ALBERT

Description: Publication year: 2012 Source: Geoscience Frontiers 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 N 2 isotherm 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. Graphical Abstract 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, Volume 3, Issue 2 R. Damian Nance, Gabriel Gutiérrez-Alonso, J. Duncan Keppie, Ulf Linnemann, J. Brendan Murphy, Cecilio Quesada, Rob A. Strachan, Nigel H. Woodcock 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. Graphical Abstract 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: 2012 Source: Geoscience Frontiers Hongchen Jiang, Hailiang Dong

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 2 C. Casquet, C.W. Rapela, R.J. Pankhurst, E.G. Baldo, C. Galindo, C.M. Fanning, J.A. Dahlquist, J. Saavedra 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 Brian P. Hedlund, Jessica K. Cole, Amanda J. Williams, Weiguo Hou, Enmin Zhou, Wenjun Li, Hailiang Dong 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 from ≤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 phyla Firmicutes and Deinococcus-Thermus . Firmicutes include neutrophilic or alkaliphilic Anoxybacillus , Bacillus , Caldalkalibacillus , Caldanaerobacter , Laceyella , and Geobacillus , as well as thermoacidophilic Alicyclobacillus and Sulfobacillus . Isolates from the Deinococcus-Thermus phylum include several Meiothermus and Thermus species. Many of these bacteria synthesize thermostable polymer-degrading enzymes that may be useful for biotechnology. The thermoacidophilic archaea Acidianus , Metallosphaera , and Sulfolobus have also been isolated and studied. A few studies have reported the isolation of thermophilic viruses belonging to Siphoviridae (TTSP4 and TTSP10) and Fuselloviridae (STSV1) infecting Thermus spp. and Sulfolobus spp., 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. Graphical Abstract Highlights ► The Rehai Geothermal Field, Yunnan Province, China, hosts thermophilic Bacteria, Archaea, and viruses. ► Cultivated Bacteria belong to Firmicutes and Deinococcus-Thermus phyla; Archaea belong to the Sulfolobales. ► The Tengchong PIRE project is an international team that studies the geobiology of Rehai.

Description: Publication year: 2012 Source: Geoscience Frontiers John J.W. Rogers Steady decline in the percentage of 235 U in terrestrial uranium made natural fission impossible after about 1.8 Ga.Fission before 1.8 Ga disturbed the lead isotope system at various places worldwide, such as Oklo, Gabon, and may have caused the first lead isotope paradox. Fission in areas of high uranium concentration may also have generated enough heat to localize sparse Archean and Paleoproterozoic UHT belts. The oldest widespread orogenic systems formed at approximately 2.0 to 1.8 Ga after fission stopped contributing to the earth’s heat flow. These early orogenic systems partly created the supercontinent Columbia. Graphical Abstract Graphical Abstract Highlights ► Natural fission of 235 U was a significant source of heat before about 2 Ga. ► Fission developed depleted Archean lower crust that now has a low heat generation and is an inaccessible depleted reservoir that accounts for the first lead isotope paradox. ► The earth was cool enough by 2.0–1.8 Ga that widespread networks of orogenic belts could develop, partly generating the supercontinent Columbia.

Description: Publication year: 2012 Source: Geoscience Frontiers Li Wu, Feng Li, Cheng Zhu, Lan Li, Bing Li Holocene environmental change and environmental archaeology are important components of an international project studying the human-earth interaction system. This paper reviews the progress of Holocene environmental change and environmental archaeology research in the Yangtze River Valley over the last three decades, that includes the evolution of large freshwater lakes, Holocene transgression and sea level changes, Holocene climate change and East Asian monsoon variation, relationship between the rise and fall of primitive civilizations and environmental changes, cultural interruptions and paleoflood events, as well as relationship between the origin of agriculture and climate change. These research components are underpinned by the dating of lacustrine sediments, stalagmites and peat to establish a chronology of regional environmental and cultural evolution. Interdisciplinary and other environment proxy indicators need to be used in comparative studies of archaeological site formation and natural sedimentary environment in the upper, middle and lower reaches of the Yangtze River Valley. Modern technology such as remote sensing, molecular bioarchaeology, and virtual reality, should be integrated with currently used dating, geochemical, sedimentological, and paleobotanical methods of analysis in environmental archaeology macro- and micro-studies, so as to provide a greater comprehensive insight into Holocene environmental and cultural interaction and change in the Yangtze River Valley area. Graphical Abstract Highlights ► The timing of formation of the modern Taihu Lake and Chaohu Lake inferred to be less than 3–2 kyr BP. ► New evidence not consistent with high sea level from 7.0–5.0 kyr BP. ► Neolithic cultural sequences established in the Yangtze Valley. ► The relationship between early agriculture and climate display complex patterns

Description: Publication year: 2012 Source: Geoscience Frontiers Basem A. Zoheir Field and remote sensing studies reveal that Au-bearing quartz±carbonate lodes in the Romite deposit, in the extreme South Eastern Desert of Egypt, are controlled by NNE-striking shear zones that splay from the ca. 660–550 Ma Hamisana Zone. Quartz in releasing bends with sinistral shear geometry and abundant boudinaged quartz-carbonate lodes with serrate ribboned fabrics suggest vein formation within a transpressive wrench system. Ubiquitous hydrothermal quartz, carbonate, and subordinate chlorite and sericite within the shear zones and as slivers in veins, indicate that gold deposition and hydrothermal alteration occurred under greenschist facies conditions. The Al IV in chlorite indicates a formation temperature of ∼300 ºC, comparable with temperatures estimated from arsenopyrite composition for grains intimately associated with gold in quartz veins. The new geological and geochemical data indicate that splays off the Hamisana Zone are potential gold exploration targets. Quartz veins along the high order (2 nd or 3 rd ) structures of this crustal-scale shear zone are favourable targets. In the Romite deposit and in surrounding areas, a Au-As-Cu-Sb-Co-Zn geochemical signature characterizes mineralized zones, and particularly rock chips with 〉 1000 ppm As and high contents of Cu, Zn, and Co target the better mineralized areas. The carbonate δ 13 C PDB and δ 18 O SMOW isotope signatures preclude an organic source of the ore fluid, but metamorphic and magmatic sources are still valid candidates. The intense deformation and lack of magmatism in the deposit area argue for metamorphic dewatering of greenstone rocks as the most likely fluid source. The narrow ranges of δ 13 C (–4.6‰ to –3.1‰) and δ 18 O (11.9‰ to 13.7‰) in carbonate minerals in lodes imply a corresponding uniformity to the ambient temperature and δ 13 C CO2 ( δ 13 C ΣC ) of the ore fluids. The calculated δ 18 O H2O values of 6.9‰ to 7.9‰ for ore fluids, based on δ 18 O values of vein quartz further suggest a likely metamorphic origin. Graphical Abstract Highlights ► Silicified, NNE-SSW shear splays off Hamisana Zone are gold-bearing. ► Morphology and micrstructures of vein quartz suggest syn-kinematic formation. ► Au endowment and alteration occurred under greenschist facies conditions. ► Romite gold deposit has a Au-As-Cu-Sb-Co-Zn geochemical signature. ► Stable isotopes of quartz and carbonate suggest a likely metamorphic ore fluid.

Description: Publication year: 2012 Source: Geoscience Frontiers G.F. Ufimtsev This paper attempts to review the descriptions on the genetic series of neotectonic forms in Eurasia. Morphotectonically, the Eurasian continental block exhibits a radial-concentric pattern consisting of four kinds of tectonic units: platforms, rejuvenated and youthful mobile belts, and the continent-ocean transition zones. Vast areas of young and ancient platforms, such as Siberia, have experienced slow-rate Late-Cenozoic uplift and little interior deformation. The youthful orogenic belts are clustered into the giant Alpine-Himalayan megabelt. The rejuvenated mountain belts are characterized by a variety of structural-morphological types of orogens, such as domelike uplifts, block uplifts and intermountain basins. The continent-ocean transition zones in eastern Asia, including marginal rifts and extensional basins, are resulted from interaction between the continental block and Pacific Ocean and Philippine Sea since the Late Cenozoic. One of the conspicuous features of Eurasia is that most areas lie in the largest geoid depression of the Earth, and the NS trending Uralian-Oman lineament expresses a break on the geoid slope, implying a relationship to deep structure, including density inhomogeneities, downward to the core-mantle interface. Besides, the Eurasian continent fully demonstrates morphotectonic and recent geodynamic features of the Northern Hemisphere of the Earth, just in contrast to that of the Southern Hemisphere. It is best to view the surface morphotectonics and deep structure of the Earth as a geodynamic ensemble which has spawned the large-scale geomorphic features on the surface. Graphical Abstract Highlights ► Morphotectonic structure of the Eurasian continental block characterized. ► Radial-concentric pattern of basic morphotectonics elements identified. ► Tectonic landforms and deep structure are combined into stable parageneses.

