Eastern Myanmar is the key position linking between SW Yunnan and northern Thailand for better understanding of Tethyan evolution.However,the actual location and evolution of the Tethyan suture zone are still unclear ...Eastern Myanmar is the key position linking between SW Yunnan and northern Thailand for better understanding of Tethyan evolution.However,the actual location and evolution of the Tethyan suture zone are still unclear in eastern Myanmar.The present study focuses on the geochronological,geochemical and zircon Lu-Hf isotopic study on the plutonic rocks,including granite,diorite and gabbroic rocks,from the Tachileik area,eastern Myanmar.These plutonic rocks yielded zircon U-Pb weighted mean ages of ca.353–355 Ma,suggesting the Early Carboniferous emplacement.The Tachileik granites are high-K calc-alkaline,weakly peraluminous and have low P2O5 contents,which are typical features of I-type granites.They have positive zircon ε_(Hf)(t)values(+4.5−+7.4)with T_(DM2) ages of 981–825 Ma,indicating a juvenile mafic lower crust source.The Tachileik gabbros and diorites show high Al_(2)O_(3) contents and Mg#,but low TiO_(2) and K_(2)O contents,belonging to tholeiitic and calc-alkaline basalt series.They are characterized by enrichments in large ion lithophile elements(LILEs,e.g.,Rb,Ba and Sr),depletions in high field strength elements(HFSEs)and distinctly negative Nb and Ta anomalies,similar to the volcanic arc basalt.The zircon Hf isotopic(+4.7−+7.1)and whole-rock geochemical data imply that the Tachileik gabros and diorites probably resulted from partial melting of lithospheric mantle in the spinel stability field within an arc-related setting.The magmatic rocks can be grouped to the Late Devonian–Early Carboniferous magmatic rock and pyroclastic rock zone from SW Yunnan to northern Thailand based on their age and geochemical characters.The zone was formed in the post-collisional extension-related tectonic setting of the Proto-Tethys.This study provides important evidences for the evolution of the Proto-Tethys in Southwest Yunnan and Southeast Asia.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
Based on drilling,mud logging,core,seismic and imaging logging data,this paper studies the identification and evolution process of negative inversion structures in the Carboniferous buried hills in the No.1 and No.2 f...Based on drilling,mud logging,core,seismic and imaging logging data,this paper studies the identification and evolution process of negative inversion structures in the Carboniferous buried hills in the No.1 and No.2 fault zones of Weixinan Sag,Beibu Gulf Basin,China,and reveals the controls of these structures on high-quality reservoirs.The No.2 fault zone develops significant negative inversion structures in the Carboniferous buried hills,as a result of multi-stage transformations of compressive-tensile stress fields in the period from the Late Hercynian to the Himalayan.The Hercynian carbonates laid the material basis for the formation of high-quality reservoirs.The negative inversion structures mainly control the development of high-quality reservoirs in buried hills through:(1)creating large-scale fractures to increase reservoir space and improve oil-gas flow pathways;(2)regulating stratigraphic differential denudation to highlight dominant lithology for later reservoir transformation;(3)shaping the paleogeomorphological highlands to provide favorable conditions for superficial karstification.The negative inversion structures form a high-quality,composite reservoir space with the synergistic existence of superficial dissolution fractures/cavities and burial-enhanced karst systems through the coupling of fracture network creation,formation denudation screening and multi-stage karst transformation.The research results have guided the breakthrough of the first exploratory well with a daily oil production over 1000 m^(3)in carbonate buried-hill reservoir in the Beibu Gulf Basin,and provide referential geological basis for finding more reserves and achieving higher production in the Carboniferous buried hills in the Weixinan Sag.展开更多
The origins of peloidal micrites in reefal limestone are not yet well understood.Moscovian microbial reefs with abundant peloidal micrites from Guizhou,South China,provide an opportunity to study the peloids and their...The origins of peloidal micrites in reefal limestone are not yet well understood.Moscovian microbial reefs with abundant peloidal micrites from Guizhou,South China,provide an opportunity to study the peloids and their geological significance for this time interval.Three types of peloids are differentiated:microbial,lithic,and bioclastic peloids.Microbial peloids that are well-sorted and may form in situ by microbial activities.The poorly sorted lithic peloids are derived from erosion and redeposition of the micrite matrix caused by the bottom turbulence induced by periodic storms.Bioclastic peloids are completely micritized fragments of hard parts and shells.Microbial boring and encrustations promote the processes of micritization.Microbial peloids commonly develop in zones with low or normal energy levels,and contribute to the construction and stabilization of the framework.In contrast,the occurrence of lithic peloids reflects that the reefs are destroyed by bottom turbulence during growth.It is suggested that the microbial reefs were deposited under a dynamic balance between constructional versus destructive processes.By comparative analysis,the peloids as microbial in origin play a key role in the growth and stabilization of bioconstructions during Carboniferous,which should be paid more attention in the studies of Carboniferous buildups.展开更多
High-Mg andesite/diorite(HMA)is useful for identifying subduction-related processes in orogenic belts,including the identification of ophiolites formed in suprasubduction zone(SSZ)environments.The E'rentaolegai hi...High-Mg andesite/diorite(HMA)is useful for identifying subduction-related processes in orogenic belts,including the identification of ophiolites formed in suprasubduction zone(SSZ)environments.The E'rentaolegai high-Mg diorite from the Diyanmiao ophiolite in central Inner Mongolia,North China,has been investigated revealing low-K tholeiitic-calc-alkaline characteristics and have SiO_(2)contents of 53.44-54.92 wt%,MgO contents of 8.44-9.54 wt%,and Mg~#of 54.35-57.60,with variable Fe_(2)O_(3)(7.51-8.61 wt%),Al_(2)O_(3)(11.95-15.09 wt%),and Na_(2)O(3.42-3.94 wt%)contents,low K_(2)O(0.34-0.97 wt%),TiO_(2)(0.35-0.67 wt%),and P2O5(0.12-0.15 wt%)contents,and high Ni(43-193 ppm)and Cr(189-556 ppm)contents.Samples collected have low total rare earth element(REE)contents(30.58-77.80 ppm),with flat or slightly right-dipping REE patterns(La_(N)/Yb_(N)=2.19-3.11)and a lack of pronounced Eu anomalies.The samples are also enriched in large-ion lithophile elements(LILEs,e.g.,K,Rb,Ba,U,and Sr)and depleted in high field strength elements(e.g.,Ta,Nb,Ti,and P).The E'rentaolegai high-Mg diorite has characteristics typical of HMA,and are similar to those of sanukites from the Setouchi Arc in SW Japan.They also display high positiveε_(Nd)(t)values(+6.32 to+7.80),comparable to the values of their host rocks.Petrogenetic analyses suggest that the E'rentaolegai HMA was probably formed by the interaction of partial melts and aqueous fluids from subducted sediments with mantle peridotite.Zircon U-Pb dating reveals that the high-Mg diorite crystallized at 313.6±2.4 Ma,i.e.,late Carboniferous.Combining our data with the temporal and spatial distribution of the Diyanmiao SSZ-type ophiolite,we propose that the eastern Paleo-Asian Ocean had not closed by the late Carboniferous,but intra-oceanic subduction was ongoing.A new model of the initiation of subduction in the eastern PAO during the late Paleozoic.