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Abstract:The Sinuiju Formation in Paekto-dong, Sinuiju City in the Democratic People’s Republic of Korea has yielded Mesozoic nonmarine bivalve fossils, which is the first occurrence of such in the DPRK. Based on these fossil specimens, a new Cretaceous bivalve assemblage, the Arguniella yanshanensis-Sphaerium anderssoni Assemblage is erected. This assemblage includes Arguniella yanshanensis, A. lingyuanensis and Sphaerium anderssoni and can be compared with the Jehol Biota. The age of the Sinuiju Formation is also clarified and on the basis of the bivalves and the presence of a Eosestheria–Ephemeropsis–Lycoptera (E–E–L) assemblage, the formation is not Upper Jurassic, but Lower Cretaceous in age.

Abstract:Transpressional deformation has played an important role in the late Neoproterozoic evolution of the Arabian-Nubian Shield including the Central Eastern Desert of Egypt. The Ghadir Shear Belt is a 35 km-long, NW-oriented brittle-ductile shear zone that underwent overall sinistral transpression during the Late Neoproterozoic. Within this shear belt, strain is highly partitioned into shortening, oblique, extensional and strike-slip structures at multiple scales. Moreover, strain partitioning is heterogeneous along-strike giving rise to three distinct structural domains. In the East Ghadir and Ambaut shear belts, the strain is pure-shear dominated whereas the narrow sectors parallel to the shear walls in the West Ghadir Shear Zone are simple-shear dominated. These domains are comparable to splay-dominated and thrust-dominated strike-slip shear zones. The kinematic transition along the Ghadir shear belt is consistent with separate strike-slip and thrust-sense shear zones. The earlier fabric (S1), is locally recognized in low strain areas and SW-ward thrusts. S2 is associated with a shallowly plunging stretching lineation (L2), and defines ~NW-SE major upright macroscopic folds in the East Ghadir shear belt. F2 folds are superimposed by ~NNW–SSE tight-minor and major F3 folds that are kinematically compatible with sinistral transpressional deformation along the West Ghadir Shear Zone and may represent strain partitioning during deformation. F2 and F3 folds are superimposed by ENE–WSW gentle F4 folds in the Ambaut shear belt. The sub-parallelism of F3 and F4 fold axes with the shear zones may have resulted from strain partitioning associated with simple shear deformation along narrow mylonite zones and pure shear-dominant deformation in fold zones. Dextral ENE-striking shear zones were subsequently active at ca. 595 Ma, coeval with sinistral shearing along NW- to NNW-striking shear zones. The occurrence of upright folds and folds with vertical axes suggests that transpression plays a significant role in the tectonic evolution of the Ghadir shear belt. Oblique convergence may have been provoked by the buckling of the Hafafit gneiss-cored domes and relative rotations between its segments. Upright folds, fold with vertical axes and sinistral strike-slip shear zones developed in response to strain partitioning. The West Ghadir Shear Zone contains thrusts and strike-slip shear zones that resulted from lateral escape tectonics associated with lateral imbrication and transpression in response to oblique squeezing of the Arabian-Nubian Shield during agglutination of East and West Gondwana.

Abstract:This study provides an integrated interpretation for the Mesozoic - Cenozoic tectonothermal evolutionary history of the Permian strata in the Qishan area of the southwestern Weibei Uplift, Ordos Basin. Apatite fission-track and apatite/zircon (U-Th)/He thermochronometry, bitumen reflectance, thermal conductivity of rocks, paleotemperature recovery, and basin modeling were used to restore the Meso-Cenozoic tectonothermal history of the Permian Strata. The Triassic AFT data have a pooled age of ~180±7 Ma with one age peak and P(χ2)=86%. The average value of corrected apatite (U-Th)/He age of two Permian sandstones is ~168±4 Ma and a zircon (U-Th)/He age from the Cambrian strata is ~231±14 Ma. Bitumen reflectance and maximum paleotemperature of two Ordovician mudstones are 1.81%, 1.57% and ~210°C, ~196°C respectively. After undergoing a rapid subsidence and increasing temperature in Triassic influenced by intrusive rocks in some areas, the Permian strata experienced four cooling-uplift stages after the time when the maximum paleotemperature reached in late Jurassic: (1) A cooling stage (~163 Ma to ~140 Ma) with temperatures ranging from ~132°C to ~53°C and a cooling rate of ~3°C/Ma, an erosion thickness of ~1900 m and an uplift rate of ~82 m/Ma; (2) A cooling stage (~140 Ma to ~52 Ma) with temperatures ranging from ~53°C to ~47°C and a cooling rate less than ~0.1°C /Ma, an erosion thickness of ~300 m and an uplift rate of ~3 m/Ma; (3) (~52 Ma to ~8 Ma) with ~47°C to ~43°C and ~0.1°C /Ma, an erosion thickness of ~500 m and an uplift rate of ~11 m/Ma; (3) (~8 Ma to present ) with ~43°C to ~20°C and ~3°C/Ma, an erosion thickness of ~650 m and an uplift rate of ~81 m/Ma. The tectonothermal evolutionary history of the Qishan area in Triassic was influenced by the interaction of the Qinling Orogeny and the Weibei Uplift, and the south Qishan area had the earliest uplift-cooling time compared to other parts within the Weibei Uplift. The early Eocene at ~52 Ma and the late Miocene at ~8 Ma, as two significant turning points after which both the rate of uplift and the rate of temperature changed rapidly, were two key time for the uplift-cooling history of the Permian strata in the Qishan area of the southwestern Weibei Uplift, Ordos Basin.