Description: Publication year: 2012 Source: Geoscience Frontiers, Available online 14 February 2012 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. 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, Available online 5 January 2012 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 includesAmphistegina,OperculinaandAlveolinellain 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. ▪ Highlights ► Relict benthic foraminifera from 85-135 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, Available online 10 January 2012 Liang Shen, Tandong Yao, Baiqing Xu, Hongmei Wang, Nianzhi Jiao, ... 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 mLto 0–1720 CFU mLin 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, andActinobacteria, with theFirmicutesbeing 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. Highlights ► Culturable bacteria in the core fell into 12 genera，belonged to four groups： Firmicutes , alpha-Proteobacteria , gamma-Proteobacteria , and Actinobacteria. ► The abundances of cultivable bacteria and pigment-producing isolates varied synchronously with depth along the ice core: higher abundance in the middle, and lower at the top and bottom. Suggesting that the middle part was hospitable for the microbial survival. ► To combine the approaches of both direct and enrichment cultivations may be a better way to explore the microbial diversity in ice core.

Description: Publication year: 2011 Source: Geoscience Frontiers, Available online 28 December 2011 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. ▪ 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: 2011 Source: Geoscience Frontiers, Available online 27 December 2011 M. Economou-Eliopoulos, D. Antivachi, Ch. Vasilatos, I. Megremi An integrated approach was performed on the soil, plant-crops and groundwater system at the Thiva basin, to evaluate the extent and intensity of the heavy metal contamination, the percentage of metals transferred into plants/crops (bio-accumulation) and the potential sources of contamination.Heavy metal contents (230–310 Cr, 1200–2200 Ni, 50–80 Co, 880–1150 Mn and 44,500–66,200 Fe all in ppm ) in the Thiva soils are higher than those in the Assopos basin. An increasing trend in the heavy metal contents, from the Assopos to the Thiva basin (Mouriki), indicates that the metal source is probably the Ni-laterites and ophiolites, located towards north. On the other hand, groundwater samples from domestic and irrigation wells throughout the Thiva basin exhibit relatively low (8–37 ppb) concentrations in Cr compared to the Assopos (up to 150 ppb). The plots of Cr versus Mg/Ca, Mg/Na versus Ca/Na, B versus Si/(Si + Na) and Mg/Si versus Ca/Si ratios revealed a low degree of salinization in the Thiva compared to that in the Assopos (Avlida) basin. The low Cr concentration (average 23 ppb, during dry period) in the Thiva wells may be related with their depth (〉120 m), in contrast to shallow wells in the central Euboea (hundreds ppb Cr) and points to a solution of a crucial environmental problem in Euboea and Assopos basin by using the deep karst-type aquifer instead the shallow-Neogene one.The average Cr contents (dry weight) ranges from 1.7 to 4.6 ppm (average 2.2) in carrots, potatoes and onions. The percentage of soil metals Crtotal, Cr(VI), Ni, Mn and Fe ranges between 0.06 and 3.2 (average 0.53 ± 0.4), whilst that for Cu and Zn ranges from 16 to 81 (average 36 ± 24). The Cr transfer to plants is low, due to the high resistance of chromite (main host of Cr), but the determined Cr contents in plant-crops in the Thiva basin are higher than normal or sufficient values. Although minimal uptake for growth and production for Cr, Ni, Zn and Cu is still lacking, furthermore research is required in order to restrict heavy metal accumulation and ensure sustainability. Highlights ► Contamination of water by Cr(VI) in the Thiva–Assopos Basins correlated to human activities. ► Mg/Na vs Ca/Na and B vs Si/(Si + Na) plots provide evidence for water salinization. ► Cr, Mg, Mn, Fe, Co contents in soil increase from the Assopos Basin towards the Thiva Basin.

Description: Publication year: 2011 Source: Geoscience Frontiers, Available online 17 December 2011 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 indicate that soil input had little influence on the composition of GDGTs in Tibetan hot springs. On the other hand, ring index and TEX86values were both positively correlated with incubation temperature, suggesting that the structure of archaeal lipids changed in response to varying temperature during incubation. 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: 2011 Source: Geoscience Frontiers, Available online 21 December 2011 X. Mo, M. Santosh, X. Wan

Description: Publication year: 2011 Source: Geoscience Frontiers, Available online 16 December 2011 Gaoyuan Li, Hongchen Jiang, Weiguo Hou, Shang Wang, Liuqin Huang, ... The microbial diversity in Wuli Area, Qinghai-Tibetan Plateau was investigated using 16S rRNA gene phylogentic 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 intoProteobacteria,Acidobacteria,Deinococci,Sphingobacteria,Flavobacteria,Nitrospirae,Actinobacteria,Gemmatimonadetes, and unclassified- Bacteria; and the archaeal clones could be classified intoCrenarchaeotaandThaumarchaeota. Among the major groups,ProteobacteriaandCrenarchaeotawere 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.

Description: Publication year: 2011 Source: Geoscience Frontiers, Available online 10 December 2011 Lawrence H. Tanner, Xin Wang, Alesha C. Morabito The Yan’an Formation of the OrdosBasin is a sequence of four members, consisting of siliclastic 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 OrdosBasin 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. 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: 2011 Source: Geoscience Frontiers, Available online 9 December 2011 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: 2011 Source: Geoscience Frontiers, Available online 23 November 2011 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: 2011 Source: Geoscience Frontiers, Available online 1 December 2011 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: 2011 Source: Geoscience Frontiers, Available online 9 November 2011 Wenlong Ding, Chao Li, Chunyan Li, Changchun Xu, Kai Jiu, ... 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, Available online 20 October 2011 Chongwen Yu By applying the ‘theory of synchronization’ from the science of complexity to studying the regional regularity of ore formation within the Nanling region of South China, a characteristic target-pattern regional ore zonality has been discovered. During the early and late Yanshanian epoch (corresponding respectively to the Jurassic and Cretaceous periods), two centers of ore formation emerged successively in the Nanling region; the former is mainly for rare metals (W, Sn, Mo, Bi, Nb) and one rare-earth element (La) and was generated in the Jurassic period; whereas the latter is mainly for base metals (Cu, Pb, Zn, Sb, Hg), noble metals (Au, Ag), and one radioactive element (U) and was generated in the Cretaceous period. Centers of ore formation were brought about by interface dynamics respectively at the Qitianling and Jiuyishan districts in southern Hunan Province. The characteristic giant nonlinear target-pattern regional ore zonality was generated respectively from the two centers of ore formation by the spatio-temporal synchronization process of the Nanling complex metallogenic system. It induced the collective dynamics and cooperative behavior of the system and displayed the configuration of the regional ore zonality. Then dynamical clustering transformed the configuration into rudimentary ordered coherent structures. Phase dynamics eventually defined the spatio-temporal structures of the target-pattern regional ore zonality and determined their localization and distribution. The integral successive processes of synchronization-dynamical clustering-phase dynamics accomplished the regional ore zonality by way of “multiple field dynamics” of spatio-temporal superposition of multiple coupled pulsatory solitary wave trains of the zonal sequences of different ores. A new methodology for revealing regional ore zonality is developed, which will encourage further investigation of the formation of deep-seated ore resources and the onset of large-scale mineralization.