展开更多
Based on the coalbed methane(CBM)/coal-rock gas(CRG)geological,geophysical,and experimental testing data from the Daji block in the Ordos Basin,the coal-forming and hydrocarbon generation&accumulation characterist...Based on the coalbed methane(CBM)/coal-rock gas(CRG)geological,geophysical,and experimental testing data from the Daji block in the Ordos Basin,the coal-forming and hydrocarbon generation&accumulation characteristics across different zones were dissected,and the key factors controlling the differential CBM/CRG enrichment were identified.The No.8 coal seam of the Carboniferous Benxi Formation in the Daji block is 8-10 m thick,typically overlain by limestone.The primary hydrocarbon generation phase occurred during the Early Cretaceous.Based on the differences in tectonic evolution and CRG occurrence,and with the maximum vitrinite reflectance of 2.0%and burial depth of 1800 m as boundaries,the study area is divided into deeply buried and deeply preserved,deeply buried and shallowly preserved,and shallowly buried and shallowly preserved zones.The deeply buried and deeply preserved zone contains gas content of 22-35 m^(3)/t,adsorbed gas saturation of 95%-100%,and formation water with total dissolved solid(TDS)higher than 50000 mg/L.This zone features structural stability and strong sealing capacity,with high gas production rates.The deeply buried and shallowly preserved zone contains gas content of 16-20 m^(3)/t,adsorbed gas saturation of 80%-95%,and formation water with TDS of 5000-50000 mg/L.This zone exhibits localized structural modification and hydrodynamic sealing,with moderate gas production rate.The shallowly buried and shallowly preserved zone contains gas content of 8-16 m^(3)/t,adsorbed gas saturation of 50%-70%,and formation water with TDS lower than 5000 mg/L.This zone experienced intense uplift,resulting in poor sealing and secondary alteration of the primary gas reservoir,with partial adsorbed gas loss,and low gas production rate.A depositional unification and structural divergence model is proposed,that is,although coal seams across the basin experienced broadly similar depositional and tectonic histories,differences in tectonic intensity have led to spatial heterogeneity in the maximum burial depth(i.e.,thermal maturity of coal)and current burial depth and occurrence of CRG(i.e.,gas content and occurrence state).The research results provide valuable guidance for advancing the theoretical understanding of CBM/CRG enrichment and for improving exploration and development practices.展开更多
The Tianshan Carboniferous post-collisional rift volcanic rocks occur in northwestern China as a large igneous province. Based on petrogeochemical data, the Tianshan Carboniferous post-collisional rift basic lavas can...The Tianshan Carboniferous post-collisional rift volcanic rocks occur in northwestern China as a large igneous province. Based on petrogeochemical data, the Tianshan Carboniferous post-collisional rift basic lavas can be classified into two major magma types: (1) the low-Ti/Y type situated in the eastern-central Tianshan area, which exhibits low Ti/Y (<500), Ce/Yb (<15) and SiO2 (43-55%), and relatively high Fe2O3T (6.4-11.5%); (2) the high-Ti/Y type situated in the western Tianshan area, which has high Ti/Y (>500), Ce/Yb (>11) and SiO2 (49-55%), and relatively low Fe2O3T (5.8-7.8%). Elemental data suggest that chemical variations of the low-Ti/Y and high-Ti/Y lavas cannot be explained by fractional crystallization from a common parental magma. The Tianshan Carboniferous basic lavas originated most likely from an OIB-like asthenospheric mantle source (87Sr/86Sr(t) ≈ 0.703-0.705, eNd(0 = +4 to +7). The crustal contamination and continental lithospheric mantle have also contributed significantly to the formation of the basic lavas of the Tianshan Carboniferous post-collisional rift. The silicic lavas were probably generated by partial melting of the crust. The data of this study show that spatial petrogeochemical variations exist in the Carboniferous post-collisional rift volcanics province in the Tianshan region. Occurrence of the thickest volcanics dominated by tholeiitic lavas may imply that the center of the mantle-melting anomaly (mantle plume) was in the eastern Tianshan area at that time. The basic volcanic magmas in the eastern Tianshan area were generated by a relatively high degree of partial melting of the mantle source around the spinel-garnet transition zone, whereas the alkaline basaltic lavas are of the dominant magma type in the western Tianshan area, which were generated by a low degree of partial melting of the mantle source within the stable garnet region, thus the basic lavas of the western Tianshan area might have resulted from relatively thick lithosphere and low geothermal gradient.展开更多
The Wupata'erkan Group, also called Wupata'erkan Formation, distributed in the South Tianshan, Xinjiang, China, mainly consists of gray and dark gray fine-grained clastic rocks, interlayered with volcanic rock...The Wupata'erkan Group, also called Wupata'erkan Formation, distributed in the South Tianshan, Xinjiang, China, mainly consists of gray and dark gray fine-grained clastic rocks, interlayered with volcanic rocks, carbonates and cherts. Some ultra-basic rocks (blocks) punctuate the formation. The formation was variously assigned to Silurian-Middle Devonian, Silurian-Lower Devonian, and pre-Devonian, mainly based on Atrypa bodini Mansuy, Hypothyridina parallelepipedia (Brour.) and Prismatophyllum hexagonum Yoh collected from the limestone interlayers, respectively. However, radiolarian fossils obtained from 24 chert specimens of the Wupata'erkan Group, mainly include Albaillella sp. cf. A. undulata Deflandre, Albaillella sp. cf. A. paradoxa Deflandre, Albaillella cf. A. deflandrei Gourmelon, Albaillella sp. cf. A. indensis Won, Albaillella sp. cf. A. excelsa Ishiga, Kito and Imoto, Albaillella sp. and Latentifistulidae gen. et. sp. indet., are earliest Carboniferous and Late Permian. The earliest Carboniferous assemblage is characterized by Albaillella sp. cf. A. undulata Deflandre, Albaillella sp. cf. A. paradoxa Deflandre, Albaillella cf. A. deflandrei Gourmelon and Albaillella sp. cf. A. indensis Won, and the Late Permian assemblage by Albaillella sp. cf. A. excelsa Ishiga, Kito and Imoto. This new stratigraphic evidence indicates that the Wupata'erkan Group is possibly composed of rocks with different ages from Silurian to Permian, and therefore, it is probably an ophiolite melange. The discovery of Late Permian Albaillella sp. cf. A. excelsa provides more reliable evidence supporting the existence of a Permian relic ancient oceanic basin in the western part of Xinjiang South Tianshan.展开更多
