Based on the test and experimental data from exploration well cores of the Upper Paleozoic in the central-eastern Ordos Basin,combined with structural,burial depth and fluid geochemistry analyses,this study reveals th...Based on the test and experimental data from exploration well cores of the Upper Paleozoic in the central-eastern Ordos Basin,combined with structural,burial depth and fluid geochemistry analyses,this study reveals the fluid characteristics,gas accumulation control factors and accumulation modes in the Upper Paleozoic coal reservoirs.The study indicates findings in two aspects.First,the 1500-1800 m interval represents the critical transition zone between open fluid system in shallow-medium depths and closed fluid system in deep depths.The reservoirs above 1500 m reflect intense water invasion,with discrete pressure gradient distribution,and the presence of methane mixed with varying degrees of secondary biogenic gas,and they generally exhibit high water saturation and adsorbed gas undersaturation.The reservoirs deeper than 1800 m,with extremely low permeability,are self-sealed,and contains closed fluid systems formed jointly by the hydrodynamic lateral blocking and tight caprock confinement.Within these systems,surface runoff infiltration is weak,the degree of secondary fluid transformation is minimal,and the pressure gradient is relatively uniform.The adsorbed gas saturation exceeds 100%in most seams,and the free gas content primarily ranges from 1 m^(3)/t to 8 m^(3)/t(greater than 10 m^(3)/t in some seams).Second,the gas accumulation in deep coals is primarily controlled by coal quality,reservoir-caprock assemblage,and structural position governed storage,wettability and sealing properties,under the constraints of the underground temperature and pressure conditions.High-rank,low-ash yield coals with limestone and mudstone caprocks show superior gas accumulation potential.Positive structural highs and wide and gentle negative structural lows are favorable sites for gas enrichment,while slope belts of fold limbs exhibit relatively lower gas content.This research enhances understanding of gas accumulation mechanisms in coal reservoirs and provides effective parameter reference for precise zone evaluation and innovation of adaptive stimulation technologies for deep resources.展开更多
Subduction initiation is a critical part of the plate tectonic system,but its geodynamic process is still poorly understood due to the lack of well-preserved geological records.Based on new zircon U–Pb–Hf isotopic a...Subduction initiation is a critical part of the plate tectonic system,but its geodynamic process is still poorly understood due to the lack of well-preserved geological records.Based on new zircon U–Pb–Hf isotopic and whole-rock geochemical data,we report the first discovery of a latest Cambrian–Early Ordovician forearc-arc rock sequence in the Eastern Alps.This sequence includes granitic gneisses,amphibolites,and amphibole plagiogneisses from the ophiolitic Speik Complex and Gleinalpe Complex.These rocks exhibit geochemical affinities with typical oceanic plagiogranites,forearc basalts(FABs),and island arc basalts,respectively.The latest Cambrian plagiogranitic protoliths(491±2 Ma)are shearing-type plagiogranites that were formed in the tectonic setting of forearc spreading.The latest Cambrian FABs(496–489 Ma)have similar geochemical compositions and positiveεHf(t)values(+2.5 to+14.9)to the depleted mid-ocean ridge basalts.However,they show depletion in high field strength elements(HFSEs;e.g.,Nb,Ta,and Zr)and have relatively low Ti/V ratios.These features suggest that they were derived from a depleted mantle source modified by subducting slab-released components in a forearc environment.The Early Ordovician basaltic protoliths(476–472 Ma)of amphibole plagiogneisses show enrichment in large ion lithophile elements and depletion in HFSEs(e.g.Nb,Ta,Zr,and Hf),implying a mature island arc environment.These metaigneous rocks,along with the coeval boninite-like high-Mg amphibolites near the study area,form a typical rock sequence resembling that of the Izu–Bonin–Mariana(IBM)arc system.The Speik and Gleinalpe complexes document a complete magmatic evolution from subduction initiation to mature arc development within the West Proto-Tethys Ocean.Integrating our new data with published work,we reconstruct the late Ediacaran–early Paleozoic tectonic evolution of the northern Gondwana.During the late Ediacaran–early Cambrian,the rollback of the West Proto-Tethys oceanic plate triggered the separation of the Wechsel-Silvretta-Gleinalpe continental arc from the northern Gondwana.This process led to the formation of the Speik back-arc oceanic basin,a southwestern branch of the West Proto-Tethys Ocean.In the latest Cambrian–Early Ordovician,subduction initiation occurred in the Speik Ocean,which subsequently developed into an intra-oceanic arc system.During the Early Devonian,the Speik Ocean closed and the Wechsel-Silvretta-Gleinalpe continental arc reattached to the Gondwana,as evidenced by the metamorphic event at ca.400 Ma.展开更多
The Yarlung Zangbo Suture Zone(YZSZ)on the southern margin of the Lhasa block and the Tangjia-Sumdo ultrahigh-pressure metamorphic belt(TSMB)within the block represent natural laboratories for the study of plate tecto...The Yarlung Zangbo Suture Zone(YZSZ)on the southern margin of the Lhasa block and the Tangjia-Sumdo ultrahigh-pressure metamorphic belt(TSMB)within the block represent natural laboratories for the study of plate tectonics and oceanic slab subduction.It is generally believed that these two zones represent the remnants of the ancient oceanic crust and upper mantle of the Yarlung Zangbo Neo-Tethys(YZNT)and the Tangjia-Sumdo Paleo-Tethys(TSPT).However,the evolutionary patterns and spatiotemporal relationships of the TSPT and the YZNT have been debated.展开更多
This study presents whole-rock major,trace elements and Sr-Nd-Hf isotopic compositions,as well as zircon UPb geochronological data,for the peraluminous and aluminous granitoids in northern Guangdong Province,South Chi...This study presents whole-rock major,trace elements and Sr-Nd-Hf isotopic compositions,as well as zircon UPb geochronological data,for the peraluminous and aluminous granitoids in northern Guangdong Province,South China,in order to investigate their petrogenesis and tectonic implications.The Qingzhou granodiorites(458.5-455.4 Ma)are peraluminous(A/CNK=1.05-1.96).They have relatively high initial^(87)Sr/^(86)Sr ratios(I_(Sr)=0.7087-0.7148),lowε_(Nd)(t)values(-11.2 to-10.1)and a variety of zirconε_(Hf)(t)values in the range-13.4 to+4.81.By contrast,the Damaoshan granodiorites(458.1 Ma)are metaluminous(A/CNK=0.79-0.94)in composition,with I_(Sr)values of 0.7083 to 0.7110,ε_(Nd)(t)values of-7.92 to-5.28 and zirconε_(Nf)(t)values of-8.69 to-2.06.The Gaoshou quartz diorites(449 Ma)are metaluminous-peraluminous.Their I_(Sr)values vary from 0.7104 to 0.7111 withε_(Nd)(t)values from-9.64 to-8.63.Geochemical data and Sr-Nd-Hf isotope compositions indicate that the Qingzhou,Damaoshan and Gaoshou intrusions are primarily derived from the partial melting of metagreywackes,tonalitic rocks and amphibolite,respectively.The crustal materials in northern Guangdong,from top to bottom consist of Paleozoic sequences,metasediments with a V_(p)of<6.0 km/s,metaigneous rocks with a V_(p)of 6.3-6.7 km/s and amphibolite with a V_(p)of~7.03 km/s.展开更多
Rocks in the Cathaysia Block record multiple tectonic events and provide a window to understand the evolution of the South China Block.This study reports geochronological,geochemical and Sr-Nd-Hf isotopic data for gne...Rocks in the Cathaysia Block record multiple tectonic events and provide a window to understand the evolution of the South China Block.This study reports geochronological,geochemical and Sr-Nd-Hf isotopic data for gneiss,granite,and migmatite in Zhenghe.The gneiss yielded an upper intercept age of 1,942 Ma,reflecting reworking of protolith.The migmatites formed at 399 Ma,slightly earlier than the granite(~392 Ma).Melanosomes displayed nearly flat chondritenormalized rare earth element patterns,along with(^(87)Sr/^(86)Sr)i and ε_(Nd)(t)values of 0.70620.7155 and−11.0 to 0.3,exhibiting a lower crustal affinity.Geochemical characteristics of the leucosome and granite differed from those of the melanosome,and the degree of element enrichment or depletion was higher.The Sr-Nd isotopic compositions of granite and leucosome were different,but both suggest a crustal origin.In addition,the gneiss revealed a Mesozoic tectono—metamorphic overprint,likely related to crust thickening.Our research suggests that late Paleozoic anatexis resulted from collision between the Gondwana continent and the West Cathaysia Block.Underthrusting of the East Cathaysia Block beneath the West Cathaysia Block contributed to Mesozoic orogeny.Our new data document Paleoproterozoic reworking,Paleozoic anatexis,and Triassic metamorphism,providing novel insights into evolution of the Cathaysia Block.展开更多
0 INTRODUCTION The Haidewula uranium deposit is located in the Haidewula volcanic basin,which hosts a suite of basic,intermediate to felsic volcanic and subvolcanic rocks,including basalt,trachyte,trachyandesite.Previ...0 INTRODUCTION The Haidewula uranium deposit is located in the Haidewula volcanic basin,which hosts a suite of basic,intermediate to felsic volcanic and subvolcanic rocks,including basalt,trachyte,trachyandesite.Previous geochronological studies of the intrusions within this volcanic basin suggest that they primarily formed during the Silurian and Triassic periods(Dai et al.,2025;Sun et al.,2024;Wang et al.,2024;Zhu et al.,2022;Lei et al.,2021).展开更多