Description: Publication year: 2011 Source: Geoscience Frontiers, Available online 7 October 2011 Weihua Ao, Wenhui Huang, Chengmin Weng, Xiuling Xiao, Dameng Liu, ... Multiple sets of thick coal beds characterized by simple structure and shallow burial depth were developed in the Early and Middle Jurassic strata of the Ordos Basin, northwestern China. The huge reserves of this high quality coal have a high commercial value. We studied the coal’s petrologic characteristics and its maceral distribution to determine the maceral’s contribution to generation of oil and gas. The results show that the Jurassic coals in the Ordos Basin have special petrological features because of the Basin’s unique depositional environment which was mainly a series of high-stand swamps in the upper fluvial system. These petrographic features are a result of the development of typical inland lakes where some sand bodies were formed by migrating rivers. After burial, the peat continued to undergo oxidizing conditions, this process generated extensive higher inertinite contents in the coals and the vitrinite components were altered to semi-vitrinite. The macroscopic petrographic types of these Jurassic coals are mainly semi-dull coal, dull coal, semilustrous and lustrous coal. The proportions of semi-dull coal and dull coal are higher in the basin margins, especially in the area near the northern margin. The numbers of semilustrous and lustrous coals increase southwards and towards the central basin. This situation indicates that different coal-forming swamp environments have major controlling effects on the coal components. Another observation is that in the Ordos’ coal sequences, especially in the lower part, some sandstone beds are thick, up to 20 m with a coarse grain size. The higher fusinite content in the macerals accompanies a higher semi-vitrinite content with more complete and regular plant cell structure. The fusinite structure is clear and well preserved. After burial, the lithology of the roof and floor rocks can continue to affect the evolution of coal petrology. The sand bodies in the roof and floor exhibit good physical conditions so that pore water can maintain a long-term state of oxidation, circulation and connection to the coal. So coal components remain in an oxidation environment for a long time. Conversely, in the basin center, lacustrine facies developed and peat was rapidly covered by mudstone after burial and subsequent coal beds rapidly entered a reducing environment. As a result, abundant gelatification occurred and the vitrinite content increased. Exinite often accumulated in a specific position in the coal bed. Although the average exinite content is not high on the whole, it does significantly contribute to the total hydrocarbon generation. The exinite content has been underestimated, especially the amorphous bituminous fluid and its importance is emphasized here. The reason is that the fluid flows easily into fusinite which has strong rigidity, or flows into some fissures, where it is commonly neglected.

Description: Publication year: 2012 Source: Geoscience Frontiers, Available online 17 February 2012 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 inw(FeO) (14.13%–16.09%) andw(MnO) (24.21%–27.44%). The rocks have high SiO2, alkalis, FeOt/MgO, TiO2/MgO and low Al2O3, CaO withw(Na2O)/w(K2O)〉 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 initialSr/Sr ratios (0.706–0.708), low and negativeɛNd(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. 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: 2011 Source: Geoscience Frontiers, Available online 7 October 2011 V.I. Starostin, O.G. Sorokhtin The origin of PGE–Cu–Ni sulfide deposits of Norilsk and Talnakh located in the northwest flank of the Triassic basalt trap formation of Siberia is considered. It is shown that ore elements of these deposits (probably, except Fe) are derived from the crust rather than from the mantle. They entered the basalts owing to a remobilization (recycling) of ore elements from the Paleoproterozoic sediments and from the rocks of the Siberian platform’s basement. Prospecting criteria for similar deposits are as follows: (1) a presence of a large Paleoproterozoic aulacogen and a related magmatic sulfide Cu–Ni mineralization; (2) a confinement of perspective areas to troughs associated with long-lived deep fault zones; (3) association with mobile orogenic belts, island-arc systems and tectonomagmatic activation zones; (4) temporal association with boundaries of global periods characterized by active processes of continental breakup and large-scale trap magmatism. A combination of several factors (the first one is obligatory) is favorable for the discovery of a large ore body.

Description: Publication year: 2012 Source: Geoscience Frontiers, Available online 10 February 2012 Dedong Li, Yuwang Wang, Jingbin Wang, Zhaohua Luo, Jiulong Zhou, ... 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 kmfor diabase, 0.014–0.068 kmfor quartz diorite and 0.011–0.034 kmfor 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. 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: 2012 Source: Geoscience Frontiers, Available online 3 February 2012 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. 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, Available online 11 February 2012 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 wt.% SiO2), with subordinate felsic volcanics (67-75 wt.% SiO2). The felsic volcanics are dacitic to rhyolitic in composition and are typically enriched in LREE (La/SmN= 3.09-3.90) with high REE contents (256-588 ppm), moderately fractionated REE patterns (CeN/YbN= 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. 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: 2011 Source: Geoscience Frontiers, Available online 30 December 2011 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 to the driving force of this tectonic stress field. The average value of the stress indexR’ is about 2.09, which indicates a variation from strike slip to compressive tectonic stress regime in the study area in 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. 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, Available online 17 December 2011 Linqi Xia, Zuchun Xia, Xueyi Xu, Xiangmin Li, Zhongping Ma Early Cambrian and Mid–Late Neoproterozoic volcanic rocks in China are widespread on several Precambrian continental blocks, which had aggregated to form part of the Rodinia supercontinent by ca. 900 Ma. On the basis of petrogeochemical data, the basic lavas can be classified into two major magma types: HT (Ti/Y 〉 500) and LT (Ti/Y 〈 500) that can be further divided into HT1 (Nb/La 〉 0.85) and HT2 (Nb/La ≤ 0.85), and LT1 (Nb/La 〉 0.85) and LT2 (Nb/La ≤ 0.85) subtypes, respectively. The geochemical variation of the HT2 and LT2 lavas can be accounted for by lithospheric contamination of asthenosphere- (or plume-) derived magmas, whereas the parental magmas of the HT1 and LT1 lavas did not undergo, during their ascent, pronounced lithospheric contamination. These volcanics exhibit at least three characteristics: (1) most have a compositional bimodality; (2) they were formed in an intracontinental rift setting; and (3) they are genetically linked with mantle plumes or a mantle surperplume. This rift-related volcanism at end of the Mid–Neoproterozoic and Early Cambrian coincided temporally with the separation between Australia–East Antarctica, South China and Laurentia and between Australia and Tarim, respectively. The Mid–Late Neoproterozoic volcanism in China is the geologic record of the rifting and break-up of the supercontinent Rodinia.

Description: Publication year: 2011 Source: Geoscience Frontiers, Available online 29 December 2011 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 analyse 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.

Description: Publication year: 2011 Source: Geoscience Frontiers, Available online 16 December 2011 Yong Zhang, Xin Su, Fang Chen, Yuanyuan Wang, Lu Jiao, ... 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 analysis. Here, we show that microbial abundance and diversity along with geochemistry profiles of the sediment core revealed a coupled reaction between sulfate reduction and methane oxidation. Acridine orange direct count results showed that microbial abundance ranges from 10to 10cells/g sediment (wet weight). The depth-related variation of the abundance showed the same trend as the methane concentration profile. Phylogenetic analysis indicated presence of sulfate-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, sulfate concentration and total organic carbon. Marine Benthic Group B,Chloroflexiand JS1 were predominant phylotypes of the archaeal and bacterial libraries, respectively. Highlights ▶ Abyssal microbial community from methane seepage. ▶ Low abundance, high diversity and unique composition. ▶ Major phylotypes participated in the geochemical processes related to methane vent.

Description: Publication year: 2011 Source: Geoscience Frontiers, Available online 13 December 2011 Prosanta K. Khan, Partha Pratim Chakraborty, G. Tarafdar, S. Mohanty The disastrousMw9.3 (seismic moment 1.0×10dyn/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. 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: 2011 Source: Geoscience Frontiers, Available online 15 December 2011 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: 2011 Source: Geoscience Frontiers, Available online 16 December 2011 Weiguo Hou, Bin Lian, Hailiang Dong, Hongchen Jiang, Xingliang Wu Ectomycorrhizal fungi, a group of widespread symbiotic fungi with plant, obtain carbon source from trees and improve plant mineral nutrient uptake with their widespread hyphal network. Ectomycorrhizal fungi can be used as inoculants to improve the survival rates of plantation. Saprophytic fungi use the nutrition from the debris of plant or animals, and it is difficult to distinguish the saprophytic and ectomycorrhizal fungi by morphological and anatomic methods. In this research, the differences of stable carbon and nitrogen isotopic compositions of these fungi were analyzed. The results showed that the abundances ofC of were higher than those of ectomycorrhizal fungi and the abundances ofN of saprophytic fungi were lower than those of ectomycorrhizal fungi. Such differences of stable carbon and nitrogen isotopic compositions between ectomycorrhizal fungi and saprophytic fungi can be ascribed to their different nutrition sources and ecological functions. These results collectively indicate that stable carbon and nitrogen isotopic compositions are an effective proxy for distinguishing between ectomycorrhizal and saprophytic fungi. Highlights ► Ectomycorrhizal and saprophytic macro fungi are hard to distinguish with anatomical and genetic methods. ► Isotopic compositions of fungal fruit bodies can be used to distinguish ectomycorrhizal and saprophytic fungi. ► The trophic manners give rise to the differences in isotopic compositions of the two categories of fungi.

