Original sedimentary manganese(Mn)deposits and supergene Mn ores are important Mn resources in China.However,the geochemical information from Chinese supergene Mn ores is scarce,and the relationship between sedimentar...Original sedimentary manganese(Mn)deposits and supergene Mn ores are important Mn resources in China.However,the geochemical information from Chinese supergene Mn ores is scarce,and the relationship between sedimentary Mn deposits and supergene Mn ores is ambiguous.In this study,we collected the original Mn-bearing dolomitic sandstones(ZK20-3 drillcore)and supergene Mn ores(Longmen Section)from eastern Hebei,North China for systematic petrographic,mineralogical and geochemical analyses.Our new data help us to figure out the transformation from original Mn-bearing deposits to supergene ores.The main minerals of original Mn-bearing dolomitic sandstones are quartz and feldspar,with minor muscovite,dolomite,rhodochrosite,ankerite,and kutnohorite.Supergene Mn-oxide ores only emerged in the middle part of the Longmen(LM)Section,and mainly contain quartz,pyrolusite,cryptomelane,todorokite and occasional dolomite.The possible transformation sequence of Mn minerals is:kutnohorite/rhodochrosite→pyrolusite(Ⅰ)→cryptomelane(todorokite)→todorokite(cryptomelane)→pyrolusite(Ⅱ).For Mn-oxide ores,Fe,Na and Si are enriched but Al,Ca,Mg and K are depleted with the enrichment of Mn.For original and supergene ores,the total rare earth element+ytterbium(∑REY)contents range from 105.68×10^(-6)to 250.56×10^(-6)and from 18.08×10^(-6)to 176.60×10^(-6),respectively.Original Mn ores have similar slightly LREE-enriched patterns,but the purer Mn-oxide ore shows a HREE-enriched pattern.In the middle part of the LM Section,positive Ce anomalies in Mn-oxide ores indicate the precipitation of Ce-bearing minerals.It implies the existence of geochemical barriers,which changed p H and Eh values due to the long-time influence of groundwater.展开更多
The Cretaceous Koum Basin is a rift-related half-graben in northern Cameroon,which constitutes a portion of the Yola Arm of the Upper Benue Trough.This study presents the first comprehensive dataset combining mineral-...The Cretaceous Koum Basin is a rift-related half-graben in northern Cameroon,which constitutes a portion of the Yola Arm of the Upper Benue Trough.This study presents the first comprehensive dataset combining mineral-ogical,bulk-rock geochemical,and stable C-H-O isotopic data for dark-gray,finegrained mudstones from the basin,providing new insights into its sediment source,paleoenvironment,and geodynamic setting.The mudstones primarily consist of phyllosilicates(~8.6%),feldspars(~30.5%),carbonates(~13.7%),and minor iron oxides(~2.7%),with vermiculite,illite,and kaolinite as the main clay minerals.The presence of analcime,ankerite,and dolomite suggests low-grade metamorphism and/or hydrothermal alteration.Fe_(2)O_(3)/K_(2)O(1.52-6.40)and SiO_(2)/Al_(2)O_(3)(2.97-4.68)ratios classify the mudstones as compositionally immature shales(ICV~1.64)with low-moderate chemical weathering(CIA~56.35;PIA~59.74;R^(3+)/R^(3+)+R^(2+)+M^(+)~0.51).Trace element ratios(Th/Sc~1.70,Zr/Sc~1.33,La/Sc~6.30,La/Th~4.14)indicate an intermediate igneous provenance from a continental crustal source.Paleoenviron-mental proxies suggest deposition in a dynamic basin environment marked by fluctuating redox(C org/P:0.21-178.34)and salinity(Sr/Ba:0.34-3.25;N-values:48-35.92)conditions,ranging from oxic to anoxic and brackish to saline.Major element data(SiO_(2) vs.Al_(2)O_(3)+K_(2)O+Na_(2)O)indicate a semi-arid regime,while Paleoclimatic indicators such as Sr/Cu(1.88-37.47)and C-values(0.12-0.93)suggests alter-nating humid and arid conditions.Notably,stable isotope data,reported here for the first time in the Koum Basin,reveal a predominantly terrestrial,fluvial-deltaic C_(3) plant source for organic carbon(δ^(13)C-25.2‰ to -35.2‰)and complex fluid-rock interactions involving meteoric and magmatic-metamorphic fluids under a warm,equatorial climate(δ^(18)O+3.6‰to +24.9‰,δ^(2)H-104‰ to-50‰).The combined mineralogical,geochemical,and isotopic data point to deposition in a tectonically active continental arc setting,with contributions from ocean island arc and passive margin sources.展开更多
A cluster of serpentinite bodies has been recognized tectonically emplaced within the greenschist-amphibolite-facies metamorphic terrane in Hong'an,western Dabie orogen,central China.Two types of serpentinites are...A cluster of serpentinite bodies has been recognized tectonically emplaced within the greenschist-amphibolite-facies metamorphic terrane in Hong'an,western Dabie orogen,central China.Two types of serpentinites are identified on the basis of integrated petrographic,mineralogical and geochemical study.The first type,represented by Yinshanzhai serpentinite complex(Group 1)comprises heterogeneous lithology as a massive serpentinite matrix“intruded”by antigoriteenriched serpentinite lenses.They are both pseudomorphic textured with different mineral assemblages indicating an increasing temperature-pressure condition.Serpentinite matrix(Group 1a)is chemically characterized by high MgO/SiO_(2)and low Al_(2)O_(3)/SiO_(2),Ti and Ca contents,suggesting a depleted mantle wedge origin.The coexistence of compositionally-heterogeneous chromite with highCr^(#)(0.78-0.96)and intermediate-Cr^(#)(0.59-0.70)pristine cores indicates extensive mantle melting.Meanwhile,extremely high Fo olivine relicts(96-97)with considerably higher MnO and lower NiO contents than mantle olivine indicate that they are metamorphic products from serpentine decomposition.Accordingly,we propose that Yinshanzhai serpentinite complex experienced two distinct episodes of hydration.The serpentinite lenses(Group 1b)show higher SiO_(2)and lower MgO concentrations.Nevertheless,the trace elements of groups 1a and 1b are consistent:U-shaped REE patterns,positive Eu anomalies and enrichment of LILE(i.e.,Cs,U)are all identified as forearc properties.They are affected by reducing slab-derived fluids in forearc mantle,with f_(O2)of 1 to 2 logarithmic units below f_(O2)of fayalite-magnetite-quartz buffer(FMQ-2~FMQ-1).The second type is antigorite-serpentinites(Group2)represented by Ximaoshan and Wangchunwan blocks.They are non-pseudomorphic,with no primary framework silicate surviving.Fertile compositions(i.e.,higher Al_(2)O_(3)and Al_(2)O_(3)/SiO_(2),nearly flat REE patterns)and conjoint enrichment of LILE with HFSE suggest melt/rock interaction.Negative Ce,Eu anomalies,and enriched U relative to alkaline elements demonstrate interactions with more oxidized seawater or seafloor fluids(FMQ~FMQ-1).Remarkable Sr negative anomalies may be attributed to Sr release during lizardite/antigorite transition in subduction zone,indicating interaction with low-Sr slab fluids.We propose that Group 2 serpentinites originate either from mantle wedge or abyssal peridotites,refertilized by mantle melts,then hydrated in seafloor or shallow forearc and entrapped into subduction channel.Combined with geochronology and tectonic constraints of associated eclogites in Hong'an terrane,the two types of serpentinites may correlate with subduction of different oceanic basins during the late Paleozoic and/or Proterozoic eras.It raises possibility of defining an ophiolitic setting in Hong'an Orogen for which further evidence is required.展开更多
The Chinese Altai,a key component of the Central Asian Orogenic Belt(CAOB),represents a significant Phanerozoic accretionary orogenic belt.The oceanic-continental subduction processes spanning the Cambrian to Carbonif...The Chinese Altai,a key component of the Central Asian Orogenic Belt(CAOB),represents a significant Phanerozoic accretionary orogenic belt.The oceanic-continental subduction processes spanning the Cambrian to Carboniferous and subsequent intracontinental extension since the Triassic have been well documented in the Chinese Altai,the southwestern segment of the CAOB.Deciphering the petrogenetic evolution of this region during the Permian is thus crucial for advancing our understanding of its tectonic transitions.However,the Permian tectonic setting of the Chinese Altai remains contentious.To address this knowledge gap,this study presents new geochronological and geochemical data for the Jiangjunshan pluton in the southern Chinese Altai.Zircon U-Pb geochronology reveals that the gabbro and two-mica alkali feldspar granite—which collectively constitute the primary lithology of the Jiangjunshan pluton—were emplaced at∼272±3.5 and∼272±1.6 Ma,respectively.Geochemically,the gabbro exhibits pronounced light rare-earth element(LREE)depletion,low Nb/Yb(0.39–0.46)and Ti/V(23.7–25.3)ratios,and trace-element signatures akin to normal mid-ocean ridge basalts(N-MORB).However,its conspicuous Nb-Ta depletion parallels that of island arc basalts.Depleted Hf-Nd isotopic compositions(ε_(Hf)(t)=+0.60 to+4.63,ε_(Nd)(t)=+6.32 to+7.80)in the gabbro,coupled with negligible correlation betweenε_(Nd)(t)and SiO2 contents imply limited crustal assimilation during magma evolution.Petrological modeling,based on Sm/Yb and La concentrations,suggests the gabbroic melt derived from∼8%–20%spinel lherzolte mantle melting.Analogously depleted Hf-Nd isotopes(ε_(Hf)(t)=+6.81 to+9.10,ε_(Nd)(t)=+0.79 to+1.45)in the granite,together with petrographic evidence lacking mafic-ultramafic xenoliths,point to a juvenile lower-crustal source.Integrating the gabbro’s N-MORB-like affinity with arc-specific features,regional ultrahigh-temperature metamorphism in southern Chinese Altai,and Permian tectonics,we propose a ridge-subduction regime as the likely petrogenetic setting for the Jiangjunshan magmas.During ridge subduction,upwelling of asthenospheric mantle beneath the ridge induced partial melting of the lithospheric mantle,giving rise to the parental magma of the Jiangjunshan gabbro.This mafic magma underplating subsequently heated the juvenile lower crust,triggering its partial melting and generating the parental magma of the two-mica alkali feldspar granite.Our model indicates that ridge-subduction-related magmatism persisted in the Chinese Altai until the Middle Permian,followed by a tectonic shift from oceanic-continental subduction to intracontinental extension.展开更多