Abstract:Fracture prediction is a technical issue in the field of petroleum exploration and production worldwide. Although there are many approaches to predict the distribution of cracks underground, these approaches have some limitations. To resolve these issues, we ascertained the relation between numerical simulations of tectonic stress and the predicted distribution of fractures from the perspective of geologic genesis, based on the characteristics of the shale reservoir in the Longmaxi Formation in Dingshan; the features of fracture development in this reservoir were considered. 3D finite element method (FEM) was applied in combination with rock mechanical parameters derived from the acoustic emissions. The paleotectonic stress field of the crack formation period was simulated for the Longmaxi Formation in the Dingshan area. The splitting factor in the study area was calculated based on the rock breaking criterion. The coefficient of fracture development was selected as the quantitative prediction classification criteria for the cracks. The results show that a higher coefficient of fracture development indicates a greater degree of fracture development. On the basis of the fracture development coefficient classification, a favorable area was identified for the development of fracture prediction in the study area. The prediction results indicat

Abstract:Xuanwei Formation is composed of mudstone, siltstone, and sandstone, with local conglomerate. However, its provenance and tectonic setting have been scarcely studied. In this paper, we use sedimentology, electron probe microanalysis (EPMA), and detrital zircon dating to investigate its source area and depositional tectonic setting. The facies assemblages indicate that it formed in alluvial fan and fluvial river sedimentary environments. The strata thicknesses and facies distribution indicate that the sediment supply was from the west. The results of EPMA show that chromian spinels within the sediments are characterized by high Cr# and varying Mg#. Discrimination plots suggest that these spinels were sourced from large igneous province (LIP) magmatic rocks. The laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb chronology of detrital zircons suggests that the sediments were derived from intermediate–acid igneous rocks dating back to 251–260?Ma. We could, therefore, conclude that the provenance of the Xuanwei Formation is from Emeishan basalt and synchronous felsic igneous rocks, which is consistent with the composition of the detrital framework. The detrital zircon dates also suggest that felsic magmatism occurred during the Late Permian, not after the eruption of the Emeishan basalt. Based on the sedimentary successions and provenance analysis, the tectonic setting for Xuanwei Formation deposition was a volcanic rifted margin.

Abstract:The depositional and metamorphic ages and provenances of the Ailaoshan (ALS) Group in the Ailaoshan-Red River (ALS-RR) shear zone, southwestern South China Block (SCB), were investigated to constrain the tectonic history of the southwestern SCB. In this study, we use petrology, geochemical analysis, zircon cathodoluminescence imaging and U-Pb geochronology to analyse samples of quartzite, garnet-bearing two-mica schist and metapelite. The age spectra of detrital zircon grains from these metasediments show two dominant age peaks at 550–424 Ma and 876–730 Ma and two subordinate peaks at 970–955 Ma and ~2450 Ma. The youngest peak, corresponding to the early Palaeozoic, accounts for more than 20% of the total dates and constrains the deposition of the ALS Group to the Palaeozoic rather than the Palaeoproterozoic as traditionally thought. Moreover, two peaks of metamorphic ages corresponding to the Permo-Triassic and Cenozoic were also identified, and these ages document the tectonothermal events associated with the Indosinian collision between the Indochina Block and the SCB and the Himalayan collision between the Indian and Asian plates. Geochemical data suggest that the provenances of the ALS Group were dominated by continental arc and recycled metasedimentary rocks. The comparison of probability density distribution plots of the detrital zircon U-Pb age data indicates that the Neoproterozoic?detritus in the ALS Group was probably derived from the arc-related Neoproterozoic intrusive bodies in the northwestern and southwestern SCB. Furthermore, the early Palaeozoic detritus might have been sourced from eroded early Palaeozoic strata and magmatic plutons in Cathaysia and volcanic rocks in the western Indochina Block.

