 Source: Geoscience Frontiers, Available online 23 December 2011 R. Damian Nance, Gabriel Gutiérrez-Alonso, J. Duncan Keppie, Ulf Linnemann, J. Brendan Murphy, ... The Rheic Ocean was one of the most important oceans of the Paleozoic Era. It lay between Laurentia and Gondwana from the Early Ordovician and closed to produce the vast Ouachita-Alleghanian-Variscan orogen during the assembly of Pangea. Rifting began in the Cambrian as a continuation of Neoproterozoic orogenic activity and the ocean opened in the Early Ordovician with the separation of several Neoproterozoic arc terranes from the continental margin of northern Gondwana along the line of a former suture. The rapid rate of ocean opening suggests it was driven by slab pull in the outboard Iapetus Ocean. The ocean reached its greatest width with the closure of Iapetus and the accretion of the peri-Gondwanan arc terranes to Laurentia in the Silurian. Ocean closure began in the Devonian and continued through the Mississippian as Gondwana sutured to Laurussia to form Pangea. The ocean consequently plays a dominant role in the Appalachian-Ouachita orogeny of North America, in the basement geology of southern Europe, and in the Paleozoic sedimentary, structural and tectonothermal record from Middle America to the Middle East. Its closure brought the Paleozoic Era to an end. Highlights ► The Rheic Ocean separated Gondwana and Laurussia as the principal interior ocean of the Paleozoic. ► Its evolution dominates the geology of southern Europe, eastern North America and northern Africa following the closure of the Iapetus Ocean in the Silurian. ► Closure of the Rheic Ocean in the late Paleozoic created the vast Ouachita-Appalachian-Variscan orogen and assembled the greater part of Pangea.

Description: Publication year: 2011 Source: Geoscience Frontiers, Available online 16 December 2011 Andong Wang, Yican Liu The crustal growth of the North China Craton (NCC) during the Neoarchean time (2.5–2.8 Ga) is a hotly controversial topic, with some proposing that the main crustal growth occurred in the late Neoarchean (2.5–2.6 Ga), in agreement with the time of the magmatism, whereas others suggest that the main crustal accretion took place during early Neoarchean time (2.7–2.8 Ga), consistent with the time of crustal-formation of other cratons in the world. Zircon U–Pb ages and Hf isotope compositions can provide rigorous constraints on the time of crustal growth and the evolution and tectonic division of the NCC. In this contribution, we make a comprehensive review of zircon Hf isotope data in combination with zircon U–Pb geochronology and some geochemistry data from various divisions of the NCC with an aim to constrain the Neoarchean crustal growth of the NCC. The results suggest that both 2.7–2.8 Ga and 2.5–2.6 Ga crustal growth are distributed over the NCC and the former is much wider than previously suggested. The Eastern block is characterized by the main 2.7–2.8 Ga crustal growth with local new crustal-formation at 2.5–2.6 Ga, and the Yinshan block is characterized by ∼2.7 Ga crustal accretion as revealed by Hf-isotope data of detrital zircons from the Zhaertai Group. Detrital zircon data of the Khondalite Belt indicate that the main crustal growth period of the Western block is Paleoproterozoic involving some ∼2.6 Ga and minor early- to middle-Archean crustal components, and the crustal accretion in the Trans-North China Orogen (TNCO) has a wide age range from 2.5 Ga to 2.9 Ga with a notable regional discrepancy. Zircon Hf isotope compositions, coupled with zircon ages and other geochemical data suggest that the southern margin may not be an extension of the TNCO, and the evolution and tectonic division of the NCC is more complex than previously proposed, probably involving multi-stage crustal growth and subduction processes. However, there is no doubt that 2.7–2.8 Ga magmatism and crustal-formation are more widely distributed than previously considered, which is further supported by the data of zircons from Precambrian lower crustal rocks, overlying sedimentary cover, modern river sediments and late Neoarchean syenogranites.

Description: Publication year: 2011 Source: Geoscience Frontiers, Available online 13 December 2011 N. Natarajan, G. Suresh Kumar A numerical model is developed for investigating the evolution of fracture permeability in a coupled fracture matrix system in the presence of fracture-skin with simultaneous colloidal and bacterial transport, by taking into account the effects of thermal stress and silica precipitation/dissolution, which is computed using linear reaction kinetics. The non-linear coupled equations are numerically modeled using the fully implicit finite difference method and a constant continuous source is adopted while modeling thermal, contaminant, colloidal and bacterial transport. Due to co-colloid bacterial transport under non-isothermal conditions, in a coupled fracture-skin-matrix system, the fracture apertures vary spatially, with a corresponding pressure variation for a constant discharge. A series of numerical experiments were conducted for analyzing the spatial variation of fracture aperture in response to the combined effects of thermal stress, silica precipitation/dissolution, and simultaneous colloidal and bacterial transport in the presence of the fracture-skin. The simulation results suggest that temperature and contaminant concentration of the mobile fluid within the fracture increases with reduction in initial fracture aperture. The pattern of variation followed by the fracture aperture is nearly the same in the presence and absence of bacterial transport but the magnitude of the fracture aperture is low under the influence of bacterial transport. The variation in the fracture aperture resulting from precipitation/dissolution and thermoelastic stress is significant when the fracture aperture is very low and reduces with increment in fracture aperture. The variation in fracture aperture and pressure remains the same for both undersaturated and supersaturated fluid entering the fracture due to the influence of bacterial transport at the inlet of the fracture. Highlights ► Temperature and contaminant concentration increase with decreasing fracture aperture. ► Bacterial growth reduces the reservoir efficiency due to reduction of permeability. ► Contaminants form substrate for bacteria which causes fracture aperture reduction.

Description: Publication year: 2011 Source: Geoscience Frontiers, Available online 17 December 2011 Brian P. Hedlund, Jessica K. Colea, Amanda J. Williams, Weiguo Hou, Enmin Zhou, ... The Rehai Geothermal Field, located in Tengchong County, in central-western Yunnan Province, is the largest and most intensively studied geothermal field in China. A wide physicochemical diversity of springs (ambient to ∼97°C; pH ≤1.8 to ≥9.3) provides a multitude of niches for extremophilic microorganisms. A variety of studies have focused on the cultivation, identification, basic physiology, taxonomy, and biotechnological potential of thermophilic microorganisms from Rehai. Thermophilic bacteria isolated from Rehai belong to the phylaFirmicutesandDeinococcus-Thermus.Firmicutesinclude neutrophilic or alkaliphilicAnoxybacillus,Bacillus,Caldalkalibacillus,Caldanaerobacter,Laceyella,andGeobacillus, as well as thermoacidophilicAlicyclobacillusandSulfobacillus.Isolates from theDeinococcus-Thermusphylum include severalMeiothermusandThermusspecies. Many of these bacteria synthesize thermostable polymer-degrading enzymes that may be useful for biotechnology. The thermoacidophilic archaeaAcidianus,Metallosphaera, andSulfolobushave also been isolated and studied. A few studies have reported the isolation of thermophilic viruses belonging toSiphoviridae(TTSP4 and TTSP10) andFuselloviridae(STSV1) infectingThermusspp. andSulfolobusspp., respectively. More recently, cultivation-independent studies using 16S rRNA gene sequences, shotgun metagenomics, or “functional gene” sequences have revealed a much broader diversity of microorganisms than represented in culture. Studies of the gene and mRNA encoding the large subunit of the ammonia monooxygenase (amoA) of ammonia-oxidizing Archaea (AOA) and the tetraether lipid crenarchaeol, a potential biomarker for AOA, suggest a wide diversity, but possibly low abundance, of thermophilic AOA in Rehai. Finally, we introduce the Tengchong Partnerships in International Research and Education (PIRE) project, an international collaboration between Chinese and U.S. scientists with the goal of promoting international and interdisciplinary cooperation to gain a more holistic and global view of life in terrestrial geothermal springs.

Description: Publication year: 2011 Source: Geoscience Frontiers, Available online 12 December 2011 F.J. Luque, E. Crespo-Feo, J.F. Barrenechea, L. Ortega Stable carbon isotope geochemistry provides important information for the recognition of fundamental isotope exchange processes related to the movement of carbon in the lithosphere and permits the elaboration of models for the global carbon cycle. Carbon isotope ratios in fluid-deposited graphite are powerful tools for unravelling the ultimate origin of carbon (organic matter, mantle, or carbonates) and help to constrain the fluid history and the mechanisms involved in graphite deposition. Graphite precipitation in fluid-deposited occurrences results from CO2- and/or CH4-bearing aqueous fluids. Fluid flow can be considered as both a closed (without replenishment of the fluid) or an open system (with renewal of the fluid by successive fluid batches). In closed systems, carbon isotope systematics in graphite is mainly governed by Rayleigh precipitation and/or by changes in temperature affecting the fractionation factor between fluid and graphite. Such processes result in zoned graphite crystals or in successive graphite generations showing, in both cases, isotopic variation towards progressiveC orC enrichment (depending upon the dominant carbon phase in the fluid, CO2or CH4, respectively). In open systems, in which carbon is episodically introduced along the fracture systems, the carbon systematics is more complex and individual graphite crystals may display oscillatory zoning because of Rayleigh precipitation or heterogeneous variations ofδC values when mixing of fluids or changes in the composition of the fluids are the mechanisms responsible for graphite precipitation.

Description: Publication year: 2011 Source: Geoscience Frontiers, Available online 10 December 2011 Yadong Wang, Jianjing Zheng, Weilin Zhang, Shiyuan Li, Xingwang Liu, ... Geologists agree that the collision of the Indian and Asian plates caused uplift of the Tibet Plateau. However, controversy still exists regarding the modes and mechanisms of the Tibetan Plateau uplift. Geology has recorded this uplift well in the Qaidam Basin. This paper analyzes the tectonic and sedimentary evolution of the western Qaidam Basin using sub-surface seismic and drill data. The Cenozoic intensity and history of deformation in the Qaidam Basin have been reconstructed based on the tectonic developments, faults growth index, sedimentary facies variations, and the migration of the depositional depressions. The changes in the sedimentary facies show that lakes in the western Qaidam Basin had gone from inflow to still water deposition to withdrawal. Tectonic movements controlled deposition in various depressions, and the depressions gradually shifted southeastward. In addition, the morphology of the surface structures in the western Qaidam Basin shows that the Cenozoic tectonic movements controlled the evolution of the Basin and divided it into (a) the southern fault terrace zone, (b) a central Yingxiongling orogenic belt, and (c) the northern fold-thrust belt; divided by the XI fault (Youshi fault) and Youbei fault, respectively. The field data indicate that the western Qaidam Basin formed in a Cenozoic compressive tectonic environment caused by the India–Asia plate collision. Further, the Basin experienced two phases of intensive tectonic deformation. The first phase occurred during the Middle Eocene–Early Miocene (Xia Ganchaigou Fm. and Shang Ganchaigou Fm., 43.8–22 Ma), and peaked in the Early Oligocene (Upper Xia Ganchaigou Fm., 31.5 Ma). The second phase occurred between the Middle Miocene and the Present (Shang Youshashan Fm. and Qigequan Fm., 14.9–0 Ma), and was stronger than the first phase. The tectonic–sedimentary evolution and the orientation of surface structures in the western Qaidam Basin resulted from the Tibetan Plateau uplift, and recorded the periodic northward growth of the Plateau. Recognizing this early tectonic–sedimentary evolution supports the previous conclusion that northern Tibet responded to the collision between India and Asia shortly after its initiation. However, the current results reveal that northern Tibet also experienced another phase of uplift during the late Neogene. The effects of these two stages of tectonic activity combined to produce the current Tibetan Plateau.

Description: Publication year: 2011 Source: Geoscience Frontiers, Available online 3 December 2011 C. Casquet, C.W. Rapela, R.J. Pankhurst, E.G. Baldo, C. Galindo, ... The role played by Paleoproterozoic cratons in southern South America from the Mesoproterozoic to the Early Cambrian is reconsidered here. This period involved protracted continental amalgamation that led to formation of the supercontinent Rodinia, followed by Neoproterozoic continental break-up, with the consequent opening of Clymene and Iapetus oceans, and finally continental re-assembly as Gondwana through complex oblique collisions in the Late Neoproterozoic to Early Cambrian. The evidence for this is based mainly on a combination of precise U-Pb SHRMP dating and radiogenic isotope data for igneous and metamorphic rocks from a large area extending from the Rio de la Plata craton in the east to the Argentine Precordillera in the west and as far north as Arequipa in Peru. Our interpretation of the paleogeographical and geodynamic evolution invokes a hypothetical Paleoproterozoic block (MARA) embracing basement ultimately older than 1.7 Ga in the Western Sierras Pampeanas (Argentina), the Arequipa block (Peru), the Rio Apa block (Brazil), and probably also the Paraguaia block (Bolivia).

Description: Publication year: 2011 Source: Geoscience Frontiers, Available online 11 December 2011 Syed Amer Mahmood, Richard Gloaguen Landscapes in tectonically active Hindu Kush (NW Pakistan and NE Afghanistan) result from a complex integration of the effects of vertical and horizontal crustal block motions as well as erosion and deposition processes. Active tectonics in this region has greatly influenced the drainage system and geomorphic expressions. The study area is a junction of three important mountain ranges (Hindu Kush-Karakorum-Himalayas) and is thus an ideal natural laboratory to investigate the relative tectonic activity resulting from the India-Eurasia collision. We evaluate active tectonics using DEM derived drainage network and geomorphic indices hypsometric integral (HI), stream-length gradient (SL), fractal dimension (FD), basin asymmetry factor (AF), basin shape index (Bs), valley floor width to valley height ratio (Vf) and mountain front sinuosity (Smf). The results obtained from these indices were combined to yield an index of relative active tectonics (IRAT) using GIS. The average of the seven measured geomorphic indices was used to evaluate the distribution of relative tectonic activity in the study area. We defined four classes to define the degree of relative tectonic activity: class 1very high (1.0≤IRAT〈1.3); class 2high (1.3≥IRAT〈1.5); class 3—moderate (1.5≥IRAT〈1.8); and class 4—low (1.8≥IRAT). In view of the results, we conclude that this combined approach allows the identification of the highly deformed areas related to active tectonics. Landsat imagery and field observations also evidence the presence of active tectonics based on the deflected streams, deformed landforms, active mountain fronts and triangular facets. The indicative values of IRAT are consistent with the areas of known relative uplift rates, landforms and geology. Highlights ► Evaluation of DEM based geomorphic indices to study active tectonics in Hindu Kush. ► Index of relative active tectonics (IRAT) using GIS. ► Very high, high and moderate IRAT classes consistent with the known uplift rates.

Description: Available online 28 December 2012 Publication year: 2012 Source: Geoscience Frontiers The Earth was born from a giant impact at 4.56 Ga. It is generally thought that the Earth subsequently cooled, and hence shrunk, over geologic time. However, if the Earth’s convection was double-layered, there must have been a peak of expansion during uni-directional cooling. We computed the expansion-contraction effect using first principles calculation. The result shows a radius about 120 km larger than that of the present Earth immediately after the consolidation of the magma-ocean on the surface, and subsequent shrinkage of about 110 km in radius within about 10 m.y., followed by gradual expansion of 11 km in radius due to radiogenic heating in the lower mantle in spite of cooling in the upper mantle in the Archean. This was due to double-layered convection in the Archean with final collapse of overturn with contraction of about 8 km in radius, presumably by the end of the Archean. Since then, the Earth has gradually cooled down to reduce its radius by around 12 km. Geologic evidence supports the late Archean mantle overturn ca. 2.6 Ga, such as the global distribution of super-liquidus flood basalts on nearly all cratonic fragments (〉35 examples). If our inference is correct, the surface environment of the Earth must have undergone extensive volcanism and emergence of local landmasses, because of the thin ocean cover (3–5 km thickness). Global unconformity appeared in cratonic fragments with stromatolite back to 2.9 Ga with a peak at 2.6 Ga. The global magmatism brought extensive crustal melting to yield explosive felsic volcanism to transport volcanic ash into the stratosphere during the catastrophic mantle overturn. This event seems to be recorded by sulfur mass-independent fractionation (SMIF) at 2.6 Ga. During the mantle overturn, a number of mantle plumes penetrated into the upper mantle and caused local upward doming of by ca. 2–3 km which raised local landmasses above sea-level. The consequent increase of atmospheric oxygen enabled life evolution from prokyaryotes to eukyaryotes by 2.1 Ga, or even earlier in the Earth history. Graphical abstract Highlights ► Expanding-contracting effects of the Earth calculated using the first principles calculation. ► Density analysis in the upper and lower mantle indicates mantle overturn at 2.8 Ga. ► The catastrophic mantle overturn supports many geological evidences.