A systematic study of early Paleozoic S-type granites in Pinghe enhances our understanding of the tectonic evolution of proto-Tethys and provides a foundation for exploring rare metal deposits in the region.The Pinghe...A systematic study of early Paleozoic S-type granites in Pinghe enhances our understanding of the tectonic evolution of proto-Tethys and provides a foundation for exploring rare metal deposits in the region.The Pinghe granites consist of monzogranite and leucogranite.Zircon U-Pb dating shows that the emplacement ages of the monzogranite and leucogranite are 502.0 Ma and 500.9 Ma,respectively.All samples have high SiO_(2) content and a weakly to strongly peraluminous character(A/CNK=1.08-1.23),consistent with S-type granites.The monzogranite has relatively high CaO,Sr,Ba,and CaO/Na_(2)O ratios but lower Rb.In contrast,the leucogranite has lower CaO,Sr,Ba,and CaO/Na_(2)O ratios but higher Rb.The similar ε_(Nd)(t)values(−9.3 to−8.4)and Pb isotopic compositions((^(206)Pb/^(204)Pb)t=18.03-19.36,(^(207)Pb/^(204)Pb)t=15.66-15.76,(^(208)Pb/^(204)Pb)t=37.97-38.55)suggest that the monzogranite formed through partial melting of crustal greywacke,while the leucogranite originated from partial melting of crustal pelite.Regional geological studies suggest that these S-type granites in Pinghe were emplaced in an active continental margin setting,associated with the westward subduction of the proto-Tethys oceanic slab.The geochemical characteristics of leucogranite are consistent with those of tungsten-tin-related granites,indicating significant metallogenic potential for W and Sn deposits.展开更多
Eastern Sichuan Basin is a critical region for oil and gas production in China,and the thermal effect of the Emeishan Mantle Plume(EMP) on the basin remains unclear,which limits the study of the Paleozoic hydrocarbon ...Eastern Sichuan Basin is a critical region for oil and gas production in China,and the thermal effect of the Emeishan Mantle Plume(EMP) on the basin remains unclear,which limits the study of the Paleozoic hydrocarbon accumulation process.Thus,clarifying the thermal history is crucial for oil and gas evaluation and exploration.This study combines zircon fission track(ZFT),zircon(U-Th)/He(ZHe),and vitrinite reflectance analyses to reconstruct the thermal history since the Paleozoic and investigate the maturity evolution of Paleozoic source rocks in the eastern Sichuan Basin.Additionally,the contributing factors of the Permian abnormal heat flow and the thermal effect range of the EMP were analyzed.Thermal history results show a stable low heat flow phase(45-55 mW/m^(2)) from the Cambrian to Permian,a rapid increase to peak values(62-70 mW/m^(2)) during the Middle Permian,and a gradual decline to current stable values(47-62 mW/m^(2)) from the Triassic onward.Thermal evolution revealed that Paleozoic source rocks exhibited maturation stagnation due to tectonic events,while the Permian peak heat flow and the Jurassic-Late Cretaceous rapid burial accelerated maturation.The Cambrian Qiongzhusi Formation and Silurian Longmaxi Formation source rocks began generating hydrocarbons(R_(equ)=0.5%) in the Late Cambrian-Late Ordovician and Late Silurian-Early Devonian,respectively,while it was Late Permian-Early Triassic for Permian source rocks.Peak maturity(R_(equ)> 2%) occurred in the Late Cretaceous,with natural gas as the dominant product The EMP significantly influenced the thermal regime of the western and central Sichuan Basin,with a thermal effect radius of~600-650 km.In contrast,the Permian thermal anomaly in the eastern Sichuan Basin is attributed to the lithospheric extension associated with the Middle Permian Kaijiang-Liangping trough.These findings provide critical insights for deep and ultra-deep gas exploration and enhance the understanding of the EMP's regional thermal impacts.展开更多
The International Geoscience Program project IGCP-580(started in 2009),focuses on the application of magnetic susceptibility(MS)as a paleoclimatic proxy on Paleozoic sedimentary rocks and on the characterization of th...The International Geoscience Program project IGCP-580(started in 2009),focuses on the application of magnetic susceptibility(MS)as a paleoclimatic proxy on Paleozoic sedimentary rocks and on the characterization of the magnetic susceptibility signal.Here we provide a summary of the scientific targets behind the project and a summary of the organized activities.This project concerns three main issues:the first one consists of compiling the available MS data from the different researchers and continuing the collection of new data(with a main focus on the Devonian).The second issue focuses on the identification of the nature and origin of the magnetic minerals carrying MS signal.The last issue concerns the application of MS as a correlation,cyclostratigraphic and paleoclimatic tool.The IGCP-580 community consists of 245 researchers,from 45 countries(including Kenya,Namibia,Vietnam,Iran,Uzbekistan,Algeria,Tunisia,Colombia,Nigeria,India,etc.).During the project,we organized five meetings(Belgium,China,Czech Republic,Austria,Canada),three special sessions in international meetings and eight field workshops,as well as various training sessions.展开更多
The Tianshan range could have been built by both late Early Paleozoicaccretion and Late Paleozoic collision events. The late Early Paleozoic Aqqikkudug-Weiya suture ismarked by Ordovician ophiolitic melange and a Silu...The Tianshan range could have been built by both late Early Paleozoicaccretion and Late Paleozoic collision events. The late Early Paleozoic Aqqikkudug-Weiya suture ismarked by Ordovician ophiolitic melange and a Silurian flysch sequence, high-pressure metamorphicrelics, and mylonitized rocks. The Central Tianshan belt could principally be an Ordovician volcanicarc; whereas the South Tianshan belt, a back-arc basin. Macro- and microstructures, along withunconformities, provide some kinematic and chronological constraints on 2-phase ductile deformation.The earlier ductile deformation occurring at ca. 400 Ma was marked by north-verging ductileshearing, yielding granulite-bearing ophiolitic melange blocks and garnet-pyroxene-facies ductiledeformation, and the later deformation, a dextral strike-slip tectonic process, occurred during theLate Carboniferous-Early Permian. Early Carboniferous molasses were deposited unconformably onpre-Carboniferous metamorphic and ductilely sheared rocks, implying the end of the early orogeny.The large-scale ductile strike-slip along the Aqqikkudug-Weiya zone was possibly caused by thesecond tectonic event, the Hercynian collision between the northern Tarim block and the southernSiberian block. Late Paleozoic granitic magmatism and superimposed structures overprinted this EarlyPaleozoic deformation belt. Results of geometric and kinematic studies suggest that the primaryframework of the Southern-Central Tianshan belt, at least the eastern part of the Tianshan belt, wasbuilt by these two phases of accretion events.展开更多
The Lower Paleozoic shale in south China has a very high maturity and experienced strong tectonic defor- mation. This character is quite different from the North America shale and has inhibited the shale gas evaluatio...The Lower Paleozoic shale in south China has a very high maturity and experienced strong tectonic defor- mation. This character is quite different from the North America shale and has inhibited the shale gas evaluation and exploration in this area. The present paper reports a com- prehensive investigation of maturity, reservoir properties, fluid pressure, gas content, preservation conditions, and other relevant aspects of the Lower Paleozoic shale from the Sichuan Basin and its surrounding areas. It is found that within the main maturity range （2.5 % 〈 EqRo 〈 3.5 %） of the shale, its porosity develops well, having a positive cor- relation with the TOC content, and its gas content is con- trolled mainly by the preservation conditions related to the tectonic deformation, but shale with a super high maturity （EqRo 〉 3.5 %） is considered a high risk for shale gas exploration. Taking the southern area of the Sichuan Basin and the southeastern area of Chongqing as examples of uplifted/folded and faulted/folded areas, respectively, geo- logical models of shale gas content and loss were proposed. For the uplifted/folded area with a simple tectonic defor- mation, the shale system （with a depth 〉 2000 m） has lar- gely retained overpressure during uplifting without a great loss of gas, and an industrial shale gas potential is generally possible. However, for the faulted/folded area with a strong tectonic deformation, the sealing condition of the shale system was usually destroyed to a certain degree with a great loss of free gas, which decreased the pressure coefficient and resulted in a low production capacity. It is predicted that the deeply buried shale （〉3000 m） has a greater gas potential and will become the focus for further exploration and development in most of the south China region （outside the Sichuan Basin）.展开更多
Detailed global plate motion models that provide a continuous description of plate boundaries through time are an effective tool for exploring processes both at and below the Earth's surface. A new generation of n...Detailed global plate motion models that provide a continuous description of plate boundaries through time are an effective tool for exploring processes both at and below the Earth's surface. A new generation of numerical models of mantle dynamics pre-and post-Pangea timeframes requires global kinematic descriptions with full plate reconstructions extending into the Paleozoic(410 Ma). Current plate models that cover Paleozoic times are characterised by large plate speeds and trench migration rates because they assume that lowermost mantle structures are rigid and fixed through time. When used as a surface boundary constraint in geodynamic models, these plate reconstructions do not accurately reproduce the present-day structure of the lowermost mantle. Building upon previous work, we present a global plate motion model with continuously closing plate boundaries ranging from the early Devonian at 410 Ma to present day.We analyse the model in terms of surface kinematics and predicted lower mantle structure. The magnitude of global plate speeds has been greatly reduced in our reconstruction by modifying the evolution of the synthetic Panthalassa oceanic plates, implementing a Paleozoic reference frame independent of any geodynamic assumptions, and implementing revised models for the Paleozoic evolution of North and South China and the closure of the Rheic Ocean. Paleozoic(410-250 Ma) RMS plate speeds are on average ～8 cm/yr, which is comparable to Mesozoic-Cenozoic rates of ～6 cm/yr on average.Paleozoic global median values of trench migration trend from higher speeds(～2.5 cm/yr) in the late Devonian to rates closer to 0 cm/yr at the end of the Permian(～250 Ma), and during the Mesozoic-Cenozoic(250-0 Ma) generally cluster tightly around ～1.1 cm/yr. Plate motions are best constrained over the past 130 Myr and calculations of global trench convergence rates over this period indicate median rates range between 3.2 cm/yr and 12.4 cm/yr with a present day median rate estimated at～5 cm/yr. For Paleozoic times(410-251 Ma) our model results in median convergence rates largely～5 cm/yr. Globally,～90% of subduction zones modelled in our reconstruction are determined to be in a convergent regime for the period of 120-0 Ma. Over the full span of the model, from 410 Ma to 0 Ma,～93% of subduction zones are calculated to be convergent, and at least 85% of subduction zones are converging for 97% of modelled times. Our changes improve global plate and trench kinematics since the late Paleozoic and our reconstructions of the lowermost mantle structure challenge the proposed fixity of lower mantle structures, suggesting that the eastern margin of the African LLSVP margin has moved by as much as ～1450 km since late Permian times(260 Ma). The model of the plate-mantle system we present suggests that during the Permian Period, South China was proximal to the eastern margin of the African LLSVP and not the western margin of the Pacific LLSVP as previous thought.展开更多