Abstract:The precise seismic substructural interpretation of the Turkwal oil field in the Central Potwar region of district Chakwal of Pakistan has been carried out. The research work was confined to the large fore-thrust that serves as an anticlinal structural trap through ten 2D seismic lines. A precise seismic substructural model of the Eocene Chorgali Limestone with precise orientation of thrust and oblique slip faults shows the presence of a huge fracture, which made this deposit a good reservoir. The abrupt surface changes in dip azimuth for the Eocene Chorgali Limestone verifies the structural trends and also the presence of structural traps in the Turkwal field. The logs of three wells (Turkwal deep X-2, Turkwal-01 and Fimkassar-01) were analyzed for petrophysical studies, well synthetic results and generation of an Amplitude Versus Offset (AVO) model for the area. The AVO model of Turkwal deep X-2 shows abrupt changes in amplitude, which depicts the presence of hydrocarbon content. Well correlation technique was used to define the overall stratigraphic setting and the thickness of the reservoir formation in two wells, Turkwal-01 and Turkwal deep X-2. The Eocene Chorgali Limestone in Turkwal-01 is an upward thrusted anticlinal structure and because of the close position of both wells to the faulted anticlinal structure, its lesser thickness differs compared to Turkwal deep X-2. The overall results confirm that the Turkwal field is comparable to several similar thrust-bound oil-bearing structures in the Potwar basin.

Abstract:Zircon dating, geochemical and Nd-Sr isotopic analyses have been determined for samples from two granitic intrusions in the Talate mining district, Chinese Altay. Our data suggest that these intrusions were emplaced from 462.5 Ma to 457.8 Ma. These rocks have strong affinity to peralumious S-type granite and are characterized by prominent negative Eu anomalies (δEu=0.20–0.35), strong depletion in Ba, Sr, P, Ti, Nb, Ta and positive anomalies in Rb, Th, U, K, La, Nd, Zr, Hf. Nd-Sr isotopic compositions of the whole rock show negative εNd(t) values (?1.21 to ?0.08) and Mesoproterozoic Nd model ages (T2DM=1.20–1.30 Ga). Their precursor magmas were likely derived from the partial dehydration melting of Mesoproterozoic mica-rich pelitic sources and mixed with minor mantle-derived components, under relatively low P (≤1 kbar) and high T (746–796°C) conditions. A ridge subduction model may account for the early Paleozoic geodynamic process with mantle-derived magmas caused by Ordovician ridge subduction and the opening of a slab window underplated and/or intraplated in the middle–upper crust, which triggered extensive partial melting of the shallow crust to generate diverse igneous rocks, and provided the heat for the crustal melting and juvenile materials for crustal growth.