Zircon U-Pb ages,major and trace elements and Sr-Nd-Hf isotope data of the diabase in the Zhangjiakou District were studied to investigate its derivation and tectonic implications.Zircon U-Pb ages indicate that the di...Zircon U-Pb ages,major and trace elements and Sr-Nd-Hf isotope data of the diabase in the Zhangjiakou District were studied to investigate its derivation and tectonic implications.Zircon U-Pb ages indicate that the diabase was emplaced at∼130 Ma or younger,and captured zircons cluster at∼147,∼240,∼430 and∼465 Ma.The diabase is characterized by minor variations in SiO_(2)(49.35 wt.%–52.10 wt.%),TiO_(2)(1.65 wt.%–1.77 wt.%),Al_(2)O_(3)(17.00 wt.%–18.26 wt.%),MgO(4.28 wt.%–4.93 wt.%),CaO(6.69 wt.%–7.90 wt.%)and Mg^(#)(48–54).It has no significant Eu anomaly and displays enrichment in large ion lithophile elements(Rb,Ba and Sr)and depletion in high field strength elements(Nb,Ta,P and Ti).The diabase exhibits homogeneous Sr((^(87)Sr/^(86)Sr)i=0.70606–0.70701)and Nd(ε_(Nd)(t)=−13.6 to−13.2)isotopic compositions.These features suggest that the parental magma was derived from partial melting of the ancient lower crust,relating to mantle upwelling that was triggered by the stagnant slabs or lithospheric detachment associated with the westward subduction of the Paleo-Pacific Plate.The Early Paleozoic inherited igneous zircons in the diabase suggest that the northern margin of the North China Craton(NCC)likely underwent southward subduction of the Paleo-Asian Ocean.展开更多
The pervasively distributed granitoids in South China contributed greatly to regional polymetallic mineralization,including tungsten,tin,copper,gold,rare metals,and rare earth elements(REEs).To ascertain the dynamic b...The pervasively distributed granitoids in South China contributed greatly to regional polymetallic mineralization,including tungsten,tin,copper,gold,rare metals,and rare earth elements(REEs).To ascertain the dynamic backgrounds,rock types and genesis of the parent rocks related to the Early-Middle Jurassic ionic rare earth mineralization,typical deposits at Muzishan,Xiahu,and Zudong were investigated by conducting petrographic,geochronologic,whole-rock geochemical,and Sr-Nd-Pb isotope analyses,which found that the parent rocks from the Muzishan deposit were the A1-type K-feldspar granite(~195 Ma),from the Zudong deposit were the A2-type monzogranite(~171 Ma),and from the Xiahu deposit were the I-type monzogranite(~167 Ma).All the three granitic rocks underwent different degrees of fractionation,with the Xiahu granite experiencing the highest degree,followed by the Zudong granite,and the Muzishan granite undergoing the lowest degree.The Muzishan granite was concluded to be formed under an intraplate extensional tectonic regime influenced by the hotspots or the mantle plume.The Zudong granite was formed in a post-arc extensional setting related to subduction-collision-rollback of the paleo-Pacific Plate,which caused upwelling of the asthenosphere,thinning of the lithosphere,and partial melting of crustal materials.The Xiahu granite was generated under a transitional tectonic setting of extension and compression,triggered by delamination and rollback of the paleo-Pacific Plate.展开更多
Elemental concentrations of the siliciclastic sediments from a sedimentary basin provide clues on paleo-weathering,paleoclimate,provenance,and tectonic setting of the basin.Records for Permo-Triassic mass extinction a...Elemental concentrations of the siliciclastic sediments from a sedimentary basin provide clues on paleo-weathering,paleoclimate,provenance,and tectonic setting of the basin.Records for Permo-Triassic mass extinction and climatic fluctuations are commonly traced from the sediments in the Gondwana basins.Nevertheless,our understanding on sedimentation,provenance,and regional tectonics of the Raniganj Basin,a Gondwana basin in the eastern India is poor.Minerals including clay particles and major and trace element concentrations of the siliciclastic sediments from different formations of the Raniganj Basin have been studied to establish the paleo-weathering,paleoclimate,provenance,and tectonic settings of the basin.This study suggests that the Talchir Formation experienced cold and dry climatic conditions at the sediment source area,while the Barakar,Raniganj,and Panchet formations had prevailing semiarid climates.The sources of the siliciclastic sediments are from the felsic rocks of the Chotanagpur Granite Gneissic Complex(CGGC).Further,the geochemical results suggest a rift-like(passive)tectonic setting for the Raniganj Basin,while few samples represent the collision tectonic setting of the basement CGGC,formed due to collision of major Indian blocks during the Paleo-Neoproterozoic time.展开更多
Lower Carboniferous clastic sedimentary rocks(i.e.,the Nanduan Formation)in the Changning-Menglian belt of the southeastern Tibetan Plateau may provide new insights into the tectonic evolution of the Paleo-Tethys Ocea...Lower Carboniferous clastic sedimentary rocks(i.e.,the Nanduan Formation)in the Changning-Menglian belt of the southeastern Tibetan Plateau may provide new insights into the tectonic evolution of the Paleo-Tethys Ocean.This paper presents new petrographic,geochemical,and detrital zircon U-Pb age data to constrain the provenance and depositional setting of these rocks.Sandstone samples of the Nanduan Formation are all quartz arenites(Q_(92-99)F_(1-7)L_(0-2))with high SiO_(2)contents(85.1 wt.%-95.2 wt.%;average=90.9 wt.%),indicating high compositional maturity.They exhibit fractionated rare earth element(REE)patterns,with light REE enrichment[(La/Yb)_(N)=6.48-12.1]and negative Eu anomalies(Eu/Eu^(*)=0.53-0.74),and marked negative Sr-Cs-V-Cr-Ni anomalies in upper continental crust-normalised multi-element diagrams.The geochemical features and heavy mineral assemblages suggest that sediments were mainly derived from ancient sedimentary rocks in cratonic interiors or stable continental areas,and were probably deposited in a passive continental margin setting.Detrital zircon U-Pb dating(n=256)of the Nanduan Formation sandstones defines three distinct age peaks in the Pan-African(600-500 Ma),younger Grenvillian(950-850 Ma),and older Grenvillian(1250-1000 Ma).Their zircon age spectra are similar to those of Lower Paleozoic sedimentary rocks(i.e.,the Mengtong and Mengdingjie groups)in the BaoshanSibumasu Block,but significantly different from those of older rocks in the Simao-Indochina and other surrounding blocks(i.e.,the western Yangtze,western Cathaysia,western Qiangtang,Tethyan Himalaya,and Lhasa blocks).This suggests that the Nanduan Formation was deposited at the margin of the Baoshan-Sibumasu Block.Combining the new data presented in this study with published data,we suggest that the Nanduan Formation and underlying Lancang Group were deposited in the same setting during the Early and Late Paleozoic,respectively.展开更多
The Erlian Basin is one of the most important multi-energy basins in China.The Baiyanhua area of the Chuanjing depression in the western Erlian Basin has recently become a favorable area for new progress in sandstone-...The Erlian Basin is one of the most important multi-energy basins in China.The Baiyanhua area of the Chuanjing depression in the western Erlian Basin has recently become a favorable area for new progress in sandstone-type uranium prospecting.However,the Cretaceous source-to-sink evolution of the Chuanjing depression in the Erlian Basin is poorly known.This paper presents the systematic geochemical and zircon U-Pb studies on the Saihantala Formation and Erlian Formation in the Baiyanhua area.The data obtained are functionally important for revealing the provenance and tectonic setting of the source rocks.The results show that the upper part of the Saihantala Formation and the lower part of the Erlian Formation are mainly composed of felsic sedimentary rocks.The source rocks originated from a continental margin arc environment in terms of tectonic setting.The detrital zircons ages have the dominant populations at ca.250-270 Ma,with two subdominant age groups at ca.1400-1800 and 1900-2100 Ma,respectively.Combined with the tectono-sedimentary evolution of the Chuanjing depression,we conclude that:(1)the provenance of the Cretaceous strata was mostly sourced from the Baiyanhua uplift;(2)the water depth became shallow in the Southern Sangendalai sag during the middle period of Saihantala,further preventing the formation of coal beds;(3)the formation of Baiyanhua uplift might provide the beneficial tectonic condition for uranium mineralization in the upper Saihantala Formation in southern Sangendalai sag.This is significant for us to understand the space allocation of coal and uranium in Chuanjing depression and evaluate the uranium metallogenic prospects in southern Sangendalai sag.展开更多
The Xing'an-Inner Mongolia Orogen is a critical tectonic unit for constraining the evolution of the Paleo-Asian Ocean.However,the location and time of the closure of the Paleo-Asian Ocean are still debated.Here,we...The Xing'an-Inner Mongolia Orogen is a critical tectonic unit for constraining the evolution of the Paleo-Asian Ocean.However,the location and time of the closure of the Paleo-Asian Ocean are still debated.Here,we select a representative basin in Dashizhai in northeastern China,using U-Pb zircon geochronology and geochemistry to analyze the sedimentary facies,depositional ages,and provenance.The results show that the ages of the Dashizhai Formation range from 400 to 347 Ma,the Shoushangou Formation range from 400 to 348 Ma,the Zhesi Formation range from 307 to 252 Ma,and the Linxi Formation range from 299 to 241 Ma.The Dashizhai Formation is composed of metamorphic andesite and clastic rocks.The Shoushangou Formation comprises siltstone,rhyolite,and argillaceous siltstone.The Zhesi and Linxi Formations are composed of mudstone and argillaceous siltstone.Geochemical data shows that these rocks are enriched in light rare earth elements and depleted in Eu with various La/Sc,Th/Sc,and La/Co ratios.The Permian Dashizhai Basin is from Permian volcanic and felsic igneous rocks from the Ergun,Xing'an,and Songliao blocks.The absence of the Late Carboniferous strata in the Dashizhai Basin indicates an extension setting during this period.Furthermore,we suggest the Xing'an-Inner Mongolia Orogen was an uplifting process associated with evolution the Paleo-Asian Ocean during the Late Permian.展开更多