The East Kunlun Orogenic Belt(EKOB) provides an important link to reconstruct the evolution of the Proto-Tethys and Paleo-Tethys realm. The EKOB is marked by widespread Early Paleozoic magmatism.Here we report the pet...The East Kunlun Orogenic Belt(EKOB) provides an important link to reconstruct the evolution of the Proto-Tethys and Paleo-Tethys realm. The EKOB is marked by widespread Early Paleozoic magmatism.Here we report the petrology, bulk geochemistry, zircon Ue Pb dating and, Lue Hf and SreN d isotopic data of the Early Paleozoic granitic rocks in Zhiyu area of the southern EKOB. Based on the zircon U-Pb dating, these granitoids, consisting of diorite, granodiorite and monzogranite, were formed during 450 -430 Ma the Late Ordovician to Middle Silurian. The diorite and granodiorite are high Sr/Y ratio as adakitic affinities, and the monzogranite belongs to highly fractionated I-type. Their(^(87)Sr/^(86)Sr)ivalues range from 0.7059 to 0.7085, εNd(t) values from -1.6 to -6.0 and the zircon εHf(t) values show large variations from +9.1 to -8.6 with Hf model ages(T_(DM2)) about 848 Ma and 1970 Ma. The large variations of whole-rock Nd and zircon Hf isotopes demonstrate strong isotopic heterogeneity of the source regions which probably resulted from multi-phase underplating of mantle-derived magmas. Geochemical and isotopic studies proved that the diorite and granodiorite had been derived from partial melting of heterogeneous crustal source with variable contributions from ancient continental crust and juvenile components, and the monzogranites were representing fractional crystallization and crustal contamination for arc magma. The Early Paleozoic adakitic rocks and high-K calc-alkaline granitoids in the southern EKOB were likely emplaced in a continental marginal arc setting possibly linked to the southwards subduction of the Paleo Kunlun Ocean and the magma generation is linked to partial melting of thickened continental crust induced by underplating of mantle-derived magmas.展开更多
The Ordos Basin is a significant petroliferous basin in the central part of China.The Carboniferous and Permian deposits of transitional and continental facies are the main gas-bearing layers in the north part of the ...The Ordos Basin is a significant petroliferous basin in the central part of China.The Carboniferous and Permian deposits of transitional and continental facies are the main gas-bearing layers in the north part of the basin.The Carboniferous and Permian natural gas reservoirs in the northern Ordos Basin are mainly tight sandstone reservoirs with low porosity and low permeability,developing lots of ＂sweet spots＂ with comparatively high porosity and permeability.The tight sandstones in the study area are gas-bearing,and the sweet spots are rich in gas.Sweet spots and tight sandstones are connected rather than being separated by an interface seal.Sweet spot sand bodies are vertically and horizontally overlapped,forming a large gas reservoir group.In fact,a reservoir formed by a single sweet spot sand body is an open gas accumulation.In the gentle dipping geological setting and with the source rocks directly beneath the tight reservoirs over a large area,the balance between gas charging into tight reservoirs from source rocks and gas loss from tight reservoirs through caprock is the key of gas accumulation in tight sandstones.Both the non-Darcy flow charging driven by source-reservoir excess pressure difference and the diffusion flow charging driven by source-reservoir gas concentration difference play an important role in gas accumulation.The results of mathematical modeling indicate that the gas accumulation cannot be formed by just one of the above mechanisms.The diffusion of gas from source rocks to reservoirs is a significant mechanism of tight sandstone gas accumulation.展开更多
The Cambrian to Cretaceous paleomagnetic data from Chinese continental and adjacent blocks were collected using principles to obtain reliable and high-precision paleomagnetic data and to pay attention to the similarit...The Cambrian to Cretaceous paleomagnetic data from Chinese continental and adjacent blocks were collected using principles to obtain reliable and high-precision paleomagnetic data and to pay attention to the similarity of paleobiogeography and the coordination of tectonic evolution.The Chinese continental blocks were laid up on the reconstruction of proposed global paleocontinents with almost the same scale.Thus,it can be clearly recognized that the global continents,including Chinese continental blocks,range along latitudes on the southern side of the equator during the Early Paleozoic. In the Paleozoic,Chinese continental blocks were still located among the Laurentia,Siberia and Gondwana plates,following the fast moving of the Siberia Plate northwards,the amalgamation in a north-south direction at the western parts of the Laurentia and Gondwana plates,and the Iapetus and Rheic Oceans were subducted,eventually to form a uniform Pangea in the Late Paleozoic.The Australian and Indian plates of Eastern Gondwana moved and dispersed gradually southwards, continued to extend the Paleo-Tethys Ocean.The Chinese continental and adjacent blocks were still located in the Paleo-Tethys Ocean,preserved the status of dispersion,gradually moving northwards, showing characteristics of ranging along a north-south orientation until the Permian.In addition,a series of local collisions happened during the Triassic,and consequently most of the Chinese continental blocks were amalgamated into the Pangea,except for the Gangdise and Himalayan blocks. There was a counter-clockwise rotation of the Eastern Asian continent in the Jurassic and northwards migration of the Chinese continent in varying degrees during the Cretaceous,but the Himalayan and Indian plates did not collide into the Chinese continent during this period.展开更多
The eastern margin of the Qaidam Basin lies in the key tectonic location connecting the Qinling, Qilian and East Kunlun orogens. The paper presents an investigation and analysis of the geologic structures of the area ...The eastern margin of the Qaidam Basin lies in the key tectonic location connecting the Qinling, Qilian and East Kunlun orogens. The paper presents an investigation and analysis of the geologic structures of the area and LA-ICP MS zircon U-Pb dating of Paleozoic and Mesozoic magmatisms of granitoids in the basement of the eastern Qaidam Basin on the basis of 16 granitoid samples collected from the South Qilian Mountains, the Qaidam Basin basement and the East Kunlun Mountains. According to the results in this paper, the basement of the basin, from the northern margin of the Qaidam Basin to the East Kunlun Mountains, has experienced at least three periods of intrusive activities of granitoids since the Early Paleozoic, i.e. the magmatisms occurring in the Late Cambrian （493.1±4.9 Ma）, the Silurian （422.9±8.0 Ma-420.4±4.6 Ma） and the Late Permian-Middle Triassic （257.8±4.0 Ma-228.8＋1.5 Ma）, respectively. Among them, the Late Permian - Middle Triassic granitoids form the main components of the basement of the basin. The statistics of dated zircons in this paper shows the intrusive magmatic activities in the basement of the basin have three peak ages of 244 Ma （main）, 418 Ma, and 493 Ma respectively. The dating results reveal that the Early Paleozoic magmatism of granitoids mainly occurred on the northern margin of the Qaidam Basin and the southern margin of the Qilian Mountains, with only weak indications in the East Kunlun Mountains. However, the distribution of Permo-Triassic （P-T） granitoids occupied across the whole basement of the eastern Qaidam Basin from the southern margin of the Qilian Mountains to the East Kunlun Mountains. An integrated analysis of the age distribution of P-T granitoids in the Qaidam Basin and its surrounding mountains shows that the earliest P-T magmatism （293.6-270 Ma） occurred in the northwestern part of the basin and expanded eastwards and southwards, resulting in the P-T intrusive magmatism that ran through the whole basin basement. As the Cenozoic basement thrust system developed in the eastern Qaidam Basin, the nearly N-S-trending shortening and deformation in the basement of the basin tended to intensify from west to east, which went contrary to the distribution trend of N-S-trending shortening and deformation in the Cenozoic cover of the basin, reflecting that there was a transformation of shortening and thickening of Cenozoic crust between the eastern and western parts of the Qaidam Basin, i.e., the crustal shortening of eastern Qaidam was dominated by the basement deformation （triggered at the middle and lower crust）, whereas that of western Qaidam was mainly by folding and thrusting of the sedimentary cover （the upper crust）.展开更多