Abundant and well-preserved fossil radiolarians found from the Artencasher Formation, Heiyingshan of Baicheng County, Xinjiang Uygur Autonomous Region, are identified, including 15 species and 2 unnamed species in 9 g...Abundant and well-preserved fossil radiolarians found from the Artencasher Formation, Heiyingshan of Baicheng County, Xinjiang Uygur Autonomous Region, are identified, including 15 species and 2 unnamed species in 9 genera. The fauna is dominated by the Family Entactiniidae of Spumellaria. According to the faunal characteristics, the radiolarians may be divided into five assemblages, namely, the Triaenosphaera sicarius, Entatinosphaera palimbola, Entactinia vulgaris, Belowea cf. variabilis and Archocyrtium sp assemblages. The fauna may be correlated with that from the Early Carboniferous of Frankenwald and Rein in Germany. Thus, ophiolite was formed in the Carboniferous, while the age of collision between the ***Ili plate and the Tarim plate is Early Carboniferous.展开更多
Petrogeochemical data are reported for silicic volcanic rocks from the Tianshan Carboniferous rift, with the aim of discussing the petrogenesis of silicic magmas. Incompatible element vs. incompatible element diagrams...Petrogeochemical data are reported for silicic volcanic rocks from the Tianshan Carboniferous rift, with the aim of discussing the petrogenesis of silicic magmas. Incompatible element vs. incompatible element diagrams display smooth positive trends for the Tianshan Carboniferous rift-related volcanic rocks; the isotope ratios of the silicic lavas [^87Sr/^86S（t）=0.699880.70532; eNd（t）=4.76-8.00; ^206pb/^204pb（t）=17.435-18.017; ^207Pb/^204Pb（t）=15.438-15.509; ^208Pb/^204Pb（t） = 37.075-37.723] encompass those of the basic lavas. These data suggest a genetic link between rhyolites and basalts, but are not definitive in establishing whether silicic rocks are related to basalts through fractional crystallization or partial melting. Geochemical modeling of incompatible vs. compatible elements excludes the possibility that silicic melts are generated by the melting of basaltic rocks, and indicates a derivation by fractional crystallization plus moderate assimilation of wall rocks （AFC） starting from intermediate rocks to silicic rocks. Continuous AFC from basalt to rhyolite, with small rates of crustal assimilation, best explains the geochemical data. The presence or absence of bimodal volcanism （the ＂Daly Gap＂） might be related to cooling rates of magma chambers. In central and eastern Tianshan, the crust was thinner and the cooling rates of the magma chamber within the crust were greater. These conditions resulted in a rapid fall in temperature within the magma reservoir and caused a narrow temperature interval over which intermediate melts formed, effectively reducing the volume of the intermediate melts.展开更多
Based on comprehensive analysis of the drilling core, slice analysis, FMI image well log- ging and other well logging data, the features of the Carboniferous volcanic rocks fracture reservoirs in Hongshanzui oilfield...Based on comprehensive analysis of the drilling core, slice analysis, FMI image well log- ging and other well logging data, the features of the Carboniferous volcanic rocks fracture reservoirs in Hongshanzui oilfield of Junggar Basin have been studied. According to contributing factor, the fracture reservoirs were divided into diagenetic fractures, tectonic fractures, weathered fractures and dissolving fractures. And the diagenetic fractures were further divided into three subclasses of conden- sation contraction fractures, intergravel fractures and intercrystal fractures. The fracture reservoirs were also divided into 4 categories, such as high-angle fractures, oblique fractures, mesh fractures and low-angle fractures according to fracture attitude. With the FMI image logging and other Jogging in- formation, the scale logging by the core method was adopted, our study shows that the fracture of tuff was the most developed, and the fracture density can be reached 11.46 bar/m, followed by the lava, and the sedimentary rock fracture was the lowest level. The fractures thickness in the region of 300 m apart from weather crust was accounted for 80.3% of the total thickness. Because of image logging data is li- mited, the method of drilling wells trajectory to calculate the fracture trend was proposed. The fracture trend was divided into two groups NE and NW. The secondary pore-fracture forming and distribution were controlled by fracture system, formed the beneficial passage system of the oil and gas, the fracture system was the key factor in restricting oil and gas accumulation, and was crucial for the volcanic rocks reservoirs.展开更多
In South China four depositional sequences are recognized in the upper part of Upper Devonian and Tournaisian. They are named SQ0 SQ1, SQ2 and SQ3 in ascending order. SQ0 is Strunian (uppermost Devonian), and the othe...In South China four depositional sequences are recognized in the upper part of Upper Devonian and Tournaisian. They are named SQ0 SQ1, SQ2 and SQ3 in ascending order. SQ0 is Strunian (uppermost Devonian), and the other three Tournaisian in age. These four depositional sequences appear to correlate fairly well with the four sequence recognized in Europe, North America and other areas. This may suggest that these sequences are synchronous depos- its resulted from the eustatic changes. The present study on sequence stratigraphy, biostratigraphy and event stratigraphy indicates that in neritic facies areas of South China, the Devonian-Carboniferous boundary, matching the boundary between Siphonodella praesulcata zone and S. sulcata zone in pelagic facies areas, is not only higher than the top of the Cystophrentis zone, but also higher than the top of the Devonian-Carboniferous boundary event bed. In neritic facies areas, the Devonian-Carbonifrerous boundary is marked by the most distinct transgressive surface within the Cystophrentiseudouralina interval zone, i. e. at the base of the TST of the SQ1. This boundary coincides with the top surface of the event bed resulted from the eustatic fall, and approximately corresponds to the basal part of Rseudouralina assemblage zone.展开更多