Description: Publication year: 2011 Source: Geoscience Frontiers, Available online 25 November 2011 Pengyuan Li, Jinjiang Zhang, Lei Guo, Xiongying Yang A large-scale pop-up structure occurs at the front of the northern Dabashan thrust belt (NDTB), bound by the NNE-dipping Chengkou fault to the south, and the SSW-dipping Gaoqiao fault to the north. The pop-up structure shows different features along its strike as a direct reflection of the intensity of tectonic activity. To the northwest, the structure is characterized by a two-directional thrust system forming a positive flower-like structure. In contrast, the southeastern part is composed of the vertical Chengkou fault and a series of N-directed backthrusts, showing a semi-flower-like structure. We present results from Ar-Ar dating of syntectonic microthermal metamorphic sericite which show that the Chengkou fault experienced intense deformation during the mid-Mesozoic Yanshanian epoch (about 143.3 Ma), causing rapid uplift and thrusting of the northern Dabashan thrust belt. During the propagation of this thrust, a series of backthrusts formed because of the obstruction from the frontier of Dabashan thrust belt, leading to the development of the pop-up structure.

Description: Publication year: 2011 Source: Geoscience Frontiers, Available online 13 December 2011 Shang Wang, Raymond M. Dong, Christina Z. Dong, Liuqin Huang, Hongchen Jiang, ... 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 microenvironments 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. 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: 2011 Source: Geoscience Frontiers, Available online 2 December 2011 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 hywith a close relation to grass land areas, degraded forests and deciduous forests on the steep side-slopes (with highLS). 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: 2011 Source: Geoscience Frontiers, Available online 8 October 2011 Jozef Michalík, Daniela Reháková During the last decades, several integrated studies of Tethyan Jurassic/Cretaceous boundary sections from different countries were published with the objective to indicate problems for the selection of biological, chemical or physical markers suitable for identification of the Jurassic/Cretaceous boundary – the only system boundary within the Phanerozoic still not fixed by GSSP. Drawing the boundary between the Jurassic and Cretaceous systems is a matter of global scale discussions. The problem of proposing possible J/K boundary stratotypes results from lack of a global index fossils, global sea level drop, paleogeographic changes causing development of isolated facies areas, as well as from the effect of Late Cimmerian Orogeny. This contribution summarizes and comments data on J/K boundary interval obtained from several important Tethyan sections and shows still existing problems and discrepancies in its determination.

Description: Publication year: 2011 Source: Geoscience Frontiers, Available online 19 October 2011 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 theP–Tpath. The core domains of orthopyroxene porphyroblasts have up towt(Al2O3) 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 aP–Trange of 1012–960 °C and 9.4 kbar. TheP–Tphase topologies computed using isochemical sections calculated in the model system Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O (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. TheseP–Tresults 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 atP 〈 10 kbar, inferred from micro-structural relations among various minerals. After high-temperature decompression from the metamorphic peak, theP–Tpath followed a near isobaric cooling stage toT 〈 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: 2011 Source: Geoscience Frontiers, Available online 17 November 2011 Jinfu Shu We have performed measurements of minerals based on the synchrotron source for single crystal and powder X-ray diffraction, inelastic scattering, spectroscopy and radiography by using diamond anvil cells. We investigated the properties of iron (Fe), iron-magnesium oxides (Fe, Mg)O, silica(SiO2), iron-magnesium silicates (Fe, Mg)SiO3under simulated high pressure-high temperature extreme conditions of the Earth’s crust, upper mantle, low mantle, core-mantle boundary, outer core, and inner core. The results provide a new window on the investigation of the mineral properties at Earth’s conditions.

Description: Publication year: 2012 Source: Geoscience Frontiers, Available online 17 February 2012 Yuwang Wang, Jingbin Wang, Lijuan Wang, Lingli Long, Pingzhi Tang, ... 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 SiO2spans 38.8 to 46.8 wt.%. Basalt and gabbro are geochemically similar and are characterized by low FeOt(10.9 wt.%), total alkali (Na2O+K2O=2.58 wt.%) and TiO2(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. 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 Abdullah Kaygusuz, Ferkan Sipahi, Nurdane İlbeyli, Mehmet Arslan, Bin Chen, Emre Aydınçakır 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), ε N 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 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: Publication year: 2012 Source: Geoscience Frontiers 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. 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: Publication year: 2012 Source: Geoscience Frontiers 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. 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: Publication year: 2011 Source: Geoscience Frontiers Weiguo Hou, Bin Lian, Hailiang Dong, Hongchen Jiang, Xingliang Wu Ectomycorrhizal fungi, a group of widespread symbiotic fungi with plant, obtain carbon source from trees and improve plant mineral nutrient uptake with their widespread hyphal network. Ectomycorrhizal fungi can be used as inoculants to improve the survival rates of plantation. Saprophytic fungi use the nutrition from the debris of plant or animals, and it is difficult to distinguish the saprophytic and ectomycorrhizal fungi by morphological and anatomic methods. In this research, the differences of stable carbon and nitrogen isotopic compositions of these fungi were analyzed. The results showed that the abundances of 13 C of were higher than those of ectomycorrhizal fungi and the abundances of 15 N of saprophytic fungi were lower than those of ectomycorrhizal fungi. Such differences of stable carbon and nitrogen isotopic compositions between ectomycorrhizal fungi and saprophytic fungi can be ascribed to their different nutrition sources and ecological functions. These results collectively indicate that stable carbon and nitrogen isotopic compositions are an effective proxy for distinguishing between ectomycorrhizal and saprophytic fungi. Graphical Abstract Highlights ► Ectomycorrhizal and saprophytic macro fungi are hard to distinguish with anatomical and genetic methods. ► Isotopic compositions of fungal fruit bodies can be used to distinguish ectomycorrhizal and saprophytic fungi. ► The trophic manners give rise to the differences in isotopic compositions of the two categories of fungi.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 1 Jinfu Shu We have performed measurements of minerals based on the synchrotron source for single crystal and powder X-ray diffraction, inelastic scattering, spectroscopy and radiography by using diamond anvil cells. We investigated the properties of iron (Fe), iron-magnesium oxides (Fe, Mg)O, silica(SiO 2 ), iron-magnesium silicates (Fe, Mg)SiO 3 under simulated high pressure-high temperature extreme conditions of the Earth’s crust, upper mantle, low mantle, core-mantle boundary, outer core, and inner core. The results provide a new window on the investigation of the mineral properties at Earth’s conditions.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 1 Pengyuan Li, Jinjiang Zhang, Lei Guo, Xiongying Yang A large-scale pop-up structure occurs at the front of the northern Dabashan thrust belt (NDTB), bound by the NNE-dipping Chengkou fault to the south, and the SSW-dipping Gaoqiao fault to the north. The pop-up structure shows different features along its strike as a direct reflection of the intensity of tectonic activity. To the northwest, the structure is characterized by a two-directional thrust system forming a positive flower-like structure. In contrast, the southeastern part is composed of the vertical Chengkou fault and a series of N-directed backthrusts, showing a semi-flower-like structure. We present results from Ar-Ar dating of syntectonic microthermal metamorphic sericite which show that the Chengkou fault experienced intense deformation during the mid-Mesozoic Yanshanian epoch (about 143.3 Ma), causing rapid uplift and thrusting of the northern Dabashan thrust belt. During the propagation of this thrust, a series of backthrusts formed because of the obstruction from the frontier of Dabashan thrust belt, leading to the development of the pop-up structure.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 1 Guoxiang Chi, Chunji Xue, Hairuo Qing, Wei Xue, Jiangwei Zhang, Yunqiang Sun The Jinding Zn-Pb deposit has been generally considered to have formed from circulating basinal fluids in a relatively passive way, with fluid flow being controlled by structures and sedimentary facies, similar to many other sediments-hosted base metal deposits. However, several recent studies have revealed the presence of sand injection structures, intrusive breccias, and hydraulic fractures in the open pit of the Jinding deposit and suggested that the deposit was formed from explosive release of overpressured fluids. This study reports new observations of fluid overpressure-related structures from underground workings (Paomaping and Fengzishan), which show clearer crosscutting relationships than in the open pit. The observed structures include: 1) sand (±rock fragment) dikes injecting into fractures in solidified rocks; 2) sand (±rock fragment) bodies intruding into unconsolidated or semi-consolidated sediments; 3) disintegrated semi-consolidated sand bodies; and 4) veins and breccias formed from hydraulic fracturing of solidified rocks followed by cementation of hydrothermal minerals. The development of ore minerals (sphalerite) in the cement of the various clastic injection and hydraulic fractures indicate that these structures were formed at the same time as mineralization. The development of hydraulic fractures and breccias with random orientation indicates small differential stress during mineralization, which is different from the stress field with strong horizontal shortening prior to mineralization. Fluid flow velocity may have been up to more than 11 m/s based on calculations from the size of the fragments in the clastic dikes. The clastic injection and hydraulic fracturing structures are interpreted to have formed from explosive release of overpressured fluids, which may have been related to either magmatic intrusions at depth or seismic activities that episodically tapped an overpressured fluid reservoir. Because the clastic injection and hydraulic structures are genetically linked with the mineralizing fluid source, they can be used as a guide for mineral exploration.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 1 Weihua Ao, Wenhui Huang, Chengmin Weng, Xiuling Xiao, Dameng Liu, Xiuyi Tang, Ping Chen, Zhigen Zhao, Huan Wan, Robert B. Finkelman Multiple sets of thick coal beds characterized by simple structure and shallow burial depth were developed in the Early and Middle Jurassic strata of the Ordos Basin, northwestern China. The huge reserves of this high quality coal have a high commercial value. We studied the coal’s petrologic characteristics and its maceral distribution to determine the maceral’s contribution to generation of oil and gas. The results show that the Jurassic coals in the Ordos Basin have special petrological features because of the Basin’s unique depositional environment which was mainly a series of high-stand swamps in the upper fluvial system. These petrographic features are a result of the development of typical inland lakes where some sand bodies were formed by migrating rivers. After burial, the peat continued to undergo oxidizing conditions, this process generated extensive higher inertinite contents in the coals and the vitrinite components were altered to semi-vitrinite. The macroscopic petrographic types of these Jurassic coals are mainly semi-dull coal, dull coal, semilustrous and lustrous coal. The proportions of semi-dull coal and dull coal are higher in the basin margins, especially in the area near the northern margin. The numbers of semilustrous and lustrous coals increase southwards and towards the central basin. This situation indicates that different coal-forming swamp environments have major controlling effects on the coal components. Another observation is that in the Ordos’ coal sequences, especially in the lower part, some sandstone beds are thick, up to 20 m with a coarse grain size. The higher fusinite content in the macerals accompanies a higher semi-vitrinite content with more complete and regular plant cell structure. The fusinite structure is clear and well preserved. After burial, the lithology of the roof and floor rocks can continue to affect the evolution of coal petrology. The sand bodies in the roof and floor exhibit good physical conditions so that pore water can maintain a long-term state of oxidation, circulation and connection to the coal. So coal components remain in an oxidation environment for a long time. Conversely, in the basin center, lacustrine facies developed and peat was rapidly covered by mudstone after burial and subsequent coal beds rapidly entered a reducing environment. As a result, abundant gelatification occurred and the vitrinite content increased. Exinite often accumulated in a specific position in the coal bed. Although the average exinite content is not high on the whole, it does significantly contribute to the total hydrocarbon generation. The exinite content has been underestimated, especially the amorphous bituminous fluid and its importance is emphasized here. The reason is that the fluid flows easily into fusinite which has strong rigidity, or flows into some fissures, where it is commonly neglected.