The upper Paleozoic natural gas reservoirs in the Ordos basin are generally characterized by a large gas-bearing area and low reserve abundance. On such a geological background, there still exist gas-enriched zones, w...The upper Paleozoic natural gas reservoirs in the Ordos basin are generally characterized by a large gas-bearing area and low reserve abundance. On such a geological background, there still exist gas-enriched zones, with relatively high outputs, high reserve abundance and stably distributed gas layers. The gas-enriched layers with relatively high permeability （the lower limit permeability is 0.5×10^-3μm^2） are key factors for the enrichment and high output of natural gas. Based on core observation, analytic results of inclusions, and a great deal of drilling data, we proposed the following four mechanisms for the formation of high-quality reservoirs： （1） in the source area the parent rocks are mainly metamorphic rocks and granites, which are favorable to keeping primary porosity; （2） under the condition of low A/S （accommodation/sediment supply） ratios, sandstone complex formed due to multistage fluvial stacking and filling are coarse in grain size with a high degree of sorting, low content of mud and good physical properties; （3） early-stage recharge of hydrocarbons restricted compaction and cementation, and thus are favorable to preservation of primary pores; （4） microfractures caused by the activity of basement faults during the Yanshan Movement stage can not only improve the permeability of tight sandstones, but also afford vertical pathways for hydrocarbon gas migration.展开更多
During the Paleozoic, the Ordos area in the western North China Plate was located at the intersecting position of microplates and controlled by their interaction. The structural framework in the Ordos area, which unde...During the Paleozoic, the Ordos area in the western North China Plate was located at the intersecting position of microplates and controlled by their interaction. The structural framework in the Ordos area, which underwent transformations in the Ordovician, the Carboniferous and the Permian respectively, was dominated by the alternation of uplift and depression. The transformations of structural framework are utilized as the clues to investigate the microplates＇ interacting type and its response in the Ordos area. According to the regional structural evolution, the Ordos area is simplified into an isopachous, isotropic and elastic shell model, and under proposed various boundary conditions, three series of numerical simulations corresponding to the three structural transformations are carried out to determine the detailed tectonic constraints. Numerical simulations reveal that the structure of the uplift and depression, which is similar to the actual pattern, develops only under one special boundary condition in each of the three series, indicating that the structural framework responds to the unique tectonic background. The simulation results show that in the Early Paleozoic, the L-shaped paleouplift formed nearby the southwestern corner of the Ordos area because the intensity of the compressions in the southern and western boundaries resulting from the ocean-continent collisions was similar. In the Late Paleozoic, it evolved into continent-continent （or arc-continent） interaction in the southern and northern boundaries; in the preliminary stage of the interaction, since the interface between the North China Plate and the plates on the south and north was narrow, the relative acting force was little and the regional western boundary immobile, and the structural framework in the basin was characterized by the N-S trending slender-waist-shaped uplift; as the interface between the plates expanded gradually, the extrusive force in the southern and northern boundaries of the North China Plate increased, resulting in the paleogeographic divisions showing E-W trending, and, the western boundary of the basin was extruded westward due to the intense compression inducing the local NE trending of paleogeographic division in the central area. The simulation results further reflect that the symmetry of the uplift-depression pattern is restricted by that of the boundary conditions, suggesting that the Paleozoic structural transformations of the Ordos area under boundary constraints accord with the universal physical symmetrical principle.展开更多
The hydrocarbon potential of the Hangjinqi area in the northern Ordos Basin is not well known, compared to the other areas of the basin, despite its substantial petroleum system.Restoration of a depth-converted seismi...The hydrocarbon potential of the Hangjinqi area in the northern Ordos Basin is not well known, compared to the other areas of the basin, despite its substantial petroleum system.Restoration of a depth-converted seismic profile across the Hangjinqi Fault Zone（HFZ） in the eastern Hangjinqi area shows one compression that created anticlinal structures in the Late Triassic, and two extensions in ~Middle Jurassic and Late Early Cretaceous, which were interrupted by inversions in the Late Jurassic–Early Early Cretaceous and Late Cretaceous, respectively.Hydrocarbon generation at the well locations in the Central Ordos Basin（COB） began in the Late Triassic.Basin modeling of Well Zhao-4 suggests that hydrocarbon generation from the Late Carboniferous–Early Permian coal measures of the northern Shanbei Slope peaked in the Early Cretaceous, predating the inversion in the Late Cretaceous.Most source rocks in the Shanbei Slope passed the main gas-migration phase except for the Hangjinqi area source rocks（Well Jin-48）.Hydrocarbons generated from the COB are likely to have migrated northward toward the anticlinal structures and traps along the HFZ because the basin-fill strata are dipping south.Faulting that continued during the extensional phase（Late Early Cretaceous） of the Hangjinqi area probably acted as conduits for the migration of hydrocarbons.Thus, the anticlinal structures and associated traps to the north of the HFZ might have trapped hydrocarbons that were charged from the Late Carboniferous–Early Permian coal measures in the COB since the Middle Jurassic.展开更多
Based on the analysis of Upper Paleozoic source rocks, source-reservoir-caprock assemblage, and gas accumulation characteristics in the Ordos Basin, the gas accumulation geological model of total petroleum system is d...Based on the analysis of Upper Paleozoic source rocks, source-reservoir-caprock assemblage, and gas accumulation characteristics in the Ordos Basin, the gas accumulation geological model of total petroleum system is determined. Then, taking the Carboniferous Benxi Formation and the Permian Taiyuan Formation and Shanxi Formation as examples, the main controlling factors of gas accumulation and enrichment are discussed, and the gas enrichment models of total petroleum system are established. The results show that the source rocks, faults and tight reservoirs and their mutual coupling relations control the distribution and enrichment of gas. Specifically, the distribution and hydrocarbon generation capacity of source rocks control the enrichment degree and distribution range of retained shale gas and tight gas in the source. The coupling between the hydrocarbon generation capacity of source rocks and the physical properties of tight reservoirs controls the distribution and sweet spot development of near-source tight gas in the basin center. The far-source tight gas in the basin margin is mainly controlled by the distribution of faults, and the distribution of inner-source, near-source and far-source gas is adjusted and reformed by faults. Generally, the Upper Paleozoic gas in the Ordos Basin is recognized in four enrichment models: inner-source coalbed gas and shale gas, inner-source tight sandstone gas, near-source tight gas, and far-source fault-transported gas. In the Ordos Basin, inner-source tight gas and near-source tight gas are the current focuses of exploration, and inner-source coalbed gas and shale gas and far-source gas will be important potential targets in the future.展开更多
基金Supported by the National Natural Science Foundation of China(42130802,42272200)CNPC Science and Technology Major Project(2023ZZ18)+1 种基金PetroChina Changqing Oilfield Major Science and Technology Project(2023DZZ01)Technology Project of PetroChina Coalbed Methane Company Limited(2023-KJ-18)。
文摘Based on the test and experimental data from exploration well cores of the Upper Paleozoic in the central-eastern Ordos Basin,combined with structural,burial depth and fluid geochemistry analyses,this study reveals the fluid characteristics,gas accumulation control factors and accumulation modes in the Upper Paleozoic coal reservoirs.The study indicates findings in two aspects.First,the 1500-1800 m interval represents the critical transition zone between open fluid system in shallow-medium depths and closed fluid system in deep depths.The reservoirs above 1500 m reflect intense water invasion,with discrete pressure gradient distribution,and the presence of methane mixed with varying degrees of secondary biogenic gas,and they generally exhibit high water saturation and adsorbed gas undersaturation.The reservoirs deeper than 1800 m,with extremely low permeability,are self-sealed,and contains closed fluid systems formed jointly by the hydrodynamic lateral blocking and tight caprock confinement.Within these systems,surface runoff infiltration is weak,the degree of secondary fluid transformation is minimal,and the pressure gradient is relatively uniform.The adsorbed gas saturation exceeds 100%in most seams,and the free gas content primarily ranges from 1 m^(3)/t to 8 m^(3)/t(greater than 10 m^(3)/t in some seams).Second,the gas accumulation in deep coals is primarily controlled by coal quality,reservoir-caprock assemblage,and structural position governed storage,wettability and sealing properties,under the constraints of the underground temperature and pressure conditions.High-rank,low-ash yield coals with limestone and mudstone caprocks show superior gas accumulation potential.Positive structural highs and wide and gentle negative structural lows are favorable sites for gas enrichment,while slope belts of fold limbs exhibit relatively lower gas content.This research enhances understanding of gas accumulation mechanisms in coal reservoirs and provides effective parameter reference for precise zone evaluation and innovation of adaptive stimulation technologies for deep resources.