Description: Publication year: 2012 Source: Geoscience Frontiers B.P. Singh The Paleogene succession of the Himalayan foreland basin is immensely important as it preserves evidence of India-Asia collision and related records of the Himalayan orogenesis. In this review, the depositional regime of the Paleogene succession of the Himalayan foreland basin and variations in composition of the Hinterland at different stages of the basin developments are presented here. The Paleogene succession of the western Himalayan foreland basin developed in two stages, i. e. syn-collisional stage and post-collisional stage. At the onset, chert breccia containing fragments derived from the hanging walls of faults and reworked bauxite developed as a result of erosion of the forebulge. The overlying Early Eocene succession possibly deposited in a coastal system, where carbonates represent barriers and shales represent lagoons. Up-section, the Middle Eocene marl beds likely deposited on a tidal flat. The Late Eocene/Oligocene basal Murree beds, containing tidal bundles, indicate that a mixed or semi-diurnal tidal system deposited the sediments and the sedimentation took place in a tide-dominated estuary. In the higher-up, the succession likely deposited in a river-dominated estuary or in meandering rivers. In the beginning of the basin evolution, the sediments were derived from the Precambrian basement or from the metasediments/volcanic rocks possessing terrains of the south. The Early and Middle Eocene (54.7–41.3 Ma) succession of the embryonic foreland possibly developed from the sediments derived from the Trans-Himalayan schists and phyllites and Indus ophiolite of the north during syn-collisional stage. The detrital minerals especially the lithic fragments and the heavy minerals suggest the provenance for the Late Eocene/Oligocene sequences to be from the recycled orogenic belt of the Higher Himalaya, Tethyan Himalaya and the Indus-suture zone from the north during post-collisional stage. This is also supported by the paleocurrent measurements those suggest main flows directed towards southeast, south and east with minor variations. This implies that the river system stabilized later than 41 Ma and the Higher Himalaya attained sufficient height around this time. The chemical composition of the sandstones and mudstones occurring in the early foreland basin sequences are intermediate between the active and passive continental margins and/or same as the passive continental margins. The sedimentary succession of this basin has sustained a temperature of about 200 °C and undergone a burial depth of about 6 km. Graphical abstract Graphical Abstract Highlights ► Paleogene succession in the Himalayan foreland basin deposited in a coastal system. ► Sediments derived from the Trans-Himalayan metamorphic rocks and Indus-Suture zone. ► Continental sedimentation began and river system stabilised later than 41 Ma when Higher Himalaya started uplifting.

Description: Publication year: 2012 Source: Geoscience Frontiers Yener Eyuboglu, M. Santosh, Francis O. Dudas, Enver Akaryalı, Sun-Lin Chung, Kemal Akdağ, Osman Bektaş The eastern Pontides orogenic belt provides a window into continental arc magmatism in the Alpine–Himalayan belt. The late Mesozoic–Cenozoic geodynamic evolution of this belt remains controversial. Here we focus on the nature of the transition from the adakitic to non-adakitic magmatism in the Kale area of Gumushane region in NE Turkey where this transition is best preserved. The adakitic lithologies comprise porphyries and hyaloclastites. The porphyries are represented by biotite-rich andesites, hornblende-rich andesite and dacite. The hayaloclastites represent the final stage of adakitic activity and they were generated by eruption/intrusion of adakitic andesitic magma into soft carbonate mud. The non-adakitic lithologies include basaltic-andesitic volcanic and associated pyroclastic rocks. Both rock groups are cutting by basaltic dikes representing the final stage of the early Cenozoic magmatism in the study area. We report zircon U-Pb ages of 48.71 ± 0.74 Ma for the adakitic rocks, and 44.68 ± 0.84 Ma for the non-adakitic type, suggesting that there is no significant time gap during the transition from adakitic to non-adakitic magmatism. We evaluate the origin, magma processes and tectonic setting of the magmatism in the southern part of the eastern Pontides orogenic belt. Our results have important bearing on the late Mesozoic–Cenozoic geodynamic evolution of the eastern Mediterranean region. Graphical abstract Graphical Abstract Highlights ► Transition from adakitic to non-adakitic magmatism in a continental arc. ► New geochemical and geochronological data from adakitic and non-adakitic rocks of the eastern Pontides orogenic belt. ► Adakitic hyaloclastites reported for the first time from the eastern Pontides belt. ► Early Cenozoic adakitic and non-adakitic magmas generated by slab window processes in a south-dipping subduction zone.

Description: Publication year: 2012 Source: Geoscience Frontiers Hisako Shimizu, Toshiaki Tsunogae, M. Santosh A synthesis of the petrological characters of granulite facies rocks that contain equilibrium sapphirine + quartz assemblage from two localities (Tonagh Island (TI) and Priestley Peak (PP)) in the Napier Complex, East Antarctica, provides unequivocal evidence for extreme crustal metamorphism possibly associated with the collisional orogeny during Neoarchean. The reaction microstructures associated with sapphirine + quartz vary among the samples, probably suggesting different tectonic conditions during the metamorphic evolution. Sapphirine and quartz in TI sample were probably in equilibrium at the peak stage, but now separated by corona of Grt + Sil + Opx suggesting near isobaric cooling after the peak metamorphism, whereas the Spr + Qtz + Sil + Crd + Spl assemblage replaces garnet in PP sample suggesting post-peak decompression. The application of mineral equilibrium modeling on the TI sample in NCKFMASHTO system yields a peak p – T range of 1010–1090 °C and 8–10 kbar, followed by cooling toward a retrograde stage of 800–1000 °C and 7.5–10.5 kbar, possibly along a counterclockwise p – T path. In contrast, the peak condition of the PP sample shows 1000–1050 °C and 〉12 kbar, which was followed by the formation of Spr + Qtz corona around garnet at 930–970 °C and 6.7–7.7 kbar, suggesting decompression possibly along a clockwise p – T trajectory. Such contrasting p – T paths are consistent with a recent model on the structural framework of the Napier Complex that correlates the two areas to different crustal blocks. The different p – T paths obtained from the two localities might reflect the difference in the tectonic framework of these rocks within a complex Neoarchean subduction/collision belt. Graphical abstract Graphical Abstract Highlights ► Extreme crustal metamorphism in Napier Complex associated with Neoarchean collisional orogeny. ► Computed p – T range of 1010–1090 °C and 8–10 kbar, and 1000–1050 °C and 〉12 kbar. ► Contrasting p – T paths suggest discrete crustal domains juxtaposed during Neoarchean subduction-collision tectonics.

Description: Publication year: 2012 Source: Geoscience Frontiers Daniel E. Harlov High-grade dehydration of amphibolite-facies rocks to granulite-facies is a process that can involve partial melting, fluid-aided solid-state dehydration, or varying degrees of both. On the localized meter scale, solid-state dehydration, due to CO 2 -rich fluids traveling along some fissure or crack and subsequently outwards along the mineral grain boundaries of the surrounding rock, normally is the means by which the breakdown of biotite and amphibole to orthopyroxene and clinopyroxene occur. Various mineral textures and changes in mineral chemistry seen in these rocks are also seen in more regional orthopyroxene-clinopyroxene-bearing rocks which, along with accompanying amphibolite-facies rocks, form traverses of lower crust. This suggests that solid-state dehydration during high-grade metamorphism could occur on a more regional scale. The more prominent of these fluid-induced textures in the granulite-facies portion of the traverse take the form of micro-veins of K-feldspar along quartz grain boundaries and the formation of monazite inclusions in fluorapatite. The fluids believed responsible take the form of concentrated NaCl and KCl brines from a basement ultramafic magma heat source traveling upwards along grain boundaries. Additional experimental work involving CaSO 4 dissolution in NaCl brines, coupled with natural observation of oxide and sulfide mineral associations in granulite-facies rocks, have demonstrated the possibility that NaCl-brines, with a CaSO 4 component, could impose the oxygen fugacity on these rocks as opposed to the oxygen fugacity being inherent in their protoliths. These results, taken together, lend credence to the idea that regional chemical modification of the lower crust is an evolutionary process controlled by fluids migrating upwards from the lithospheric mantle along grain boundaries into and through the lower crust where they both modify the rock and are modified by it. Their presence allows for rapid mass and heat transport and subsequent mineral genesis and mineral re-equilibration in the rocks through which they pass. Graphical Abstract

Description: Available online 3 November 2012 Publication year: 2012 Source: Geoscience Frontiers The Sinai Peninsula has been recognized as a subplate of the African Plate located at the triple junction of the Gulf of Suez rift, the Dead Sea Transform fault, and the Red Sea rift. The upper and lower crustal structures of this tectonically active, rapidly developing region are yet poorly understood because of many limitations. For this reason, a set of P- and S-wave travel times recorded at 14 seismic stations belonging to the Egyptian N ational S eismographic N etwork (ENSN) from 111 local and regional events are analyzed to investigate the crustal structures and the locations of the seismogenic zones beneath central and southern Sinai. Because the velocity model used for routine earthquake location by ENSN is one-dimensional, the travel-time residuals will show lateral heterogeneity of the velocity structures and unmodeled vertical structures. Seismic activity is strong along the eastern and southern borders of the study area but low to moderate along the northern boundary and the Gulf of Suez to the west. The crustal V p / V s ratio is 1.74 from shallow (depth ≤ 10 km) earthquakes and 1.76 from deeper (depth 〉 10 km) crustal events. The majority of the regional and local travel time residuals are positive relative to the Preliminary Reference Earth Model (PREM), implying that the seismic stations are located above widely distributed, tectonically-induced low-velocity zones. These low-velocity zones are mostly related to the local crustal faults affecting the sedimentary section and the basement complex as well as the rifting processes prevailing in the northern Red Sea region and the ascending of hot mantle materials along crustal fractures. The delineation of these low-velocity zones and the locations of big crustal earthquakes enable the identification of areas prone to intense seismotectonic activities, which should be excluded from major future development projects and large constructions in central and southern Sinai. Graphical abstract Highlights ► High crustal V p / V s ratio is observed, which is consistent with the rifting processes. ► Positive travel time residuals implying the presence of tectonically-induced low V p zones. ► Consistent results between the low V p and high V p / V s ratio and other geophysical observations.

Description: November 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 6 The Venda Nova Pluton (VNP) is a zoned ring structure emplaced in the southern portion of the Neoproterozoic Araçuai Belt, in Espírito Santo, Brazil. It is a slightly westward tilted cylinder-like intrusion, with an almost circular horizontal section. In the center of this structure, an off-centered gabbro-noritic core, surrounded by syeno-monzonitic rocks, intrudes an outer ring of charnockites and norite. These envelop the syeno-monzonitic and gabbro-noritic center, as a narrow discontinuous belt. While, in the core intrusion, mingling and mixing processes are widespread and well documented in the literature, in the outer ring, the norite and charnockite layers show predominantly homogeneous and isotropic internal structures. Nevertheless, smaller interaction zones between charnockites and norite denote a comparatively more restricted mingling process. The norite is a fine-grained rock with hypidiomorphic granular to intergranular texture. The charnockites are medium-grained and made up of: (a) orthopyroxene-tonalite, (b) orthopyroxene-quartz-diorite, and (c) orthopyroxene-granodiorite with hypidiomorphic granular to porphyritic textures. In all lithotypes both ortho- and clinopyroxene are replaced by hornblende and biotite. Two contrasting compositional sequences have been recognized, based on whole rock geochemistry: (1) a basic, with tholeiitic affinities (norite) and, (2) an intermediate, medium-K calc-alkaline, comprising the charnockites. Estimated crystallization temperatures, which have been calculated from micro-probe analysis of pyroxenes, range from 915 ± 25 °C to 960 ± 50 °C. Re-equilibration temperature (ilmenite-magnetite calibration) is around 600 ± 50 °C. This indicates oxygen fugacities four order of magnitude below the FMQ-buffer and a reduced environment. Coeval pressure conditions estimated from the Al-content in hornblende range from 5.5 ± 0.6 kbar. Data obtained for the norite point toward an evolution from the partial melting of an anhydrous tholeiitic mantle magma. The charnockites may correspond to the differentiation of a calc-alkaline parental magma. The later could be the hybrid product from the contamination and mixing between the anhydrous tholeiitic magma with other deeper crustal sources. Further the magmatic system evolved through fractionation of orthopyroxene, clinopyroxene, plagioclase and ilmenite. Our results support the hypothesis for the evolution of the Venda Nova Pluton through a mantle-crust delamination process probably related to the collapse of the Araçuai orogeny. Graphical abstract Highlights ► The calcic charnockitic intrusion is related to the collapse of the Brasiliano Araçuaí Belt (G5 Supersuite). ► Petrogenetic constraints point toward reducing conditions and emplacement under 16 km in depth. ► The evolution of the pluton was possibly controlled by mantle-crust delamination process.

Description: November 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 6 High-grade dehydration of amphibolite-facies rocks to granulite-facies is a process that can involve partial melting, fluid-aided solid-state dehydration, or varying degrees of both. On the localized meter scale, solid-state dehydration, due to CO 2 -rich fluids traveling along some fissure or crack and subsequently outwards along the mineral grain boundaries of the surrounding rock, normally is the means by which the breakdown of biotite and amphibole to orthopyroxene and clinopyroxene occur. Various mineral textures and changes in mineral chemistry seen in these rocks are also seen in more regional orthopyroxene-clinopyroxene-bearing rocks which, along with accompanying amphibolite-facies rocks, form traverses of lower crust. This suggests that solid-state dehydration during high-grade metamorphism could occur on a more regional scale. The more prominent of these fluid-induced textures in the granulite-facies portion of the traverse take the form of micro-veins of K-feldspar along quartz grain boundaries and the formation of monazite inclusions in fluorapatite. The fluids believed responsible take the form of concentrated NaCl- and KCl- brines from a basement ultramafic magma heat source traveling upwards along grain boundaries. Additional experimental work involving CaSO 4 dissolution in NaCl-brines, coupled with natural observation of oxide and sulfide mineral associations in granulite-facies rocks, have demonstrated the possibility that NaCl-brines, with a CaSO 4 component, could impose the oxygen fugacity on these rocks as opposed to the oxygen fugacity being inherent in their protoliths. These results, taken together, lend credence to the idea that regional chemical modification of the lower crust is an evolutionary process controlled by fluids migrating upwards from the lithospheric mantle along grain boundaries into and through the lower crust where they both modify the rock and are modified by it. Their presence allows for rapid mass and heat transport and subsequent mineral genesis and mineral re-equilibration in the rocks through which they pass. Graphical abstract Highlights ► High-grade, fluid-aided dehydration of amphibolite- to granulite-facies rock. ► Comparison with localized, solid-state CO 2 -induced dehydration zones. ► Regional solid-state dehydration fluids include concentrated NaCl-KCl brines.

Description: September 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 5 The fact that several half-grabens and normal faults developed in the Lower–Middle Cambrian of Tazhong (central Tarim Basin) and Bachu areas in Tarim Basin, northwest China, indicates that Tarim Basin was under extensional tectonic setting at this time. The half-grabens occur within a linear zone and the normal faults are arranged in en echelon patterns with gradually increasing displacement eastward. Extensional tectonics resulted in the formation of a passive continental margin in the southwest and a cratonic margin depression in the east, and most importantly, influenced the development of a three-pronged rift in the northeast margin of the Tarim Basin. The fault system controlled the development of platform – slope – bathyal facies sedimentation of mainly limestone-dolomite-gypsum rock-saline rock-red beds in the half-grabens. The NW-SE trending half-grabens reflect the distribution of buried basement faults. Graphical abstract Highlights ► Half-grabens and normal faults developed in the Lower-Middle Cambrian in Tarim Basin. ► Extensional tectonics resulted in the formation of a passive continental margin. ► Normal fault system controls distribution of “platform–slope–basin facies”.

Description: July 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 4 Non-marine ostracodes, charophytes and palynomorphs are abundant in most Cretaceous lacustrine basins of East Asia. However, their ranges are not directly integrated with marine biota that defines the Cretaceous stages. Non-biotic events such as magnetochrons and radiometric ages in these terrestrial deposits enable their correlation with marine strata. The SK1 north and south composited cores in the Songliao Basin present a continuous section of Upper Cretaceous non-marine fossil and magnetochron successions in superposed order. These chronostratigraphic events are integrated with marine events by an X / Y graphic plot between the core data and a global database of Global Section and Stratotype Points (GSSP) and key reference sections. This plot projects stage boundaries in marine sections into the SK1 section and interpolates numerical ages to the first and last occurrences of biota and to lithostratigraphic boundaries. This stratigraphic experiment tests and refines age calibrations based on both manual interpolation of depths to numerical ages and cyclostratigraphy. Ages derived by interpolation are similar and ages by cyclostratigraphy are older because stage boundaries are calibrated to a different age scale. Graphical abstract Highlights ► Non-biotic Late Cretaceous events in terrestrial deposits of the Songliao Basin correlate with marine strata. ► Non-marine events are integrated with marine events by an X/Y graphic plot between core data and global database. ► The plot interpolates numerical ages to fossil ranges and to lithostratigraphic boundaries.