Abstract:Precambrian banded iron formation (BIF) is one of the most important mineral resources in China, mostly abundant in the North China Craton (NCC) with relatively less common in South China. Since the BIF and siliceous rocks both originated from chemical deposition, the syngenetic BIF and Siliceous rocks can help evaluate their environment of formation. We examine here the mineralogy and geochemistry of siliceous rocks associated with the Tieshanmiao Formation BIF, aiming to decipher the conditions of formation of both BIF and Siliceous rocks in the Wuyang area in the NCC. Analysis of the geochemical characteristics of whole rock shows that the SiO2 content of the siliceous rock ranges from 90.11% to 94.85% and is relatively high overall. Trace element contents of Ba and U are also high, the Ba/Sr ratio ranges from 3.89 to 25.28 and the U/Th ratio ranges from 0.09 to 0.20. Finally, the ΣREE value of rare earth elements ranges from 57.03 ppm to 152.59 ppm, and these indexes all indicate that siliceous rock resulted from hydrothermal deposition. Plots of Al2O3-SiO2, SiO2/(K2O+Na2O)-MnO2/TiO2 and Mn-10×(Cu+Co+Ni)-Fe in discrimination diagrams also verify this interpretation. However, both the MgO content, ranging from 0.16 to 0.32, and the Fe/Ti ratio, ranging from 2.50 to 9.72, suggest that terrigenous material was added during the depositional process. Major and trace element parameters of siliceous rock, such as the Al/(A1+Fe+Mn) ratio (from 0.81 to 0.93), MnO/TiO2 (from 0.00 to 0.17), Al/(Al+Fe) (from 0.82 to 0.93), Sc/Th ratio (from 0.21 to 0.50), U/Th (from 0.09 to 0.20), (La/Yb)N (from 0.83 to 3.04), and the (La/Ce)N (from 0.01 to 0.02) all imply that the siliceous rock formed in a continental margin. In addition, the Sr/Ba ratio from 0.08 to 0.26, the δCe value from 0.31 to 0.90, and the δEu value from 0.14 to 0.58, all indicate that the siliceous rock was formed at a relatively deeper water depth and under weak hydrodynamic conditions. Siliceous rock and BIF formed in the same geological setting, with the SiO2/(K2O+Na2O) ratio of siliceous rock ranging from 28.61 to 47.43, the SiO2/Al2O3 ratio from 16.53 to 32.37, and the SiO2/MgO ratio from 287.28 to 592.81, which are all in agreement with chemical deposition associated with volcanic eruptions. The Al2O3/TiO2 ratio from 37.82 to 50.30 indicates that the magma source of siliceous rock was of slightly intermediate composition. During the Late Archean in the Wuyang area, the high concentration and high purity SiO2 quickly precipitated from hydrothermal fluids to finally result in the accumulation of siliceous rock in a marginal sea, while the input corresponding to iron formation components was deposited to form iron formation layers, and limestone was only the product formed during the deposition intervals of siliceous rock and iron formations. In this study, the synsedimentary siliceous rocks of BIF act as a new way to provide direct evidence to understand the formation environment of BIF due to its high geochemical stability.

Abstract:The Tafresh granitoids are located at the central part of the Urumieh-Dokhtar Magmatic Arc (UDMA) in Iran. These rocks, mainly consisting of diorite and granodiorite, were emplaced during the Early Miocene. They are composed of varying proportions of plagioclase + K-feldspar + hornblende ± quartz ± biotite. Discrimination diagrams and chemical indices of amphibole phases reveal a calc-alkaline affinity and fall clearly in the crust-mantle mixed source field. The estimated pressure, derived from Al in amphibole barometry, is approximately 3 Kb. The granitoids are I-type, metaluminous and belong to the calc-alkaline series. They are all enriched in light rare earth elements and large ion lithophile elements, depleted in high field strength elements and display geochemical features typical of subduction-related calc-alkaline arc magmas. Most crystal size distribution (CSD) line patterns from the granitoids show a non-straight trend which points to the effect of physical processes during petrogenesis?. The presence of numerous mafic enclaves, sieve texture and oscillatory zoning along with the CSD ?results show that magma mixing in the magma chamber had an important role in the petrogenesis of Tafresh granitoids. Moreover, the CSD analysis suggests that the plagioclase crystals were crystallized in a time span of less than 1000 years, which is indicative of shallow depth magma crystallization.

Abstract:Compared to other Mo provinces, few studies focused on the South China Mo Province (SCMP), especially for Early Cretaceous Mo mineralization. The Lufeng porphyry Mo deposit in the SCMP is characterized by disseminated and veinlet-type mineralization in granite porphyry, gneiss, and rhyolite. In this study, six molybdenite samples yield a Re–Os isochron age of 108.0±1.8 Ma, which is consistent with the zircon U–Pb age of the granite porphyry (108.4±0.8 Ma). The coincidence of magmatic and hydrothermal activities indicates that Mo mineralization was associated with the intrusion of granite porphyry during the late Early Cretaceous. A compilation of U–Pb and Re–Os chronological data suggests that an extensive and intensive Mo mineralization event occurred in the SCMP during the late Early Cretaceous. The marked difference in molybdenite Re contents between Cu-bearing (85–536 ppm) and Cu-barren (1.3–59 ppm) Mo deposits of the late Early Cretaceous indicates that the ore-forming materials were derived from strong crust–mantle interactions. Together with regional petrological and geochemical data, this study suggests that late Early Cretaceous Mo mineralization in the SCMP occurred in an extensional setting associated with the roll-back of the Paleo-Pacific slab.