Background The Bundelkhand Craton is significant for preserving the multiphase granitoids magmatism from Paleoarchean to Neoarchean periods.It consists of a variety of granite rocks,including TTGs,sanukitoids,and high...Background The Bundelkhand Craton is significant for preserving the multiphase granitoids magmatism from Paleoarchean to Neoarchean periods.It consists of a variety of granite rocks,including TTGs,sanukitoids,and high-K granitoids.This study presents geochemical characteristics of high-silica(68.97 wt.%–73.99 wt.%),low-silica(58.73wt.%–69.94 wt.%),and high K_(2)O(2.77 wt.%–6.16 wt.%)contents of granitoids.Objective The data on Bundelkhand Craton’s granitic magmatism and geodynamics is not sufficiently robust.Geochemical data from this study will be used to further understand the origin,source,and petrogenesis of granitoid rocks and their implications for the evolution of geodynamics.Methodology Twenty-one samples were collected and analyzed for major,trace,and REE elements.Major elements were measured using X-ray fluorescence spectrometry(XRF),and trace and REE elements were analyzed by ICP-MS.Standard procedures from the Geological Survey of India were followed.Results The geochemical analysis presents high-silica(68.97-73.99 wt.%),low-silica(58.73-69.94 wt.%),and high K_(2)O(2.77-6.16 wt.%)contents in granitoids,classified as granite-granodiorite.The rocks are calcic to calcalkalic,magnesian,and range from peraluminous to metaluminous composition.REE patterns showed strong LREE enrichment relative to HREEs,with prominent negative Eu anomalies corresponding to earlier plagioclase fractionation.Multi-element patterns revealed negative anomalies in Nb,Sr,P,and Ti and positive anomalies in Pb.Conclusion The geochemical signatures attributed to the post-collisional magma generation and continental crustal contamination.The studied rocks show A-type and A2-type lineage,suggesting they originated from the melting of continental crust during transitional/post-collisional tectonic activity.The formation of hybrid granitoids in the Bundelkhand Craton is connected to the fractionation of hybrid magmas in shallow-seated magma chambers during these tectonic processes.展开更多
Recent studies have highlighted the presence of lithium enrichment in coals within the Ordos Basin,which has garnered significant attention due to the potential economic value.However,most research has concentrated pr...Recent studies have highlighted the presence of lithium enrichment in coals within the Ordos Basin,which has garnered significant attention due to the potential economic value.However,most research has concentrated primarily on the coal seams of the Taiyuan and Shanxi formations,with limited reports on the Benxi Formation.To address this gap,our study focused on elucidating the geochemical characteristics and origins of the lithium enrichment in the No.8 coal of the Benxi Formation through the use of optical microscopy and inductively coupled plasma mass spectrometry(ICP-MS).The results showed that the No.8 coal was a bituminous coal,characterized by medium ash yield,low volatile matter,high total sulfur content and medium vitrinite proportion.The No.8 coal was enriched in Li(average 91.7 ppm,CC=6.55)and Zr(average 191 ppm,CC=5.30),the unusual enrichment of Li being primarily located in the middle of the coal.The minerals in the coal were predominantly clay minerals,along with minor amounts of pyrite,quartz and calcite.The occurrence mode of Li in the No.8 coal was associated with aluminosilicate minerals,presumably kaolinite.Based on geochemical characteristics,the sedimentary source of the No.8 coal was intermediate-felsic volcanic rock from the Yinshan oldland.The enrichment of Li can be attributed to the supply of terrestrial debris from the Yinshan oldland and the depositional environment.Our analysis identifies three distinct stages of lithium enrichment,emphasizing the critical role played by the terrestrial debris,as well as the acidic to partially reducing conditions,in facilitating this process.In conclusion,our study sheds light on the mechanisms underlying lithium enrichment in the No.8 coal of the Benxi Formation,highlighting the significance of geological factors in shaping the distribution and concentration of critical metals in coal.展开更多
To investigate the Early Cretaceous magmatic activity and tectonic evolution in the Xiaoqinggou mining area of Jilin Province,the authors conducted petrological,geochemical,and isotopic analyses of diorite rocks.The f...To investigate the Early Cretaceous magmatic activity and tectonic evolution in the Xiaoqinggou mining area of Jilin Province,the authors conducted petrological,geochemical,and isotopic analyses of diorite rocks.The findings show that the zircons exhibit distinct magmatic growth zoning,confirming their magmatic origin.LA–ICP–MS zircon U–Pb dating yielded an age of 128.7±2.2 Ma,corresponding to Early Cretaceous.Geochemical data reveal that the diorite rocks are high and potassium but low in sodium,classifying them within the peraluminous,high-potassium calc-alkaline series.They are enriched in large ion lithophile elements(e.g.,K,Ba and Rb)and depleted in high field strength elements(e.g.,Nb,Ta and Ti).TheδEu values range from 1.07 to 1.14,indicating weakly positive Eu anomalies.Regional comparisons and integrated studies suggest that the Xiaoqinggou diorite rocks formed in a volcanic island arc setting,associated with the westward subduction of the Paleo-Pacific plate beneath the Eurasian continent in an extensional tectonic environment.This study provides a theoretical basis for further exploration of the Xiaoqinggou deposit.展开更多
This study presents LA–ICP–MS U–Pb dating and whole-rock geochemical analyses of the Late Triassic Gangshan harzburgite in the Qingyuan area,with the aim of elucidating its petrogenesis and further constraining the...This study presents LA–ICP–MS U–Pb dating and whole-rock geochemical analyses of the Late Triassic Gangshan harzburgite in the Qingyuan area,with the aim of elucidating its petrogenesis and further constraining the early Mesozoic tectonic evolution of the eastern segment of the northern margin of the North China Block(NCB).Zircons from the harzburgites exhibit typical oscillatory growth zoning or striped absorp-tion in cathodoluminescence images.U–Pb analyses of zircons yield ages ranging from 2525 Ma to 225 Ma,with two youngest ages(225±7 Ma)indicating that the harzburgites were formed during Late Triassic.Geochemical analyses of the Gangshan harzburgites show that the rocks have low concentrations of SiO_(2)(42.38%–42.85%)and Al_(2)O_(3)(3.31%–3.33%),along with high concentrations of MgO(41.32%–41.76%),Cr(4856×10^(-6)–5191×10^(-6))and Ni(1942×10^(-6)–2041×10^(-6)).They also display low REE abundances(∑REE=4.38×10^(-6)–4.69×10^(-6))and flat REE patterns with low(La/Yb)_(N) ratios(1.24–1.56)and slightly po-sitive Eu anomalies(δEu=1.13–1.16).These features suggest that the Gangshan harzburgites are cumulates of basaltic magma derived from the depleted lithospheric mantle.Combined with previous studies,these Late Triassic mafic–ultramafic rocks,together with coeval granitoids in adjacent regions,constitute a typical bimodal association,suggesting that they formed in a post-orogenic extensional environment after the final closure of the Paleo-Asian Ocean.展开更多
Light oil and gas reservoirs are abundant in the Ordovician marine carbonate reservoir in Shunbei Oilfield,Tarim Basin.This presents a compelling geological puzzle,as ultra-deep reservoirs undergo intense alteration a...Light oil and gas reservoirs are abundant in the Ordovician marine carbonate reservoir in Shunbei Oilfield,Tarim Basin.This presents a compelling geological puzzle,as ultra-deep reservoirs undergo intense alteration and complex petroleum accumulation processes.A comprehensive suite of geochemical analyses,including molecular components,carbon isotope composition,homogenization temperature of saline inclusions,and burial-thermal history of single wells,was conducted to elucidate the genesis of these ancient reservoirs.Three petroleum filling events have been identified in the study area:Late Caledonian,Hercynian-Indosinian,and Himalayan,through analysis of homogenization temperatures of brine inclusions and burial-thermal histories.Additionally,the oil in the study area has undergone significant alteration processes such as biodegradation,thermal alteration,mixing,evaporative fractionation,and gas invasion.This study particularly emphasizes the influential role of Himalayan gas filling-induced evaporation fractionation and gas invasion in shaping the present petroleum phase distribution.Furthermore,analysis of light hydrocarbon and diamondoid parameters indicates the oil within the study area is at a high maturity stage,with equivalent vitrinite reflectance values ranging from 1.48%to 1.99%.Additionally,the analysis of light hydrocarbons,aromatics,and thiadiamondoids indicates that TSR should occur in reservoirs near the gypsum-salt layers in the Cambrian.The existence of the Cambrian petroleum system in the study area is strongly confirmed when considering the analysis results of natural gas type(oil cracking gas),evaporative fractionation,and gas invasion.Permian local thermal anomalies notably emerge as a significant factor contributing to the destruction of biomarkers in oil.For oil not subject to transient,abnormal thermal events,biomarker reliability extends to at least 190℃.In conclusion,examining the special formation mechanisms and conditions of various secondary processes can offer valuable insights for reconstructing the history of petroleum accumulation in ultradeep reservoirs.This research provides a scientific foundation for advancing our knowledge of petroleum systems and underscores the importance of hydrocarbon geochemistry in unraveling ultra-deep,complex geological phenomena.展开更多
The giant Jiama deposit is a post-collisional porphyry Cu-polymetallic system located in the Gangdese metallogenic belt of Xizang.It consists of three deposits:The Main deposit,the Zegulangbei deposit,and the South Pi...The giant Jiama deposit is a post-collisional porphyry Cu-polymetallic system located in the Gangdese metallogenic belt of Xizang.It consists of three deposits:The Main deposit,the Zegulangbei deposit,and the South Pit deposit according to exploration and research.The South Pit deposit is a high-grade Cu-Pb-Zn deposit,but its genesis is unclear.To investigate its genesis,a detailed study was conducted on the deposit geology,geochronology and amphibole geochemistry.The results indicate that the weighted average 206Pb/238U age of the zircons from the granite porphyry in the South Pit is 15.38±0.45 Ma,and the molybdenite from the mineralized skarn yield a ReOs isochron age of 15.23±0.22 Ma,in line with the age of the Main deposit(15.7-14.3 Ma).The amphiboles in the granite porphyry of the South Pit,magnesiohornblende and actinolite,are high in Mg and Ca and low in K.They crystallized at temperatures of 705-7490C,pressures of 0.44-0.67 kbar,oxygen fugacity of-14.31--13.69(NNO),and depths of 1.7-2.5 km.Mapping of structure and alteration indicates that the South Pit skarn developed due to the metasomatism of marble of hornfels or carbonate in fold hinge dilation and an interlayer detachment zone by magmatic hydrothermal fluids.According to the age of magmatism and geological features,the South Pit deposit and the Main deposit have originated from the same Miocene magmatism,but the South Pit deposit was affected by the gliding nappe tectonic system.The amphibole geochemistry indicates that the ore-related magma of the South Pit has a high oxygen fugacity and is rich in water.展开更多