Description: November 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 6 Charnockites sensu lato (charnockite-enderbite series) are lower crustal felsic rocks typically characterised by the presence of anhydrous minerals including orthopyroxene and garnet. They either represent dry (H 2 O-poor) felsic magmas that are emplaced in the lower crust or granitic intrusions that have been dehydrated during a subsequent granulite facies metamorphic event. In the first case, post-magmatic high-temperature recrystallisation may result in widespread metamorphic granulite microstructures, superimposed or replacing the magmatic microstructures. Despite recrystallisation, magmatic remnants may still be found, notably in the form of melt-related microstructures such as melt inclusions. For both magmatic charnockites and dehydrated granites, subsequent fluid-mineral interaction at intergrain boundaries during retrogradation are documented by microstructures including K-feldspar microveins and myrmekites. They indicate that a large quantity of low-H 2 O activity salt-rich brines, were present (together with CO 2 under immiscible conditions) in the lower crust. Graphical abstract Highlights ► Igneous and metamorphic charnockites can be identified by typical microstructures. ► Microstructures can be obliterated by metamorphic recrystallisation. ► Charnockites may be affected by high-temperature metasomatism.

Description: November 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 6 Large charnockite massifs occur in the high-grade Southern Granulite Terrain (SGT) and Eastern Ghats Belt (EGB) crustal provinces of Peninsular India. Available geochronological data indicate that the magmatism is episodic, associated with distinct orogenic cycles in the different crustal domains. The geochemical data also indicate a change in composition from trondhjemitic at ∼3.0–2.9 Ga to dominantly tonalitic at ∼2.6–2.5 Ga to tonalitic-granodiorite-granitic at ∼2.0–1.9 Ga to dominantly tonalitic at 1.7–1.6 Ga to quartz monzonitic or tonalitic at ∼1.0–0.9 Ga to granodiorite-granitic at ∼0.8–0.7 Ga. The trondhjemitic and tonalitic end members are metaluminous, magnesian and calcic to calc-alkalic, characteristic of magnesian group charnockites. The granodioritic to granitic end members are metaluminous to slightly peraluminous, ferroan and calc-alkalic to alkali-calcic, characteristic of ferroan group charnockites. The quartz monzonitic end members are metaluminous to peraluminous, magnesian to ferroan and calcic to calc-alkalic, neither characteristic of the magnesian group nor of the ferroan group of charnockites. Based on the occurrence and difference in composition of the charnockite massifs, it is suggested that the charnockite magmatism registers the crustal growth of the Indian plate on its southern (SGT) and eastern (EGB) sides, along active continental margins by accretion of arcs. Graphical abstract Highlights ► Charnockite magmatism in Peninsular India is episodic. ► Least differentiated end members are similar to magnesian group charnockites. ► Episodic charnockite magmatism registers the crustal growth of the Indian plate.

Description: November 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 6 Incipient charnockites represent granulite formation on a mesoscopic scale and have received considerable attention in understanding fluid processes in the deep crust. Here we report new petrological data from an incipient charnockite locality at Rajapalaiyam in the Madurai Block, southern India, and discuss the petrogenesis based on mineral phase equilibrium modeling and pseudosection analysis. Rajapalaiyam is a key locality in southern India from where diagnostic mineral assemblages for ultrahigh-temperature (UHT) metamorphism have been reported. Proximal to the UHT rocks are patches and lenses of charnockite (Kfs + Qtz + Pl + Bt + Opx + Grt + Ilm) occurring within Opx-free Grt-Bt gneiss (Kfs + Pl + Qtz + Bt + Grt + Ilm + Mt) which we report in this study. The application of mineral equilibrium modeling on the charnockitic assemblage in NCKFMASHTO system yields a p - T range of ∼820 °C and ∼9 kbar. Modeling of the charnockite assemblage in the MnNCKFMASHTO system indicates a slight shift of the equilibrium condition toward lower p and T (∼760 °C and ∼7.5 kbar), which is consistent with the results obtained from geothermobarometry (710–760 °C, 6.7–7.5 kbar), but significantly lower than the peak temperatures (〉1000 °C) recorded from the UHT rocks in this locality, suggesting that charnockitization is a post-peak event. The modeling of T versus molar H 2 O content in the rock (M(H 2 O)) demonstrates that the Opx-bearing assemblage in charnockite and Opx-free assemblage in Grt-Bt gneiss are both stable at M(H 2 O) = 0.3 mol%–0.6 mol%, and there is no significant difference in water activity between the two domains. Our finding is in contrast to the previous petrogenetic model of incipient charnockite formation which envisages lowering of water activity and stabilization of orthopyroxene through breakdown of biotite by dehydration caused by the infiltration of CO 2 -rich fluid. T - X Fe 3+ (=Fe 2 O 3 /(FeO + Fe 2 O 3 ) in mole) pseudosections suggest that the oxidation condition of the rocks played a major role on the stability of orthopyroxene; Opx is stable at X Fe 3+ 〈0.03 in charnockite, while Opx-free assemblage in Grt-Bt gneiss is stabilized at X Fe 3+ 〉0.12. Such low oxygen fugacity conditions of X Fe 3+ 〈0.03 in the charnockite compared to Grt-Bt gneiss might be related to the infiltration of a reduced fluid (e.g., H 2 O + CH 4 ) during the retrograde stage. Graphical abstract Highlights ► Charnockite formation at ∼820 °C and ∼9 kbar based on NCKFMASHTO pseudosections. ► Lower p and T (∼760 °C and ∼7.5 kbar) if MnNCKFMASHTO system is applied. ► Charnockite formation by the infiltration of a reduced fluid (e.g., H 2 O + CH 4 ).

Description: November 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 6 Examples of the mightiest energy releases by great earthquakes and volcanic eruptions and hypotheses providing explanations for them are analyzed along with the results of some recently published researches and visualizations. The emerging conclusions are that the mechanism of the strong earthquake is a chemical explosion; that volcanic eruption is a special type of earthquake wherein the hypocenter rises to the earth-surface; and that there is an association between the seismic-volcanic processes and mantle “fluids” and the lack of energy for mantle plumes. A conceptual system of hypotheses is put forward to explain the conservation of energy during Earth’s accretion, its quasi-stable release by primordial H- and He-degassing and of the crucial role of the energy of degassing-comprising-reactions in endogenic processes. Specific mechanisms and chemical processes are proposed for the gas-liquid mantle plumes melting through the solid mantle using heat-energy released in reactions of their metamorphic and chemical transformation under gradual decrease of pressure and temperature; volcanic gases are put forward as energy carriers. 3 He performance as a unique measuring transformer correlative to the internal heat flow was used for calculation of energy release by degassing; it equals to 5.12 × 10 20 J/yr, an amount of energy five-fold greater than the entire energy loss involved in earthquake and volcanic activity. The hypotheses proposed are objectively testable. Graphical abstract Highlights ► Energy-outputs of mega-cataclysms and other facts are explained by the proposed energy-source. ► During Earth accretion H and He were stored in its interior under ultrahigh pT -conditions. ► The giant energy invested in H-He trapping is queasy-constantly released by their degassing.

Description: November 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 6

Description: Available online 29 October 2012 Publication year: 2012 Source: Geoscience Frontiers A series of Cretaceous plutons is present in the eastern Pontides of northeastern Turkey. The Turnagöl intrusion is the least studied and, thus, the least understood plutons in the orogen. This intrusion consists of hornblende-biotite granodiorites emplaced at 78 Ma based on LA-ICP-MS U-Pb zircon dating. It is of sub-alkaline affinity, belongs to the medium to high-K calc-alkaline series, and displays features typical of I-type granites. The rocks of the intrusion are enriched in large-ion lithophile elements and light rare earth-elements with negative Eu anomalies (Eu/Eu* = 0.69–0.82), but are deficient in high-field-strength elements. They have a small range of ( 87 Sr/ 86 Sr) i (0.7060–0.7063), ɛ N d i (−2.6 to −3.1), and δ 18 O (+8.1 to +9.1) values. Their Pb isotopic ratios are 206 Pb/ 204 Pb = 18.63–18.65, 207 Pb/ 204 Pb = 15.62–15.63, and 208 Pb/ 204 Pb = 38.53–38.55. The fractionation of plagioclase, hornblende, and Fe-Ti oxides had key functions in the evolution of the Turnagöl intrusion. The crystallization temperatures of the melts ranged from 758 to 885 °C as determined by zircon and apatite saturation thermometry. All these characteristics, combined with the low values of K 2 O/Na 2 O and (Na 2 O + K 2 O)/(FeO t  + MgO + TiO 2 ), as well as the high values of (CaO + FeO t  + MgO + TiO 2 ), suggest an origin by dehydration melting from a metabasaltic lower crustal source. Graphical abstract Highlights ► Geochemical, geochronological and Sr-Nd-Pb-O isotopic data on Turnagöl intrusion. ► Geochemical data show an affinity to I-type granites. ► Origin of the magma correlated to dehydration melting of a mafic crustal source.

Description: September 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 5 The Erlangmiao granite intrusion is located in the eastern part of the East Qinling Orogen. The granite contains almost 99 vol.% felsic minerals with accessory garnet, muscovite, biotite, zircon, and Fe-Ti oxide. Garnet is the dominant accessory mineral, shows zoned texture, and is rich in w (FeO) (14.13%–16.09%) and w (MnO) (24.21%–27.44%). The rocks have high SiO 2 , alkalis, FeO t /MgO, TiO 2 /MgO and low Al 2 O 3 , CaO with w (Na 2 O)/ w (K 2 O)〉 1. Their Rb, Ga, Ta, Nb, Y, and Yb contents are high and Sr, Ba, Eu, Zr, P, and Ti contents are low. These features indicate that the Erlangmiao granite is a highly evolved metaluminous A-type. Garnet crystallized at the expense of biotite from the MnO-rich evolved melt after fractionation of biotite, plagioclase, K-feldspar, zircon, apatite, and ilmenite. The relatively high initial 87 Sr/ 86 Sr ratios (0.706–0.708), low and negative ɛ Nd (120 Ma) values (−6.6 to −9.0), and old Nd model ages (1.5–1.7 Ga) suggest that the rocks were probably formed by partial melting of the Paleoproterozoic granitic gneisses from the basement, with participation of depleted mantle in an extensional setting. Graphical abstract Highlights ► FeO-, MnO-rich garnet crystallized at the expense of biotite from MnO-rich granitic magma. ► Granite formed from a highly evolved metaluminous A-type magma. ► Granite magma derived through the melting of Paleoproterozoic granitic gneisses.

Description: Publication year: 2012 Source: Geoscience Frontiers Andreas Prokoph, Hafida el Bilali, Richard Ernst Large Igneous Provinces (LIPs) are considered a relevant cause for mass extinctions of marine life throughout Earth’s history. Their flood basalts and associated intrusions can cause significant release of SO 4 and CO 2 and consequently, cause major environmental disruptions. Here, we reconstruct the long-term periodic pattern of LIP emplacement and its impact on ocean chemistry and biodiversity from δ 34 S sulfate of the last 520 million years (Ma) under particular consideration of the preservation limits of LIP records. A combination of cross-wavelet and other time-series analysis methods has been applied to quantify a potential chain of linkage between LIP emplacement periodicity, geochemical changes and the Phanerozoic marine genera record. We suggest a mantle plume cyclicity represented by LIP volumes ( V ) of V = –(350–770)10 3 km 3 sin(2π t /170 Ma) + (300–650)10 3 km 3 sin(2π t /64.5 Ma+2.3) for t =time in Ma. A shift from the 64.5 Ma to a weaker ∼28–35 Ma LIP cyclicity during the Jurassic contributes together with probably independent changes in the marine sulfur cycle to less ocean anoxia, and a general stabilization of ocean chemistry and increasing marine biodiversity throughout the last ∼135 Ma. The LIP cycle pattern is coherent with marine biodiversity fluctuations corresponding to a reduction of marine biodiversity of ∼120 genera/Ma at ∼600 × 10 3 km 3 LIP eruption volume. The 62–65 Ma LIP cycle pattern as well as excursion in δ 34 S sulfate and marine genera reduction suggest a not-yet identified found LIP event at ∼440–450 Ma. Graphical abstract Graphical Abstract Highlights ► 140 and 65 Ma cyclic eruptions of large igneous provinces (LIP) control ocean chemistry and marine biodiversity. ► Since ∼135 Ma a ∼32 Ma cyclicity became dominated in LIP and marine biodiversity records. ► Cycle amplitudes relate to reduction of ∼120 marine genera at 〉∼600×10 3 km 3 LIP eruption volume.

Description: Publication year: 2012 Source: Geoscience Frontiers J. Brendan Murphy, R. Damian Nance The supercontinent cycle has had a profound effect on the Earth’s evolution since the Late Archean but our understanding of the forces responsible for it operation remains elusive. Supercontinents appear to form by two end-member processes: extroversion, in which the oceanic lithosphere surrounding the supercontinent (exterior ocean) is preferentially subducted (e.g. Pannotia), and introversion in which the oceanic lithosphere formed between dispersing fragments of the previous supercontinent (interior ocean) is preferentially subducted (e.g. Pangea). Extroversion can be explained by “top–down” geodynamics, in which a supercontinent breaks up over a geoid high and amalgamates above a geoid low. Introversion, on the other hand, requires that the combined forces of slab-pull and ridge push (which operate in concert after supercontinent break-up) must be overcome in order to enable the previously dispersing continents to turn inward. Introversion may begin when subduction zones are initiated along boundaries between the interior and exterior oceans and become trapped within the interior ocean. We speculate that the reversal in continental motion required for introversion may be induced by slab avalanche events that trigger the rise of superplumes from the core-mantle boundary. Graphical abstract Graphical Abstract Highlights ► Supercontinents form by two end-member processes: extroversion and introversion. ► Extroversion can be explained by top–down geodynamic models. ► Introversion requires reversals in plate motions, maybe triggered by a superplume.

Description: Publication year: 2012 Source: Geoscience Frontiers Oleg G. Safonov, Elizaveta I. Kovaleva, Svetlana A. Kosova, H.M. Rajesh, Georgy A. Belyanin, Maria A. Golunova, Dirk D. Van Reenen Reaction textures and fluid inclusions in the ∼2.0 Ga pyroxene-bearing dehydration zones within the Sand River biotite-hornblende orthogneisses (Central Zone of the Limpopo Complex) suggest that the formation of these zones is a result of close interplay between dehydration process along ductile shear zones triggered by H 2 O-CO 2 -salt fluids at 750–800 °C and 5.5–6.2 kbar, partial melting, and later exsolution of residual brine and H 2 O-CO 2 fluids during melt crystallization at 650–700 °C. These processes caused local variations of water and alkali activity in the fluids, resulting in various mineral assemblages within the dehydration zone. The petrological observations are substantiated by experiments on the interaction of the Sand River gneiss with the H 2 O-CO 2 -(K, Na)Cl fluids at 750 and 800 °C and 5.5 kbar. It follows that the interaction of biotite-amphibole gneiss with H 2 O-CO 2 -(K, Na)Cl fluids is accompanied by partial melting at 750–800 °С. Orthopyroxene-bearing assemblages are characteristic for temperature 800 °С and are stable in equilibrium with fluids with low salt concentrations, while salt-rich fluids produce clinopyroxene-bearing assemblages. These observations are in good agreement with the petrological data on the dehydration zones within the Sand River orthogneisses. Graphical abstract

Description: Publication year: 2012 Source: Geoscience Frontiers H.M. Rajesh, M. Santosh Graphical abstract Graphical Abstract Highlights ► Charnockites are important components of lower continental crust. ► Charnockites occurring as massive plutons are of igneous origin. ► (Incipient) Charnockites are granulite facies metamorphic rocks.

Description: Publication year: 2012 Source: Geoscience Frontiers Nicholas Arndt Massif anorthosites form when basaltic magma differentiates in crustal magma chambers to form low-density plagioclase and a residual liquid whose density was greater than that of enclosing crustal rocks. The plagioclase and minor pyroxene crystallized in situ on the floor of the magma chamber to produce the anorthosite complex, and the residual liquid migrated downwards, eventually to solidify as dense Fe-rich cumulates some of which were removed to the mantle. These movements were facilitated by high temperatures in Proterozoic continental crust, thus explaining the restriction of large anorthosite massifs to this period in Earth history Graphical abstract Graphical Abstract Highlights ► The fate of residual liquid left after plagioclase accumulates in massif anorthosites is unknown. ► This liquid is denser than crustal rock and migrated downwards into the lower crust. ► The predominance of massif anothosites in the Proterozoic may be related to the thermal state of continental crust.