Description: Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 1 Lanlan Shi, Shide Mao The IAPWS-95 formulation explicit in Helmholtz free energy proposed by Wagner and Pruβ (2002) is the best equation of state of water, from which all thermodynamic properties can be obtained over a wide T – p range from 273.16 to 1273 K and from 0 to 1000 MPa with experimental accuracy. This paper reports the applications of the IAPWS-95 formulation in fluid inclusion and mineral-water phase equilibria. A reliable and highly efficient calculation method is presented for the saturated properties of water so that the formulation can be conveniently applied in the study of fluid inclusion, such as calculating homogenization pressures, homogenization densities (or molar volumes), volume fractions and isochores. Meanwhile, the univariant curves of some mineral-dehydration reactions are calculated based on the IAPWS-95 formulation. The computer code of the IAPWS-95 formulation can be obtained from the corresponding author.

Description: Publication year: 2011 Source: Geoscience Frontiers 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. Graphical Abstract 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: 2011 Source: Geoscience Frontiers Xun Sun, Chunyan Sun, Jiangyun Xiang, Jihui Jia, Panfeng Li, Zhibin Zhang 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 (GC) 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. Graphical Abstract 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 M. Economou-Eliopoulos, D. Antivachi, Ch. Vasilatos, I. Megremi An integrated approach was performed on the soil, plant-crops and groundwater system at the Thiva basin, to evaluate the extent and intensity of the heavy metal contamination, the percentage of metals transferred into plants/crops (bio-accumulation) and the potential sources of contamination. Heavy metal contents (230–310 Cr, 1200–2200 Ni, 50–80 Co, 880–1150 Mn and 44,500–66,200 Fe all in ppm ) in the Thiva soils are higher than those in the Assopos basin. An increasing trend in the heavy metal contents, from the Assopos to the Thiva basin (Mouriki), indicates that the metal source is probably the Ni-laterites and ophiolites, located towards north. On the other hand, groundwater samples from domestic and irrigation wells throughout the Thiva basin exhibit relatively low (8–37 ppb) concentrations in Cr compared to the Assopos (up to 150 ppb). The plots of Cr versus Mg/Ca, Mg/Na versus Ca/Na, B versus Si/(Si + Na) and Mg/Si versus Ca/Si ratios revealed a low degree of salinization in the Thiva compared to that in the Assopos (Avlida) basin. The low Cr concentration (average 23 ppb, during dry period) in the Thiva wells may be related with their depth (〉120 m), in contrast to shallow wells in the central Euboea (hundreds ppb Cr) and points to a solution of a crucial environmental problem in Euboea and Assopos basin by using the deep karst-type aquifer instead the shallow-Neogene one. The average Cr contents (dry weight) ranges from 1.7 to 4.6 ppm (average 2.2) in carrots, potatoes and onions. The percentage of soil metals Cr total , Cr(VI), Ni, Mn and Fe ranges between 0.06 and 3.2 (average 0.53 ± 0.4), whilst that for Cu and Zn ranges from 16 to 81 (average 36 ± 24). The Cr transfer to plants is low, due to the high resistance of chromite (main host of Cr), but the determined Cr contents in plant-crops in the Thiva basin are higher than normal or sufficient values. Although minimal uptake for growth and production for Cr, Ni, Zn and Cu is still lacking, furthermore research is required in order to restrict heavy metal accumulation and ensure sustainability. Graphical Abstract Highlights ► Contamination of water by Cr(VI) in the Thiva–Assopos Basins correlated to human activities. ► Mg/Na vs Ca/Na and B vs Si/(Si + Na) plots provide evidence for water salinization. ► Cr, Mg, Mn, Fe, Co contents in soil increase from the Assopos Basin towards the Thiva Basin.

Description: Publication year: 2011 Source: Geoscience Frontiers Linqi Xia, Zuchun Xia, Xueyi Xu, Xiangmin Li, Zhongping Ma Early Cambrian and Mid–Late Neoproterozoic volcanic rocks in China are widespread on several Precambrian continental blocks, which had aggregated to form part of the Rodinia supercontinent by ca. 900 Ma. On the basis of petrogeochemical data, the basic lavas can be classified into two major magma types: HT (Ti/Y 〉 500) and LT (Ti/Y 〈 500) that can be further divided into HT1 (Nb/La 〉 0.85) and HT2 (Nb/La ≤ 0.85), and LT1 (Nb/La 〉 0.85) and LT2 (Nb/La ≤ 0.85) subtypes, respectively. The geochemical variation of the HT2 and LT2 lavas can be accounted for by lithospheric contamination of asthenosphere- (or plume-) derived magmas, whereas the parental magmas of the HT1 and LT1 lavas did not undergo, during their ascent, pronounced lithospheric contamination. These volcanics exhibit at least three characteristics: (1) most have a compositional bimodality; (2) they were formed in an intracontinental rift setting; and (3) they are genetically linked with mantle plumes or a mantle surperplume. This rift-related volcanism at end of the Mid–Neoproterozoic and Early Cambrian coincided temporally with the separation between Australia–East Antarctica, South China and Laurentia and between Australia and Tarim, respectively. The Mid–Late Neoproterozoic volcanism in China is the geologic record of the rifting and break-up of the supercontinent Rodinia.