In the Pearl River Mouth Basin of the northern South China Sea,extensive commercial shallow gas reservoirs have recently been discovered.However,their formation mechanisms remain poorly constrained.This study employs ...In the Pearl River Mouth Basin of the northern South China Sea,extensive commercial shallow gas reservoirs have recently been discovered.However,their formation mechanisms remain poorly constrained.This study employs integrated petroleum geological and geochemical datasets to elucidate shallow gas systems' genesis and geochemical signatures.Key findings demonstrate that shallow gas reservoirs exhibit distinct geochemical differentiation from deep thermogenic counterparts,characterized by elevated dryness coefficients(>0.9),depleted methane δ^(13)C values(-52‰ to-34.4‰),and^(13)C-enriched ethane and propane isotopes resulting from migration fractionation.The anaerobic environment minimizes microbial alteration,while the complex marine geology challenges conventional interpretations of isotopic source indicators.Light hydrocarbon analysis identifies type Ⅱ_(2)-Ⅲ kerogen as the primary thermogenic gas source,with southern reservoirs showing sapropelic organic matter signatures consistent with oil-cracking origins.Notably,mixed-source reservoirs display an inverse δ^(13)C relationship between carbon dioxide and methane,contrasting with positive correlations typically observed in biogenic gas from carbon dioxide reduction.Quantitative end-member modeling constrains biogenic contributions to ≤30%,confirming thermogenic dominance despite active methanogenesis.Shallow gas accumulation is a dynamic process involving simultaneous charge and diffusion.Synthesizing these insights with prior research,we propose a genetic model for shallow gas reservoirs,highlighting significant differences in source rock maturity,kerogen types,enrichment layers,migration channels,and water depths relative to deep-water counterparts.展开更多
Cenozoic trachytes are characteristic of some active volcanic fields in China.In particular,the origin and mechanisms of the evolution of trachytes from the Tianchi(Changbaishan)volcano(TV,China/North Korea)are poorly...Cenozoic trachytes are characteristic of some active volcanic fields in China.In particular,the origin and mechanisms of the evolution of trachytes from the Tianchi(Changbaishan)volcano(TV,China/North Korea)are poorly known.Here,we present new geochronological,geochemical and isotopic data on two trachytic suites outcropping on the northern and southern upper slopes of TV.Detailed zircon laser ablation-multicollector-inductively coupled plasma-mass spectrometry(LA-MC-ICP-MS)U-Pb dating,Rb-Sr isochron dating of plagioclase and hornblende,^(40)Ar/^(39)Ar chronology with mineral chemistry,whole-rock element and Sr-Nd-Pb isotope data are used to explore their origins and evolutionary mechanisms during the late Middle Pleistocene.Our data indicate that the trachytes mainly consist of sanidine,orthoclase and plagioclase,with minor albite,quartz and hornblende.They formed at 0.353-0.346 Ma(lava flow from the northern slope)and 0.383-0.311 Ma(lava flow from the southern slope),respectively.The TV trachytes are characterized by high K_(2)O/Na_(2)O and AR values,with low A/CNK and Mg~#values.They are enriched in rare earth elements(REEs;except Eu),depleted in Sr and Ba,crystallizing at 742-858℃.The TV trachytes have high(^(87)Sr/^(86)Sr)_i values(0.70776-0.71195),positiveε_(Nd)(t)values(0.61-2.93)and radiogenic^(206)Pb/^(204)Pb values(17.515-17.806).These values are similar to those of the Pleistocene and Holocene TV trachytes.Geochemical data indicate that they were formed by fractional crystallization from a basaltic melt and assimilated upper crust material.The trace element pattern of the studied trachytes is consistent with an evolution from basaltic melts representative of an enriched mantle source.The vent from which the trachytic magma was erupted probably collapsed inside the caldera during the TV'Millennium'eruption(ME)in 946 AD.The contemporaneous emission of basaltic and trachytic magma during the Middle-Late Pleistocene suggests the coexistence of fissural basaltic volcanism and central-type trachytic volcanism,the latter of which was associated with a magma chamber in the upper crust during the TV cone-construction stage.展开更多
Lower Paleozoic black shales are important source rocks worldwide.The Upper Ordovician-Lower Silurian Renheqiao Formation of the Baoshan Block is a low-maturity equivalent of the Wufeng-Longmaxi(WF-LMX)Shale of the Si...Lower Paleozoic black shales are important source rocks worldwide.The Upper Ordovician-Lower Silurian Renheqiao Formation of the Baoshan Block is a low-maturity equivalent of the Wufeng-Longmaxi(WF-LMX)Shale of the Sichuan Basin.However,organic matter(OM)characteristics in these low-maturity Lower Paleozoic shales are not well understood.In this study,50 Renheqiao Formation shale samples collected from seven outcrop sections and one drill core were investigated with organic petrology,organic geochemistry,R_(o)ck-Eval pyrolysis,N_(2) and CO_(2) adsorption,and scanning electron microscope(SEM)analyses to study the OM content,type,thermal maturity,and the development of OM-hosted pores in these Lower Paleozoic shales.The total organic carbon(TOC)content of the Renheqiao Formation shales varies,with the maximum content of 10.07 wt%.R_(o)ck-Eval pyrolysis results show that present OM in the Renheqiao Formation shales is Type IV kerogen,a result of advanced thermal maturation.Graptolite reflectance(GR_(o))ranges from 1.26%to 1.85%,and equivalent vitrinite reflectance(EqR_(o))converted from GR_(o) ranges from 1.08%to 1.51%,indicating that the studied Renheqiao Formation shales are dominantly within the late-mature stage.EqR_(o) based on R_(o)ck-Eval T_(max) shows large variations,which indicates that R_(o)ck-Eval T_(max) is not a reliable thermal maturity indicator for the Lower Paleozoic Renheqiao Formation shales.Caution should be applied when assessing the thermal maturity of high-maturity black shales based on T_(max) when the S2 values are too low.Organic petrographic observations show that OM in these shales is dominated by solid bitumen(>70 vol%of total OM),with minor contributions by graptolites and chitinozoans.The specific surface area and pore volume of shales are controlled by TOC content.Organic pores are hosted by solid bitumen and were not observed in graptolites when examined under the SEM.Although the Renheqiao Formation has a lower thermal maturity than the over-mature WF-LMX Shale,it is mature enough that primary oil-prone macerals have been thermally transformed and could not be identified under the microscope.展开更多
Permian—Triassic granitoids are widely distributed along the Jinshajiang suture belt,eastern Xizang,and are regarded as the result of the tectonic-magmatic activity associated with the evolution of Paleo-Tethys Ocean...Permian—Triassic granitoids are widely distributed along the Jinshajiang suture belt,eastern Xizang,and are regarded as the result of the tectonic-magmatic activity associated with the evolution of Paleo-Tethys Ocean.This paper focuses on the high-K calc-alkaline I-type Rennong(~235 Ma)and Jiaduoling(~232 Ma)granitoid plutons,eastern Xizang,which are enriched in light rare earth elements(LREEs)and large ion lithophile elements(LILEs),but depleted in high field strength elements(HFSEs)with moderate-weak negative Eu anomalies(0.61–0.90).The Rennong granites are characterized by uniform zircon ε_(Hf)(t)values(-7.3 to-3.5)and negative ε_(Nd)(t)values(-7.6 to-5.7),with old two-stage Nd model ages(T_(DM2)=1.51-1.46 Ga)and was likely formed by partial melting of the basement rocks,whereas the Jiaduoling rock samples have variable zircon ε_(Hf)(t)values(-5.7 to+5.5)but negativeεNd(t)values(-7.6 to-7.7)and are proposed to be formed by hybridization of mantle-derived mafic magma,Rennong felsic magma and sediments.Mafic microgranular enclaves(MMEs)in the Jiaduoling granitic rocks,have similar zircon U-Pb ages(~237 Ma)and zircon ε_(Hf)(t)values(-4.4 to+6.3)to the host rocks,indicating that zircons in the MMEs were actually xenocrysts that formed at an early stage in the granitic magma chamber.These results reveal that the break-off of the Jinshajiang oceanic slab beneath Changdu(Qamdo)-Simao Block was in a post-collisional setting,resulted in the upwelling of asthenosphere in the Late Triassic,and then,generated the wide-spread intermediate-felsic magmatism along the Jinshajing belt,including the Rennong and Jiaduoling plutons.展开更多
基金supported by the National Key R&D Program of China(No.2022YFF0800200)the NSFC(Nos.U1812402 and 42072131)+6 种基金Most Special Fund(No.MSFGPMR33)from the State Key Laboratory of GPMRthe CUG Scholar Scientific Research Funds(No.2022036)the NSF of Hebei Province(No.D2021334001)Research Project of Talent Engineering Training of Hebei Province(No.B2020005007)Research Project of Postdoctoral Scientific Research Station of HBGMR(No.454-0602-YBN-Z9E4)Natural Science Foundation of Hebei Province(No.D2021334001)the Central Government Guides Local Funds for Scientific and Technological Development(No.236Z7608 G)。
文摘Original sedimentary manganese(Mn)deposits and supergene Mn ores are important Mn resources in China.However,the geochemical information from Chinese supergene Mn ores is scarce,and the relationship between sedimentary Mn deposits and supergene Mn ores is ambiguous.In this study,we collected the original Mn-bearing dolomitic sandstones(ZK20-3 drillcore)and supergene Mn ores(Longmen Section)from eastern Hebei,North China for systematic petrographic,mineralogical and geochemical analyses.Our new data help us to figure out the transformation from original Mn-bearing deposits to supergene ores.The main minerals of original Mn-bearing dolomitic sandstones are quartz and feldspar,with minor muscovite,dolomite,rhodochrosite,ankerite,and kutnohorite.Supergene Mn-oxide ores only emerged in the middle part of the Longmen(LM)Section,and mainly contain quartz,pyrolusite,cryptomelane,todorokite and occasional dolomite.The possible transformation sequence of Mn minerals is:kutnohorite/rhodochrosite→pyrolusite(Ⅰ)→cryptomelane(todorokite)→todorokite(cryptomelane)→pyrolusite(Ⅱ).For Mn-oxide ores,Fe,Na and Si are enriched but Al,Ca,Mg and K are depleted with the enrichment of Mn.For original and supergene ores,the total rare earth element+ytterbium(∑REY)contents range from 105.68×10^(-6)to 250.56×10^(-6)and from 18.08×10^(-6)to 176.60×10^(-6),respectively.Original Mn ores have similar slightly LREE-enriched patterns,but the purer Mn-oxide ore shows a HREE-enriched pattern.In the middle part of the LM Section,positive Ce anomalies in Mn-oxide ores indicate the precipitation of Ce-bearing minerals.It implies the existence of geochemical barriers,which changed p H and Eh values due to the long-time influence of groundwater.