Description: Publication year: 2012 Source: Geoscience Frontiers Kenji Kawai, Shinji Yamamoto, Taku Tsuchiya, Shigenori Maruyama It has been thought that granitic crust, having been formed on the surface, must have survived through the Earth’s evolution because of its buoyancy. At subduction zones continental crust is predominantly created by arc magmatism and is returned to the mantle via sediment subduction, subduction erosion, and continental subduction. Granitic rocks, the major constituent of the continental crust, are lighter than the mantle at depths shallower than 270 km, but we show here, based on first principles calculations, that beneath 270 km they have negative buoyancy compared to the surrounding material in the upper mantle and transition zone, and thus can be subducted in the depth range 270–660 km. This suggests that there can be two reservoirs of granitic material in the Earth, one on the surface and the other at the base of the mantle transition zone (MTZ). The accumulated volume of subducted granitic material at the base of the MTZ might amount to about six times the present volume of the continental crust. Our calculations also show that the seismic velocities of granitic material in the depth range from 270 km to 660 km are faster than those of the surrounding mantle. This could explain the anomalous seismic-wave velocities observed around 660 km depth. The observed seismic scatterers and reported splitting of the 660 km discontinuity could be due to jadeite dissociation, chemical discontinuities between granitic material and the surrounding mantle, or a combination thereof. Graphical abstract Graphical Abstract Highlights ► Presence of considerable amount of granitic materials in the mantle transition zone. ► This explains anomalous seismic velocities around the 670 km discontinuity. ► Our new model provides many interdisciplinary consequences.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 4 Lawrence H. Tanner, Xin Wang, Alesha C. Morabito The Yan'an Formation of the Ordos Basin is a sequence of four members, consisting of siliciclastic sediments deposited in alluvial, lacustrine and mire settings during the Middle Jurassic. Samples collected from Members Two and Four contain abundant blackened plant material identified through standard analytical techniques as fusain (fossil charcoal). The occurrence of fusain in fluvial sandstones at multiple horizons in the outcrops, combined with the previously reported high concentration of inertinite in the coals of Member One, indicates that paleowildfire was a common occurrence in the Ordos Basin during Yan'an deposition. Sedimentary evidence from Yan'an outcrops suggests that the paleoclimate was seasonal during deposition of Members Two through Four, which may have contributed to the wildfire frequency. The presence of fusain in the Yan'an Formation indicates that atmospheric oxygen levels were clearly above the minimum required for sustained combustion during the Middle Jurassic. This conclusion contradicts previous geochemical models for paleoatmospheric composition, but supports more recent studies. Graphical abstract Graphical abstract Highlights ► Abundant fusian in the Middle Jurassic Yan'an Formation (Ordos Basin, China). ► The presence of fusain indicates that paleowildfire was common during Yan'an deposition. ► Atmospheric oxygen levels over minimum value for sustained combustion during Middle Jurassic.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 4 Syed Amer Mahmood, Richard Gloaguen Landscapes in tectonically active Hindu Kush (NW Pakistan and NE Afghanistan) result from a complex integration of the effects of vertical and horizontal crustal block motions as well as erosion and deposition processes. Active tectonics in this region have greatly influenced the drainage system and geomorphic expressions. The study area is a junction of three important mountain ranges (Hindu Kush-Karakorum-Himalayas) and is thus an ideal natural laboratory to investigate the relative tectonic activity resulting from the India-Eurasia collision. We evaluate active tectonics using DEM derived drainage network and geomorphic indices hypsometric integral (HI), stream-length gradient (SL), fractal dimension (FD), basin asymmetry factor (AF), basin shape index ( B s ), valley floor width to valley height ratio ( Vf ) and mountain front sinuosity ( S mf ). The results obtained from these indices were combined to yield an index of relative active tectonics (IRAT) using GIS. The average of the seven measured geomorphic indices was used to evaluate the distribution of relative tectonic activity in the study area. We defined four classes to define the degree of relative tectonic activity: class 1 __ very high (1.0 ≤ IRAT 〈 1.3); class 2 __ high (1.3 ≥ IRAT 〈 1.5); class 3—moderate (1.5 ≥ IRAT 〈 1.8); and class 4—low (1.8 ≥ IRAT). In view of the results, we conclude that this combined approach allows the identification of the highly deformed areas related to active tectonics. Landsat imagery and field observations also evidence the presence of active tectonics based on the deflected streams, deformed landforms, active mountain fronts and triangular facets. The indicative values of IRAT are consistent with the areas of known relative uplift rates, landforms and geology. Graphical abstract Graphical abstract Highlights ► Evaluation of DEM based geomorphic indices to study active tectonics in Hindu Kush. ► Index of relative active tectonics (IRAT) using GIS. ► Very high, high and moderate IRAT classes consistent with the known uplift rates.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 4 N. Natarajan, G. Suresh Kumar A numerical model is developed for investigating the evolution of fracture permeability in a coupled fracture-matrix system in the presence of fracture-skin with simultaneous colloidal and bacterial transport, by taking into account the effects of thermal stress and silica precipitation/dissolution, which is computed using linear reaction kinetics. The non-linear coupled equations are numerically modeled using the fully implicit finite difference method and a constant continuous source is adopted while modeling thermal, contaminant, colloidal and bacterial transport. Due to co-colloid bacterial transport under non-isothermal conditions, in a coupled fracture-skin-matrix system, the fracture apertures vary spatially, with a corresponding pressure variation for a constant discharge. A series of numerical experiments were conducted for analyzing the spatial variation of fracture aperture in response to the combined effects of thermal stress, silica precipitation/dissolution, and simultaneous colloidal and bacterial transport in the presence of the fracture-skin. The simulation results suggest that temperature and contaminant concentration of the mobile fluid within the fracture increases with reduction in initial fracture aperture. The pattern of variation followed by the fracture aperture is nearly the same in the presence and absence of bacterial transport but the magnitude of the fracture aperture is low under the influence of bacterial transport. The variation in the fracture aperture resulting from precipitation-dissolution and thermoelastic stress is significant when the fracture aperture is very low and reduces with increment in fracture aperture. The variation in fracture aperture and pressure remains the same for both undersaturated and supersaturated fluid entering the fracture due to the influence of bacterial transport at the inlet of the fracture. Graphical abstract Graphical abstract Highlights ► Temperature and contaminant concentration increase with decreasing fracture aperture. ► Bacterial growth reduces the reservoir efficiency due to reduction of permeability. ► Contaminants form substrate for bacteria which causes fracture aperture reduction.

Description: Publication year: 2012 Source: Geoscience Frontiers Carlos J. Chernicoff, Eduardo O. Zappettini, João O.S. Santos, Neal J. McNaughton, Elena Belousova We have carried out zircon U-Pb SHRIMP dating and Hf isotope determinations on a biotite paraschist and on a tonalitic orthogneiss of the Yaminué Complex, and re-evaluate this Complex in the broader context of the tectonic evolution of the Patagonia composite terrane. In the metasedimentary unit (msuYC), the youngest detrital zircon dated at 318 ± 5 Ma (Mississippian/Pennsylvanian boundary) indicates a Pennsylvanian (or younger) depositional age. The three main age populations peak at 474, 454 and 374 Ma. Preliminary Hf isotope data for two detrital zircons (447 and 655 Ma) yielded ε (Hf) values of – 0.32 and 0.48, indicating that their primary sources contained small amounts of recycled crustal components (of Calymmian age; T DM 1.56 Ga). Zircons from the orthogneiss (miuYC; intrusive into msuYC) show a crystallization age of 261.3 ± 2.7 Ma (Capitanian; late middle Permian) which is broadly coeval with deformation, and Neoarchean – Paleoproterozoic inheritance. Meaningful core-rim relationship between Neoarchean zircon cores and late Permian rims is well defined, indicating the occurrence of Archean crust in this sector of Patagonia. Hf T DM of Permian zircons is mainly Meso – Paleoarchean (2.97 – 3.35 Ga), with highly negative ε (Hf) values (ca. – 33). Hf T DM of inherited Neoarchean zircon cores is also Meso – Paleoarchean (3.14 – 3.45 Ga) but more juvenile ( ε (Hf) = – 0.3). Hf isotopes reinforce the presence of unexposed ancient crust in this area. Combining geological and isotope data, as well as geophysical models, we identify the Yaminué Complex within the La Esperanza-Yaminué crustal block flanked by two other, distinct crustal blocks: the Eastern block which forms part of the Patagonia terrane sensu stricto , located in the eastern Patagonian region, and the Western block forming part of the Southern Patagonia terrane. Their origins and timing of amalgamation to form the Patagonia Composite Terrane are also discussed. Graphical abstract Graphical Abstract Highlights ► Youngest detrital zircon in metasedimentary units 317.8 ± 4.9 Ma. ► Metaigneous unit inherited from Neoarchean–Paleoproterozoic. ► Hf evidence for ancient crust.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 4 Bhaskar Kundu

Description: Publication year: 2012 Source: Geoscience Frontiers Yanhong Pan, Jingeng Sha, Yaqiong Wang, Xiaolin Zhang, Xiaogang Yao, Bo Peng, Xin Rao Abstract The brackish-water bivalve Waagenoperna Tokuyama, 1959 is reported from the Lower Jurassic Badaowan Formation at four localities, along the southern margin and western margin of the Junggar Basin. Taphonomic features recorded in the field indicate that it occurs in autochthonous or parautochthonous assemblages. The autecology of Waagenoperna therefore yields information on the palaeoenvironment of the area. The restriction of Waagenoperna to marine and brackish-water settings suggests that the sea water once reached these areas during the Sinemurian. This paper discusses the palaeogeographic implications and suggests an ingression of the sea from the west to the western and southern part of the Junggar Basin. Additionally, the two Waagenoperna species collected from the Haojiaogou section in the Junggar Basin are taxonomically documented. Graphical abstract Graphical Abstract

Description: Publication year: 2012 Source: Geoscience Frontiers A.M. Gorodnitskiy, Yu.V. Brusilovskiy, A.N. Ivanenko, A.M. Filin, N.A. Shishkina New methods are presented for processing and interpretation of shallow marine differential magnetic data, including constructing maps of offshore total magnetic anomalies with an extremely high resolution of up to 1–2 nT, mapping weak anomalies of 5–10 nT caused by mineralization effects at the contacts of hydrocarbons with host rocks, estimating depths to upper and lower boundaries of anomalous magnetic sources, and estimating thickness of magnetic layers and boundaries of tectonic blocks. Horizontal dimensions of tectonic blocks in the so-called “seismic gap” region in the central Kuril Arc vary from 10 to 100 km, with typical dimensions of 25–30 km. The area of the “seismic gap” is a zone of intense tectonic activity and recent volcanism. Deep sources causing magnetic anomalies in the area are similar to the “magnetic belt” near Hokkaido. In the southern and central parts of Barents Sea, tectonic blocks with widths of 30 to 100 km, and upper and lower boundaries of magnetic layers ranging from depths of 10 to 5 km and 18 to 30 km, respectively, are calculated. Models of the magnetic layer underlying the Mezen Basin in an inland part of the White Sea–Barents Sea paleorift indicate depths to the lower boundary of the layer of 12 to 30 km. Weak local magnetic anomalies of 2–5 nT in the northern and central Caspian Sea were identified using the new methods, and drilling confirms that the anomalies are related to concentrations of hydrocarbon. Two layers causing magnetic anomalies are identified in the northern Caspian Sea from magnetic anomaly spectra. The upper layer lies immediately beneath the sea bottom and the lower layer occurs at depths between 30–40 m and 150–200 m. Graphical abstract Graphical Abstract Highlights ► The new algorithms for processing marine magnetic gradient surveys are presented. ► Our approach allows to map and interpret the weak (up to 2–5 nT) magnetic anomalies. ► It was applied to resolve the geometry of magnetic layers.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 4 Prosanta K. Khan, Partha Pratim Chakraborty, G. Tarafder, S. Mohanty The disastrous M w 9.3 (seismic moment 1.0 × 10 30 dyn/cm) earthquake that struck northwest Sumatra on 26 December 2004 and triggered ∼30 m high tsunami has rejuvenated the quest for identifying the forcing behind subduction related earthquakes around the world. Studies reveal that the strongest part (elastic core) of the oceanic lithosphere lie between 20 and 60 km depth beneath the upper (∼7 km thick) crustal layer, and compressive stress of GPa order is required to fail the rock-layers within the core zone. Here we present evidences in favor of an intraplate origin of mega-earthquakes right within the strong core part (at the interface of semi-brittle and brittle zone), and propose an alternate model exploring the flexing zone of the descending lithosphere as the nodal area for major stress accumulation. We believe that at high confining pressure and elevated temperature, unidirectional cyclic compressive stress loading in the flexing zone results in an increase of material yield strength through strain hardening, which transforms the rheology of the layer from semi-brittle to near-brittle state. The increased compressive stress field coupled with upward migration of the neutral surface (of zero stress fields) under non-coaxial deformation triggers shear crack. The growth of the shear crack is initially confined in the near-brittle domain, and propagates later through the more brittle crustal part of the descending oceanic lithosphere in the form of cataclastic failure. Graphical abstract Graphical abstract Highlights ► Strain-hardening and upward migration of neutral surface under compression. ► Transformation of rheological character from semi-brittle to near-brittle. ► Triggering of mega-earthquake at the rheological interface.

Description: Publication year: 2012 Source: Geoscience Frontiers Julio Cezar Mendes, Cristina M.P. De Campos The Venda Nova Pluton (VNP) is a zoned ring structure emplaced in the southern portion of the Neoproterozoic Araçuai Belt, in Espírito Santo, Brazil. It is a slightly westward tilted cylinder-like intrusion, with an almost circular horizontal section. In the center of this structure, an off-centered gabbro-noritic core, surrounded by syeno-monzonitic rocks, intrudes an outer ring of charnockites and norite. These envelop the syeno-monzonitic and gabbro-noritic center, as a narrow discontinuous belt. While, in the core intrusion, mingling and mixing processes are widespread and well documented in the literature, in the outer ring, the norite and charnockite layers show predominantly homogeneous and isotropic internal structures. Nevertheless, smaller interaction zones between charnockites and norite denote a comparatively more restricted mingling process. The norite is a fine-grained rock with hypidiomorphic granular to intergranular texture. The charnockites are medium-grained and made up of: (a) orthopyroxene-tonalite, (b) orthopyroxene-quartz-diorite, and (c) orthopyroxene-granodiorite with hypidiomorphic granular to porphyritic textures. In all lithotypes both ortho- and clinopyroxene are replaced by hornblende and biotite. Two contrasting compositional sequences have been recognized, based on whole rock geochemistry: (1) a basic, with tholeiitic affinities (norite) and, (2) an intermediate, medium-K calc-alkaline, comprising the charnockites. Estimated crystallization temperatures, which have been calculated from micro-probe analysis of pyroxenes, range from 915 ± 25 °C to 960 ± 50 °C. Re-equilibration temperature (ilmenite-magnetite calibration) is around 600 ± 50 °C. This indicates oxygen fugacities four order of magnitude below the FMQ-buffer and a reduced environment. Coeval pressure conditions estimated from the Al-content in hornblende range from 5.5 ± 0.6 kbar. Data obtained for the norite point towards an evolution from the partial melting of an anhydrous tholeiitic mantle magma. The charnockites may correspond to the differentiation of a calc-alkaline parental magma. The later could be the hybrid product from the contamination and mixing between the anhydrous tholeiitic magma with other deeper crustal sources. Further the magmatic system evolved through fractionation of orthopyroxene, clinopyroxene, plagioclase and ilmenite. Our results support the hypothesis for the evolution of the Venda Nova pluton through a mantle-crust delamination process probably related to the collapse of the Araçuai orogeny. Graphical abstract Graphical Abstract Highlights ► The calcic charnockitic intrusion is related to the collapse of the Brasiliano Araçuaí Belt (G5 Supersuite). ► Petrogenetic constraints point towards reducing conditions and emplacement under 16 km in depth. ► The evolution of the pluton was possibly controlled by mantle-crust delamination process.