Description: November 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 6 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: Available online 19 November 2012 Publication year: 2012 Source: Geoscience Frontiers Archaea have unique glycerol dialkyl glycerol tetraether (GDGT) lipids that can be used to develop paleotemperature proxies such as TEX 86 . This research is to validate proposed GDGT proxies for paleotemperature determination in the South China Sea (SCS). Samples were collected from core-top sediments (0–5 cm) in the northern SCS. Total lipids were extracted to obtain core GDGTs, which were identified and quantified using liquid chromatography-mass spectrometry (LC-MS). The abundance of isoprenoidal GDGTs ( i GDGTs) ranged from 271.5 to 1266.3 ng/g dry sediment, whereas the branched GDGTs ( b GDGTs), supposedly derived from terrestrial sources, ranged from 22.2 to 56.7 ng/g dry sediment. The TEX 86 -derived sea surface temperatures ranged from 20.9°C in the coast (water depth 〈 160 m) to 27.9 °C offshore (water depth 〉 1000 m). TEX 86 -derived temperatures near shore (〈160 m water depth) averaged 23.1 ± 2.5 °C ( n = 4), which were close to the satellite-derived winter mean sea surface temperature (average 22.6 ± 1.0 °C, n = 4); whereas the TEX 86 -derived temperatures offshore averaged 27.4 ± 0.3 °C ( n = 7) and were consistent with the satellite mean annual sea surface temperature (average 26.8 ± 0.4 °C, n = 7). These results suggest that TEX 86 may record the sea surface mean annual temperature in the open ocean, while it likely records winter sea surface temperature in the shallower water. Graphical abstract Highlights ► Glycerol dialkyl glycerol tetraethers (GDGTs) are determined from the northern South China Sea. ► TEX 86 could record the sea surface mean annual temperature in the open ocean. ► In the shallower water, TEX 86 -derived temperature is likely to present winter sea surface temperature instead of the sea surface mean annual temperature.

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: 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 National Seismographic Network (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 Most Phanerozoic oolites are marked by ooids with a diameter less than 2 mm. Observations on a Neoproterozoic oolite have 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 in both the specific geological period and 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: November 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 6 Holocene environmental change and environmental archaeology are important components of an international project studying the human-earth interaction system. This paper reviews the progress of Holocene environmental change and environmental archaeology research in the Yangtze River Valley over the last three decades, that includes the evolution of large freshwater lakes, Holocene transgression and sea-level changes, Holocene climate change and East Asian monsoon variation, relationship between the rise and fall of primitive civilizations and environmental changes, cultural interruptions and palaeoflood events, as well as relationship between the origin of agriculture and climate change. These research components are underpinned by the dating of lacustrine sediments, stalagmites and peat to establish a chronology of regional environmental and cultural evolution. Interdisciplinary and other environment proxy indicators need to be used in comparative studies of archaeological site formation and natural sedimentary environment in the upper, middle and lower reaches of the Yangtze River Valley. Modern technology such as remote sensing, molecular bioarchaeology, and virtual reality, should be integrated with currently used dating, geochemical, sedimentological, and palaeobotanical methods of analysis in environmental archaeology macro- and micro-studies, so as to provide a greater comprehensive insight into Holocene environmental and cultural interaction and change in the Yangtze River Valley area. Graphical abstract Highlights ► The timing of formation of the modern Taihu Lake and Chaohu Lake inferred to be less than 3–2 kyr BP. ► New evidence not consistent with high sea-level from 7.0 to 5.0 kyr BP. ► Neolithic cultural sequences established in the Yangtze Valley. ► The relationship between early agriculture and climate displays complex patterns.

Description: September 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 5 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: November 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 6 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 N 2 isotherm 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. Graphical abstract 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: Available online 12 November 2012 Publication year: 2012 Source: Geoscience Frontiers 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 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: 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 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 Highlights ► Four genetic settings of charnockite are identified. ► A magmatic variety results from crystallization of hot anhydrous melt. ► The other magmatic variety results from fluid gradients in contact zones. ► A thermally driven metamorphic variety is described at hot intrusion margins. ► Other metamorphic charnockites result from CO 2 dominated dehydration.

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: November 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 6 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 °C. Orthopyroxene-bearing assemblages are characteristic for temperature 800 °C 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 Highlights ► Petrological and experimental study of unique pyroxene-bearing dehydration zone. ► Reaction textures, fluid inclusions, thermobarometry, and experiment at 5.5 kbar and 750 and 800 °C. ► Results suggest interplay of an influx of CO 2 -rich and brine fluids and partial melting.

Description: November 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 6 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 Highlights ► Coal measure of the Ordos Basin as source rocks for both CBM and tight gas. ► Tight gas has typical characteristics of a modified basin-centered gas model. ► CBM is a self-generation-reservoir whereas tight gas is near-generation-reservoir.

Description: Available online 1 November 2012 Publication year: 2012 Source: Geoscience Frontiers 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 paper, 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. 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 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: Available online 17 September 2012 Publication year: 2012 Source: Geoscience Frontiers 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 of 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 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 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: September 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 5 Field and remote sensing studies reveal that Au-bearing quartz ± carbonate lodes in Romite deposit, in the extreme South Eastern Desert of Egypt, are controlled by NNE-striking shear zones that splay from the ca. 660–550 Ma Hamisana Zone. Quartz in releasing bends with sinistral shear geometry and abundant boudinaged quartz-carbonate lodes with serrate ribboned fabrics suggest vein formation throughout a transpressive wrench system. Ubiquitous hydrothermal quartz, carbonate, and subordinate chlorite and sericite within the shear zones and as slivers in veins, indicate that gold deposition and hydrothermal alteration occurred under greenschist facies conditions. The Al (IV) in chlorite indicates a formation temperature of ∼300 °C, comparable with temperatures estimated from arsenopyrite composition for grains intimately associated with gold in quartz veins. The new geological and geochemical data indicate that splays off the Hamisana Zone are potential gold exploration targets. Quartz veins along the high order (2nd or 3rd) structures of this crustal-scale shear zone are favorable targets. In the Romite deposit and in surrounding areas, a Au-As-Cu-Sb-Co-Zn geochemical signature characterizes mineralized zones, and particularly rock chips with 〉1000 ppm As and high contents of Cu, Zn, and Co target the better mineralized areas. The carbonate δ 13 C PDB and δ 18 O SMOW isotope signatures preclude an organic source of the ore fluid, but metamorphic and magmatic sources are still valid candidates. The intense deformation and lack of magmatism in the deposit area argue for metamorphic dewatering of greenstone rocks as the most likely fluid source. The narrow ranges of δ 13 C (−4.6‰ to −3.1‰) and δ 18 O (11.9‰–13.7‰) in carbonate minerals in lodes imply a corresponding uniformity to the ambient temperature and δ 13 C CO 2 ( δ 13 C ΣC ) of the ore fluids. The calculated δ 18 O H 2 O values of 6.9‰–7.9‰ for ore fluids, based on δ 18 O values of vein quartz further suggest a likely metamorphic origin. Graphical abstract Highlights ► Silicified, NNE-SSW shear splays off Hamisana Zone are gold-bearing. ► Morphology and microstructures of vein quartz suggest syn-kinematic formation. ► Au endowment and alteration occurred under greenschist facies conditions. ► Romite gold deposit has a Au-As-Cu-Sb-Co-Zn geochemical signature. ► Stable isotopes of quartz and carbonate suggest a likely metamorphic ore fluid.