Abstract:Detailed studies on U-Pb ages and Hf isotope have been carried out in zircons from a carbonatite dyke associated with the Bayan Obo giant REE-Nb-Fe deposit, northern margin of the North China Craton (NCC), which provide insights into the plate tectonic in Paleoproterozoic. Analyses of small amounts of zircons extracted from a large sample of the Wu carbonatite dyke have yielded two ages of late Archaean and late Paleoproterozoic (with mean 207Pb/206Pb ages of 2521±25 Ma and 1921±14 Ma, respectively). Mineral inclusions in the zircon identified by Raman spectroscopy are all silicate minerals, and none of the zircon grains has the extremely high Th/U characteristic of carbonatite, which are consistent with crystallization of the zircon from silicate, and the zircon is suggested to be derived from trapped basement complex. Hf isotopes in the zircon from the studied carbonatite are different from grain to grain, suggesting the zircons were not all formed in one single process. Majority of εHf(t) values are compatible with ancient crustal sources with limited juvenile component. The Hf data and their TDM2 values also suggest a juvenile continental growth in Paleoproterozoic during the period of 1940–1957 Ma. Our data demonstrate the major crustal growth during the Paleoproterozoic in the northern margin of the NCC, coeval with the assembly of the supercontinent Columbia, and provide insights into the plate tectonic of the NCC in Paleoproterozoic.

Abstract:The Sanshandao Au deposit is located in the famous Sanshandao metallogenic belt, Jiaodong area. To date, accumulative Au resources of 1000 t have been identified from the belt. Sanshandao is a world-class gold deposit with Au mineralization hosted in Early Cretaceous Guojialing-type granites. Thus, studies on the genesis and ore-forming element sources of the Sanshandao Au deposit are crucial. He and Ar isotopic analyses of fluid inclusions from pyrite (the carrier of Au) indicate that the fluid inclusions have 3He/4He=0.043–0.21 Ra with an average of 0.096 Ra and 40Ar/36Ar=488–664 with an average of 570.8. These values represent the initial He and Ar isotopic compositions of ore-forming fluids for trapped fluid inclusions. The comparison of H–O isotopic characteristics combined with deposit geology and wall rock alteration reveals that the ore-forming fluids of the Sanshandao Au deposit show mixed crust–mantle origin characteristics, and they mainly comprise crust-derived fluid mixed with minor mantle-derived fluid and meteoric water during the uprising process. The ore-forming elements were generally sourced from pre-Cambrian meta-basement rocks formed by Mesozoic reactivation and mixed with minor shallow crustal and mantle components.

Abstract:The multiscale transport mechanism of methane in unconventional reservoirs is dominated by slip and transition flows resulting from the ultra-low permeability of micro/nano-scale pores, which requires consideration of the microscale and rarefaction effects. Traditional continuum-based computational fluid dynamics (CFD) becomes problematic when modeling micro-gaseous flow in these multiscale pore networks because of its disadvantages in the treatment of cases with a complicated boundary. As an alternative, the lattice Boltzmann method (LBM), a special discrete form of the Boltzmann equation, has been widely applied to model the multi-scale and multi-mechanism flows in unconventional reservoirs, considering its mesoscopic nature and advantages in simulating gas flows in complex porous media. Consequently, numerous LBM models and slip boundary schemes have been proposed and reported in the literature. This study investigates the predominately reported LBM models and kinetic boundary schemes. The results of these LBM models systematically compare to existing experimental results, analytical solutions of Navier-Stokes, solutions of the Boltzmann equation, direct simulation of Monte Carlo (DSMC) and information-preservation DSMC (IP_DSMC) results, as well as the numerical results of the linearized Boltzmann equation by the discrete velocity method (DVM). The results point out the challenges and limitations of existing multiple-relaxation-times LBM models in predicting micro-gaseous flow in unconventional reservoirs.