Description: Publication year: 2012 Source: Geoscience Frontiers G.H. Grantham, P. Mendonidis, R.J. Thomas, M. Satish-Kumar Four different varieties of charnockitic rocks, with different modes of formation, from the Mesoproterozoic Natal belt are described and new C isotope data presented. Excellent coastal exposures in a number of quarries and river sections make this part of the Natal belt a good location for observing charnockitic field relationships. Whereas there has been much debate on genesis of charnockites and the use of the term charnockite, it is generally recognized that the stabilization of orthopyroxene relative to biotite in granitoid rocks is a function of low a H 2 O (± high CO 2 ), high temperature, and composition (especially Fe/(Fe+Mg)). From the Natal belt exposures, it is evident that syn-emplacement, magmatic crystallization of charnockite can arise from mantle-derived differentiated melts that are inherently hot and dry (as in the Oribi Gorge granites and Munster enderbite), as well as from wet granitic melts that have been affected through interaction with dry country rock to produce localized charnockitic marginal facies in plutons (as in the Portobello granite). Two varieties of post-emplacement sub-solidus charnockites are also evident. These include charnockitic aureoles developed in leucocratic, biotite, garnet granite adjacent to cross-cutting enderbitic veins that are attributed to metamorphic-metasomatic processes (as in the Nicholson’s Point granite, a part of the Margate Granite Suite), as well as nebulous, patchy charnockitic veins in the Margate Granite that are attributed to anatectic metamorphic processes under low- a H 2 O fluid conditions during a metamorphic event. These varieties of charnockite show that the required physical conditions of their genesis can be achieved through a number of geological processes, providing some important implications for the classification of charnockites, and for the interpretation of charnockite genesis in areas where poor exposure obscures field relationships. Graphical abstract

Description: Publication year: 2012 Source: Geoscience Frontiers Lihua Liu, Fei Wu, Stefan Haderlein, Peter Grathwohl Subcooled liquid solubility is the water solubility for a hypothetical state of liquid. It is an important parameter for multicomponent nonaqueous phase liquids (NAPLs) containing polycyclic aromatic hydrocarbons (PAHs), which can exist as liquids even though most of the solutes are solid in their pure form at ambient temperature. So far, subcooled liquid solubilities were estimated from the solid water solubility and fugacity ratio of the solid and (subcooled) liquid phase, but rarely derived from experimental data. In our study, partitioning batch experiments were performed to determine the subcooled liquid solubility of PAHs in NAPL-water system. For selected PAH, a series of batch experiments were carried out at increased mole fractions of the target component in the NAPL and at a constant NAPL/water volume ratio. The equilibrium aqueous PAH concentrations were measured with HPLC and/or GC-MS. The subcooled liquid solubility was derived by extrapolation of the experimental equilibrium aqueous concentration to a mole fraction of unity. With the derived subcooled liquid solubility, the fugacity ratio and enthalpy of fusion of the solute were also estimated. Our results show a good agreement between the experimentally determined and published data. Graphical Abstract Highlights ► Partitioning batch experiment to determinate the saturated aqueous phase concentration. ► Extrapolating the experimental results to obtain the subcooled liquid solubility. ► Activity coefficient, fugacity ratio and enthalpy of fusion of the test PAHs were derived

Description: Publication year: 2012 Source: Geoscience Frontiers Arie Lev Gilat, Alexander Vol Examples of the mightiest energy releases by great earthquakes and volcanic eruptions and hypotheses providing explanations for them are analyzed along with the results of some recently published researches and visualizations. The emerging conclusions are that the mechanism of the strong earthquake is a chemical explosion; that volcanic eruption is a special type of earthquake wherein the hypocenter rises to the earth-surface; and that there is an association between the seismic-volcanic processes and mantle “fluids” and the lack of energy for mantle plumes. A conceptual system of hypotheses is put forward to explain the conservation of energy during Earth’s accretion, its quasi-stable release by primordial H- and He-degassing and of the crucial role of the energy of degassing-comprising-reactions in endogenic processes. Specific mechanisms and chemical processes are proposed for the gas-liquid mantle plumes melting through the solid mantle using heat-energy released in reactions of their metamorphic and chemical transformation under gradual decrease of pressure and temperature; volcanic gases are put forward as energy carriers. 3 He performance as a unique measuring transformer correlative to the internal heat flow was used for calculation of energy release by degassing; it equals to 5.12 × 10 20 J/yr, an amount of energy five-fold greater than the entire energy loss involved in earthquake and volcanic activity. The hypotheses proposed are objectively testable. Graphical Abstract Highlights ► Energy-outputs of mega-cataclysms and other facts are explained by the proposed energy-source. ► During Earth accretion H and He were stored in its interior under ultrahigh pT -conditions. ► The giant energy invested in H-He trapping is queasy-constantly released by their degassing.

Description: Publication year: 2012 Source: Geoscience Frontiers Yangxiao Zhou, Dianwei Dong, Jiurong Liu, Wenpeng Li Monitoring of regional groundwater levels provides important information for quantifying groundwater depletion and assessing impacts on the environment. Historically, groundwater level monitoring wells in Beijing Plain, China, were installed for assessing groundwater resources and for monitoring the cone of depression. Monitoring wells are clustered around well fields and urban areas. There is urgent need to upgrade the existing monitoring wells to a regional groundwater level monitoring network to acquire information for integrated water resources management. A new method was proposed for designing a regional groundwater level monitoring network. The method is based on groundwater regime zone mapping. Groundwater regime zone map delineates distinct areas of possible different groundwater level variations and is useful for locating groundwater monitoring wells. This method was applied to Beijing Plain to upgrade a regional groundwater level monitoring network. Graphical Abstract Highlights ► A new method for designing a groundwater level monitoring network is proposed. ► A regional groundwater level monitoring network for Beijing plain is upgraded. ► The network will provide sufficient information for groundwater resources management.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 3 Gaoyuan Li, Hongchen Jiang, Weiguo Hou, Shang Wang, Liuqin Huang, Huilei Ren, Shicai Deng, Hailiang Dong The microbial diversity in Wuli Area, Qinghai-Tibetan Plateau was investigated using 16S rRNA gene phylogenetic analyses. A total of 117 bacterial and 66 archaeal 16S rRNA gene clones were obtained from the Wuli cold springs. The bacterial clones could be classified into Proteobacteria , Acidobacteria , Deinococci , Sphingobacteria , Flavobacteria , Nitrospirae , Actinobacteria , Gemmatimonadetes , and unclassified-bacteria; and the archaeal clones could be classified into Crenarchaeota and Thaumarchaeota . Among the major groups, Proteobacteria and Crenarchaeota were dominant in the bacterial and archaeal 16S rRNA gene clone libraries, respectively. The clone sequences obtained in Wuli cold springs were closely related to those from cold habitats, such as snow/ice/soils on high mountains or at high latitude. Especially, the microbial community composition of Wuli Area was more similar to that in Tibetan glaciers than cold environments of other locations. The data presented in this study have implications for a better understanding of microbial diversity in cold springs on the Qinghai-Tibetan Plateau. Graphical Abstract Highlights ► Microbial diversity in Wuli cold springs (WCS) on the Tibetan Plateau identified. ► Microbial community (MC) related to those from other cold habitats. ► MC similar to those in Tibetan glaciers than to other low-T habitats.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 3 Shang Wang, Raymond M. Dong, Christina Z. Dong, Liuqin Huang, Hongchen Jiang, Yuli Wei, Liang Feng, Deng Liu, Guifang Yang, Chuanlun Zhang, Hailiang Dong The Three Gorges Dam (TGD) of the Yangtze River, China, is one of the largest irrigation and hydroelectric engineering projects in the world. The effects of huge man-made projects like TGD on fauna and macrophyte are obvious, mainly through changes of water dynamics and flow pattern; however, it is less clear how microorganisms respond to such changes. This research was aimed to examine differences in microbial diversity at different seasons and locations (in front of and behind the TGD). In addition, differences between particle-attached and free-living communities were also examined. The community structures of total and potentially active microorganisms in the water columns behind and in front of the TGD were analyzed with the DNA- and RNA-based 16S rRNA gene phylogenetic approaches over three different seasons. Clone libraries of 16S rRNA genes were prepared after amplification from extracted DNA and, for some samples, after preparing cDNA from extracted rRNA. Differences were observed between sites at different seasons and between free-living and particle-attached communities. Both bacterial and archaeal communities were more diverse in summer than in winter, due to higher nutrient levels and warmer temperature in summer than in winter. Particle-attached microorganisms were more diverse than free-living communities, possibly because of higher nutrient levels and heterogeneous geochemical micro-environments in particles. Spatial variations in bacterial community structure were observed, i.e., the water reservoir behind the TGD (upstream) hosted more diverse bacterial populations than in front of the dam (downstream), because of diverse sources of sediments and waters from upstream to the reservoir. These results have important implications for our understanding of responses of microbial communities to environmental changes in river ecosystems affected by dam construction. Graphical Abstract Highlights ► Diversity of microbial plankton across the Three Gorges Dam (TGD). ► Microbial plankton in summer more diverse than that in winter. ► Microbial plankton behind the TGD is more diverse than in front of the dam.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 3 S. Mohanty Reconstruction of the Neoproterozoic supercontinent Rodinia shows near neighbour positions of the South Indian Cratons and Western Australian Cratons. These cratonic areas are characterized by extensive Paleoproterozoic tectonism. Detailed analysis of the spatio-temporal data of the Satpura Mountains of India indicates presence of at least three episodes of Proterozoic orogeny at ∼2100–1900 Ma, ∼1850 Ma and ∼1650 Ma, and associated basin development and closing. A subdued imprint of the Grenville orogeny (∼950 Ma) is also found in rock records of this Mountain Belt. The Capricorn Orogen of Western Australia also shows three episodes of orogeny: Opthalmian–Glenburgh Orogeny (2100–1950 Ma), Capricorn Orogeny (∼1800 Ma) and Mangaroon Orogeny (∼1650 Ma), and basin opening and closing related to these tectonic movements. These broad similarities suggest their joint evolution possibly in a near neighbour position during Paleoproterozoic Era. In view of juxtaposition of the Western Australia along the east coast of India, at the position of the Eastern Ghats, during Archean, it is suggested that the breaking of this Archean megacraton at ∼2400 Ma led to northward movement of the broken components and formation of the Satpura–Capricorn Orogen (at ∼2100 and ∼1800 Ma) due to the collision of cratonic blocks with the pre-existing northern cratonic nuclei of India and Western Australia. This is also the time of formation of the supercontinent Columbia. A phase of basin opening followed the ∼1800 Ma event, followed by another phase of collisional event at ∼1600 Ma at the site of the Satpura–Capricorn Orogen. Subsequent evolutions of the Satpura and the Capricorn Orogens differ slightly, indicating separate evolutional history.

Description: Publication year: 2012 Source: Geoscience Frontiers Pinghua Liu, Fulai Liu, Hong Yang, Fang Wang, Jianhui Liu High-pressure (HP) granulites widely occur as enclaves within tonalite-trondhjemite-granodiorite (TTG) gneisses of the early Precambrian metamorphic basement in the Shandong Peninsula, southeast part of the North China Craton (NCC). Based on cathodoluminescence (CL), laser Raman spectroscopy and in-situ U-Pb dating, we characterize the zircons from the HP granulites and group them into three main types: inhetrited (magmatic) zircon, HP metamorphic zircon and retrograde zircon. The inherited zircons with clear or weakly defined magmatic zoning contain inclusions of apatites, and 207 Pb/ 206 Pb ages of 2915–2890 Ma and 2763 –2510 Ma, correlating with two magmatic events in the Archean basement. The homogeneous HP metamorphic zircons contain index minerals of high pressure metamorphism including garnet, clinopyroxene, plagioclase, quartz, rutile and apatite, and yield 207 Pb/ 206 Pb ages between 1900–1850 Ma, marking the timing of peak HP granulite facies metamorphism. The retrograde zircons contain inclusions of orthopyroxene, plagioclase, quartz, apatite and amphibole, and yield the youngest 207 Pb/ 206 Pb ages of 1840–1820 Ma among the three groups, which we correlate to the medium- to low-pressure granulite facies retrograde metamorphism. The data presented in this study suggest subduction of Meso- and Neoarchean magmatic protoliths to lower crust depths where they were subjected to HP granulite facies metamorphism during Paleoproterozoic (1900–1850 Ma). Subsequently, the HP granulites were exhumated to upper crust levels, and were overprinted by medium to low-pressure granulite and amphibolite facies retrograde event at ca. 1840–820 Ma. Graphical Abstract Highlights ► HP granulite facies mineral inclusions identified in metamorphic zircons. ► U-Pb ages of zircon domains with HP granulite facies inclusions range from 1925 ± 27 to 1853 ± 21. ► The ages represent the timing of peak HP granulite facies metamorphism in the basement of Shandong Peninsula.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 3 Yong Zhang, Xin Su, Fang Chen, Yuanyuan Wang, Lu Jiao, Hailiang Dong, Yongyang Huang, Hongchen Jiang South China Sea (SCS) is the largest Western Pacific marginal sea. However, microbial studies have never been performed in the cold seep sediments in the SCS. In 2004, “SONNE” 177 cruise found two cold seep areas with different water depth in the northern SCS. Haiyang 4 area, where the water depth is around 3000 m, has already been confirmed for active seeping on the seafloor, such as microbial mats, authigenic carbonate crusts and bivalves. We investigated microbial abundance and diversity in a 5.55-m sediment core collected from this cold seep area. An integrated approach was employed including geochemistry and 16S rRNA gene phylogenetic analyses. Here, we show that microbial abundance and diversity along with geochemistry profiles of the sediment core revealed a coupled reaction between sulphate reduction and methane oxidation. Acridine orange direct count results showed that microbial abundance ranges from 10 5 to 10 6  cells/g sediment (wet weight). The depth-related variation of the abundance showed the same trend as the methane concentration profile. Phylogenetic analysis indicated the presence of sulphate-reducing bacteria and anaerobic methane-oxidizing archaea. The diversity was much higher at the surface, but decreased sharply with depth in response to changes in the geochemical conditions of the sediments, such as methane, sulphate concentration and total organic carbon. Marine Benthic Group B, Chloroflexi and JS1 were predominant phylotypes of the archaeal and bacterial libraries, respectively. Graphical Abstract Highlights ▶ Abyssal microbial community from methane see page. ▶ Low abundance, high diversity and unique composition. ▶ Major phylotypes participated in the geochemical processes related to methane vent.

Description: Publication year: 2012 Source: Geoscience Frontiers Dmitry A. Ruban Many gastropod taxa went extinct during the Late Cretaceous. The stratigraphic ranges of 268 genera permit to establish the longevity of extinction victims for each stage of this epoch. “Young” taxa (originated within 3 epochs before the extinction) prevailed among victims of the extinctions in all stages. The proportion of “old” taxa (originated before the Cretaceous) that went extinct was the highest in the Cenomanian, and it was the lowest in the Coniacian and the Maastrichtian. It appears that the end-Cretaceous mass extinction affected chiefly “young” taxa. However, the comparison with the earlier time intervals suggests that this pattern of selectivity by generic longevity was not specific for the noted catastrophe, but, in contrast, it was typical for the entire Late Cretaceous. The latest Cenomanian environmental perturbation (OAE2) caused a stronger extinction of “old” taxa, and thus, this biotic crisis was less selective by generic longevity. This hypothesis, however, is not proven by the statistical test. Graphical Abstract Highlights ► Young gastropod genera prevailed among victims of the end-Cretaceous mass extinction. ► Established selectivity by taxa longevity was not specific for the mass extinction. ► The latest Cenomanian crisis was less selective by generic longevity

Description: Publication year: 2012 Source: Geoscience Frontiers H.M. Rajesh Large charnockite massifs occur in the high-grade Southern Granulite Terrain (SGT) and Eastern Ghats Belt (EGB) crustal provinces of Peninsular India. Available geochronological data indicate that the magmatism is episodic, associated with distinct orogenic cycles in the different crustal domains. The geochemical data also indicate a change in composition from trondhjemitic at ∼3.0–2.9 Ga to dominantly tonalitic at ∼2.6–2.5 Ga to tonalitic-granodiorite-granitic at ∼2.0–1.9 Ga to dominantly tonalitic at 1.7–1.6 Ga to quartz monzonitic or tonalitic at ∼1.0–0.9 Ga to granodiorite-granitic at ∼0.8–0.7 Ga. The trondhjemitic and tonalitic end members are metaluminous, magnesian and calcic to calc-alkalic, characteristic of magnesian group charnockites. The granodioritic to granitic end members are metaluminous to slightly peraluminous, ferroan and calc-alkalic to alkali-calcic, characteristic of ferroan group charnockites. The quartz monzonitic end members are metaluminous to peraluminous, magnesian to ferroan and calcic to calc-alkalic, neither characteristic of the magnesian group nor of the ferroan group of charnockites. Based on the occurrence and difference in composition of the charnockite massifs, it is suggested that the charnockite magmatism registers the crustal growth of the Indian plate on its southern (SGT) and eastern (EGB) sides, along active continental margins by accretion of arcs. Graphical abstract Graphical Abstract Highlights ► Charnockite magmatism in Peninsular India is episodic. ► Least differentiated end members are similar to magnesian group charnockites. ► Episodic charnockite magmatism registers the crustal growth of the Indian plate

Description: Publication year: 2012 Source: Geoscience Frontiers Tetsuya Tokiwa, Kimikazu Tsusaka, Makoto Matsubara, Taiki Ishikawa, Daisuke Ogawa This paper focuses on the formation mechanism of fractures induced by excavation of a gallery in soft sedimentary rocks in the Horonobe area of Japan. Detailed fracture mapping of the gallery indicates that the fractures consist of both pre-existing shear fractures and excavation damaged zone (EDZ) fractures. EDZ fractures correspond to weak planes associated with bedding planes or transgranular cracks. The EDZ fractures terminate against pre-existing shear fractures. Therefore, even for excavations in soft sedimentary rocks, formation of the EDZ fractures are controlled by pre-existing fractures and earlier weak planes. Graphical abstract Graphical Abstract Highlights ► Fractures can be divided into pre-existing shear fractures and EDZ fractures. ► EDZ fractures correspond to weak planes such as bedding planes or transgranular cracks. ► Even for excavations in soft rocks, formation of the EDZ fractures is controlled by weak planes.