基金supported by the National Natural Science Foundation of China(Grant Nos.42272244 and 91755212)Taishan Scholars(Grant No.ts20190918).
文摘Subduction initiation is a critical part of the plate tectonic system,but its geodynamic process is still poorly understood due to the lack of well-preserved geological records.Based on new zircon U–Pb–Hf isotopic and whole-rock geochemical data,we report the first discovery of a latest Cambrian–Early Ordovician forearc-arc rock sequence in the Eastern Alps.This sequence includes granitic gneisses,amphibolites,and amphibole plagiogneisses from the ophiolitic Speik Complex and Gleinalpe Complex.These rocks exhibit geochemical affinities with typical oceanic plagiogranites,forearc basalts(FABs),and island arc basalts,respectively.The latest Cambrian plagiogranitic protoliths(491±2 Ma)are shearing-type plagiogranites that were formed in the tectonic setting of forearc spreading.The latest Cambrian FABs(496–489 Ma)have similar geochemical compositions and positiveεHf(t)values(+2.5 to+14.9)to the depleted mid-ocean ridge basalts.However,they show depletion in high field strength elements(HFSEs;e.g.,Nb,Ta,and Zr)and have relatively low Ti/V ratios.These features suggest that they were derived from a depleted mantle source modified by subducting slab-released components in a forearc environment.The Early Ordovician basaltic protoliths(476–472 Ma)of amphibole plagiogneisses show enrichment in large ion lithophile elements and depletion in HFSEs(e.g.Nb,Ta,Zr,and Hf),implying a mature island arc environment.These metaigneous rocks,along with the coeval boninite-like high-Mg amphibolites near the study area,form a typical rock sequence resembling that of the Izu–Bonin–Mariana(IBM)arc system.The Speik and Gleinalpe complexes document a complete magmatic evolution from subduction initiation to mature arc development within the West Proto-Tethys Ocean.Integrating our new data with published work,we reconstruct the late Ediacaran–early Paleozoic tectonic evolution of the northern Gondwana.During the late Ediacaran–early Cambrian,the rollback of the West Proto-Tethys oceanic plate triggered the separation of the Wechsel-Silvretta-Gleinalpe continental arc from the northern Gondwana.This process led to the formation of the Speik back-arc oceanic basin,a southwestern branch of the West Proto-Tethys Ocean.In the latest Cambrian–Early Ordovician,subduction initiation occurred in the Speik Ocean,which subsequently developed into an intra-oceanic arc system.During the Early Devonian,the Speik Ocean closed and the Wechsel-Silvretta-Gleinalpe continental arc reattached to the Gondwana,as evidenced by the metamorphic event at ca.400 Ma.
基金supported by the Science and Technology Research Program of Chongqing Municipal Education Commission(Grant No.KJQN202404310,KJQN202304302)National Natural Science Foundation of China(41972118).
文摘The Yarlung Zangbo Suture Zone(YZSZ)on the southern margin of the Lhasa block and the Tangjia-Sumdo ultrahigh-pressure metamorphic belt(TSMB)within the block represent natural laboratories for the study of plate tectonics and oceanic slab subduction.It is generally believed that these two zones represent the remnants of the ancient oceanic crust and upper mantle of the Yarlung Zangbo Neo-Tethys(YZNT)and the Tangjia-Sumdo Paleo-Tethys(TSPT).However,the evolutionary patterns and spatiotemporal relationships of the TSPT and the YZNT have been debated.
基金supported by the China Geological Survey Project(No.DD20243455)the National Natural Science Foundation of China(NSFC Project 41302046)。
文摘This study presents whole-rock major,trace elements and Sr-Nd-Hf isotopic compositions,as well as zircon UPb geochronological data,for the peraluminous and aluminous granitoids in northern Guangdong Province,South China,in order to investigate their petrogenesis and tectonic implications.The Qingzhou granodiorites(458.5-455.4 Ma)are peraluminous(A/CNK=1.05-1.96).They have relatively high initial^(87)Sr/^(86)Sr ratios(I_(Sr)=0.7087-0.7148),lowε_(Nd)(t)values(-11.2 to-10.1)and a variety of zirconε_(Hf)(t)values in the range-13.4 to+4.81.By contrast,the Damaoshan granodiorites(458.1 Ma)are metaluminous(A/CNK=0.79-0.94)in composition,with I_(Sr)values of 0.7083 to 0.7110,ε_(Nd)(t)values of-7.92 to-5.28 and zirconε_(Nf)(t)values of-8.69 to-2.06.The Gaoshou quartz diorites(449 Ma)are metaluminous-peraluminous.Their I_(Sr)values vary from 0.7104 to 0.7111 withε_(Nd)(t)values from-9.64 to-8.63.Geochemical data and Sr-Nd-Hf isotope compositions indicate that the Qingzhou,Damaoshan and Gaoshou intrusions are primarily derived from the partial melting of metagreywackes,tonalitic rocks and amphibolite,respectively.The crustal materials in northern Guangdong,from top to bottom consist of Paleozoic sequences,metasediments with a V_(p)of<6.0 km/s,metaigneous rocks with a V_(p)of 6.3-6.7 km/s and amphibolite with a V_(p)of~7.03 km/s.
基金supported by Science and Technology Achievements Transformation Projects(HE2513,HE2333)China Geological Survey Project(DD20242526,DD20242275)+1 种基金National Natural Science Foundation of China(Grant No.42162013)open foundation project of the Key Laboratory of Polar Geology and Marine Mineral Resources(China University of Geosciences,Beijing),Ministry of Education(PGMR-2023-305).
文摘Rocks in the Cathaysia Block record multiple tectonic events and provide a window to understand the evolution of the South China Block.This study reports geochronological,geochemical and Sr-Nd-Hf isotopic data for gneiss,granite,and migmatite in Zhenghe.The gneiss yielded an upper intercept age of 1,942 Ma,reflecting reworking of protolith.The migmatites formed at 399 Ma,slightly earlier than the granite(~392 Ma).Melanosomes displayed nearly flat chondritenormalized rare earth element patterns,along with(^(87)Sr/^(86)Sr)i and ε_(Nd)(t)values of 0.70620.7155 and−11.0 to 0.3,exhibiting a lower crustal affinity.Geochemical characteristics of the leucosome and granite differed from those of the melanosome,and the degree of element enrichment or depletion was higher.The Sr-Nd isotopic compositions of granite and leucosome were different,but both suggest a crustal origin.In addition,the gneiss revealed a Mesozoic tectono—metamorphic overprint,likely related to crust thickening.Our research suggests that late Paleozoic anatexis resulted from collision between the Gondwana continent and the West Cathaysia Block.Underthrusting of the East Cathaysia Block beneath the West Cathaysia Block contributed to Mesozoic orogeny.Our new data document Paleoproterozoic reworking,Paleozoic anatexis,and Triassic metamorphism,providing novel insights into evolution of the Cathaysia Block.