To explore the geological characteristics and exploration potential of the Carboniferous Benxi Formation coal rock gas in the Ordos Basin,this paper presents a systematic research on the coal rock distribution,coal ro...To explore the geological characteristics and exploration potential of the Carboniferous Benxi Formation coal rock gas in the Ordos Basin,this paper presents a systematic research on the coal rock distribution,coal rock reservoirs,coal rock quality,and coal rock gas features,resources and enrichment.Coal rock gas is a high-quality resource distinct from coalbed methane,and it has unique features in terms of burial depth,gas source,reservoir,gas content,and carbon isotopic composition.The Benxi Formation coal rocks cover an area of 16×104km^(2),with thicknesses ranging from 2 m to 25 m,primarily consisting of bright and semi-bright coals with primitive structures and low volatile and ash contents,indicating a good coal quality.The medium-to-high rank coal rocks have the total organic carbon(TOC)content ranging from 33.49%to 86.11%,averaging75.16%.They have a high degree of thermal evolution(Roof 1.2%-2.8%),and a high gas-generating capacity.They also have high stable carbon isotopic values(δ13C1of-37.6‰to-16‰;δ13C2of-21.7‰to-14.3‰).Deep coal rocks develop matrix pores such as gas bubble pores,organic pores,and inorganic mineral pores,which,together with cleats and fractures,form good reservoir spaces.The coal rock reservoirs exhibit the porosity of 0.54%-10.67%(averaging 5.42%)and the permeability of(0.001-14.600)×10^(-3)μm^(2)(averaging 2.32×10^(-3)μm^(2)).Vertically,there are five types of coal rock gas accumulation and dissipation combinations,among which the coal rock-mudstone gas accumulation combination and the coal rock-limestone gas accumulation combination are the most important,with good sealing conditions and high peak values of total hydrocarbon in gas logging.A model of coal rock gas accumulation has been constructed,which includes widespread distribution of medium-to-high rank coal rocks continually generating gas,matrix pores and cleats/fractures in coal rocks acting as large-scale reservoir spaces,tight cap rocks providing sealing,source-reservoir integration,and five types of efficient enrichment patterns(lateral pinchout complex,lenses,low-amplitude structures,nose-like structures,and lithologically self-sealing).According to the geological characteristics of coal rock gas,the Benxi Formation is divided into 8 plays,and the estimated coal rock gas resources with a buried depth of more than 2000 m are more than 12.33×10^(12)m^(3).The above understandings guide the deployment of risk exploration.Two wells drilled accordingly obtained an industrial gas flow,driving the further deployment of exploratory and appraisal wells.Substantial breakthroughs have been achieved,with the possible reserves over a trillion cubic meters and the proved reserves over a hundred billion cubic meters,which is of great significance for the reserves increase and efficient development of natural gas in China.展开更多
Geochronological and geochemical analyses were performed on K-feldspar granites and monzonitic granites from the Xilinhot area, Inner Mongolia, China. Zircon U/Pb ages indicate that the two types granites were emplace...Geochronological and geochemical analyses were performed on K-feldspar granites and monzonitic granites from the Xilinhot area, Inner Mongolia, China. Zircon U/Pb ages indicate that the two types granites were emplaced during the Lower Carboniferous. The K-feldspar granites （332 Ma） have the typical A-type granite characteristics of a post-collision setting. The monzonitic granites have an emplacement age of 323 Ma. Zircon tHf values of the former range from ＋12.8 to ＋14.2, with an av- erage TDM2 of 453 Ma. The latter have lower zircon ~Hf values, ranging from ＋5.4 to ＋10.7, with an av- erage TDM2 of 798 Ma. The strong, positive ~nf values of the zircon indicate that both sets of samples are from a juvenile crust formed in an oceanic crust subduction stage, although the monzonitic granite may have undergone a hybridization of crustal materials. These results indicate a younger post orogenic event. The Paleo-Asian Ocean had closed before the Early Carboniferous and the Xilinhot area started its post-orogenic evolution with an extensional tectonic environment durin~ the Early Carboniferous.展开更多
Volcanic rocks in the Bangxi-Chenxing tectonic zone provide important carries for better understanding the Late Paleozoic tectonic evolution in Hainan and its temporal-spatial pattern of the eastern Paleotethyan evolu...Volcanic rocks in the Bangxi-Chenxing tectonic zone provide important carries for better understanding the Late Paleozoic tectonic evolution in Hainan and its temporal-spatial pattern of the eastern Paleotethyan evolution. This paper presents a set of new geochronological and geochemical data on the andesitic and dacitic rocks along the Bangxi-Chenxing tectonic zone in central Hainan. The rep- resentative andesitic and dacitic samples yield similar zircon U-Pb ages of 353^-3 and 351^-7 Ma, respec- tively, being of Early Carboniferous origin. These volcanic rocks are characterized by low TiO2 and high A1203 contents and are enriched in LILEs and LREEs but depletion in HFSEs, along with negative fNd（t） Values of =1.4-- -4.7 and high STSr/S6Sr（i） ratios of 0.707 2-0.710 1. Geochemical signatures suggest that the andesitic and dacitic samples might originate from a metasomatized wedge modified by the slab-derived component in a continental arc setting. In combination with the available data, it is pro- posed for the development of a Carboniferous continental arc in response to the eastern Paleotethyan evolution. The Bangxi-Chenxing tectonic zone might westerly link with the Jinshajiang-Ailaoshan-Song Ma suture zone, constituting an assemblage boundary between the South China and Indochina blocks.展开更多