Description: Publication year: 2012 Source: Geoscience Frontiers A. Krishnakanta Singh, R.K. Bikramaditya Singh The Abor volcanics outcroping in the core of the Siang window in the Eastern Himalaya comprise voluminous mafic volcanics (47%–56% w(SiO 2 )), with subordinate felsic volcanics (67%–75% w(SiO 2 )). The felsic volcanics are dacitic to rhyolitic in composition and are typically enriched in LREE (La/Sm N  = 3.09–3.90) with high REE contents (256–588 ppm), moderately fractionated REE patterns (Ce N /Yb N  = 6.54–9.52) and pronounced negative Eu anomalies (Eu/Eu* = 0.55–0.72). Wide variations in Rb/Zr, K/Rb and La/Sm ratios suggest that they were derived from magmas which were randomly contaminated with crustal material. Chemical characteristics and petrogenetic modelling indicate that the dacites were generated by ∼15% partial melting of a mafic source leaving a residue with 55% plagioclase, 14% orthoclase, 18% clinopyroxene, 5% orthopyroxene, 8% hornblende. The silica-rich rhyodacites and rhyolites were derived from a dacite magma source by a higher degree (〉45%) fractional crystallization of an assemblage consisting of 70% plagioclase, 12% clinopyroxene, 7% amphibole and 11% magnetite. The associated LREE-LILE enrichment and pronounced negative anomalies for HFSE (Nb, P, and Ti) exhibited by these felsic volcanics are characteristic of continental rift volcanism, implying that they were emplaced during lithospheric extension. Graphical Abstract Highlights ► The less siliceous dacites generated by ∼15% partial melting of a mafic source. ► The silica-rich rhyodacites and rhyolites derived from a dacite magma source by higher degree (〉45%) fractional crystallization. ► The felsic and mafic volcanics were emplaced in an extensional tectonic environment.

Description: Publication year: 2012 Source: Geoscience Frontiers Mohamed K. Salah Seismic anisotropy and its main features along the convergent boundary between Africa and Iberia are detected through the analysis of teleseismic shear-wave splitting. Waveform data generated by 95 teleseismic events recorded at 17 broadband stations deployed in the western Mediterranean region are used in the present study. Although the station coverage is not uniform in the Iberian Peninsula and northwest Africa, significant variations in the fast polarization directions and delay times are observed at stations located at different tectonic domains. Fast polarization directions are oriented predominantly NW-SE at most stations which are close to the plate boundary and in central Iberia; being consistent with the absolute plate motion in the region. In the northern part of the Iberian Peninsula, fast velocity directions are oriented nearly E–W; coincident with previous results. Few stations located slightly north of the plate boundary and to the southeast of Iberia show E–W to NE-SW fast velocity directions, which may be related to the Alpine Orogeny and the extension direction in Iberia. Delay times vary significantly between 0.2 and 1.9 s for individual measurements, reflecting a highly anisotropic structure beneath the recording stations. The relative motion between Africa and Iberia represents the main reason for the observed NW-SE orientations of the fast velocity directions. However, different causes of anisotropy have also to be considered to explain the wide range of the splitting pattern observed in the western Mediterranean region. Many geophysical observations such as the low Pn velocity, lower lithospheric Q values, higher heat flow and the presence of high conductive features support the mantle flow in the western Mediterranean, which may contribute and even modify the splitting pattern beneath the studied region. Graphical Abstract Highlights ► Fast velocity axes near Africa-Iberia plate boundary have mainly NW-SE orientations. ► Some stations show NE-SW fast axes; parallel to the extension direction in the Iberian Peninsula. ► The complex splitting observed at some sites is due to active dynamic flow in the asthenosphere.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 1 Vsevolod Prokofiev, Ivan Baksheev, Lidiya Zorina, Boris Belyatsky, Vladimir Ustinov, Nadezhda Krivitskaya Zoned tourmaline (schorl-dravite) in the matrix of hydrothermal explosive breccia and ore veins in gold deposits, Chita region, Eastern Transbaikalia, Russia, are associated with Na- and K-rich porphyry-type subvolcanic intrusives. δ 18 O values of tourmaline from three gold deposits (Darasun, Talatui, Teremkinskoye) are +8.3‰, +7.6‰, and +6.0‰ and calculated δ 18 O values of fluids responsible for the tourmalinization are +7.3‰, +7.7‰, and +4.2‰, respectively. These data imply an igneous fluid source, except at the Teremkin deposit where mixing with meteoric water is indicated. Wide ranges of Fe 3+ /Fe tot and the presence of vacancies characterize the Darasun deposit tourmaline indicating wide ranges of ƒ (O 2 ) and pH of mineralizing fluids. Initial stage tourmalines from the gold deposits of the Darasun ore district are dravite or high mg schorl. Second stage tourmaline is characterized by oscillatory zoning but with Fe generally increasing towards crystal rims indicating decreasing temperature. Third stage tourmaline formed unzoned crystals with x Mg (mole fraction of Mg) close to that of the first stage tourmaline, due to a close association with pyrite and arsenopyrite. From Fe 3+ /Fe tot values, chemical composition and crystallization temperatures, log f (O 2 ) of mineralizing fluids ranged from ca. −25 to −20, much higher than for the gold-bearing beresite–listvenite association, indicating that tourmalinization was not related to gold mineralization.

Description: Publication year: 2012 Source: Geoscience Frontiers Liang Shen, Tandong Yao, Baiqing Xu, Hongmei Wang, Nianzhi Jiao, Shichang Kang, Xiaobo Liu, Yongqin Liu Ice melt water from a 22.27 m ice core which was drilled from the East Rongbuk Glacier, Mt. Everest was incubation in two incubation ways: plate melt water directly and enrichment melt water prior plate, respectively. The abundance of cultivable bacteria ranged from 0–295 CFU mL −1 to 0–1720 CFU mL −1 in two incubations with a total of 1385 isolates obtained. Comparing to direct cultivation, enrichment cultivation recovered more bacteria. Pigment-producing bacteria accounted for an average of 84.9% of total isolates. Such high percentage suggested that pigment production may be an adaptive physiological feature for the bacteria in ice core to cope with strong ultraviolet radiation on the glacier. The abundances of cultivable bacteria and pigment-producing isolates varied synchronously along depth: higher abundance in the middle and lower at the top and bottom. It indicated that the middle part of the ice core was hospitable for the microbial survival. Based on the physiological properties of the colonies, eighty-nine isolates were selected for phylogenetic analysis. Obtained 16S rRNA gene sequences fell into four groups: Firmicutes , Alpha-Proteobacteria , Gamma-Proteobacteria , and  Actinobacteria , with the Firmicutes being dominant. Microbial compositions derived from direct and enrichment cultivations were not overlapped. We suggest that it is a better way to explore the culturable microbial diversity in ice core by combining the approaches of both direct and enrichment cultivation. Graphical Abstract Highlights ► Culturable bacteria in the core belong to 12 genera and four groups. ► The abundance of cultivable bacteria and pigment-producing isolates vary synchronously with depth along the ice core. ► Our data suggest that the middle part was hospitable for the microbial survival.

Description: Publication year: 2012 Source: Geoscience Frontiers Xiang Gao, Pingkang Wang, Dairong Li, Qiang Peng, Chengshan Wang, Hongwen Ma The well SK-I in the Songliao Basin is the first scientific borehole targeting the continental Cretaceous strata in China. Oval concretions, thin laminae and beds of dolostone are found intercalated within mudstone and organic-rich black shale in the Nenjiang Formation of Campanian age. Low ordered ferruginous dolomite is composed of euhedral–subhedral rhombs with cloudy nucleus and light rims formed during the diagenesis, which are typical features of replacement. The heavy carbon isotopes ( δ 13 C PDB – 1.16–16.0) are results of both the fermentation of organic matter by microbes and degassing of carbon dioxide during the period of diagenesis, and the presence of light oxygen isotopes ( δ 18 O PDB – 18.53∼−5.1) is a characteristic feature of fresh water influence which means the carbonate may have been altered by ground water or rainwater in the late diagenesis. Marine water incursions into the normally lacustrine basin have been proved by both the salinity of Z value and the occurrence of foraminifera in the same strata where dolomite occurs. Pyrite framboids observed by SEM are usually enclosed in the dolomite crystals or in the mudstones, supporting the sulfate reducing bacteria (SRB). The formation of both dolomite and pyrite are associated with marine water incursions, which not only supply magnesium ion for dolomite, but also result in limited carbonate precipitation in the basin. The presence of pyrite framboids indicates the development of an anoxic environment associated with salinity stratification in the lake. The dolomite in the Nenjiang Formation is the results of marine water incursions, diagenetic replacement of calcareous carbonate and sulfate reducing bacteria (SRB). Graphical Abstract Highlights ► Dolomite shows rhombs, with replacement structure of cloudy nucleus and light rims. ► δ 13 C PDB values suggest fermentation of organic matter by microbes. ► Salinity of Z value and occurrence of foraminifera proved marine water incursions. Pyrite framboids in the dolomite crystals suggest sulfate reducing bacteria (SRB).

Description: Publication year: 2011 Source: Geoscience Frontiers Gongwen Wang, Lei Huang Three-dimensional geological modeling (3DGM) assists geologists to quantitatively study in three-dimensional (3D) space structures that define temporal and spatial relationships between geological objects. The 3D property model can also be used to infer or deduce causes of geological objects. 3DGM technology provides technical support for extraction of diverse geoscience information, 3D modeling, and quantitative calculation of mineral resources. Based on metallogenic concepts and an ore deposit model, 3DGM technology is applied to analyze geological characteristics of the Tongshan Cu deposit in order to define a metallogenic model and develop a virtual borehole technology; a BP neural network and a 3D interpolation technique were combined to integrate multiple geoscience information in a 3D environment. The results indicate: (1) on basis of the concept of magmatic-hydrothermal Cu polymetallic mineralization and a porphyry Cu deposit model, a spatial relational database of multiple geoscience information for mineralization in the study area (geology, geophysics, geochemistry, borehole, and cross-section data) was established, and 3D metallogenic geological objects including mineralization stratum, granodiorite, alteration rock, and magnetic anomaly were constructed; (2) on basis of the 3D ore deposit model, 23,800 effective surveys from 94 boreholes and 21 sections were applied to establish 3D orebody models with a kriging interpolation method; (3) combined 23,800 surveys involving 21 sections, using VC++ and OpenGL platform, virtual borehole and virtual section with BP network, and an improved inverse distance interpolation (IDW) method were used to predict and delineate mineralization potential targets (Cu-grade of cell not less than 0.1%); (4) comparison of 3D ore bodies, metallogenic geological objects of mineralization, and potential targets of mineralization models in the study area, delineated the 3D spatial and temporal relationship and causal processes among the ore bodies, alteration rock, metallogenic stratum, intrusive rock, and the Tongshan Fault. This study provides important technical support and a scientific basis for assessment of the Tongshan Cu deposit and surrounding exploration and mineral resources. Graphical Abstract Highlights ► 3D model of Tongshan deposit delineates 5 geological units. ► Application of 3D modeling to calculate ore resources. ► Reconstruction of orebody which is affected by Tongshan fault.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 2 N.S. Magesh, N. Chandrasekar, John Prince Soundranayagam Integration of remote sensing data and the geographical information system (GIS) for the exploration of groundwater resources has become a breakthrough in the field of groundwater research, which assists in assessing, monitoring, and conserving groundwater resources. In the present paper, various groundwater potential zones for the assessment of groundwater availability in Theni district have been delineated using remote sensing and GIS techniques. Survey of India toposheets and IRS-1C satellite imageries are used to prepare various thematic layers viz. lithology, slope, land-use, lineament, drainage, soil, and rainfall were transformed to raster data using feature to raster converter tool in ArcGIS. The raster maps of these factors are allocated a fixed score and weight computed from multi influencing factor (MIF) technique. Moreover, each weighted thematic layer is statistically computed to get the groundwater potential zones. The groundwater potential zones thus obtained were divided into four categories, viz., very poor, poor, good, and very good zones. The result depicts the groundwater potential zones in the study area and found to be helpful in better planning and management of groundwater resources.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 2 Andong Wang, Yican Liu The crustal growth of the North China Craton (NCC) during the Neoarchean time (2.5–2.8 Ga) is a hotly controversial topic, with some proposing that the main crustal growth occurred in the late Neoarchean (2.5–2.6 Ga), in agreement with the time of the magmatism, whereas others suggest that the main crustal accretion took place during early Neoarchean time (2.7–2.8 Ga), consistent with the time of crustal-formation of other cratons in the world. Zircon U-Pb ages and Hf isotope compositions can provide rigorous constraints on the time of crustal growth and the evolution and tectonic division of the NCC. In this contribution, we make a comprehensive review of zircon Hf isotope data in combination with zircon U-Pb geochronology and some geochemistry data from various divisions of the NCC with an aim to constrain the Neoarchean crustal growth of the NCC. The results suggest that both 2.7–2.8 Ga and 2.5–2.6 Ga crustal growth are distributed over the NCC and the former is much wider than previously suggested. The Eastern block is characterized by the main 2.7–2.8 Ga crustal growth with local new crustal-formation at 2.5–2.6 Ga, and the Yinshan block is characterized by ∼2.7 Ga crustal accretion as revealed by Hf-isotope data of detrital zircons from the Zhaertai Group. Detrital zircon data of the Khondalite Belt indicate that the main crustal growth period of the Western block is Paleoproterozoic involving some ∼2.6 Ga and minor Early- to Middle-Archean crustal components, and the crustal accretion in the Trans-North China Orogen (TNCO) has a wide age range from 2.5 Ga to 2.9 Ga with a notable regional discrepancy. Zircon Hf isotope compositions, coupled with zircon ages and other geochemical data suggest that the southern margin may not be an extension of the TNCO, and the evolution and tectonic division of the NCC is more complex than previously proposed, probably involving multi-stage crustal growth and subduction processes. However, there is no doubt that 2.7–2.8 Ga magmatism and crustal-formation are more widely distributed than previously considered, which is further supported by the data of zircons from Precambrian lower crustal rocks, overlying sedimentary cover, modern river sediments and Late Neoarchean syenogranites.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 2 F.J. Luque, E. Crespo-Feo, J.F. Barrenechea, L. Ortega Stable carbon isotope geochemistry provides important information for the recognition of fundamental isotope exchange processes related to the movement of carbon in the lithosphere and permits the elaboration of models for the global carbon cycle. Carbon isotope ratios in fluid-deposited graphite are powerful tools for unravelling the ultimate origin of carbon (organic matter, mantle, or carbonates) and help to constrain the fluid history and the mechanisms involved in graphite deposition. Graphite precipitation in fluid-deposited occurrences results from CO 2 - and/or CH 4 -bearing aqueous fluids. Fluid flow can be considered as both a closed (without replenishment of the fluid) or an open system (with renewal of the fluid by successive fluid batches). In closed systems, carbon isotope systematics in graphite is mainly governed by Rayleigh precipitation and/or by changes in temperature affecting the fractionation factor between fluid and graphite. Such processes result in zoned graphite crystals or in successive graphite generations showing, in both cases, isotopic variation towards progressive 13 C or 12 C enrichment (depending upon the dominant carbon phase in the fluid, CO 2 or CH 4 , respectively). In open systems, in which carbon is episodically introduced along the fracture systems, the carbon systematics is more complex and individual graphite crystals may display oscillatory zoning because of Rayleigh precipitation or heterogeneous variations of δ 13 C values when mixing of fluids or changes in the composition of the fluids are the mechanisms responsible for graphite precipitation.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 2

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 2 Xuanxue Mo, M. Santosh, Xiaoqiao Wan

Description: Publication year: 2012 Source: Geoscience Frontiers Mingxiang Mei, Jinhan Gao Most Phanerozoic oolites are marked by ooids with a diameter less than 2 mm. Observations on a Neoproterozoic oolite has resulted in a change of concept. The term ‘pisolite’ that traditionally referred to oolites with a grain size of more than 2 mm, is now restricted to those coated carbonate grains formed by meteoritic freshwater diagenesis; oolites with a grain size of more than 2 mm are now defined as ‘giant’. Particular unusual giant oolites within a set of oolitic-bank limestones with thicknesses of more than 40 m in the top part of the Lower Triassic (Induan) Daye (Ruiping) Formation at the Lichuan section in the western part of Hubei Province in South China, represent an important sedimentological phenomenon both in the specific geological period and in the geological setting that is related to the end-Permian biological mass extinction. Like the giant oolites of the Neoproterozoic that represent deposits where oolites formed in a vast low-angle carbonate ramp at that special geological period, the Triassic Daye Formation at the study section are significant because they provide a comparative example to help understand the evolving carbonate world reflected by oolites, the origin of which is still uncertain, and they give insight into the sedimentation pattern of the desolate sea floor, which resulted from the mass extinction at the turn of the Permian into the Triassic. Graphical Abstract Highlights ► We report and characterize the giant oolites from Induan. ► The oolites constitute a new type of anachronistic facies. ► We propose the possibility of a microbial origin for the oolites.