基金financially supported by projects from the National Natural Science Foundation of China(No.42321001)the Qinghai Provincial Department of Science and Technology Key R&D Project(No.2025-SF-141)+1 种基金the Qinghai“Kunlun Talent”Program(Qing RC Talent Zi(2024)No.1)the Academician Zhao Pengda Innovation Center in Qinghai Geological Bureau of Nuclear Industry。
文摘0 INTRODUCTION The Haidewula uranium deposit is located in the Haidewula volcanic basin,which hosts a suite of basic,intermediate to felsic volcanic and subvolcanic rocks,including basalt,trachyte,trachyandesite.Previous geochronological studies of the intrusions within this volcanic basin suggest that they primarily formed during the Silurian and Triassic periods(Dai et al.,2025;Sun et al.,2024;Wang et al.,2024;Zhu et al.,2022;Lei et al.,2021).
基金funded by the Science and Technology Department of Yunnan Province(202303AA080006)the National Natural Science Foundation of China(41972312 and 41672329).
文摘A systematic study of early Paleozoic S-type granites in Pinghe enhances our understanding of the tectonic evolution of proto-Tethys and provides a foundation for exploring rare metal deposits in the region.The Pinghe granites consist of monzogranite and leucogranite.Zircon U-Pb dating shows that the emplacement ages of the monzogranite and leucogranite are 502.0 Ma and 500.9 Ma,respectively.All samples have high SiO_(2) content and a weakly to strongly peraluminous character(A/CNK=1.08-1.23),consistent with S-type granites.The monzogranite has relatively high CaO,Sr,Ba,and CaO/Na_(2)O ratios but lower Rb.In contrast,the leucogranite has lower CaO,Sr,Ba,and CaO/Na_(2)O ratios but higher Rb.The similar ε_(Nd)(t)values(−9.3 to−8.4)and Pb isotopic compositions((^(206)Pb/^(204)Pb)t=18.03-19.36,(^(207)Pb/^(204)Pb)t=15.66-15.76,(^(208)Pb/^(204)Pb)t=37.97-38.55)suggest that the monzogranite formed through partial melting of crustal greywacke,while the leucogranite originated from partial melting of crustal pelite.Regional geological studies suggest that these S-type granites in Pinghe were emplaced in an active continental margin setting,associated with the westward subduction of the proto-Tethys oceanic slab.The geochemical characteristics of leucogranite are consistent with those of tungsten-tin-related granites,indicating significant metallogenic potential for W and Sn deposits.
基金supported by The National Natural Science Foundation of China [U2244208, 42302138]the Science Foundation of China University of Petroleum, Beijing[2462024XKQY001]。
文摘Eastern Sichuan Basin is a critical region for oil and gas production in China,and the thermal effect of the Emeishan Mantle Plume(EMP) on the basin remains unclear,which limits the study of the Paleozoic hydrocarbon accumulation process.Thus,clarifying the thermal history is crucial for oil and gas evaluation and exploration.This study combines zircon fission track(ZFT),zircon(U-Th)/He(ZHe),and vitrinite reflectance analyses to reconstruct the thermal history since the Paleozoic and investigate the maturity evolution of Paleozoic source rocks in the eastern Sichuan Basin.Additionally,the contributing factors of the Permian abnormal heat flow and the thermal effect range of the EMP were analyzed.Thermal history results show a stable low heat flow phase(45-55 mW/m^(2)) from the Cambrian to Permian,a rapid increase to peak values(62-70 mW/m^(2)) during the Middle Permian,and a gradual decline to current stable values(47-62 mW/m^(2)) from the Triassic onward.Thermal evolution revealed that Paleozoic source rocks exhibited maturation stagnation due to tectonic events,while the Permian peak heat flow and the Jurassic-Late Cretaceous rapid burial accelerated maturation.The Cambrian Qiongzhusi Formation and Silurian Longmaxi Formation source rocks began generating hydrocarbons(R_(equ)=0.5%) in the Late Cambrian-Late Ordovician and Late Silurian-Early Devonian,respectively,while it was Late Permian-Early Triassic for Permian source rocks.Peak maturity(R_(equ)> 2%) occurred in the Late Cretaceous,with natural gas as the dominant product The EMP significantly influenced the thermal regime of the western and central Sichuan Basin,with a thermal effect radius of~600-650 km.In contrast,the Permian thermal anomaly in the eastern Sichuan Basin is attributed to the lithospheric extension associated with the Middle Permian Kaijiang-Liangping trough.These findings provide critical insights for deep and ultra-deep gas exploration and enhance the understanding of the EMP's regional thermal impacts.
文摘The International Geoscience Program project IGCP-580(started in 2009),focuses on the application of magnetic susceptibility(MS)as a paleoclimatic proxy on Paleozoic sedimentary rocks and on the characterization of the magnetic susceptibility signal.Here we provide a summary of the scientific targets behind the project and a summary of the organized activities.This project concerns three main issues:the first one consists of compiling the available MS data from the different researchers and continuing the collection of new data(with a main focus on the Devonian).The second issue focuses on the identification of the nature and origin of the magnetic minerals carrying MS signal.The last issue concerns the application of MS as a correlation,cyclostratigraphic and paleoclimatic tool.The IGCP-580 community consists of 245 researchers,from 45 countries(including Kenya,Namibia,Vietnam,Iran,Uzbekistan,Algeria,Tunisia,Colombia,Nigeria,India,etc.).During the project,we organized five meetings(Belgium,China,Czech Republic,Austria,Canada),three special sessions in international meetings and eight field workshops,as well as various training sessions.
基金the supports from the National 973 Project on Westemn China (No.2001CB409804)the National Natural Science Foundation of China (grants 49772151 , 49832040)
文摘The Tianshan range could have been built by both late Early Paleozoicaccretion and Late Paleozoic collision events. The late Early Paleozoic Aqqikkudug-Weiya suture ismarked by Ordovician ophiolitic melange and a Silurian flysch sequence, high-pressure metamorphicrelics, and mylonitized rocks. The Central Tianshan belt could principally be an Ordovician volcanicarc; whereas the South Tianshan belt, a back-arc basin. Macro- and microstructures, along withunconformities, provide some kinematic and chronological constraints on 2-phase ductile deformation.The earlier ductile deformation occurring at ca. 400 Ma was marked by north-verging ductileshearing, yielding granulite-bearing ophiolitic melange blocks and garnet-pyroxene-facies ductiledeformation, and the later deformation, a dextral strike-slip tectonic process, occurred during theLate Carboniferous-Early Permian. Early Carboniferous molasses were deposited unconformably onpre-Carboniferous metamorphic and ductilely sheared rocks, implying the end of the early orogeny.The large-scale ductile strike-slip along the Aqqikkudug-Weiya zone was possibly caused by thesecond tectonic event, the Hercynian collision between the northern Tarim block and the southernSiberian block. Late Paleozoic granitic magmatism and superimposed structures overprinted this EarlyPaleozoic deformation belt. Results of geometric and kinematic studies suggest that the primaryframework of the Southern-Central Tianshan belt, at least the eastern part of the Tianshan belt, wasbuilt by these two phases of accretion events.
基金jointly supported by the National Key Basic Research Program of China (973 Program: 2012CB214700)the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB10040300)the National Natural Science Foundation of China (41321002)
文摘The Lower Paleozoic shale in south China has a very high maturity and experienced strong tectonic defor- mation. This character is quite different from the North America shale and has inhibited the shale gas evaluation and exploration in this area. The present paper reports a com- prehensive investigation of maturity, reservoir properties, fluid pressure, gas content, preservation conditions, and other relevant aspects of the Lower Paleozoic shale from the Sichuan Basin and its surrounding areas. It is found that within the main maturity range （2.5 % 〈 EqRo 〈 3.5 %） of the shale, its porosity develops well, having a positive cor- relation with the TOC content, and its gas content is con- trolled mainly by the preservation conditions related to the tectonic deformation, but shale with a super high maturity （EqRo 〉 3.5 %） is considered a high risk for shale gas exploration. Taking the southern area of the Sichuan Basin and the southeastern area of Chongqing as examples of uplifted/folded and faulted/folded areas, respectively, geo- logical models of shale gas content and loss were proposed. For the uplifted/folded area with a simple tectonic defor- mation, the shale system （with a depth 〉 2000 m） has lar- gely retained overpressure during uplifting without a great loss of gas, and an industrial shale gas potential is generally possible. However, for the faulted/folded area with a strong tectonic deformation, the sealing condition of the shale system was usually destroyed to a certain degree with a great loss of free gas, which decreased the pressure coefficient and resulted in a low production capacity. It is predicted that the deeply buried shale （〉3000 m） has a greater gas potential and will become the focus for further exploration and development in most of the south China region （outside the Sichuan Basin）.