Description: September 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 5 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 w (SiO 2 ) spans 38.8%–46.8%. Basalt and gabbro are geochemically similar and are characterized by low w (FeO t ) (10.9%), total alkali w (Na 2 O + K 2 O) = 2.58%) and w (TiO 2 ) (1.17%) 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 suprasubduction 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 Tuerkubantao 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: 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: Available online 21 August 2012 Publication year: 2012 Source: Geoscience Frontiers 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 its 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 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: Available online 4 July 2012 Publication year: 2012 Source: Geoscience Frontiers 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 Highlights ► Youngest detrital zircon in metasedimentary unit is 318 ± 5 Ma. ► Metaigneous unit (261.3 ± 2.7 Ma) inherited from Neoarchean-Paleoproterozoic. ► Hf evidence for ancient crust.

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: Available online 6 September 2012 Publication year: 2012 Source: Geoscience Frontiers 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 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 anorthosites in the Proterozoic may be related to the thermal state of continental crust.

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

Description: November 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 6 To predict the long-term behavior of arsenic (As) in soil profiles, the solid-solution partitioning of As was studied in four paddy soil profiles obtained from agricultural areas in Chengdu Plain, Southwest China. Paddy soil profile samples were collected and soil solution samples were extracted. Total As contents in soil solution and soil solid were analyzed, along with the soil solid phase properties. The As in soil solution was significantly higher in the upper layer (0–20 cm) and had a definite tendency to decrease towards 40 cm regardless of the sampling locations. When the concentration of arsenic in soil solution decreased, its content in solid phase increased. Field-based partition coefficient ( K d ) for As was determined by calculating the ratio of the amount of As in the soil solid phase to the As concentration in the soil solution. K d values varied widely in vertical samples and correlated well with soil pH, total organic carbon (TOC) and total As. The results of this study would be useful for evaluating the accumulation trends of arsenic in soil profiles and in improving the management of the agricultural soils. Graphical abstract Highlights ► Arsenic (As) in soil solution is significantly high in the upper 20 cm layer. ► Concomitant increase of As in solid phase with decrease in soil solution. ► Partition coefficient varies widely, but correlates well with soil pH, TOC and total As.

Description: September 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 5 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 Triassic sediments in the study area underwent a rapid erosion and burial in a proximal slope-basin environment by the petrographic data, while the published flow directions of Triassic turbidites in the Aba-Zoige region was 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 Highlights ▶ Old upper continental crust provenance dominated by tonalitic rocks. ▶ Late Triassic sediments deposited in a back-arc basin. ▶ The Kunlun-Qinling terrane supplied source materials to the northeast part of the Songpan-Ganzi Basin.

Description: September 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 5 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: 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: September 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 5 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: September 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 5 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: July 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 4 Steady decline in the percentage of 235 U in terrestrial uranium made natural fission impossible after about 1.8 Ga. Fission before 1.8 Ga disturbed the lead isotope system at various places worldwide, such as Oklo, Gabon, and may have caused the first lead isotope paradox. Fission in areas of high uranium concentration may also have generated enough heat to localize sparse Archean and Paleoproterozoic UHT belts. The oldest widespread orogenic systems formed at approximately 2.0–1.8 Ga after fission stopped contributing to the earth’s heat flow. These early orogenic systems partly created the supercontinent Columbia. Graphical abstract Highlights ► Natural fission of 235 U was a significant source of heat in the earth before about 2 Ga. ► Fission developed depleted Archean lower crust that now has a low heat generation. ► The lower crust is an inaccessible depleted reservoir that accounts for the first lead isotope paradox. ► The earth was cool enough by 2.0–1.8 Ga that widespread networks of orogenic belts could develop. ► Networks of orogenic belts at 1.8 Ga partly generated the supercontinent Columbia.

Description: Available online 1 August 2012 Publication year: 2012 Source: Geoscience Frontiers Six national-scale, or near national-scale, geochemical data sets for soils or stream sediments exist for the United States. The earliest of these, here termed the ‘Shacklette’ data set, was generated by a U.S. Geological Survey (USGS) project conducted from 1961 to 1975. This project used soil collected from a depth of about 20 cm as the sampling medium at 1323 sites throughout the conterminous U.S. The National Uranium Resource Evaluation Hydrogeochemical and Stream Sediment Reconnaissance (NURE-HSSR) Program of the U.S. Department of Energy was conducted from 1975 to 1984 and collected either stream sediments, lake sediments, or soils at more than 378,000 sites in both the conterminous U.S. and Alaska. The sampled area represented about 65% of the nation. The Natural Resources Conservation Service (NRCS), from 1978 to 1982, collected samples from multiple soil horizons at sites within the major crop-growing regions of the conterminous U.S. This data set contains analyses of more than 3000 samples. The National Geochemical Survey, a USGS project conducted from 1997 to 2009, used a subset of the NURE-HSSR archival samples as its starting point and then collected primarily stream sediments, with occasional soils, in the parts of the U.S. not covered by the NURE-HSSR Program. This data set contains chemical analyses for more than 70,000 samples. The USGS, in collaboration with the Mexican Geological Survey and the Geological Survey of Canada, initiated soil sampling for the North American Soil Geochemical Landscapes Project in 2007. Sampling of three horizons or depths at more than 4800 sites in the U.S. was completed in 2010, and chemical analyses are currently ongoing. The NRCS initiated a project in the 1990s to analyze the various soil horizons from selected pedons throughout the U.S. This data set currently contains data from more than 1400 sites. This paper (1) discusses each data set in terms of its purpose, sample collection protocols, and analytical methods; and (2) evaluates each data set in terms of its appropriateness as a national-scale geochemical database and its usefulness for national-scale geochemical mapping. Graphical abstract Highlights ► Six national-scale geochemical data sets (soils and sediments) for the conterminous United States. ► Each data set summarized in terms of purpose, sample collection protocols, and analytical methods. ► Each data set evaluated in terms of its strengths and weaknesses for geochemical mapping.

Description: Available online 14 August 2012 Publication year: 2012 Source: Geoscience Frontiers A study on the effect of the solar ultra-violet radiation on the human skin fibroblast cells revealed that the production of matrix metalloproteinase-2 was inhibited by the radiation. A CO 2 incubator connected by optical fibers to a reflector telescope for collecting the solar light was built at Syowa station by the 49th Japanese Antarctica Research Expedition. The direction of the telescope was continuously controlled by a sun-tracker to follow the movement of the Sun automatically. The intensity of the collected light was monitored by a portable spectrophotometer housed inside. The human skin fibroblast cells were incubated in the CO 2 chamber to investigate the effect of the solar radiation at Syowa station and were compared with those reference experiments at a laboratory in Japan. The results showed cell damage by strong UV radiation. The production of matrix metalloproteinase-2 was prompted by the moderate UV-B, but was inhibited by the strong UV-B radiation, as studied under laboratory conditions in Japan. The effect of strong solar radiation at Syowa station involving the radiation of UV-B region was estimated to be of the same extent of the radiation caused by an artificial UV-B light with the intensity more than 50 mJ/cm 2 . Graphical abstract Highlights ► The effect of solar ultra-violet radiation in Antarctica on the human skin fibroblast was studied. ► The direction of the telescope was continuously controlled by a sun-tracker to follow the Sun. ► The production of MMP-2 was prompted by the moderate UV-B, but inhibited by the strong UV-B radiation.