Description: Publication year: 2012 Source: Geoscience Frontiers Xuan Tang, Jinchuan Zhang, Ransheng Shan, Jinyu Xiong Upper Paleozoic coal measures in the Ordos Basin consist of dark mudstone and coal beds and are important source rocks for gas generation. Gas accumulations include coal-bed methane (CBM), tight gas and conventional gas in different structural areas. CBM accumulations are mainly distributed in the marginal area of the Ordos Basin, and are estimated at 3.5×10 12 m 3 . Tight gas accumulations exist in the middle part of the Yishan Slope area, previously regarded as the basin-centered gas system and now considered as stratigraphic lithologic gas reservoirs. This paper reviews the characteristics of tight gas accumulations: poor physical properties (porosity 〈 8%, permeability 〈 0.85×10 −3 μm 2 ), abnormal pressure and the absence of well-defined gas water contacts. CBM is a self-generation and self-reservoir, while gas derived from coal measures migrates only for a short distance to accumulate in a tight reservoir and is termed near-generation and near-reservoir. Both CBM and tight gas systems require source rocks with a strong gas generation ability that extends together over wide area. However, the producing area of the two systems may be significantly different. Graphical Abstract

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 2 Yadong Wang, Jianjing Zheng, Weilin Zhang, Shiyuan Li, Xingwang Liu, Xin Yang, Yuhu Liu Geologists agree that the collision of the Indian and Asian plates caused uplift of the Tibet Plateau. However, controversy still exists regarding the modes and mechanisms of the Tibetan Plateau uplift. Geology has recorded this uplift well in the Qaidam Basin. This paper analyzes the tectonic and sedimentary evolution of the western Qaidam Basin using sub-surface seismic and drill data. The Cenozoic intensity and history of deformation in the Qaidam Basin have been reconstructed based on the tectonic developments, faults growth index, sedimentary facies variations, and the migration of the depositional depressions. The changes in the sedimentary facies show that lakes in the western Qaidam Basin had gone from inflow to still water deposition to withdrawal. Tectonic movements controlled deposition in various depressions, and the depressions gradually shifted southeastward. In addition, the morphology of the surface structures in the western Qaidam Basin shows that the Cenozoic tectonic movements controlled the evolution of the Basin and divided it into (a) the southern fault terrace zone, (b) a central Yingxiongling orogenic belt, and (c) the northern fold-thrust belt; divided by the XI fault (Youshi fault) and Youbei fault, respectively. The field data indicate that the western Qaidam Basin formed in a Cenozoic compressive tectonic environment caused by the India–Asia plate collision. Further, the Basin experienced two phases of intensive tectonic deformation. The first phase occurred during the Middle Eocene–Early Miocene (Xia Ganchaigou Fm. and Shang Ganchaigou Fm., 43.8–22 Ma), and peaked in the Early Oligocene (Upper Xia Ganchaigou Fm., 31.5 Ma). The second phase occurred between the Middle Miocene and the Present (Shang Youshashan Fm. and Qigequan Fm., 14.9–0 Ma), and was stronger than the first phase. The tectonic–sedimentary evolution and the orientation of surface structures in the western Qaidam Basin resulted from the Tibetan Plateau uplift, and recorded the periodic northward growth of the Plateau. Recognizing this early tectonic–sedimentary evolution supports the previous conclusion that northern Tibet responded to the collision between India and Asia shortly after its initiation. However, the current results reveal that northern Tibet also experienced another phase of uplift during the late Neogene. The effects of these two stages of tectonic activity combined to produce the current Tibetan Plateau.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 2 V. Prasannakumar, H. Vijith, S. Abinod, N. Geetha A comprehensive methodology that integrates Revised Universal Soil Loss Equation (RUSLE) model and Geographic Information System (GIS) techniques was adopted to determine the soil erosion vulnerability of a forested mountainous sub-watershed in Kerala, India. The spatial pattern of annual soil erosion rate was obtained by integrating geo-environmental variables in a raster based GIS method. GIS data layers including, rainfall erosivity ( R ), soil erodability ( K ), slope length and steepness ( LS ), cover management ( C ) and conservation practice ( P ) factors were computed to determine their effects on average annual soil loss in the area. The resultant map of annual soil erosion shows a maximum soil loss of 17.73 t h -1 y -1 with a close relation to grass land areas, degraded forests and deciduous forests on the steep side-slopes (with high LS ). The spatial erosion maps generated with RUSLE method and GIS can serve as effective inputs in deriving strategies for land planning and management in the environmentally sensitive mountainous areas.

Description: Publication year: 2012 Source: Geoscience Frontiers Yuwang Wang, Jingbin Wang, Lijuan Wang, Lingli Long, Pingzhi Tang, Zhen Liao, Huiqiong Zhang, Yu Shi The extension of the suture zone between the Siberian and Kazakhstan continents in China has been a matter of debate because few outcrops of ophiolitic mélange have been found so far. The recently found Tuerkubantao ophiolitic mélange, which is located east of the Kekesentao Mt. in the Buerjin County of the Chinese Altay, provides an important clue for this problem. This paper presents the results of field investigation, petrology, U-Pb isotope dating of zircons and bulk-rock geochemistry of the Tuerkubantao mélange rocks. The mélange consists of fault-contacted ultramafic rocks, gabbro, diabase, basalt, flysch and granitoids. The ultramafic-mafic rocks are Mg-rich ( # Mg = 4.25=6.35) and SiO 2 spans 38.8 to 46.8 wt.%. Basalt and gabbro are geochemically similar and are characterized by low FeO t (10.9 wt.%), total alkali (Na 2 O+K 2 O=2.58 wt.%) and TiO 2 (1.17 wt.%) and affinity to the Mg-rich tholeiite series. The flat REE and trace element patterns of the ultramafic-mafic rocks are indicative of their ophiolite origin, i.e. formation in a mid-oceanic ridge setting. The fragments of low-K gneissic granite formed in supra-subduction or syn-collisional setting. Zircons from gabbro and gneissic granite yielded U-Pb ages of 363 and 355 Ma, respectively, suggesting Late Devonian mid-oceanic spreading and oceanic subduction accompanied by suprasubduction magmatism. The Tuertubantao ophiolite together with the Qiaoxiahala and Buergen ophiolites of the Kekesentao belt define an ophiolitic mélange belt extending along the Erqis fault. This belt probably belongs to the Ural-Zaisan-South Mongolian suture-shear zone formed during the subduction of the Paleo-Asian Ocean and subsequent collision of the Siberian and Kazakhstan continents. Graphical Abstract Highlights ► The Tuerkubantao ophiolitic mélange hosts MORB-type basalts and low-K gneissic granite. ► U-Pb zircon ages constrain Late Devonian oceanic ridge magmatism and subduction ► The Kekesentao ophiolite belongs to the Siberia-Kazakhstan collisional zone.

Description: Publication year: 2012 Source: Geoscience Frontiers Huatian Zhang, Jianghai Li, Shoujie Liu, Wenshan Li, M. Santosh, Honghao Wang The Khondalite Belt within the Inner Mongolia Suture Zone (IMSZ) in the North China Craton is a classic example for Paleoproterozoic ultrahigh-temperature (UHT) metamorphism. Here we report new spinel-bearing metapelitic granulites from a new locality at Xumayao within the southern domain of the IMSZ. Petrological studies and thermodynamic modeling of the spinel + quartz-bearing assemblage shows that these rocks experienced extreme metamorphism at UHT conditions. Spinel occurs in two textural settings: 1) high X Zn (Zn/(Mg + Fe II  + Zn) = 0.071–0.232) spinel with perthitic K-feldspar, sillimanite and quartz in the rock matrix; and 2) low X Zn (0.045–0.070) spinel as inclusions within garnet porphyroblasts in association with quartz and sillimanite. Our phase equilibria modeling indicates two main stages during the metamorphic evolution of these rocks: 1) near-isobaric cooling from 975 °C to 875 °C around 8 kbar, represented by the formation of garnet porphyroblasts from spinel and quartz; and 2) cooling and decompression from 850 °C, 8 kbar to below 750 °C, 6.5 kbar, represented by the break-down of garnet. The spinel + quartz assemblage is considered to have been stable at peak metamorphism, formed through the break-down of cordierite, indicating a near isothermal compression process. Our study confirms the regional extent of UHT metamorphism within the IMSZ associated with the Paleoproterozoic subduction-collision process. Graphical Abstract Highlights ► Ultrahigh-temperature (UHT) granulites reported from a new locality in the North China Craton. ► Peak p-T condition of T  〉 950 °C and p  〉 7.5 kbar defined by the stability of spinel + quartz. ► Regional UHT metamorphism and anti-clockwise p-T path.

Description: Publication year: 2012 Source: Geoscience Frontiers Dilip Saha, Vikash Tripathy A first report on tuff beds from the Owk Shale in the Proterozoic Kurnool sub-basin in southern India is presented. The rhyolitic to rhodacitic tuffs, overlying shelfal limestones formed at depths below storm wave base, have rheomorphic features indicative of viscoplastic flow, and geochemical signatures of rhyolitic to rhyodacitic unwelded to welded tuffs, similar to those described from other Proterozoic intracratonic basins like Vindhyan and Chhattisgarh basins in India. Fragmentary nature of altered glass with perlitic cracks and local admixture with intrabasinal sediments suggest phreatomagmatic reactions. The widespread and repeated occurrences of felsic tuffs in these basins, possibly derived from low degree melting of continental crust, suggest intermittent tectonothermal instability which likely influenced basinal topography and cyclic development of the carbonate platforms. Graphical Abstract Highlights ► First report of rhyodacitic tuff beds and their geochemistry from the Proterozoic Owk Shale, southern India. ► Geochemical discrimination indicates affinity with Volcanic Arc Granites, in spite of supposed intracratonic basinal setting. ► Contribution of submarine ash flow interpreted from texture and marine sediment association.

Description: Publication year: 2012 Source: Geoscience Frontiers C. Manikyamba, Robert Kerrich Greenstone belts of the eastern Dharwar Craton, India are reinterpreted as composite tectonostratigraphic terranes of accreted plume-derived and convergent margin-derived magmatic sequences based on new high-precision elemental data. The former are dominated by a komatiite plus Mg-tholeiitic basalt volcanic association, with deep water siliciclastic and BIF sedimentary rocks. Plumes melted at 〈90 km under thin rifted continental lithosphere to preserve intraoceanic and continental margin aspects. Associated alkaline basalts record subduction-recycling of Mesoarchean oceanic crust, incubated in the asthenosphere, and erupted coevally with Mg basalts from a heterogeneous mantle plume. Together, komatiites-Mg basalts-alkaline basalts plot along the Phanerozoic mantle array in Th/Yb versus Nb/Yb coordinate space, representing zoned plumes, establishing that these reservoirs were present in the Neoarchean mantle. Convergent margin magmatic associations are dominated by tholeiitic to calc-alkaline basalts compositionally similar to recent intraoceanic arcs. As well, boninitic flows sourced in extremely depleted mantle are present, and the association of arc basalts with Mg-andesites-Nb enriched basalts-adakites documented from Cenozoic arcs characterized by subduction of young (〈20 Ma), hot, oceanic lithosphere. Consequently, Cenozoic style “hot” subduction was operating in the Neoarchean. These diverse volcanic associations were assembled to give composite terranes in a subduction-accretion orogen at ∼2.7 Ga, coevally with a global accretionary orogen at ∼2.7 Ga, and associated orogenic gold mineralization. Archean lithospheric mantle, distinctive in being thick, refractory, and buoyant, formed complementary to the accreted plume and convergent margin terranes, as migrating arcs captured thick plume-plateaus, and the refractory, low density, residue of plume melting coupled with accreted imbricated plume-arc crust. Graphical Abstract Highlights ► Greenstone belts of the eastern Dharwar Craton, India, are composite tectonostratigraphic terranes. ► They have diverse volcanic plume- and arc-associations ∼2.7 Ga. ► They were assembled in a subduction-accretion orogen as migrating arcs captured thick plume-plateaus.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 1 Wenyong Li, Wenfen Lu, Yanxu Liu, Jianchun Xu The North Yellow Sea Basin is a Mesozoic and Cenozoic basin. Based on basin-margin facies, sedimentary thinning, size and shape of the basin and vitrinite reflectance, North Yellow Sea Basin is not a residual basin. Analysis of the development of the basin’s three structural layers, self-contained petroleum systems, boundary fault activity, migration of the Mesozoic–Cenozoic sedimentation centers, different basin structures formed during different periods, and superposition of a two-stage extended basin and one-stage depression basin, the North Yellow Sea Basin is recognized as a superimposed basin.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 1 C.V. Dharma Rao, M. Santosh, Reia M. Chmielowski We report equilibrium sapphirine + quartz assemblage in biotite–orthopyroxene–garnet granulites from a new locality in Panasapattu of Paderu region in the Eastern Ghats granulite belt, which provide new evidence for ultrahigh-temperature (UHT) metamorphism at 1030–1050 °C and 10 kbar in this region. The development of migmatitic texture, stabilization of the garnet–orthopyroxene–plagioclase–K-feldspar association, prograde biotite inclusions within garnet and sapphirine as well as sapphirine and cordierite inclusions within garnet in these granulites indicate that the observed peak assemblages probably formed during prograde dehydration melting of a Bt–Sill–Qtz assemblage, and constrain the prograde stage of the p – T path. The core domains of orthopyroxene porphyroblasts have up to w (Al 2 O 3 ) 9.6%, which suggest that the temperatures reached up to 1150 °C suggesting extreme crustal metamorphism. These conditions were also confirmed by the garnet–orthopyroxene thermobarometery, which yields a p – T range of 1012–960 °C and 9.4 kbar. The p – T phase topologies computed using isochemical sections calculated in the model system Na 2 O–CaO–K 2 O–FeO–MgO–Al 2 O 3 –SiO 2 –H 2 O (NCKFMASH) for metapelites, garnet-free sapphirine granulites and garnet-bearing sapphirine granulites match the melt-bearing assemblages observed in these rocks. Isochemical sections constructed in the NCKFMASH system for an average sub-aluminous metapelite bulk composition, and contoured for modal proportions of melt and garnet, as well as for the compositional isopleths of garnet, predict phase and reaction relations that are consistent with those observed in the rocks. Garnet and orthopyroxene contain Ti-rich phlogopite inclusions, suggesting formation by prograde melting reactions at the expense of phlogopite during ultrahigh-temperature conditions. These p – T results underestimate ‘peak’ conditions, in part as a result of the modification of garnet compositions in the domains where some melt was retained. The post-peak evolution is constrained by a succession of melt-present reactions that occur at p  〈 10 kbar, inferred from micro-structural relations among various minerals. After high-temperature decompression from the metamorphic peak, the p – T path followed a near isobaric cooling stage to T  〈 900 °C. The UHT rocks investigated in this study occur within a continental collision suture which witnessed prolonged subduction–accretion history prior to the final collision. We correlate the extreme metamorphism and the stabilization of UHT mineral assemblages to heat and volatile input from an upwelled asthenosphere during subduction–collision tectonics in a Proterozoic convergent plate margin.