基金supported by the Australian Governmentsupport of the Australian Government Research Training Program Scholarship+1 种基金supported by Australian Research Council grant DE160101020supported by Australian Research Council grant IH130200012 and DP130101946
文摘Detailed global plate motion models that provide a continuous description of plate boundaries through time are an effective tool for exploring processes both at and below the Earth's surface. A new generation of numerical models of mantle dynamics pre-and post-Pangea timeframes requires global kinematic descriptions with full plate reconstructions extending into the Paleozoic(410 Ma). Current plate models that cover Paleozoic times are characterised by large plate speeds and trench migration rates because they assume that lowermost mantle structures are rigid and fixed through time. When used as a surface boundary constraint in geodynamic models, these plate reconstructions do not accurately reproduce the present-day structure of the lowermost mantle. Building upon previous work, we present a global plate motion model with continuously closing plate boundaries ranging from the early Devonian at 410 Ma to present day.We analyse the model in terms of surface kinematics and predicted lower mantle structure. The magnitude of global plate speeds has been greatly reduced in our reconstruction by modifying the evolution of the synthetic Panthalassa oceanic plates, implementing a Paleozoic reference frame independent of any geodynamic assumptions, and implementing revised models for the Paleozoic evolution of North and South China and the closure of the Rheic Ocean. Paleozoic(410-250 Ma) RMS plate speeds are on average ～8 cm/yr, which is comparable to Mesozoic-Cenozoic rates of ～6 cm/yr on average.Paleozoic global median values of trench migration trend from higher speeds(～2.5 cm/yr) in the late Devonian to rates closer to 0 cm/yr at the end of the Permian(～250 Ma), and during the Mesozoic-Cenozoic(250-0 Ma) generally cluster tightly around ～1.1 cm/yr. Plate motions are best constrained over the past 130 Myr and calculations of global trench convergence rates over this period indicate median rates range between 3.2 cm/yr and 12.4 cm/yr with a present day median rate estimated at～5 cm/yr. For Paleozoic times(410-251 Ma) our model results in median convergence rates largely～5 cm/yr. Globally,～90% of subduction zones modelled in our reconstruction are determined to be in a convergent regime for the period of 120-0 Ma. Over the full span of the model, from 410 Ma to 0 Ma,～93% of subduction zones are calculated to be convergent, and at least 85% of subduction zones are converging for 97% of modelled times. Our changes improve global plate and trench kinematics since the late Paleozoic and our reconstructions of the lowermost mantle structure challenge the proposed fixity of lower mantle structures, suggesting that the eastern margin of the African LLSVP margin has moved by as much as ～1450 km since late Permian times(260 Ma). The model of the plate-mantle system we present suggests that during the Permian Period, South China was proximal to the eastern margin of the African LLSVP and not the western margin of the Pacific LLSVP as previous thought.
基金financially sponsored by The National Key Research and Development Program of China (Grant No. 2016YFC0600502)the Program of the China Geological Survey (Grant Nos. 1212011121260, 1212011220920)111 Project (B07011)
文摘The East Kunlun Orogenic Belt(EKOB) provides an important link to reconstruct the evolution of the Proto-Tethys and Paleo-Tethys realm. The EKOB is marked by widespread Early Paleozoic magmatism.Here we report the petrology, bulk geochemistry, zircon Ue Pb dating and, Lue Hf and SreN d isotopic data of the Early Paleozoic granitic rocks in Zhiyu area of the southern EKOB. Based on the zircon U-Pb dating, these granitoids, consisting of diorite, granodiorite and monzogranite, were formed during 450 -430 Ma the Late Ordovician to Middle Silurian. The diorite and granodiorite are high Sr/Y ratio as adakitic affinities, and the monzogranite belongs to highly fractionated I-type. Their(^(87)Sr/^(86)Sr)ivalues range from 0.7059 to 0.7085, εNd(t) values from -1.6 to -6.0 and the zircon εHf(t) values show large variations from +9.1 to -8.6 with Hf model ages(T_(DM2)) about 848 Ma and 1970 Ma. The large variations of whole-rock Nd and zircon Hf isotopes demonstrate strong isotopic heterogeneity of the source regions which probably resulted from multi-phase underplating of mantle-derived magmas. Geochemical and isotopic studies proved that the diorite and granodiorite had been derived from partial melting of heterogeneous crustal source with variable contributions from ancient continental crust and juvenile components, and the monzogranites were representing fractional crystallization and crustal contamination for arc magma. The Early Paleozoic adakitic rocks and high-K calc-alkaline granitoids in the southern EKOB were likely emplaced in a continental marginal arc setting possibly linked to the southwards subduction of the Paleo Kunlun Ocean and the magma generation is linked to partial melting of thickened continental crust induced by underplating of mantle-derived magmas.
基金supported by the National Basic Research Program of China (No. 2007CB209503)National Natural Science Foundation of China (No. 41102086)
文摘The Ordos Basin is a significant petroliferous basin in the central part of China.The Carboniferous and Permian deposits of transitional and continental facies are the main gas-bearing layers in the north part of the basin.The Carboniferous and Permian natural gas reservoirs in the northern Ordos Basin are mainly tight sandstone reservoirs with low porosity and low permeability,developing lots of ＂sweet spots＂ with comparatively high porosity and permeability.The tight sandstones in the study area are gas-bearing,and the sweet spots are rich in gas.Sweet spots and tight sandstones are connected rather than being separated by an interface seal.Sweet spot sand bodies are vertically and horizontally overlapped,forming a large gas reservoir group.In fact,a reservoir formed by a single sweet spot sand body is an open gas accumulation.In the gentle dipping geological setting and with the source rocks directly beneath the tight reservoirs over a large area,the balance between gas charging into tight reservoirs from source rocks and gas loss from tight reservoirs through caprock is the key of gas accumulation in tight sandstones.Both the non-Darcy flow charging driven by source-reservoir excess pressure difference and the diffusion flow charging driven by source-reservoir gas concentration difference play an important role in gas accumulation.The results of mathematical modeling indicate that the gas accumulation cannot be formed by just one of the above mechanisms.The diffusion of gas from source rocks to reservoirs is a significant mechanism of tight sandstone gas accumulation.
基金supported in part by a grant from the National Science Foundation of China(No40674046)
文摘The Cambrian to Cretaceous paleomagnetic data from Chinese continental and adjacent blocks were collected using principles to obtain reliable and high-precision paleomagnetic data and to pay attention to the similarity of paleobiogeography and the coordination of tectonic evolution.The Chinese continental blocks were laid up on the reconstruction of proposed global paleocontinents with almost the same scale.Thus,it can be clearly recognized that the global continents,including Chinese continental blocks,range along latitudes on the southern side of the equator during the Early Paleozoic. In the Paleozoic,Chinese continental blocks were still located among the Laurentia,Siberia and Gondwana plates,following the fast moving of the Siberia Plate northwards,the amalgamation in a north-south direction at the western parts of the Laurentia and Gondwana plates,and the Iapetus and Rheic Oceans were subducted,eventually to form a uniform Pangea in the Late Paleozoic.The Australian and Indian plates of Eastern Gondwana moved and dispersed gradually southwards, continued to extend the Paleo-Tethys Ocean.The Chinese continental and adjacent blocks were still located in the Paleo-Tethys Ocean,preserved the status of dispersion,gradually moving northwards, showing characteristics of ranging along a north-south orientation until the Permian.In addition,a series of local collisions happened during the Triassic,and consequently most of the Chinese continental blocks were amalgamated into the Pangea,except for the Gangdise and Himalayan blocks. There was a counter-clockwise rotation of the Eastern Asian continent in the Jurassic and northwards migration of the Chinese continent in varying degrees during the Cretaceous,but the Himalayan and Indian plates did not collide into the Chinese continent during this period.