Abstract:The Ordos Basin, as the second largest petroliferous basin of China, contains abundant oil and gas resources, oil shale, and sandstone-type uranium mineral resources. Chang 7 shale is not only the major source rock of the Mesozoic petroliferous system of the Basin, but is also crucial in determining the space-time distribution relationship of the shale section for the effective exploration and development of the Basin’s oil and gas resources. To obtain a highly precise age of the shale development section, we collected tuff samples from the top and bottom profile of the Chang 7 Member, Yishi Village, Yaoqu Town, Tongchuan District, on the southern margin of the Ordos Basin and performed high-precision chemical abrasion (CA)–isotope dilution (ID)–thermal ionization mass spectrometry (TIMS) zircon U-Pb dating on the basis of extensive laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U-Pb dating data. Our results show the precise ages of the top and bottom zircon in the Chang 7 shale to be 241.06±0.12 Ma and 241.558±0.093 Ma, respectively. We first obtained Chang 7 age data with Grade 0.1-Ma precision and then determined the age of the shale development in the Chang 7 Member to be the early-Middle Triassic Ladinian. This result is supported by paleontological evidence. The deposition duration of the Chang 7 shale is 0.5Ma with an average deposition rate of the shale section being 5.3 cm/ka. Our research results provide time scale and basic data for further investigation of the basin–mountain coupling relation of the shale section, the sedimentary environment and volcanic ash and organic-matter-rich shale development relation, and the organism break-out and organic-matter enrichment mechanism.

Abstract:Petrographic and geochemical characteristics of the Upper Triassic sandstones in the western Ordos Basin were studied to provide insight into weathering characteristics, provenance, and tectonic implications. Petrographic features show that the sandstones are characterized by low-medium compositional maturity and textural maturity. The CIA and CIW values reveal weak and moderate weathering history in the source area. The geochemical characteristics together with palaeocurrent data show that the northwestern sediments were mainly derived from the Alxa Block with a typical recycled nature, while the provenance of the western and southwestern sediments were mainly from the Qinling-Qilian Orogenic Belt. The tectonic setting discrimination diagrams signify that the parent rocks of sandstones in the western and southern Ordos Basin were mainly developed from continental island arc, which is closely related to the evolution of the Qinling-Qilian Orogenic Belt. However, the sandstones in the northwestern Ordos Basin show complex features, which may be resulted from a typical recycling process. Overall evidence from petrography, geochemistry and sedimentology, together with previous researches suggest the Kongtongshan and Helanshan areas were the southwestern and northwestern boundary of the Ordos Basin, respectively, and there was no clear boundary between the Hexi Corridor Belt and Ordos Basin, where a large, uniform sediment dispersal system developed during the Late Triassic.

Abstract:The Triassic strata in the Turpan-Hami Basin potentially chronicled the missing sedimentary record of Indosinian tectonic evolution in the Eastern Tianshan. In this study, we conducted detrital zircon U-Pb geochronological analyses on subsurface Triassic samples collected from the Turpan-Hami Basin to unravel sedimentary response of Indosinian tectonic reactivation and its geodynamics. The detrital zircon age spectra of the Triassic samples are quite different, reflecting significant provenance variability. The zircon grains in the Lower Triassic sample were mainly from the Central Tianshan, while the Jueluotag acted as a minor provenance. By contrast, the Late Paleozoic rocks in Jueluotag act as the main provenance for the Middle-Upper Triassic samples, while the Central Tianshan acted as a minor provenance. Furthermore, zircon grains in the Middle Triassic sample were mainly from the Permian rocks in Jueluotag, while Indosinian strike-slip-driven rapid exhumation brought deeper Carboniferous rocks of Jueluotag as an important age population for the Upper Triassic sample. The inter-sample variability of age spectra of the Triassic samples provides sedimentary evidence for Indosinian tectonic reactivation in the Eastern Tianshan and its periphery, which could be attributed to differential exhumation of different sources driven by coeval strike-slip tectonics along deep faults. The Indosinian tectonic behavior in the Eastern Tianshan, which is characterized by partial melting of the pre-thickened crust and strike-slip deformation, acted as a far-field respond to the coeval continental accretion occurring along the southern Eurasian margin. Additionally, our new detrital zircon data, together with previously published data in the Turpan-Hami Basin, demonstrate that there are significant changes in source-to-sink system from the Permian to the Triassic, suggesting that the Permian-Triassic unconformity in the Eastern Tianshan and its periphery was generated by Late Permian-Early Triassic tectonic contraction and inversion rather than an increasingly arid climate.