Description: Publication year: 2012 Source: Geoscience Frontiers Abhijit Mazumder, Rajiv Nigam, Pravin J. Henriques A total of 103 surface sediment samples collected from the water depth range of 15–3300 m along Vijaydurg-Karwar stretch of central west coast of India were analyzed for foraminiferal content. Relict benthic foraminiferal assemblage was noted within 50–135 m water depth. The relict benthic foraminiferal assemblage that includes Amphistegina , Operculina and Alveolinella in sediment samples within the water depth of 85–135 m indicates presence of coral reef at this depth during Early Holocene. The presence of barnacle fouling on Relict foraminifera at 60–90 m confirms the paleo-shoreline. The shallow depth zone is characterized by presence of agglutinated relict foraminifera. The agglutinated forms indicate freshwater influx, which eventually increased the sea level and subsequently deteriorated the paleo-coral reef. Graphical Abstract Highlights ► Relict benthic foraminifera from 85 to 135 m water depth along West Coast of India. ► Foraminifera indicates presence of Early Holocene coral reef. ► Freshwater influx deteriorated the paleo-coral reef.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 1 Wenlong Ding, Chao Li, Chunyan Li, Changchun Xu, Kai Jiu, Weite Zeng, Liming Wu Shale with high quartz, feldspar and carbonate, will have low Poisson’s ratio, high Young’s modulus and high brittleness. As a result, the shale is conducive to produce natural and induced fractures under external forces. In general, there is a good correlation between fracture development in shale and the volume of brittle minerals present. Shale with high TOC or abnormally high pressure has well-developed fractures. Shale fracture development also shows a positive correlation with total gas accumulation and free gas volume, i.e., the better shale fractures are developed, the greater the gas accumulation and therefore the higher the gas production. Fractures provide migration conduits and accumulation spaces for natural gas and formation water, which are favorable for the volumetric increase of free natural gas. Wider fractures in shale result in gas loss. In North America, there is a high success ratio of shale gas exploration and high gas production from high-angle fracture zones in shale. Good natural gas shows or low yield producers in the Lower Paleozoic marine organic matter-rich rocks in the Sichuan Basin are closely related to the degree of fracture development in brittle shales.

Description: Publication year: 2011 Source: Geoscience Frontiers Amir Hossein Alavi, Amir Hossein Gandomi This study presents promising variants of genetic programming (GP), namely linear genetic programming (LGP) and multi expression programming (MEP) to evaluate the liquefaction resistance of sandy soils. Generalized LGP and MEP-based relationships were developed between the strain energy density required to trigger liquefaction (capacity energy) and the factors affecting the liquefaction characteristics of sands. The correlations were established based on well established and widely dispersed experimental results obtained from the literature. To verify the applicability of the derived models, they were employed to estimate the capacity energy values of parts of the test results that were not included in the analysis. The external validation of the models was verified using statistical criteria recommended by researchers. Sensitivity and parametric analyses were performed for further verification of the correlations. The results indicate that the proposed correlations are effectively capable of capturing the liquefaction resistance of a number of sandy soils. The developed correlations provide a significantly better prediction performance than the models found in the literature. Furthermore, the best LGP and MEP models perform superior than the optimal traditional GP model. The verification phases confirm the efficiency of the derived correlations for their general application to the assessment of the strain energy at the onset of liquefaction. Graphical Abstract Highlights ► The LGP and MEP methodologies were used to evaluate the liquefaction resistance of sandy soils. ► The capacity energy was formulated in terms of several factors affecting the liquefaction potential. ► The external validation of the models was successfully verified using different statistical criteria. ► The best LGP and MEP models perform superior than several models found in the literature.

Description: Publication year: 2012 Source: Geoscience Frontiers, Available online 22 February 2012 Robert W. Scott, Xiaoqiao Wan, Chengshan Wang, Qinghua Huang Non-marine ostracodes, charophytes and palynomorphs are abundant in most Cretaceous lacustrine basins of East Asia. However, their ranges are not directly integrated with marine biota that defines the Cretaceous stages. Non-biotic events such as magnetochrons and radiometric ages in these terrestrial deposits enable their correlation with marine strata. The SK1 north and south composited cores in the Songliao Basin present a continuous section of Upper Cretaceous non-marine fossil and magnetochron successions in superposed order. These chronostratigraphic events are integrated with marine events by an X/Y graphic plot between the core data and a global database of GSSP and key reference sections. This plot projects stage boundaries in marine sections into the SK1 section and interpolates numerical ages to the first and last occurrences of biota and to lithostratigraphic boundaries. This stratigraphic experiment tests and refines age calibrations based on both manual interpolation of depths to numerical ages and cyclostratigraphy. Ages derived by interpolation are similar and ages by cyclostratigraphy are older because stage boundaries are calibrated to a different age scale. Highlights ► Non-biotic Late Cretaceous events in terrestrial deposits of the Songliao Basin correlate with marine strata. ► Non-marine events are integrated with marine events by an X/Y graphic plot between core data and global database. ► The plot interpolates numerical ages to fossil ranges and to lithostratigraphic boundaries.

Description: Publication year: 2012 Source: Geoscience Frontiers, Available online 22 February 2012 Yan Tang, Longkang Sang, Yanming Yuan, Yunpeng Zhang, Yunlong Yang Major, trace and rare earth element (REE) concentrations of Late Triassic sediments (fine-grained sandstones and mudstones) from Hongcan Well 1 in the NE part of the Songpan-Ganzi Basin, western China, are used to reveal weathering, provenance and tectonic setting of inferred source areas. The Chemical Index of Alteration (CIA) reflects a low to moderate degree of chemical weathering in a cool and somewhat dry climate, and an A-CN-K plot suggests an older upper continental crust provenance dominated by felsic to intermediate igneous rocks of average tonalite composition. Based on the various geochemical tectonic setting discrimination diagrams, the Late Triassic sediments are inferred to have been deposited in a back-arc basin situated between an active continental margin (the Kunlun-Qinling Fold Belt) and a continental island arc (the Yidun Island Arc). The petrography of the Triassic sediments reflects a proximal slope-basin environment with rapid erosion and burial, and the published flow directions of Triassic turbidites in the Aba-Zoige region is not supported Yidun Volcanic Arc source. Therefore, we suggest that the Kunlun-Qinling terrane is most likely to have supplied source materials to the northeast part of the Songpan-Ganzi Basin during the Late Triassic.

Description: Publication year: 2012 Source: Geoscience Frontiers, Available online 22 February 2012 Y. Srinivas, A. Stanley Raj, D.Hudson Oliver, D. Muthuraj, N. Chandrasekar The applications of intelligent techniques have increased exponentially in recent days to study most of the non-linear parameters. In particular, the behavior of earth resembles the non-linearity applications. An efficient tool is needed for the interpretation of geophysical parameters to study the subsurface of the earth. Artificial Neural Networks (ANN) perform certain tasks if the structure of the network is modified accordingly for the purpose it has been used. The three most robust networks were taken and comparatively analyzed for their performance to choose the appropriate network. The single-layer feed-forward neural network with the back propagation algorithm is chosen as one of the well-suited networks after comparing the results. Initially, certain synthetic data sets of all three-layer curves have been taken for training the network, and the network is validated by the field datasets collected from Tuticorin Coastal Region (78°7'30"E and 8°48'45"N), Tamil Nadu, India. The interpretation has been done successfully using the corresponding learning algorithm in the present study. With proper training of back propagation networks, it tends to give the resistivity and thickness of the subsurface layer model of the field resistivity data concerning the synthetic data trained earlier in the appropriate network. The network is trained with more Vertical Electrical Sounding (VES) data, and this trained network is demonstrated by the field data. Groundwater table depth also has been modeled. Highlights ► Vertical Electrical Sounding data in the Tuticorin region has been modeled for ground water occurrence and saline water intrusion. ► Artificial Neural Network program using Feed forward back propagation algorithm gains more advantage over conventional methods. ► Error percentage on comparing with the conventional method makes the program to extend on different type of field data. ► Synthetic Memory driven model forms the frame work of the algorithm to support any kind of rough field data. ► Saline water intrusion and ground water occurrence can be very well studied with well defined sub surface structural modeling.

Description: Publication year: 2012 Source: Geoscience Frontiers, Available online 25 February 2012 Mingxiang Mei, Jinhan Gao Most Phanerozoic oolites are marked by ooids with a diameter less than 2 mm. Observations on a Neoproterozoic oolite has resulted in a change of concept. The term ‘pisolite’ that traditionally referred to oolites with a grain size of more than 2 mm, is now restricted to those coated carbonate grains formed by meteoritic freshwater diagenesis; oolites with a grain size of more than 2 mm are now defined as ‘giant’. Particular unusual giant oolites within a set of oolitic-bank limestones with thicknesses of more than 40 m in the top part of the Lower Triassic (Induan) Daye (Ruiping) Formation at the Lichuan section in the western part of Hubei Province in South China, represent an important sedimentological phenomenon both in the specific geological period and in the geological setting that is related to the end-Permian biological mass extinction. Like the giant oolites of the Neoproterozoic that represent deposits where oolites formed in a vast low-angle carbonate ramp at that special geological period, the Triassic Daye Formation at the study section are significant because they provide a comparative example to help understand the evolving carbonate world reflected by oolites, the origin of which is still uncertain, and they give insight into the sedimentation pattern of the desolate sea floor, which resulted from the mass extinction at the turn of the Permian into the Triassic. Highlights ► We report and characterize the giant oolites from Induan. ► The oolites constitute a new type of anachronistic facies. ► We propose the possibility of a microbial origin for the oolites.

Description: Publication year: 2012 Source: Geoscience Frontiers, Available online 25 February 2012 Gao Zhiqian, Fan Tailiang The fact that several half-grabens and normal faults developed in the Lower–Middle Cambrian of Tazhong (central Tarim Basin) and Bachu areas in Tarim Basin, northwest China, indicates that Tarim Basin was under extensional tectonic setting at this time. The half-grabens occur within a linear zone and the normal faults are arranged in en echelon patterns with gradually increasing displacement eastward. Extensional tectonics resulted in the formation of a passive continental margin in the southwest and a cratonic margin depression in the east, and most importantly, influenced the development of a three-pronged rift in the northeast margin of the Tarim Basin. The fault system controlled the development of platform – slope – bathyal facies sedimentation of mainly limestone -dolomite-gypsum rock-saline rock -red beds in the half-grabens. The NW-SE trending half-grabens reflect the distribution of buried basement faults. Highlights ► Half-grabens and normal faults developed in the Lower-Middle Cambrian in Tarim Basin. ► Extensional tectonics resulted in the formation of a passive continental margin. ► Normal fault system controls distribution of “platform–slope–basin facies”

Description: Publication year: 2012 Source: Geoscience Frontiers, Available online 25 February 2012 Song Li, Dazhen Tang, Hao Xu, Zi Yang The Panguan Syncline contains abundant coal resources, which may be a potential source of coalbed methane. In order to evaluate the coalbed methane production potential in this area, we investigated the pore-fracture system of coalbed methane reservoirs, and analyzed the gas sorption and seepage capacities by using various analytical methods, including scanning electron microscopy (SEM), optical microscopy, mercury-injection test, low-temperature N2isotherm adsorption/desorption analyses, low-field nuclear magnetic resonance and methane isothermal adsorption measurements. The results show that the samples of the coal reservoirs in the Panguan Syncline have moderate gas sorption capacity. However, the coals in the study area have favorable seepage capacities, and are conductive for the coalbed methane production. The physical properties of the coalbed methane reservoirs in the Panguan Syncline are generally controlled by coal metamorphism: the low rank coal usually has low methane sorption capacity and its pore and microfractures are poorly developed; while the medium rank coal has better methane sorption capacity, and its seepage pores and microfractures are well developed, which are sufficient for the coalbed methane's gathering and exploration. Therefore, the medium rank coals in the Panguan Syncline are the most prospective targets for the coalbed methane exploration and production. Research Highlights ► Panguan Syncline is a potential target for the CBM production in Southern China. ► The movable fluid porosity has been analyzed by nuclear magnetic resonance. ► Gas sorption and seepage capacities of the coal were clearly formulated.

Description: Publication year: 2012 Source: Geoscience Frontiers, Available online 3 March 2012 Xuan Tang, Jinchuan Zhang, Ransheng Shan, Jinyu Xiong Upper Paleozoic coal measures in the Ordos Basin consist of dark mudstone and coal beds and are important source rocks for gas generation. Gas accumulations include coal-bed methane (CBM), tight gas and conventional gas in different structural areas. CBM accumulations are mainly distributed in the marginal area of the Ordos Basin, and are estimated at 3.5×10m. Tight gas accumulations exist in the middle part of the Yishan Slope area, previously regarded as the basin-centered gas system and now considered as stratigraphic lithologic gas reservoirs. This paper reviews the characteristics of tight gas accumulations: poor physical properties (porosity 〈 8%, permeability 〈 0.85×10μm), abnormal pressure and the absence of well-defined gas water contacts. CBM is a self-generation and self-reservoir, while gas derived from coal measures migrates only for a short distance to accumulate in a tight reservoir and is termed near-generation and near-reservoir. Both CBM and tight gas systems require source rocks with a strong gas generation ability that extends together over wide area. However, the producing area of the two systems may be significantly different.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 2 Dezi Wang, Liangshu Shu During the Late Mesozoic Middle Jurassic–Late Cretaceous, basin and range tectonics and associated magmatism representative of an extensional tectonic setting was widespread in southeastern China as a result of Pacific Plate subduction. Basin tectonics consists of post-orogenic (Type I) and intra-continental extensional basins (Type II). Type I basins developed in the piedmont and intraland during the Late Triassic to Early Jurassic, in which coarse-grained terrestrial clastic sediments were deposited. Type II basins formed during intra-continental crustal thinning and were characterized by the development of grabens and half-grabens. Graben basins were mainly generated during the Middle Jurassic and were associated with bimodal volcanism. Sediments in half-grabens are intercalated with rhyolitic tuffs and lavas and are Early Cretaceous in age with a dominance of Late Cretaceous–Paleogene red beds. Ranges are composed of granitoids and bimodal volcanic rocks, A-type granites and dome-type metamorphic core complexes. The authors analyzed lithological, geochemical and geochronological features of the Late Mesozoic igneous rock assemblages and proposed some geodynamical constraints on forming the basin and range tectonics of South China. A comparison of the similarities and differences of basin and range tectonics between the eastern and western shores of the Pacific is made, and the geodynamical evolution model of the Southeast China Block during Late Mesozoic is discussed. Studied results suggest that the basin and range terrane within South China developed on a pre-Mesozoic folded belt was derived from a polyphase tectonic evolution mainly constrained by subduction of the western Pacific Plate since the Late Mesozoic, leading to formation of various magmatism in a back-arc extensional setting. Its geodynamic mechanism can compare with that of basin and range tectonics in the eastern shore of the Pacific. Differences of basin and range tectonics between both shores of the Pacific, such as mantle plume formation, scales of extensional and igneous rock assemblages and the age of basin and range tectonics, were caused mainly by the Yellowstone mantle plume in the eastern shore of the Pacific.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 2 Guiting Hou This study proposes three models to explain the mechanism of the three major types of mafic dyke swarms. Parallel dyke swarms form in response to a regional stress field, e.g. the mafic dyke swarms in the North China Craton, whereas small radiating dyke swarm forms due to stress constructions around a plutonic or volcanic edifice, such as the dyke swarm at Spanish Peak, USA. The third type of radiating dyke swarm is giant fan-shaped dyke swarm such as the Mackenzie dyke swarm. Fractures that formed prior to magmatism may play a vital role in dictating the dyke swarm geometry. In most of the cases, the pre-existing fractures are induced by tectonic stresses and not by magma injection though magma injection can increase the fracture size by propagation at the dyke tip.

Description: Publication year: 2012 Source: Geoscience Frontiers Yan Tang, Longkang Sang, Yanming Yuan, Yunpeng Zhang, Yunlong Yang Major, trace and rare earth element (REE) concentrations of Late Triassic sediments (fine-grained sandstones and mudstones) from Hongcan Well 1 in the NE part of the Songpan-Ganzi Basin, western China, are used to reveal weathering, provenance and tectonic setting of inferred source areas. The Chemical Index of Alteration (CIA) reflects a low to moderate degree of chemical weathering in a cool and somewhat dry climate, and an A-CN-K plot suggests an older upper continental crust provenance dominated by felsic to intermediate igneous rocks of average tonalite composition. Based on the various geochemical tectonic setting discrimination diagrams, the Late Triassic sediments are inferred to have been deposited in a back-arc basin situated between an active continental margin (the Kunlun-Qinling Fold Belt) and a continental island arc (the Yidun Island Arc). The petrography of the Triassic sediments reflects a proximal slope-basin environment with rapid erosion and burial, and the published flow directions of Triassic turbidites in the Aba-Zoige region is not supported Yidun Volcanic Arc source. Therefore, we suggest that the Kunlun-Qinling terrane is most likely to have supplied source materials to the northeast part of the Songpan-Ganzi Basin during the Late Triassic. Graphical Abstract