基金supports by the Basic Research Foundation of the Institute of Geomechanics,CAGS,China (DZLXJK200703)the National Natural Science Foundation of China(40342015)+1 种基金SinoProbe-Deep Exploration in China(SinoProbe-08)the National Science Foundation(USA) Instrumentation and Facilities Program (EAR-0443387)
文摘The eastern margin of the Qaidam Basin lies in the key tectonic location connecting the Qinling, Qilian and East Kunlun orogens. The paper presents an investigation and analysis of the geologic structures of the area and LA-ICP MS zircon U-Pb dating of Paleozoic and Mesozoic magmatisms of granitoids in the basement of the eastern Qaidam Basin on the basis of 16 granitoid samples collected from the South Qilian Mountains, the Qaidam Basin basement and the East Kunlun Mountains. According to the results in this paper, the basement of the basin, from the northern margin of the Qaidam Basin to the East Kunlun Mountains, has experienced at least three periods of intrusive activities of granitoids since the Early Paleozoic, i.e. the magmatisms occurring in the Late Cambrian （493.1±4.9 Ma）, the Silurian （422.9±8.0 Ma-420.4±4.6 Ma） and the Late Permian-Middle Triassic （257.8±4.0 Ma-228.8＋1.5 Ma）, respectively. Among them, the Late Permian - Middle Triassic granitoids form the main components of the basement of the basin. The statistics of dated zircons in this paper shows the intrusive magmatic activities in the basement of the basin have three peak ages of 244 Ma （main）, 418 Ma, and 493 Ma respectively. The dating results reveal that the Early Paleozoic magmatism of granitoids mainly occurred on the northern margin of the Qaidam Basin and the southern margin of the Qilian Mountains, with only weak indications in the East Kunlun Mountains. However, the distribution of Permo-Triassic （P-T） granitoids occupied across the whole basement of the eastern Qaidam Basin from the southern margin of the Qilian Mountains to the East Kunlun Mountains. An integrated analysis of the age distribution of P-T granitoids in the Qaidam Basin and its surrounding mountains shows that the earliest P-T magmatism （293.6-270 Ma） occurred in the northwestern part of the basin and expanded eastwards and southwards, resulting in the P-T intrusive magmatism that ran through the whole basin basement. As the Cenozoic basement thrust system developed in the eastern Qaidam Basin, the nearly N-S-trending shortening and deformation in the basement of the basin tended to intensify from west to east, which went contrary to the distribution trend of N-S-trending shortening and deformation in the Cenozoic cover of the basin, reflecting that there was a transformation of shortening and thickening of Cenozoic crust between the eastern and western parts of the Qaidam Basin, i.e., the crustal shortening of eastern Qaidam was dominated by the basement deformation （triggered at the middle and lower crust）, whereas that of western Qaidam was mainly by folding and thrusting of the sedimentary cover （the upper crust）.
基金This research is part of a project carried out during 2002-2004 and supported by the National Basic Research Program(Grant No.2001CB209100).
文摘The upper Paleozoic natural gas reservoirs in the Ordos basin are generally characterized by a large gas-bearing area and low reserve abundance. On such a geological background, there still exist gas-enriched zones, with relatively high outputs, high reserve abundance and stably distributed gas layers. The gas-enriched layers with relatively high permeability （the lower limit permeability is 0.5×10^-3μm^2） are key factors for the enrichment and high output of natural gas. Based on core observation, analytic results of inclusions, and a great deal of drilling data, we proposed the following four mechanisms for the formation of high-quality reservoirs： （1） in the source area the parent rocks are mainly metamorphic rocks and granites, which are favorable to keeping primary porosity; （2） under the condition of low A/S （accommodation/sediment supply） ratios, sandstone complex formed due to multistage fluvial stacking and filling are coarse in grain size with a high degree of sorting, low content of mud and good physical properties; （3） early-stage recharge of hydrocarbons restricted compaction and cementation, and thus are favorable to preservation of primary pores; （4） microfractures caused by the activity of basement faults during the Yanshan Movement stage can not only improve the permeability of tight sandstones, but also afford vertical pathways for hydrocarbon gas migration.
文摘During the Paleozoic, the Ordos area in the western North China Plate was located at the intersecting position of microplates and controlled by their interaction. The structural framework in the Ordos area, which underwent transformations in the Ordovician, the Carboniferous and the Permian respectively, was dominated by the alternation of uplift and depression. The transformations of structural framework are utilized as the clues to investigate the microplates＇ interacting type and its response in the Ordos area. According to the regional structural evolution, the Ordos area is simplified into an isopachous, isotropic and elastic shell model, and under proposed various boundary conditions, three series of numerical simulations corresponding to the three structural transformations are carried out to determine the detailed tectonic constraints. Numerical simulations reveal that the structure of the uplift and depression, which is similar to the actual pattern, develops only under one special boundary condition in each of the three series, indicating that the structural framework responds to the unique tectonic background. The simulation results show that in the Early Paleozoic, the L-shaped paleouplift formed nearby the southwestern corner of the Ordos area because the intensity of the compressions in the southern and western boundaries resulting from the ocean-continent collisions was similar. In the Late Paleozoic, it evolved into continent-continent （or arc-continent） interaction in the southern and northern boundaries; in the preliminary stage of the interaction, since the interface between the North China Plate and the plates on the south and north was narrow, the relative acting force was little and the regional western boundary immobile, and the structural framework in the basin was characterized by the N-S trending slender-waist-shaped uplift; as the interface between the plates expanded gradually, the extrusive force in the southern and northern boundaries of the North China Plate increased, resulting in the paleogeographic divisions showing E-W trending, and, the western boundary of the basin was extruded westward due to the intense compression inducing the local NE trending of paleogeographic division in the central area. The simulation results further reflect that the symmetry of the uplift-depression pattern is restricted by that of the boundary conditions, suggesting that the Paleozoic structural transformations of the Ordos area under boundary constraints accord with the universal physical symmetrical principle.
基金the financial support for this study from the State Key Program of National Natural Science of China (Grant No.90814005)Natural Science Foundations of China (Grant No.41172127)+1 种基金the State Key Laboratory of Continental Dynamics (Grant No.BJ081334)the State Key Laboratory of Petroleum Resources and Prospecting (China University of Petroleum, 2008)
文摘The hydrocarbon potential of the Hangjinqi area in the northern Ordos Basin is not well known, compared to the other areas of the basin, despite its substantial petroleum system.Restoration of a depth-converted seismic profile across the Hangjinqi Fault Zone（HFZ） in the eastern Hangjinqi area shows one compression that created anticlinal structures in the Late Triassic, and two extensions in ~Middle Jurassic and Late Early Cretaceous, which were interrupted by inversions in the Late Jurassic–Early Early Cretaceous and Late Cretaceous, respectively.Hydrocarbon generation at the well locations in the Central Ordos Basin（COB） began in the Late Triassic.Basin modeling of Well Zhao-4 suggests that hydrocarbon generation from the Late Carboniferous–Early Permian coal measures of the northern Shanbei Slope peaked in the Early Cretaceous, predating the inversion in the Late Cretaceous.Most source rocks in the Shanbei Slope passed the main gas-migration phase except for the Hangjinqi area source rocks（Well Jin-48）.Hydrocarbons generated from the COB are likely to have migrated northward toward the anticlinal structures and traps along the HFZ because the basin-fill strata are dipping south.Faulting that continued during the extensional phase（Late Early Cretaceous） of the Hangjinqi area probably acted as conduits for the migration of hydrocarbons.Thus, the anticlinal structures and associated traps to the north of the HFZ might have trapped hydrocarbons that were charged from the Late Carboniferous–Early Permian coal measures in the COB since the Middle Jurassic.
基金Supported by the National Natural Science Foundation of China (41872128)the CNPC Major Science and Technology Project (2021DJ0101)。
文摘Based on the analysis of Upper Paleozoic source rocks, source-reservoir-caprock assemblage, and gas accumulation characteristics in the Ordos Basin, the gas accumulation geological model of total petroleum system is determined. Then, taking the Carboniferous Benxi Formation and the Permian Taiyuan Formation and Shanxi Formation as examples, the main controlling factors of gas accumulation and enrichment are discussed, and the gas enrichment models of total petroleum system are established. The results show that the source rocks, faults and tight reservoirs and their mutual coupling relations control the distribution and enrichment of gas. Specifically, the distribution and hydrocarbon generation capacity of source rocks control the enrichment degree and distribution range of retained shale gas and tight gas in the source. The coupling between the hydrocarbon generation capacity of source rocks and the physical properties of tight reservoirs controls the distribution and sweet spot development of near-source tight gas in the basin center. The far-source tight gas in the basin margin is mainly controlled by the distribution of faults, and the distribution of inner-source, near-source and far-source gas is adjusted and reformed by faults. Generally, the Upper Paleozoic gas in the Ordos Basin is recognized in four enrichment models: inner-source coalbed gas and shale gas, inner-source tight sandstone gas, near-source tight gas, and far-source fault-transported gas. In the Ordos Basin, inner-source tight gas and near-source tight gas are the current focuses of exploration, and inner-source coalbed gas and shale gas and far-source gas will be important potential targets in the future.