Abstract:Coal-formed gas generated from the Permo-Carboniferous coal measures has become one of the most important targets for deep hydrocarbon exploration in the Bohai Bay Basin, offshore eastern China. However, the proven gas reserves from this source rock remain low to date, and the distribution characteristics and accumulation model for the coal-formed gas are not clear. Here we review the coal-formed gas deposits formed from the Permo-Carboniferous coal measures in the Bohai Bay Basin. The accumulations are scattered, and dominated by middle-small sized gas fields, of which the proven reserves ranging from 0.002 to 149.4×108 m3 with an average of 44.30×108 m3 and a mid-point of 8.16×108 m3. The commercially valuable gas fields are mainly found in the central and southern parts of the basin. Vertically, the coal-formed gas is accumulated at multiple stratigraphic levels from Paleogene to Archaeozoic, among which the Paleogene and Permo-Carboniferous are the main reservoir strata. According to the transporting pathway, filling mechanism and the relationship between source rocks and reservoir, the coal-formed gas accumulation model can be defined into three types: “Upward migrated, fault transported gas” accumulation model, “Laterally migrated, sandbody transported gas” accumulation model, and “Downward migrated, sub-source, fracture transported gas” accumulation model. Source rock distribution, thermal evolution and hydrocarbon generation capacity are the fundamental controlling factors for the macro distribution and enrichment of the coal-formed gas. The fault activity and the configuration of fault and caprock control the vertical enrichment pattern.

Abstract:The lower Cretaceous rock units of the Koppeh-Dagh Basin of northeastern Iran were investigated here in terms of biostratigraphy, depositional setting and geochemical analyses to find out if they, alike other parts of the world, are rich in petroleum. For this purpose, a stratigraphic framework is established using calcareous nannofossil and palynological elements. A nannoplankton zonation based on which subzones of the zones CC7 – CC8 of Sissingh (1977) and their equivalent NC6 – NC8 of Roth (1978) was established indicating a Late Barremian–Albian age. Palynological assemblages led us to establish the local palynozone of Odontochitina operculata. A dominantly marginal basin to a transitional zone between shelf and basin under a dysoxic–anoxic condition with low to moderate sedimentation rates coincided with a gradual sea level rise was introduced as the environment of deposition for the strata via interpretation of the palynological parameters and quantitative palynology. The obtained data from Rock-Eval pyrolysis in compilation with palynofacies analysis reveals that the studied succession contains mainly gas-prone type III kerogen. The Spore Coloration Index (SCI) alongside with the Rock-Eval pyrolysis results (low values of HI and TOC) proves that these rock units locally produced natural gas during the time under consideration.

Abstract:The investigated area around Sarvapuram represents a part of the Karimnagar granulite terrane of the Eastern Dharwar Craton, India. Garnet–bearing gneiss is hosted as enclaves, pods within granite gneiss and charnockite. It is largely made up of garnet, orthopyroxene, cordierite, biotite, plagioclase, K–feldspar, sillimanite and quartz. The peak metamorphic stage is represented by the equilibrium mineral assemblage i.e. garnet, orthopyroxene, cordierite, biotite, plagioclase, sillimanite and quartz. Breakdown of the garnet as well as preservation of the orthopyroxene–cordierite symplectite, formation of cordierite with the consumption of the garnet + sillimanite + quartz represents the decompressional event. The thermobarometric calculations suggest a retrograde P–T path with a substantial decompression of c. 3.0 kbar. The water activity (XH2O) conditions obtained with the winTWQ program for core and symplectite compositions from garnet–bearing gneiss are 0.07–0.14 and 0.11–0.16 respectively. The quantitative estimation of oxygen fugacity in garnet–bearing gneiss reveal log fO2 values ranging from ?11.38 to ?14.05. This high oxidation state could be one of the reasons that account for the absence of graphite in these rocks.

Abstract:Based on the data of core description and sporopollen analysis, the gradual evolution of deltas in vertical direction and transition of channel types in the MPE3 block of the eastern Venezuela Basin have been surveyed by seismic phase and well logging facies interpretation. The results show that due to the great sea level rise, the sedimentary system of the Miocene Oficina Formation in the MPE3 block shifted from the distal-source sandy braided river delta to tide-affected delta, and eventually to tide-dominated delta. Vertically, during the early stage of sedimentation of Oficina Formation, the distributary channels of the delta were dominated by braided river channels. While in the later stage, as the tidal effect was gradually intensified, the channel changed from braided channel to meandering channel. On plane, as a result of differential transgression, sedimentary framework and distribution of sand bodies vary across the study area. Compared with the eastern part, the western part has more braided channels, larger channel bars, less developments of distributary bay and higher ratio of sand to mud. Whereas the braided channels in the south are larger than those in the north. It is the first time we pointed out the impact of marine transgression differences on the sedimentary facies distribution and river type transition in the study area. Factors like the structural and paleogeomorphological change, sea level variation, supply of sediments have strong influence on the evolution of sedimentary system and distribution of sandbodies. It is predicted that the major sandbody is more developed in the central south, which can guide the subsequent horizontal well development.