文摘The Cretaceous Koum Basin is a rift-related half-graben in northern Cameroon,which constitutes a portion of the Yola Arm of the Upper Benue Trough.This study presents the first comprehensive dataset combining mineral-ogical,bulk-rock geochemical,and stable C-H-O isotopic data for dark-gray,finegrained mudstones from the basin,providing new insights into its sediment source,paleoenvironment,and geodynamic setting.The mudstones primarily consist of phyllosilicates(~8.6%),feldspars(~30.5%),carbonates(~13.7%),and minor iron oxides(~2.7%),with vermiculite,illite,and kaolinite as the main clay minerals.The presence of analcime,ankerite,and dolomite suggests low-grade metamorphism and/or hydrothermal alteration.Fe_(2)O_(3)/K_(2)O(1.52-6.40)and SiO_(2)/Al_(2)O_(3)(2.97-4.68)ratios classify the mudstones as compositionally immature shales(ICV~1.64)with low-moderate chemical weathering(CIA~56.35;PIA~59.74;R^(3+)/R^(3+)+R^(2+)+M^(+)~0.51).Trace element ratios(Th/Sc~1.70,Zr/Sc~1.33,La/Sc~6.30,La/Th~4.14)indicate an intermediate igneous provenance from a continental crustal source.Paleoenviron-mental proxies suggest deposition in a dynamic basin environment marked by fluctuating redox(C org/P:0.21-178.34)and salinity(Sr/Ba:0.34-3.25;N-values:48-35.92)conditions,ranging from oxic to anoxic and brackish to saline.Major element data(SiO_(2) vs.Al_(2)O_(3)+K_(2)O+Na_(2)O)indicate a semi-arid regime,while Paleoclimatic indicators such as Sr/Cu(1.88-37.47)and C-values(0.12-0.93)suggests alter-nating humid and arid conditions.Notably,stable isotope data,reported here for the first time in the Koum Basin,reveal a predominantly terrestrial,fluvial-deltaic C_(3) plant source for organic carbon(δ^(13)C-25.2‰ to -35.2‰)and complex fluid-rock interactions involving meteoric and magmatic-metamorphic fluids under a warm,equatorial climate(δ^(18)O+3.6‰to +24.9‰,δ^(2)H-104‰ to-50‰).The combined mineralogical,geochemical,and isotopic data point to deposition in a tectonically active continental arc setting,with contributions from ocean island arc and passive margin sources.
基金funded by the National Natural Science Foundation of China(No.42130309)China Geological Survey(Nos.DD20160030,DD20190050)。
文摘A cluster of serpentinite bodies has been recognized tectonically emplaced within the greenschist-amphibolite-facies metamorphic terrane in Hong'an,western Dabie orogen,central China.Two types of serpentinites are identified on the basis of integrated petrographic,mineralogical and geochemical study.The first type,represented by Yinshanzhai serpentinite complex(Group 1)comprises heterogeneous lithology as a massive serpentinite matrix“intruded”by antigoriteenriched serpentinite lenses.They are both pseudomorphic textured with different mineral assemblages indicating an increasing temperature-pressure condition.Serpentinite matrix(Group 1a)is chemically characterized by high MgO/SiO_(2)and low Al_(2)O_(3)/SiO_(2),Ti and Ca contents,suggesting a depleted mantle wedge origin.The coexistence of compositionally-heterogeneous chromite with highCr^(#)(0.78-0.96)and intermediate-Cr^(#)(0.59-0.70)pristine cores indicates extensive mantle melting.Meanwhile,extremely high Fo olivine relicts(96-97)with considerably higher MnO and lower NiO contents than mantle olivine indicate that they are metamorphic products from serpentine decomposition.Accordingly,we propose that Yinshanzhai serpentinite complex experienced two distinct episodes of hydration.The serpentinite lenses(Group 1b)show higher SiO_(2)and lower MgO concentrations.Nevertheless,the trace elements of groups 1a and 1b are consistent:U-shaped REE patterns,positive Eu anomalies and enrichment of LILE(i.e.,Cs,U)are all identified as forearc properties.They are affected by reducing slab-derived fluids in forearc mantle,with f_(O2)of 1 to 2 logarithmic units below f_(O2)of fayalite-magnetite-quartz buffer(FMQ-2~FMQ-1).The second type is antigorite-serpentinites(Group2)represented by Ximaoshan and Wangchunwan blocks.They are non-pseudomorphic,with no primary framework silicate surviving.Fertile compositions(i.e.,higher Al_(2)O_(3)and Al_(2)O_(3)/SiO_(2),nearly flat REE patterns)and conjoint enrichment of LILE with HFSE suggest melt/rock interaction.Negative Ce,Eu anomalies,and enriched U relative to alkaline elements demonstrate interactions with more oxidized seawater or seafloor fluids(FMQ~FMQ-1).Remarkable Sr negative anomalies may be attributed to Sr release during lizardite/antigorite transition in subduction zone,indicating interaction with low-Sr slab fluids.We propose that Group 2 serpentinites originate either from mantle wedge or abyssal peridotites,refertilized by mantle melts,then hydrated in seafloor or shallow forearc and entrapped into subduction channel.Combined with geochronology and tectonic constraints of associated eclogites in Hong'an terrane,the two types of serpentinites may correlate with subduction of different oceanic basins during the late Paleozoic and/or Proterozoic eras.It raises possibility of defining an ophiolitic setting in Hong'an Orogen for which further evidence is required.
基金supported by the Xinjiang Key R&D Program(No.2022B03015-3)the National Natural Science Foundation of China(No.91962214)+1 种基金the Fundamental Research Funds for the Central Universities,Chang’an University(No.300102272201)the“Tianchi Talent”Plan to Chang-Zhi Wu.
文摘The Chinese Altai,a key component of the Central Asian Orogenic Belt(CAOB),represents a significant Phanerozoic accretionary orogenic belt.The oceanic-continental subduction processes spanning the Cambrian to Carboniferous and subsequent intracontinental extension since the Triassic have been well documented in the Chinese Altai,the southwestern segment of the CAOB.Deciphering the petrogenetic evolution of this region during the Permian is thus crucial for advancing our understanding of its tectonic transitions.However,the Permian tectonic setting of the Chinese Altai remains contentious.To address this knowledge gap,this study presents new geochronological and geochemical data for the Jiangjunshan pluton in the southern Chinese Altai.Zircon U-Pb geochronology reveals that the gabbro and two-mica alkali feldspar granite—which collectively constitute the primary lithology of the Jiangjunshan pluton—were emplaced at∼272±3.5 and∼272±1.6 Ma,respectively.Geochemically,the gabbro exhibits pronounced light rare-earth element(LREE)depletion,low Nb/Yb(0.39–0.46)and Ti/V(23.7–25.3)ratios,and trace-element signatures akin to normal mid-ocean ridge basalts(N-MORB).However,its conspicuous Nb-Ta depletion parallels that of island arc basalts.Depleted Hf-Nd isotopic compositions(ε_(Hf)(t)=+0.60 to+4.63,ε_(Nd)(t)=+6.32 to+7.80)in the gabbro,coupled with negligible correlation betweenε_(Nd)(t)and SiO2 contents imply limited crustal assimilation during magma evolution.Petrological modeling,based on Sm/Yb and La concentrations,suggests the gabbroic melt derived from∼8%–20%spinel lherzolte mantle melting.Analogously depleted Hf-Nd isotopes(ε_(Hf)(t)=+6.81 to+9.10,ε_(Nd)(t)=+0.79 to+1.45)in the granite,together with petrographic evidence lacking mafic-ultramafic xenoliths,point to a juvenile lower-crustal source.Integrating the gabbro’s N-MORB-like affinity with arc-specific features,regional ultrahigh-temperature metamorphism in southern Chinese Altai,and Permian tectonics,we propose a ridge-subduction regime as the likely petrogenetic setting for the Jiangjunshan magmas.During ridge subduction,upwelling of asthenospheric mantle beneath the ridge induced partial melting of the lithospheric mantle,giving rise to the parental magma of the Jiangjunshan gabbro.This mafic magma underplating subsequently heated the juvenile lower crust,triggering its partial melting and generating the parental magma of the two-mica alkali feldspar granite.Our model indicates that ridge-subduction-related magmatism persisted in the Chinese Altai until the Middle Permian,followed by a tectonic shift from oceanic-continental subduction to intracontinental extension.