We present zircon ages and geochemical data for the Hongshishan Carboniferous Alaskan-type mafic–ultramafic complex exposed in the Beishan area along the Sino–Mongolian boundary, southern margin of the Central Asian...We present zircon ages and geochemical data for the Hongshishan Carboniferous Alaskan-type mafic–ultramafic complex exposed in the Beishan area along the Sino–Mongolian boundary, southern margin of the Central Asian Orogenic Belt. This complex mainly consists of dunite,harzburgite, lherzolite, wehrlite, and gabbro, which intrudes Early Carboniferous volcanic rocks and reveals a zoned structure. Zircons of a gabbro sample yielded a 206Pb/238 U age of 357 ± 4 Ma, reflecting the time of Early Carboniferous magmatism. Zircon ages were also obtained for an andesite(322 ± 3 Ma) and a basaltic andesite(304 ± 2 Ma).High initial Nd isotope whole-rock values suggest that the Hongshishan gabbro [e_(Nd(t))= +9.6-+10.2] and basalt[eNd(t)= +10.0-+10.8] were derived from a depleted mantle source. Slightly lower eNd(t)values for the ultramafic rocks [eNd(t)= +8.5-+8.7] suggest some interaction of the parental magma with the continental crust. In contrast, the Late Carboniferous Quershan samples in this area represent subduction-related arc volcanic rocks with Adakite-like compositions. The early Carboniferous Hongshishan Alaskan-type complex was interpreted to represent the remnants of a magma chamber that crystallized at the base of a mature island arc, whereas the Quershan island arc volcanic rockssuggest the resurrection of the subduction process after arccontinent collision and uplift of the roots of the arc.展开更多
Geochemical analysis of sandstones from the Sardar Formation （from two stratigraphic successions） in east-central Iran were used for identification of geochemical characterization of sandstones, provenance and tecto...Geochemical analysis of sandstones from the Sardar Formation （from two stratigraphic successions） in east-central Iran were used for identification of geochemical characterization of sandstones, provenance and tectonic setting. Sandstones in the two lithostratigraphic successions have similar chemical compositions suggesting a common provenance. Bulk-rock geochemistry analysis of Carboniferous sandstones from Sardar Formation indicates that they are mainly quartz dominated and are classified as quartzarenites, sublitharenites and subarkoses, derived from acid igneous to intermediate igneous rocks. Discrimination function analysis indicates that the sandstones of Sardar Formation were derived from quartzose sedimentary provenance in a recycled orogenic setting. Also, major and trace elements in sandstones of Sardar Formation （e.g., K2O/Na2O vs. SiO2 ） indicate deposition in a stable passive continental margin （PM）. Chemical index of alteration （CIA） for these rocks （65%） suggests a moderate to relatively high degree of weathering in the source area.展开更多
Phylloid algae arc important rcef-builders in the late Carboniferous. This paper focuses on the paleoecology of phylloid algae in the Late Carboniferous on well-exposed reefs in Ziyun County, Guizhou Province. Phylloi...Phylloid algae arc important rcef-builders in the late Carboniferous. This paper focuses on the paleoecology of phylloid algae in the Late Carboniferous on well-exposed reefs in Ziyun County, Guizhou Province. Phylloid algae growing closely packed arc attached via holdfast or similar structure to substrate. They were growing in environments such as shallow water, photic zone and below the wave base with medium energy currents. They have a variety of morphological forms, such as single cup-shaped, cabbage-shaped and clustering cup-shaped. The thalli arc of certain tenacity and intensity. In the areas dominated by phylloid algae, other marine orgam＇sms arc relatively scarce. Obviously, phylloid algae arc stronger competitors for living space than other co-occurring organisms.展开更多
This paper presents new LA-ICP-MS zircon U-Pb geochronology,whole-rock major and trace element geochemistry,and Sr-Nd isotopes systematically on porphyritic granitic and K-feldspar granitic intrusions from the Dananhu...This paper presents new LA-ICP-MS zircon U-Pb geochronology,whole-rock major and trace element geochemistry,and Sr-Nd isotopes systematically on porphyritic granitic and K-feldspar granitic intrusions from the Dananhu belt,eastern Tianshan orogenic belt(ETOB).Zircon U-Pb dating indicates that the porphyritic granitic and K-feldspar granitic plutons were formed at 357±3 and 311±3 Ma,respectively.The porphyritic granites show geochemical and isotopic characteristics(high Si O2,low Mg O and Mg^#,depleted Sr-Nd isotopic values(about 0.7034 and 6.13,respectively),with Nb/Ta(13.3–14.7)and Zr/Hf(31.0–33.9)ratios)similar to those of the crustal-derived magmas.The above characteristics suggest they were probably originated from juvenile lower crustal materials.The K-feldspar granites also have high Si O2,low Mg O and Mg^#,depleted Sr-Nd isotopic values(0.7033–0.7046 and 4.41–5.67,respectively).But some trace elements contents vary widely,with variable Nb/Ta(12.7–22.7),Zr/Hf(21.3–36.1)and Nb/La(0.38–1.07)ratios,indicating that the K-feldspar granites were formed by partial melting of juvenile lower crustal materials with old crustal materials.Combined with previous data on Carboniferous granitoids in the Dananhu belt,we infer that all the Carboniferous granitic plutons in the Dananhu belt were most likely emplaced in an island arc environment(Dananhu arc).Subsequently,a tectonic transition from oceanic subduction to post-collisional extension probably occurred in the ETOB.展开更多
Carboniferous source rocks identified by drilling in Santanghu （三塘湖） Basin were evaluated for their source potential, employing organic geochemistry and RockEval pyrolysis. The organic matter origin and depositio...Carboniferous source rocks identified by drilling in Santanghu （三塘湖） Basin were evaluated for their source potential, employing organic geochemistry and RockEval pyrolysis. The organic matter origin and depositional environment of these samples were also determined through biomarker analysis. Most of the Carboniferous source rocks in Santanghu Basin are characterised by high values of total organic carbon （TOC） content and high extractable organic matter content and hydrocarbon yields, indicating that they are organicrich source rocks with high oil generative potential. The organic matter is predominantly Type I and Type II kerogen with a minor contribution of Type III kerogen, as demonstrated by its pyrolysis parameters and carbon isotope values. According to Ro （%） and T max values, most of the studied samples are at earlyto middle-thermal mature stage; only a few of the samples are at a highly mature stage （past peak oil generation）. The biomarker analysis reveals a dominance of algal/bacterial organic matter input, with a minor contribution of land plant material. Pr/Ph ratio supports a suboxic depositional condition, consistent with a neritic or marine-continental alternating environment proposed by predecessor.展开更多
基金supported by the National Natural Science Foundation of China(No.41672222)the State Key Laboratory of Geological Process and Mineral Resources,China University of Geosciences,Wuhan.