Abstract:Correct identification of water inrush sources is particularly important to prevent and control mine water disasters. Hydrochemical analysis, Fisher discriminant analysis, and geothermal verification analysis were used to identify and verify the water sources of the multi-aquifer groundwater system in Gubei coal mine, Anhui Province, North China. Results show that hydrochemical water types of the Cenozoic top aquifer included HCO3?Na+K?Ca, HCO3?Na+K?Mg and HCO3?Na+K, and this aquifer was easily distinguishable from other aquifers because of its low concentration of Na++K+ and Cl?. The Cenozoic middle and bottom aquifers, the Permian fissure aquifer, and the Taiyuan and Ordovician limestone aquifers were mainly characterized by the Cl?Na+K and SO4?Cl?Na+K or HCO3?Cl?Na+K water types, and their hydrogeochemistries were similar. Therefore, water sources could not be identified via hydrochemical analysis. Fisher model was established based on the hydrogeochemical characteristics, and its discrimination rate was 89.19%. Fisher discrimination results were improved by combining them with the geothermal analysis results, and this combination increased the identification rate to 97.3 % and reasonably explained the reasons behind two water samples misjudgments. The methods described herein are also applicable to other mines with similar geological and hydrogeological conditions in North China.

Abstract:Amphibole is a rock-forming mineral widely existing on the earth. It is easily dissolved and altered during the later stage of diagenesis and mineralization, and often forms chloritization, which is an important indicator for prospecting. To explore amphibole’s dissolution process and alteration mechanism, dissolution experiments were carried out under acidic conditions using pargasite-rich amphibole as raw material, and the effects of temperature, pH, and experiment duration on amphibole alteration were investigated. Experimental samples and products were analyzed using X-ray diffractometer, field emission scanning electron microscope, electron probe micro analyzer, and transmission electron microscopy. It was found that many pores and erosion edges are produced after amphibole dissolution, and there is a clear interface between the dissolved residual portion and the parent. The dissolved residual portion remains in the amphibole phase, but as the temperature and time increase, the intensity of the diffraction peak of the phase in the product decreases, and the peak position shifts to a small angle. Many clay minerals such as chlorite and griffithite formed on the amphibole surface. In an environment with strong acidity (pH=3), the amount of chamosite increases with temperature (180°C→210°C→240°C), whereas clinochlore is only increased in a 150–210°C environment. Griffithite growth was observed in the acidic (pH=6) and low temperature (<180°C) environments. Based on this analysis, large radius Cl– enters the amphibole lattice or cracks to promote dissolution. The Al-poor and Ca- and Fe-rich regions between the edge and core of the amphibole are caused by dynamic equilibrium in amphibole dissolution and alteration process, which is an essential indicator for the beginning of amphibole dissolution-alteration. Diffusion and the coupled dissolution-reprecipitation mechanism accomplishes the process of dissolution and alteration to form clay minerals. The energy of the system determined by temperature and pH is the key to controlling the rate of growth and nucleation of clay minerals. High temperature and strong acidity will dissolve more iron from amphibole, which is conducive to chlorite growth. Compared to chlorite, griffithite is more sensitive to temperature. Griffithite attaches on the amphibole surface with a star-like in a weak acid and low-temperature environment. The results of this study can provide a mineralogical basis for the analysis of hydrothermal alteration processes and the division of alteration zones.

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Abstract:Biotite is an important hydrated ferromagnesian silicate mineral in igneous rocks and porphyry deposits. The determination of chemical compositions of biotite plays an important role in both igneous petrology and ore forming processes. This paper summarizes research results of magmatic and hydrothermal biotites exemplified by the Lakange porphyry Cu–Mo deposit and the Qulong porphyry Cu deposit in the Gangdese porphyry–skarn metallogenic belt, Tibet. Biotite mineral chemistry can provide critical insights into classification, geothermometer, geothermobarometry, oxygen fugacity, petrogenesis and tectonic setting, evaluating magmatic-hydrothermal process by halogen and halogen fugacity ratios, and distinguishing between barren and mineralized rocks. Biotite provides the latest mineralogical evidence on metallogenic prognosis and prospecting evaluation for porphyry Cu polymetallic deposits or magmatic hydrothermal deposits.

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