Description: Available online 9 August 2012 Publication year: 2012 Source: Geoscience Frontiers In more than 4 Ga of geological evolution, the Earth has twice gone through extreme climatic perturbations, when extensive glaciations occurred, together with alternating warm periods which were accompanied by atmospheric oxygenation. The younger of these two episodes of climatic oscillation preceded the Cambrian “explosion” of metazoan life forms, but similar extreme climatic conditions existed between about 2.4 and 2.2 Ga. Over long time periods, changing solar luminosity and mantle temperatures have played important roles in regulating Earth's climate but both periods of climatic upheaval are associated with supercontinents. Enhanced weathering on the orogenically and thermally buoyed supercontinents would have stripped CO 2 from the atmosphere, initiating a cooling trend that resulted in continental glaciation. Ice cover prevented weathering so that CO 2 built up once more, causing collapse of the ice sheets and ushering in a warm climatic episode. This negative feedback loop provides a plausible explanation for multiple glaciations of the Early and Late Proterozoic, and their intimate association with sedimentary rocks formed in warm climates. Between each glacial cycle nutrients were flushed into world oceans, stimulating photosynthetic activity and causing oxygenation of the atmosphere. Accommodation for many ancient glacial deposits was provided by rifting but escape from the climatic cycle was predicated on break-up of the supercontinent, when flooded continental margins had a moderating influence on weathering. The geochemistry of Neoproterozoic cap carbonates carries a strong hydrothermal signal, suggesting that they precipitated from deep sea waters, overturned and spilled onto continental shelves at the termination of glaciations. Paleoproterozoic (Huronian) carbonates of the Espanola Formation were probably formed as a result of ponding and evaporation in a hydrothermally influenced, restricted rift setting. Why did metazoan evolution not take off after the Great Oxidation Event of the Paleoproterozoic? The answer may lie in the huge scar left by the ∼2023 Ma Vredefort impact in South Africa, and in the worldwide organic carbon-rich deposits of the Shunga Event, attesting to the near-extirpation of life and possible radical alteration of the course of Earth history. Graphical abstract Highlights ► Two great climatic oscillation periods affected the Earth near the beginning and end of the Proterozoic. ► Glaciations were caused by drawdown of CO 2 on supercontinents, and ended with breakup. ► Oxygenation occurred twice but first attempts at higher evolution were ended by the Vredefort impact.

Description: Available online 16 December 2012 Publication year: 2012 Source: Geoscience Frontiers We present relative sea level (RSL) curves in Antarctica derived from glacial isostatic adjustment (GIA) predictions based on the melting scenarios of the Antarctic ice sheet since the Last Glacial Maximum (LGM) given in previous works. Simultaneously, Holocene-age RSL observations obtained at the raised beaches along the coast of Antarctica are shown to be in agreement with the GIA predictions. The differences from previously published ice loading models regarding the spatial distribution and total mass change of the melted ice are significant. These models were also derived from GIA modelling; the variations can be attributed to the lack of geological and geographical evidence regarding the history of crustal movement due to ice sheet evolution. Next, we summarise the previously published ice load models and demonstrate the RSL curves based on combinations of different ice and earth models. The RSL curves calculated by GIA models indicate that the model dependence of both the ice and earth models is significantly large at several sites where RSL observations were obtained. In particular, GIA predictions based on the thin lithospheric thickness show the spatial distributions that are dependent on the melted ice thickness at each sites. These characteristics result from the short-wavelength deformation of the Earth. However, our predictions strongly suggest that it is possible to find the average ice model despite the use of the different models of lithospheric thickness. By sea level and crustal movement observations, we can deduce the geometry of the post-LGM ice sheets in detail and remove the GIA contribution from the crustal deformation and gravity change observed by space geodetic techniques, such as GPS and GRACE, for the estimation of the Antarctic ice mass change associated with recent global warming. Graphical abstract Highlights ► Relative sea level curves based on the glacial isostatic adjustment modelling. ► Evaluation of dependence on ice melting models suggested by previous works. ► Relative sea-levels at 7 cal. kyr BP strongly dependent on the adopted models.

Description: November 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 6 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 Highlights ► Four genetic settings of charnockite are identified. ► A magmatic variety results from crystallization of hot anhydrous melt. ► The other magmatic variety results from fluid gradients in contact zones. ► A thermally driven metamorphic variety is described at hot intrusion margins. ► Other metamorphic charnockites result from CO 2 dominated dehydration.

Description: Available online 6 September 2012 Publication year: 2012 Source: Geoscience Frontiers 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 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 anorthosites in the Proterozoic may be related to the thermal state of continental crust.

Description: Available online 27 September 2012 Publication year: 2012 Source: Geoscience Frontiers 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 in NCKFMASHTO system demonstrated that Spr + Qtz stability is lowered down to 930 °C due to small Fe 3+ contents in the rocks (mole Fe 2 O 3 /(FeO + Fe 2 O 3 ) = 0.02). The TI sample yields a peak p - T range of 950–1100 °C and 7.5–11 kbar, followed by cooling toward a retrograde stage of 800–950 °C and 8–10 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 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: September 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 5 This paper attempts to review the descriptions on the genetic series of neotectonic forms in Eurasia. Morphotectonically, the Eurasian continental block exhibits a radial-concentric pattern consisting of four kinds of tectonic units: platforms, rejuvenated and youthful mobile belts, and the continent-ocean transition zones. Vast areas of young and ancient platforms, such as Siberia, have experienced slow-rate Late-Cenozoic uplift and little interior deformation. The youthful orogenic belts are clustered into the giant Alpine-Himalayan megabelt. The rejuvenated mountain belts are characterized by a variety of structural-morphological types of orogens, such as domelike uplifts, block uplifts and intermountain basins. The continent-ocean transition zones in Eastern Asia, including marginal rifts and extensional basins, are resulted from interaction between the continental block and Pacific Ocean and Philippine Sea since the Late Cenozoic. One of the conspicuous features of Eurasia is that most areas lie in the largest geoid depression of the Earth, and the NS trending Uralian-Oman lineament expresses a break on the geoid slope, implying a relationship to deep structure, including density inhomogeneities, downward to the core-mantle interface. Besides, the Eurasian continent fully demonstrates morphotectonic and recent geodynamic features of the Northern Hemisphere of the Earth, just in contrast to that of the Southern Hemisphere. It is best to view the surface morphotectonics and deep structure of the Earth as a geodynamic ensemble which has spawned the large-scale geomorphic features on the surface. Graphical abstract Highlights ► Morphotectonic structure of the Eurasian continental block characterized. ► Radial-concentric pattern of basic morphotectonics elements identified. ► Tectonic landforms and deep structure are combined into stable paragenesis.

Description: Available online 1 November 2012 Publication year: 2012 Source: Geoscience Frontiers 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 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: September 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 5 Field and remote sensing studies reveal that Au-bearing quartz ± carbonate lodes in Romite deposit, in the extreme South Eastern Desert of Egypt, are controlled by NNE-striking shear zones that splay from the ca. 660–550 Ma Hamisana Zone. Quartz in releasing bends with sinistral shear geometry and abundant boudinaged quartz-carbonate lodes with serrate ribboned fabrics suggest vein formation throughout a transpressive wrench system. Ubiquitous hydrothermal quartz, carbonate, and subordinate chlorite and sericite within the shear zones and as slivers in veins, indicate that gold deposition and hydrothermal alteration occurred under greenschist facies conditions. The Al (IV) in chlorite indicates a formation temperature of ∼300 °C, comparable with temperatures estimated from arsenopyrite composition for grains intimately associated with gold in quartz veins. The new geological and geochemical data indicate that splays off the Hamisana Zone are potential gold exploration targets. Quartz veins along the high order (2nd or 3rd) structures of this crustal-scale shear zone are favorable targets. In the Romite deposit and in surrounding areas, a Au-As-Cu-Sb-Co-Zn geochemical signature characterizes mineralized zones, and particularly rock chips with 〉1000 ppm As and high contents of Cu, Zn, and Co target the better mineralized areas. The carbonate δ 13 C PDB and δ 18 O SMOW isotope signatures preclude an organic source of the ore fluid, but metamorphic and magmatic sources are still valid candidates. The intense deformation and lack of magmatism in the deposit area argue for metamorphic dewatering of greenstone rocks as the most likely fluid source. The narrow ranges of δ 13 C (−4.6‰ to −3.1‰) and δ 18 O (11.9‰–13.7‰) in carbonate minerals in lodes imply a corresponding uniformity to the ambient temperature and δ 13 C CO 2 ( δ 13 C ΣC ) of the ore fluids. The calculated δ 18 O H 2 O values of 6.9‰–7.9‰ for ore fluids, based on δ 18 O values of vein quartz further suggest a likely metamorphic origin. Graphical abstract Highlights ► Silicified, NNE-SSW shear splays off Hamisana Zone are gold-bearing. ► Morphology and microstructures of vein quartz suggest syn-kinematic formation. ► Au endowment and alteration occurred under greenschist facies conditions. ► Romite gold deposit has a Au-As-Cu-Sb-Co-Zn geochemical signature. ► Stable isotopes of quartz and carbonate suggest a likely metamorphic ore fluid.

Description: September 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 5 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: September 2012 Publication year: 2012 Source: Geoscience Frontiers, Volume 3, Issue 5 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.