文摘Eastern Myanmar is the key position linking between SW Yunnan and northern Thailand for better understanding of Tethyan evolution.However,the actual location and evolution of the Tethyan suture zone are still unclear in eastern Myanmar.The present study focuses on the geochronological,geochemical and zircon Lu-Hf isotopic study on the plutonic rocks,including granite,diorite and gabbroic rocks,from the Tachileik area,eastern Myanmar.These plutonic rocks yielded zircon U-Pb weighted mean ages of ca.353–355 Ma,suggesting the Early Carboniferous emplacement.The Tachileik granites are high-K calc-alkaline,weakly peraluminous and have low P2O5 contents,which are typical features of I-type granites.They have positive zircon ε_(Hf)(t)values(+4.5−+7.4)with T_(DM2) ages of 981–825 Ma,indicating a juvenile mafic lower crust source.The Tachileik gabbros and diorites show high Al_(2)O_(3) contents and Mg#,but low TiO_(2) and K_(2)O contents,belonging to tholeiitic and calc-alkaline basalt series.They are characterized by enrichments in large ion lithophile elements(LILEs,e.g.,Rb,Ba and Sr),depletions in high field strength elements(HFSEs)and distinctly negative Nb and Ta anomalies,similar to the volcanic arc basalt.The zircon Hf isotopic(+4.7−+7.1)and whole-rock geochemical data imply that the Tachileik gabros and diorites probably resulted from partial melting of lithospheric mantle in the spinel stability field within an arc-related setting.The magmatic rocks can be grouped to the Late Devonian–Early Carboniferous magmatic rock and pyroclastic rock zone from SW Yunnan to northern Thailand based on their age and geochemical characters.The zone was formed in the post-collisional extension-related tectonic setting of the Proto-Tethys.This study provides important evidences for the evolution of the Proto-Tethys in Southwest Yunnan and Southeast Asia.
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.
基金Supported by the Hainan Provincial Science and Technology Special Project(ZDYF2025GXJS013)CNOOC Zhanjiang Branch Project(CCL2023ZJFN0540).
文摘Based on drilling,mud logging,core,seismic and imaging logging data,this paper studies the identification and evolution process of negative inversion structures in the Carboniferous buried hills in the No.1 and No.2 fault zones of Weixinan Sag,Beibu Gulf Basin,China,and reveals the controls of these structures on high-quality reservoirs.The No.2 fault zone develops significant negative inversion structures in the Carboniferous buried hills,as a result of multi-stage transformations of compressive-tensile stress fields in the period from the Late Hercynian to the Himalayan.The Hercynian carbonates laid the material basis for the formation of high-quality reservoirs.The negative inversion structures mainly control the development of high-quality reservoirs in buried hills through:(1)creating large-scale fractures to increase reservoir space and improve oil-gas flow pathways;(2)regulating stratigraphic differential denudation to highlight dominant lithology for later reservoir transformation;(3)shaping the paleogeomorphological highlands to provide favorable conditions for superficial karstification.The negative inversion structures form a high-quality,composite reservoir space with the synergistic existence of superficial dissolution fractures/cavities and burial-enhanced karst systems through the coupling of fracture network creation,formation denudation screening and multi-stage karst transformation.The research results have guided the breakthrough of the first exploratory well with a daily oil production over 1000 m^(3)in carbonate buried-hill reservoir in the Beibu Gulf Basin,and provide referential geological basis for finding more reserves and achieving higher production in the Carboniferous buried hills in the Weixinan Sag.
基金supported by the National Natural Science Foundation of China(Grant Nos.42272008 and 41972002).
文摘The origins of peloidal micrites in reefal limestone are not yet well understood.Moscovian microbial reefs with abundant peloidal micrites from Guizhou,South China,provide an opportunity to study the peloids and their geological significance for this time interval.Three types of peloids are differentiated:microbial,lithic,and bioclastic peloids.Microbial peloids that are well-sorted and may form in situ by microbial activities.The poorly sorted lithic peloids are derived from erosion and redeposition of the micrite matrix caused by the bottom turbulence induced by periodic storms.Bioclastic peloids are completely micritized fragments of hard parts and shells.Microbial boring and encrustations promote the processes of micritization.Microbial peloids commonly develop in zones with low or normal energy levels,and contribute to the construction and stabilization of the framework.In contrast,the occurrence of lithic peloids reflects that the reefs are destroyed by bottom turbulence during growth.It is suggested that the microbial reefs were deposited under a dynamic balance between constructional versus destructive processes.By comparative analysis,the peloids as microbial in origin play a key role in the growth and stabilization of bioconstructions during Carboniferous,which should be paid more attention in the studies of Carboniferous buildups.
基金supported by the Ministry of Science and Technology of the People’s Republic of China(Grant No.2022FY101704)the National Natural Science Foundation of China(Grant No.41972061)+1 种基金Science and Technology Innovation Team of Hebei GEO University(30801071)the China Geological Survey(Grant Nos.1212011120701 and 1212011120711)。
文摘High-Mg andesite/diorite(HMA)is useful for identifying subduction-related processes in orogenic belts,including the identification of ophiolites formed in suprasubduction zone(SSZ)environments.The E'rentaolegai high-Mg diorite from the Diyanmiao ophiolite in central Inner Mongolia,North China,has been investigated revealing low-K tholeiitic-calc-alkaline characteristics and have SiO_(2)contents of 53.44-54.92 wt%,MgO contents of 8.44-9.54 wt%,and Mg~#of 54.35-57.60,with variable Fe_(2)O_(3)(7.51-8.61 wt%),Al_(2)O_(3)(11.95-15.09 wt%),and Na_(2)O(3.42-3.94 wt%)contents,low K_(2)O(0.34-0.97 wt%),TiO_(2)(0.35-0.67 wt%),and P2O5(0.12-0.15 wt%)contents,and high Ni(43-193 ppm)and Cr(189-556 ppm)contents.Samples collected have low total rare earth element(REE)contents(30.58-77.80 ppm),with flat or slightly right-dipping REE patterns(La_(N)/Yb_(N)=2.19-3.11)and a lack of pronounced Eu anomalies.The samples are also enriched in large-ion lithophile elements(LILEs,e.g.,K,Rb,Ba,U,and Sr)and depleted in high field strength elements(e.g.,Ta,Nb,Ti,and P).The E'rentaolegai high-Mg diorite has characteristics typical of HMA,and are similar to those of sanukites from the Setouchi Arc in SW Japan.They also display high positiveε_(Nd)(t)values(+6.32 to+7.80),comparable to the values of their host rocks.Petrogenetic analyses suggest that the E'rentaolegai HMA was probably formed by the interaction of partial melts and aqueous fluids from subducted sediments with mantle peridotite.Zircon U-Pb dating reveals that the high-Mg diorite crystallized at 313.6±2.4 Ma,i.e.,late Carboniferous.Combining our data with the temporal and spatial distribution of the Diyanmiao SSZ-type ophiolite,we propose that the eastern Paleo-Asian Ocean had not closed by the late Carboniferous,but intra-oceanic subduction was ongoing.A new model of the initiation of subduction in the eastern PAO during the late Paleozoic.