基金supported by the National Natural Science Foundation of China(No.42003032)the State Key Laboratory of Nuclear Resources and Environment,East China University of Technology(No.2020Z10).
文摘Zircon U-Pb ages,major and trace elements and Sr-Nd-Hf isotope data of the diabase in the Zhangjiakou District were studied to investigate its derivation and tectonic implications.Zircon U-Pb ages indicate that the diabase was emplaced at∼130 Ma or younger,and captured zircons cluster at∼147,∼240,∼430 and∼465 Ma.The diabase is characterized by minor variations in SiO_(2)(49.35 wt.%–52.10 wt.%),TiO_(2)(1.65 wt.%–1.77 wt.%),Al_(2)O_(3)(17.00 wt.%–18.26 wt.%),MgO(4.28 wt.%–4.93 wt.%),CaO(6.69 wt.%–7.90 wt.%)and Mg^(#)(48–54).It has no significant Eu anomaly and displays enrichment in large ion lithophile elements(Rb,Ba and Sr)and depletion in high field strength elements(Nb,Ta,P and Ti).The diabase exhibits homogeneous Sr((^(87)Sr/^(86)Sr)i=0.70606–0.70701)and Nd(ε_(Nd)(t)=−13.6 to−13.2)isotopic compositions.These features suggest that the parental magma was derived from partial melting of the ancient lower crust,relating to mantle upwelling that was triggered by the stagnant slabs or lithospheric detachment associated with the westward subduction of the Paleo-Pacific Plate.The Early Paleozoic inherited igneous zircons in the diabase suggest that the northern margin of the North China Craton(NCC)likely underwent southward subduction of the Paleo-Asian Ocean.
基金supported by the Open Fund Project of the Key Laboratory of Ionic Rare Earth Resources and Environment,Ministry of Natural Resources(Grant No.2022IREE101)the Young Elite Scientists Sponsorship Program by CAST(Grant No.2022QNRC001)the Geological Investigation Project(Grant Nos.DD20243483,DD20221643).
文摘The pervasively distributed granitoids in South China contributed greatly to regional polymetallic mineralization,including tungsten,tin,copper,gold,rare metals,and rare earth elements(REEs).To ascertain the dynamic backgrounds,rock types and genesis of the parent rocks related to the Early-Middle Jurassic ionic rare earth mineralization,typical deposits at Muzishan,Xiahu,and Zudong were investigated by conducting petrographic,geochronologic,whole-rock geochemical,and Sr-Nd-Pb isotope analyses,which found that the parent rocks from the Muzishan deposit were the A1-type K-feldspar granite(~195 Ma),from the Zudong deposit were the A2-type monzogranite(~171 Ma),and from the Xiahu deposit were the I-type monzogranite(~167 Ma).All the three granitic rocks underwent different degrees of fractionation,with the Xiahu granite experiencing the highest degree,followed by the Zudong granite,and the Muzishan granite undergoing the lowest degree.The Muzishan granite was concluded to be formed under an intraplate extensional tectonic regime influenced by the hotspots or the mantle plume.The Zudong granite was formed in a post-arc extensional setting related to subduction-collision-rollback of the paleo-Pacific Plate,which caused upwelling of the asthenosphere,thinning of the lithosphere,and partial melting of crustal materials.The Xiahu granite was generated under a transitional tectonic setting of extension and compression,triggered by delamination and rollback of the paleo-Pacific Plate.
基金funded by SERB-DST,New Delhi,India for Early Career Research(ECR/2016/001100)during 2017 to 2021.
文摘Elemental concentrations of the siliciclastic sediments from a sedimentary basin provide clues on paleo-weathering,paleoclimate,provenance,and tectonic setting of the basin.Records for Permo-Triassic mass extinction and climatic fluctuations are commonly traced from the sediments in the Gondwana basins.Nevertheless,our understanding on sedimentation,provenance,and regional tectonics of the Raniganj Basin,a Gondwana basin in the eastern India is poor.Minerals including clay particles and major and trace element concentrations of the siliciclastic sediments from different formations of the Raniganj Basin have been studied to establish the paleo-weathering,paleoclimate,provenance,and tectonic settings of the basin.This study suggests that the Talchir Formation experienced cold and dry climatic conditions at the sediment source area,while the Barakar,Raniganj,and Panchet formations had prevailing semiarid climates.The sources of the siliciclastic sediments are from the felsic rocks of the Chotanagpur Granite Gneissic Complex(CGGC).Further,the geochemical results suggest a rift-like(passive)tectonic setting for the Raniganj Basin,while few samples represent the collision tectonic setting of the basement CGGC,formed due to collision of major Indian blocks during the Paleo-Neoproterozoic time.
基金financially supported by the Yunnan Fundamental Research Projects(No.202201AT070077)the Ministry-Province Cooperation Pilot Projects(No.2023ZRBSHZ059)+1 种基金the Major Science and Technology Special Plan of Yunnan Province(No.202202AG050006)the National Natural Science Foundation of China(No.41603032)。
文摘Lower Carboniferous clastic sedimentary rocks(i.e.,the Nanduan Formation)in the Changning-Menglian belt of the southeastern Tibetan Plateau may provide new insights into the tectonic evolution of the Paleo-Tethys Ocean.This paper presents new petrographic,geochemical,and detrital zircon U-Pb age data to constrain the provenance and depositional setting of these rocks.Sandstone samples of the Nanduan Formation are all quartz arenites(Q_(92-99)F_(1-7)L_(0-2))with high SiO_(2)contents(85.1 wt.%-95.2 wt.%;average=90.9 wt.%),indicating high compositional maturity.They exhibit fractionated rare earth element(REE)patterns,with light REE enrichment[(La/Yb)_(N)=6.48-12.1]and negative Eu anomalies(Eu/Eu^(*)=0.53-0.74),and marked negative Sr-Cs-V-Cr-Ni anomalies in upper continental crust-normalised multi-element diagrams.The geochemical features and heavy mineral assemblages suggest that sediments were mainly derived from ancient sedimentary rocks in cratonic interiors or stable continental areas,and were probably deposited in a passive continental margin setting.Detrital zircon U-Pb dating(n=256)of the Nanduan Formation sandstones defines three distinct age peaks in the Pan-African(600-500 Ma),younger Grenvillian(950-850 Ma),and older Grenvillian(1250-1000 Ma).Their zircon age spectra are similar to those of Lower Paleozoic sedimentary rocks(i.e.,the Mengtong and Mengdingjie groups)in the BaoshanSibumasu Block,but significantly different from those of older rocks in the Simao-Indochina and other surrounding blocks(i.e.,the western Yangtze,western Cathaysia,western Qiangtang,Tethyan Himalaya,and Lhasa blocks).This suggests that the Nanduan Formation was deposited at the margin of the Baoshan-Sibumasu Block.Combining the new data presented in this study with published data,we suggest that the Nanduan Formation and underlying Lancang Group were deposited in the same setting during the Early and Late Paleozoic,respectively.
基金funded by the project initiated by the China Geological Survey“Investigation of sandstone-type uranium deposits in the Ordos and Qaidam Basins”(No.DD20190119)the National Key Research and Development Project(No.2018YFC0604200)from the Ministry of Science and Technology of the International Geoscience Programme(No.IGCP675),which is a joint endeavor of UNESCO and IUGS。
文摘The Erlian Basin is one of the most important multi-energy basins in China.The Baiyanhua area of the Chuanjing depression in the western Erlian Basin has recently become a favorable area for new progress in sandstone-type uranium prospecting.However,the Cretaceous source-to-sink evolution of the Chuanjing depression in the Erlian Basin is poorly known.This paper presents the systematic geochemical and zircon U-Pb studies on the Saihantala Formation and Erlian Formation in the Baiyanhua area.The data obtained are functionally important for revealing the provenance and tectonic setting of the source rocks.The results show that the upper part of the Saihantala Formation and the lower part of the Erlian Formation are mainly composed of felsic sedimentary rocks.The source rocks originated from a continental margin arc environment in terms of tectonic setting.The detrital zircons ages have the dominant populations at ca.250-270 Ma,with two subdominant age groups at ca.1400-1800 and 1900-2100 Ma,respectively.Combined with the tectono-sedimentary evolution of the Chuanjing depression,we conclude that:(1)the provenance of the Cretaceous strata was mostly sourced from the Baiyanhua uplift;(2)the water depth became shallow in the Southern Sangendalai sag during the middle period of Saihantala,further preventing the formation of coal beds;(3)the formation of Baiyanhua uplift might provide the beneficial tectonic condition for uranium mineralization in the upper Saihantala Formation in southern Sangendalai sag.This is significant for us to understand the space allocation of coal and uranium in Chuanjing depression and evaluate the uranium metallogenic prospects in southern Sangendalai sag.
基金the National Natural Science Foundation of China(No.41872232)。
文摘The Xing'an-Inner Mongolia Orogen is a critical tectonic unit for constraining the evolution of the Paleo-Asian Ocean.However,the location and time of the closure of the Paleo-Asian Ocean are still debated.Here,we select a representative basin in Dashizhai in northeastern China,using U-Pb zircon geochronology and geochemistry to analyze the sedimentary facies,depositional ages,and provenance.The results show that the ages of the Dashizhai Formation range from 400 to 347 Ma,the Shoushangou Formation range from 400 to 348 Ma,the Zhesi Formation range from 307 to 252 Ma,and the Linxi Formation range from 299 to 241 Ma.The Dashizhai Formation is composed of metamorphic andesite and clastic rocks.The Shoushangou Formation comprises siltstone,rhyolite,and argillaceous siltstone.The Zhesi and Linxi Formations are composed of mudstone and argillaceous siltstone.Geochemical data shows that these rocks are enriched in light rare earth elements and depleted in Eu with various La/Sc,Th/Sc,and La/Co ratios.The Permian Dashizhai Basin is from Permian volcanic and felsic igneous rocks from the Ergun,Xing'an,and Songliao blocks.The absence of the Late Carboniferous strata in the Dashizhai Basin indicates an extension setting during this period.Furthermore,we suggest the Xing'an-Inner Mongolia Orogen was an uplifting process associated with evolution the Paleo-Asian Ocean during the Late Permian.