基金Supported by the China National Science and Technology Major Project(2025ZD1405700)CNPC Science and Technology Project(2023YQX20117).
文摘Based on the coalbed methane(CBM)/coal-rock gas(CRG)geological,geophysical,and experimental testing data from the Daji block in the Ordos Basin,the coal-forming and hydrocarbon generation&accumulation characteristics across different zones were dissected,and the key factors controlling the differential CBM/CRG enrichment were identified.The No.8 coal seam of the Carboniferous Benxi Formation in the Daji block is 8-10 m thick,typically overlain by limestone.The primary hydrocarbon generation phase occurred during the Early Cretaceous.Based on the differences in tectonic evolution and CRG occurrence,and with the maximum vitrinite reflectance of 2.0%and burial depth of 1800 m as boundaries,the study area is divided into deeply buried and deeply preserved,deeply buried and shallowly preserved,and shallowly buried and shallowly preserved zones.The deeply buried and deeply preserved zone contains gas content of 22-35 m^(3)/t,adsorbed gas saturation of 95%-100%,and formation water with total dissolved solid(TDS)higher than 50000 mg/L.This zone features structural stability and strong sealing capacity,with high gas production rates.The deeply buried and shallowly preserved zone contains gas content of 16-20 m^(3)/t,adsorbed gas saturation of 80%-95%,and formation water with TDS of 5000-50000 mg/L.This zone exhibits localized structural modification and hydrodynamic sealing,with moderate gas production rate.The shallowly buried and shallowly preserved zone contains gas content of 8-16 m^(3)/t,adsorbed gas saturation of 50%-70%,and formation water with TDS lower than 5000 mg/L.This zone experienced intense uplift,resulting in poor sealing and secondary alteration of the primary gas reservoir,with partial adsorbed gas loss,and low gas production rate.A depositional unification and structural divergence model is proposed,that is,although coal seams across the basin experienced broadly similar depositional and tectonic histories,differences in tectonic intensity have led to spatial heterogeneity in the maximum burial depth(i.e.,thermal maturity of coal)and current burial depth and occurrence of CRG(i.e.,gas content and occurrence state).The research results provide valuable guidance for advancing the theoretical understanding of CBM/CRG enrichment and for improving exploration and development practices.
文摘The Tianshan Carboniferous post-collisional rift volcanic rocks occur in northwestern China as a large igneous province. Based on petrogeochemical data, the Tianshan Carboniferous post-collisional rift basic lavas can be classified into two major magma types: (1) the low-Ti/Y type situated in the eastern-central Tianshan area, which exhibits low Ti/Y (<500), Ce/Yb (<15) and SiO2 (43-55%), and relatively high Fe2O3T (6.4-11.5%); (2) the high-Ti/Y type situated in the western Tianshan area, which has high Ti/Y (>500), Ce/Yb (>11) and SiO2 (49-55%), and relatively low Fe2O3T (5.8-7.8%). Elemental data suggest that chemical variations of the low-Ti/Y and high-Ti/Y lavas cannot be explained by fractional crystallization from a common parental magma. The Tianshan Carboniferous basic lavas originated most likely from an OIB-like asthenospheric mantle source (87Sr/86Sr(t) ≈ 0.703-0.705, eNd(0 = +4 to +7). The crustal contamination and continental lithospheric mantle have also contributed significantly to the formation of the basic lavas of the Tianshan Carboniferous post-collisional rift. The silicic lavas were probably generated by partial melting of the crust. The data of this study show that spatial petrogeochemical variations exist in the Carboniferous post-collisional rift volcanics province in the Tianshan region. Occurrence of the thickest volcanics dominated by tholeiitic lavas may imply that the center of the mantle-melting anomaly (mantle plume) was in the eastern Tianshan area at that time. The basic volcanic magmas in the eastern Tianshan area were generated by a relatively high degree of partial melting of the mantle source around the spinel-garnet transition zone, whereas the alkaline basaltic lavas are of the dominant magma type in the western Tianshan area, which were generated by a low degree of partial melting of the mantle source within the stable garnet region, thus the basic lavas of the western Tianshan area might have resulted from relatively thick lithosphere and low geothermal gradient.
基金the National Natural Science Foundation of China(Grant 40072077) the Tarim Oil Field Company.PetroChina(Grant 2098050230).
文摘The Wupata'erkan Group, also called Wupata'erkan Formation, distributed in the South Tianshan, Xinjiang, China, mainly consists of gray and dark gray fine-grained clastic rocks, interlayered with volcanic rocks, carbonates and cherts. Some ultra-basic rocks (blocks) punctuate the formation. The formation was variously assigned to Silurian-Middle Devonian, Silurian-Lower Devonian, and pre-Devonian, mainly based on Atrypa bodini Mansuy, Hypothyridina parallelepipedia (Brour.) and Prismatophyllum hexagonum Yoh collected from the limestone interlayers, respectively. However, radiolarian fossils obtained from 24 chert specimens of the Wupata'erkan Group, mainly include Albaillella sp. cf. A. undulata Deflandre, Albaillella sp. cf. A. paradoxa Deflandre, Albaillella cf. A. deflandrei Gourmelon, Albaillella sp. cf. A. indensis Won, Albaillella sp. cf. A. excelsa Ishiga, Kito and Imoto, Albaillella sp. and Latentifistulidae gen. et. sp. indet., are earliest Carboniferous and Late Permian. The earliest Carboniferous assemblage is characterized by Albaillella sp. cf. A. undulata Deflandre, Albaillella sp. cf. A. paradoxa Deflandre, Albaillella cf. A. deflandrei Gourmelon and Albaillella sp. cf. A. indensis Won, and the Late Permian assemblage by Albaillella sp. cf. A. excelsa Ishiga, Kito and Imoto. This new stratigraphic evidence indicates that the Wupata'erkan Group is possibly composed of rocks with different ages from Silurian to Permian, and therefore, it is probably an ophiolite melange. The discovery of Late Permian Albaillella sp. cf. A. excelsa provides more reliable evidence supporting the existence of a Permian relic ancient oceanic basin in the western part of Xinjiang South Tianshan.