基金Geological Survey of India,Northern Region have provided the financial funding for the study.
文摘Background The Bundelkhand Craton is significant for preserving the multiphase granitoids magmatism from Paleoarchean to Neoarchean periods.It consists of a variety of granite rocks,including TTGs,sanukitoids,and high-K granitoids.This study presents geochemical characteristics of high-silica(68.97 wt.%–73.99 wt.%),low-silica(58.73wt.%–69.94 wt.%),and high K_(2)O(2.77 wt.%–6.16 wt.%)contents of granitoids.Objective The data on Bundelkhand Craton’s granitic magmatism and geodynamics is not sufficiently robust.Geochemical data from this study will be used to further understand the origin,source,and petrogenesis of granitoid rocks and their implications for the evolution of geodynamics.Methodology Twenty-one samples were collected and analyzed for major,trace,and REE elements.Major elements were measured using X-ray fluorescence spectrometry(XRF),and trace and REE elements were analyzed by ICP-MS.Standard procedures from the Geological Survey of India were followed.Results The geochemical analysis presents high-silica(68.97-73.99 wt.%),low-silica(58.73-69.94 wt.%),and high K_(2)O(2.77-6.16 wt.%)contents in granitoids,classified as granite-granodiorite.The rocks are calcic to calcalkalic,magnesian,and range from peraluminous to metaluminous composition.REE patterns showed strong LREE enrichment relative to HREEs,with prominent negative Eu anomalies corresponding to earlier plagioclase fractionation.Multi-element patterns revealed negative anomalies in Nb,Sr,P,and Ti and positive anomalies in Pb.Conclusion The geochemical signatures attributed to the post-collisional magma generation and continental crustal contamination.The studied rocks show A-type and A2-type lineage,suggesting they originated from the melting of continental crust during transitional/post-collisional tectonic activity.The formation of hybrid granitoids in the Bundelkhand Craton is connected to the fractionation of hybrid magmas in shallow-seated magma chambers during these tectonic processes.
基金funded by a grant from the National Natural Science Foundation of China(Grant No.41772130)the Natural Science Foundation of Jiangsu Province(Grant No.BK20210521)+4 种基金the Fundamental Research Funds for the Central Universities(Grant No.2021QN1061)‘Energy and Environment Youth Talent Training Program’by China’s Energy Society,China’s Environmental Protection Foundation and the Beijing Energy Society(Grant No.RCJH2022081)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.KYCX25_2782)the Graduate Innovation Program of China University of Mining and Technology(No.2025WLKXJ003)the Fundamental Research Funds for the Central Universities(No.202500044)。
文摘Recent studies have highlighted the presence of lithium enrichment in coals within the Ordos Basin,which has garnered significant attention due to the potential economic value.However,most research has concentrated primarily on the coal seams of the Taiyuan and Shanxi formations,with limited reports on the Benxi Formation.To address this gap,our study focused on elucidating the geochemical characteristics and origins of the lithium enrichment in the No.8 coal of the Benxi Formation through the use of optical microscopy and inductively coupled plasma mass spectrometry(ICP-MS).The results showed that the No.8 coal was a bituminous coal,characterized by medium ash yield,low volatile matter,high total sulfur content and medium vitrinite proportion.The No.8 coal was enriched in Li(average 91.7 ppm,CC=6.55)and Zr(average 191 ppm,CC=5.30),the unusual enrichment of Li being primarily located in the middle of the coal.The minerals in the coal were predominantly clay minerals,along with minor amounts of pyrite,quartz and calcite.The occurrence mode of Li in the No.8 coal was associated with aluminosilicate minerals,presumably kaolinite.Based on geochemical characteristics,the sedimentary source of the No.8 coal was intermediate-felsic volcanic rock from the Yinshan oldland.The enrichment of Li can be attributed to the supply of terrestrial debris from the Yinshan oldland and the depositional environment.Our analysis identifies three distinct stages of lithium enrichment,emphasizing the critical role played by the terrestrial debris,as well as the acidic to partially reducing conditions,in facilitating this process.In conclusion,our study sheds light on the mechanisms underlying lithium enrichment in the No.8 coal of the Benxi Formation,highlighting the significance of geological factors in shaping the distribution and concentration of critical metals in coal.
文摘To investigate the Early Cretaceous magmatic activity and tectonic evolution in the Xiaoqinggou mining area of Jilin Province,the authors conducted petrological,geochemical,and isotopic analyses of diorite rocks.The findings show that the zircons exhibit distinct magmatic growth zoning,confirming their magmatic origin.LA–ICP–MS zircon U–Pb dating yielded an age of 128.7±2.2 Ma,corresponding to Early Cretaceous.Geochemical data reveal that the diorite rocks are high and potassium but low in sodium,classifying them within the peraluminous,high-potassium calc-alkaline series.They are enriched in large ion lithophile elements(e.g.,K,Ba and Rb)and depleted in high field strength elements(e.g.,Nb,Ta and Ti).TheδEu values range from 1.07 to 1.14,indicating weakly positive Eu anomalies.Regional comparisons and integrated studies suggest that the Xiaoqinggou diorite rocks formed in a volcanic island arc setting,associated with the westward subduction of the Paleo-Pacific plate beneath the Eurasian continent in an extensional tectonic environment.This study provides a theoretical basis for further exploration of the Xiaoqinggou deposit.
基金Supported by projects of the National Natural Science Foundation of China(Nos.42372063,41722204).
文摘This study presents LA–ICP–MS U–Pb dating and whole-rock geochemical analyses of the Late Triassic Gangshan harzburgite in the Qingyuan area,with the aim of elucidating its petrogenesis and further constraining the early Mesozoic tectonic evolution of the eastern segment of the northern margin of the North China Block(NCB).Zircons from the harzburgites exhibit typical oscillatory growth zoning or striped absorp-tion in cathodoluminescence images.U–Pb analyses of zircons yield ages ranging from 2525 Ma to 225 Ma,with two youngest ages(225±7 Ma)indicating that the harzburgites were formed during Late Triassic.Geochemical analyses of the Gangshan harzburgites show that the rocks have low concentrations of SiO_(2)(42.38%–42.85%)and Al_(2)O_(3)(3.31%–3.33%),along with high concentrations of MgO(41.32%–41.76%),Cr(4856×10^(-6)–5191×10^(-6))and Ni(1942×10^(-6)–2041×10^(-6)).They also display low REE abundances(∑REE=4.38×10^(-6)–4.69×10^(-6))and flat REE patterns with low(La/Yb)_(N) ratios(1.24–1.56)and slightly po-sitive Eu anomalies(δEu=1.13–1.16).These features suggest that the Gangshan harzburgites are cumulates of basaltic magma derived from the depleted lithospheric mantle.Combined with previous studies,these Late Triassic mafic–ultramafic rocks,together with coeval granitoids in adjacent regions,constitute a typical bimodal association,suggesting that they formed in a post-orogenic extensional environment after the final closure of the Paleo-Asian Ocean.
基金funded by the National Natural Science Foundations of China(Grant No.42173054)。
文摘Light oil and gas reservoirs are abundant in the Ordovician marine carbonate reservoir in Shunbei Oilfield,Tarim Basin.This presents a compelling geological puzzle,as ultra-deep reservoirs undergo intense alteration and complex petroleum accumulation processes.A comprehensive suite of geochemical analyses,including molecular components,carbon isotope composition,homogenization temperature of saline inclusions,and burial-thermal history of single wells,was conducted to elucidate the genesis of these ancient reservoirs.Three petroleum filling events have been identified in the study area:Late Caledonian,Hercynian-Indosinian,and Himalayan,through analysis of homogenization temperatures of brine inclusions and burial-thermal histories.Additionally,the oil in the study area has undergone significant alteration processes such as biodegradation,thermal alteration,mixing,evaporative fractionation,and gas invasion.This study particularly emphasizes the influential role of Himalayan gas filling-induced evaporation fractionation and gas invasion in shaping the present petroleum phase distribution.Furthermore,analysis of light hydrocarbon and diamondoid parameters indicates the oil within the study area is at a high maturity stage,with equivalent vitrinite reflectance values ranging from 1.48%to 1.99%.Additionally,the analysis of light hydrocarbons,aromatics,and thiadiamondoids indicates that TSR should occur in reservoirs near the gypsum-salt layers in the Cambrian.The existence of the Cambrian petroleum system in the study area is strongly confirmed when considering the analysis results of natural gas type(oil cracking gas),evaporative fractionation,and gas invasion.Permian local thermal anomalies notably emerge as a significant factor contributing to the destruction of biomarkers in oil.For oil not subject to transient,abnormal thermal events,biomarker reliability extends to at least 190℃.In conclusion,examining the special formation mechanisms and conditions of various secondary processes can offer valuable insights for reconstructing the history of petroleum accumulation in ultradeep reservoirs.This research provides a scientific foundation for advancing our knowledge of petroleum systems and underscores the importance of hydrocarbon geochemistry in unraveling ultra-deep,complex geological phenomena.
基金supported by the National Key Research and Development Program of China(No.2022YFC2905004)Open Fund from Sino Probe Laboratory(No.SL202405)+4 种基金the Basic Research Fund of Institute of mineral Resource,Chinese Academy of Geological Sciences(No.JKYZD202316)the National Natural Science Foundation of China(Nos.42272093,42230813)China Scholarship Council Project,and the Geological Survey Project(No.DD20230054)Science and Technology Support Project in a new round of prospecting breakthrough strategic action(No.ZKKJ202429)the Central Government Guided Local Scientific and Technological Development Funding Project(No.XZ202401YD0006)。
文摘The giant Jiama deposit is a post-collisional porphyry Cu-polymetallic system located in the Gangdese metallogenic belt of Xizang.It consists of three deposits:The Main deposit,the Zegulangbei deposit,and the South Pit deposit according to exploration and research.The South Pit deposit is a high-grade Cu-Pb-Zn deposit,but its genesis is unclear.To investigate its genesis,a detailed study was conducted on the deposit geology,geochronology and amphibole geochemistry.The results indicate that the weighted average 206Pb/238U age of the zircons from the granite porphyry in the South Pit is 15.38±0.45 Ma,and the molybdenite from the mineralized skarn yield a ReOs isochron age of 15.23±0.22 Ma,in line with the age of the Main deposit(15.7-14.3 Ma).The amphiboles in the granite porphyry of the South Pit,magnesiohornblende and actinolite,are high in Mg and Ca and low in K.They crystallized at temperatures of 705-7490C,pressures of 0.44-0.67 kbar,oxygen fugacity of-14.31--13.69(NNO),and depths of 1.7-2.5 km.Mapping of structure and alteration indicates that the South Pit skarn developed due to the metasomatism of marble of hornfels or carbonate in fold hinge dilation and an interlayer detachment zone by magmatic hydrothermal fluids.According to the age of magmatism and geological features,the South Pit deposit and the Main deposit have originated from the same Miocene magmatism,but the South Pit deposit was affected by the gliding nappe tectonic system.The amphibole geochemistry indicates that the ore-related magma of the South Pit has a high oxygen fugacity and is rich in water.
基金supported by CNOOC(China) Ltd.'s productive scientific research project"Shallow gas enrichment mechanism and favorable exploration direction in the Baiyun Sag"(Grant No.2022SKPS0082)。
文摘In the Pearl River Mouth Basin of the northern South China Sea,extensive commercial shallow gas reservoirs have recently been discovered.However,their formation mechanisms remain poorly constrained.This study employs integrated petroleum geological and geochemical datasets to elucidate shallow gas systems' genesis and geochemical signatures.Key findings demonstrate that shallow gas reservoirs exhibit distinct geochemical differentiation from deep thermogenic counterparts,characterized by elevated dryness coefficients(>0.9),depleted methane δ^(13)C values(-52‰ to-34.4‰),and^(13)C-enriched ethane and propane isotopes resulting from migration fractionation.The anaerobic environment minimizes microbial alteration,while the complex marine geology challenges conventional interpretations of isotopic source indicators.Light hydrocarbon analysis identifies type Ⅱ_(2)-Ⅲ kerogen as the primary thermogenic gas source,with southern reservoirs showing sapropelic organic matter signatures consistent with oil-cracking origins.Notably,mixed-source reservoirs display an inverse δ^(13)C relationship between carbon dioxide and methane,contrasting with positive correlations typically observed in biogenic gas from carbon dioxide reduction.Quantitative end-member modeling constrains biogenic contributions to ≤30%,confirming thermogenic dominance despite active methanogenesis.Shallow gas accumulation is a dynamic process involving simultaneous charge and diffusion.Synthesizing these insights with prior research,we propose a genetic model for shallow gas reservoirs,highlighting significant differences in source rock maturity,kerogen types,enrichment layers,migration channels,and water depths relative to deep-water counterparts.
基金financially supported by the project of the National Observation and Research Station of the Institute of Geology,China Earthquake Administration(Grant No.NORSCBS22-06)the Youth Science and Technology Development Project of the Jilin Earthquake Agency(Grant No.JZQ-202402)+1 种基金the Earthquake Science and Technology Spark Project(Grant No.XH23013B)the China Scholarship Council(Grant No.202104190014)。
文摘Cenozoic trachytes are characteristic of some active volcanic fields in China.In particular,the origin and mechanisms of the evolution of trachytes from the Tianchi(Changbaishan)volcano(TV,China/North Korea)are poorly known.Here,we present new geochronological,geochemical and isotopic data on two trachytic suites outcropping on the northern and southern upper slopes of TV.Detailed zircon laser ablation-multicollector-inductively coupled plasma-mass spectrometry(LA-MC-ICP-MS)U-Pb dating,Rb-Sr isochron dating of plagioclase and hornblende,^(40)Ar/^(39)Ar chronology with mineral chemistry,whole-rock element and Sr-Nd-Pb isotope data are used to explore their origins and evolutionary mechanisms during the late Middle Pleistocene.Our data indicate that the trachytes mainly consist of sanidine,orthoclase and plagioclase,with minor albite,quartz and hornblende.They formed at 0.353-0.346 Ma(lava flow from the northern slope)and 0.383-0.311 Ma(lava flow from the southern slope),respectively.The TV trachytes are characterized by high K_(2)O/Na_(2)O and AR values,with low A/CNK and Mg~#values.They are enriched in rare earth elements(REEs;except Eu),depleted in Sr and Ba,crystallizing at 742-858℃.The TV trachytes have high(^(87)Sr/^(86)Sr)_i values(0.70776-0.71195),positiveε_(Nd)(t)values(0.61-2.93)and radiogenic^(206)Pb/^(204)Pb values(17.515-17.806).These values are similar to those of the Pleistocene and Holocene TV trachytes.Geochemical data indicate that they were formed by fractional crystallization from a basaltic melt and assimilated upper crust material.The trace element pattern of the studied trachytes is consistent with an evolution from basaltic melts representative of an enriched mantle source.The vent from which the trachytic magma was erupted probably collapsed inside the caldera during the TV'Millennium'eruption(ME)in 946 AD.The contemporaneous emission of basaltic and trachytic magma during the Middle-Late Pleistocene suggests the coexistence of fissural basaltic volcanism and central-type trachytic volcanism,the latter of which was associated with a magma chamber in the upper crust during the TV cone-construction stage.
基金supported by the project of“Shale Gas Resources Investigation and Evaluation in the Baoshan Block”from Sinopec Exploration Company and the National Natural Science Foundation of China(41925014 and 42172192)。
文摘Lower Paleozoic black shales are important source rocks worldwide.The Upper Ordovician-Lower Silurian Renheqiao Formation of the Baoshan Block is a low-maturity equivalent of the Wufeng-Longmaxi(WF-LMX)Shale of the Sichuan Basin.However,organic matter(OM)characteristics in these low-maturity Lower Paleozoic shales are not well understood.In this study,50 Renheqiao Formation shale samples collected from seven outcrop sections and one drill core were investigated with organic petrology,organic geochemistry,R_(o)ck-Eval pyrolysis,N_(2) and CO_(2) adsorption,and scanning electron microscope(SEM)analyses to study the OM content,type,thermal maturity,and the development of OM-hosted pores in these Lower Paleozoic shales.The total organic carbon(TOC)content of the Renheqiao Formation shales varies,with the maximum content of 10.07 wt%.R_(o)ck-Eval pyrolysis results show that present OM in the Renheqiao Formation shales is Type IV kerogen,a result of advanced thermal maturation.Graptolite reflectance(GR_(o))ranges from 1.26%to 1.85%,and equivalent vitrinite reflectance(EqR_(o))converted from GR_(o) ranges from 1.08%to 1.51%,indicating that the studied Renheqiao Formation shales are dominantly within the late-mature stage.EqR_(o) based on R_(o)ck-Eval T_(max) shows large variations,which indicates that R_(o)ck-Eval T_(max) is not a reliable thermal maturity indicator for the Lower Paleozoic Renheqiao Formation shales.Caution should be applied when assessing the thermal maturity of high-maturity black shales based on T_(max) when the S2 values are too low.Organic petrographic observations show that OM in these shales is dominated by solid bitumen(>70 vol%of total OM),with minor contributions by graptolites and chitinozoans.The specific surface area and pore volume of shales are controlled by TOC content.Organic pores are hosted by solid bitumen and were not observed in graptolites when examined under the SEM.Although the Renheqiao Formation has a lower thermal maturity than the over-mature WF-LMX Shale,it is mature enough that primary oil-prone macerals have been thermally transformed and could not be identified under the microscope.
基金supported by the National Natural Science Foundation of China(Nos.42072069,41403023)China Geological Survey(No.1212011121270)the Natural Science Foundation of Hainan Province(Nos.521QN274 and 421CXTD441).
文摘Permian—Triassic granitoids are widely distributed along the Jinshajiang suture belt,eastern Xizang,and are regarded as the result of the tectonic-magmatic activity associated with the evolution of Paleo-Tethys Ocean.This paper focuses on the high-K calc-alkaline I-type Rennong(~235 Ma)and Jiaduoling(~232 Ma)granitoid plutons,eastern Xizang,which are enriched in light rare earth elements(LREEs)and large ion lithophile elements(LILEs),but depleted in high field strength elements(HFSEs)with moderate-weak negative Eu anomalies(0.61–0.90).The Rennong granites are characterized by uniform zircon ε_(Hf)(t)values(-7.3 to-3.5)and negative ε_(Nd)(t)values(-7.6 to-5.7),with old two-stage Nd model ages(T_(DM2)=1.51-1.46 Ga)and was likely formed by partial melting of the basement rocks,whereas the Jiaduoling rock samples have variable zircon ε_(Hf)(t)values(-5.7 to+5.5)but negativeεNd(t)values(-7.6 to-7.7)and are proposed to be formed by hybridization of mantle-derived mafic magma,Rennong felsic magma and sediments.Mafic microgranular enclaves(MMEs)in the Jiaduoling granitic rocks,have similar zircon U-Pb ages(~237 Ma)and zircon ε_(Hf)(t)values(-4.4 to+6.3)to the host rocks,indicating that zircons in the MMEs were actually xenocrysts that formed at an early stage in the granitic magma chamber.These results reveal that the break-off of the Jinshajiang oceanic slab beneath Changdu(Qamdo)-Simao Block was in a post-collisional setting,resulted in the upwelling of asthenosphere in the Late Triassic,and then,generated the wide-spread intermediate-felsic magmatism along the Jinshajing belt,including the Rennong and Jiaduoling plutons.