基金financially supported by the Fund for Young Geologists of the former MGMRthe Fund of Institute of Geology of CAGS
文摘Abundant and well-preserved fossil radiolarians found from the Artencasher Formation, Heiyingshan of Baicheng County, Xinjiang Uygur Autonomous Region, are identified, including 15 species and 2 unnamed species in 9 genera. The fauna is dominated by the Family Entactiniidae of Spumellaria. According to the faunal characteristics, the radiolarians may be divided into five assemblages, namely, the Triaenosphaera sicarius, Entatinosphaera palimbola, Entactinia vulgaris, Belowea cf. variabilis and Archocyrtium sp assemblages. The fauna may be correlated with that from the Early Carboniferous of Frankenwald and Rein in Germany. Thus, ophiolite was formed in the Carboniferous, while the age of collision between the ***Ili plate and the Tarim plate is Early Carboniferous.
基金support from the Land and Resources Survey Project of China(Grant nos.20011000022,200313000063)the National Natural Science Foundation of China(Grant No.40472044).
文摘Petrogeochemical data are reported for silicic volcanic rocks from the Tianshan Carboniferous rift, with the aim of discussing the petrogenesis of silicic magmas. Incompatible element vs. incompatible element diagrams display smooth positive trends for the Tianshan Carboniferous rift-related volcanic rocks; the isotope ratios of the silicic lavas [^87Sr/^86S（t）=0.699880.70532; eNd（t）=4.76-8.00; ^206pb/^204pb（t）=17.435-18.017; ^207Pb/^204Pb（t）=15.438-15.509; ^208Pb/^204Pb（t） = 37.075-37.723] encompass those of the basic lavas. These data suggest a genetic link between rhyolites and basalts, but are not definitive in establishing whether silicic rocks are related to basalts through fractional crystallization or partial melting. Geochemical modeling of incompatible vs. compatible elements excludes the possibility that silicic melts are generated by the melting of basaltic rocks, and indicates a derivation by fractional crystallization plus moderate assimilation of wall rocks （AFC） starting from intermediate rocks to silicic rocks. Continuous AFC from basalt to rhyolite, with small rates of crustal assimilation, best explains the geochemical data. The presence or absence of bimodal volcanism （the ＂Daly Gap＂） might be related to cooling rates of magma chambers. In central and eastern Tianshan, the crust was thinner and the cooling rates of the magma chamber within the crust were greater. These conditions resulted in a rapid fall in temperature within the magma reservoir and caused a narrow temperature interval over which intermediate melts formed, effectively reducing the volume of the intermediate melts.
基金supported by the National Science and Tech-nology Major Project of China(No.2008ZX05002-005)
文摘Based on comprehensive analysis of the drilling core, slice analysis, FMI image well log- ging and other well logging data, the features of the Carboniferous volcanic rocks fracture reservoirs in Hongshanzui oilfield of Junggar Basin have been studied. According to contributing factor, the fracture reservoirs were divided into diagenetic fractures, tectonic fractures, weathered fractures and dissolving fractures. And the diagenetic fractures were further divided into three subclasses of conden- sation contraction fractures, intergravel fractures and intercrystal fractures. The fracture reservoirs were also divided into 4 categories, such as high-angle fractures, oblique fractures, mesh fractures and low-angle fractures according to fracture attitude. With the FMI image logging and other Jogging in- formation, the scale logging by the core method was adopted, our study shows that the fracture of tuff was the most developed, and the fracture density can be reached 11.46 bar/m, followed by the lava, and the sedimentary rock fracture was the lowest level. The fractures thickness in the region of 300 m apart from weather crust was accounted for 80.3% of the total thickness. Because of image logging data is li- mited, the method of drilling wells trajectory to calculate the fracture trend was proposed. The fracture trend was divided into two groups NE and NW. The secondary pore-fracture forming and distribution were controlled by fracture system, formed the beneficial passage system of the oil and gas, the fracture system was the key factor in restricting oil and gas accumulation, and was crucial for the volcanic rocks reservoirs.
文摘In South China four depositional sequences are recognized in the upper part of Upper Devonian and Tournaisian. They are named SQ0 SQ1, SQ2 and SQ3 in ascending order. SQ0 is Strunian (uppermost Devonian), and the other three Tournaisian in age. These four depositional sequences appear to correlate fairly well with the four sequence recognized in Europe, North America and other areas. This may suggest that these sequences are synchronous depos- its resulted from the eustatic changes. The present study on sequence stratigraphy, biostratigraphy and event stratigraphy indicates that in neritic facies areas of South China, the Devonian-Carboniferous boundary, matching the boundary between Siphonodella praesulcata zone and S. sulcata zone in pelagic facies areas, is not only higher than the top of the Cystophrentis zone, but also higher than the top of the Devonian-Carboniferous boundary event bed. In neritic facies areas, the Devonian-Carbonifrerous boundary is marked by the most distinct transgressive surface within the Cystophrentiseudouralina interval zone, i. e. at the base of the TST of the SQ1. This boundary coincides with the top surface of the event bed resulted from the eustatic fall, and approximately corresponds to the basal part of Rseudouralina assemblage zone.
基金Supported by the PetroChina Science and Technology Major Project(2023ZZ18-03)Changqing Oilfield Major Science and Technology Project(2023DZZ01)。
文摘To explore the geological characteristics and exploration potential of the Carboniferous Benxi Formation coal rock gas in the Ordos Basin,this paper presents a systematic research on the coal rock distribution,coal rock reservoirs,coal rock quality,and coal rock gas features,resources and enrichment.Coal rock gas is a high-quality resource distinct from coalbed methane,and it has unique features in terms of burial depth,gas source,reservoir,gas content,and carbon isotopic composition.The Benxi Formation coal rocks cover an area of 16×104km^(2),with thicknesses ranging from 2 m to 25 m,primarily consisting of bright and semi-bright coals with primitive structures and low volatile and ash contents,indicating a good coal quality.The medium-to-high rank coal rocks have the total organic carbon(TOC)content ranging from 33.49%to 86.11%,averaging75.16%.They have a high degree of thermal evolution(Roof 1.2%-2.8%),and a high gas-generating capacity.They also have high stable carbon isotopic values(δ13C1of-37.6‰to-16‰;δ13C2of-21.7‰to-14.3‰).Deep coal rocks develop matrix pores such as gas bubble pores,organic pores,and inorganic mineral pores,which,together with cleats and fractures,form good reservoir spaces.The coal rock reservoirs exhibit the porosity of 0.54%-10.67%(averaging 5.42%)and the permeability of(0.001-14.600)×10^(-3)μm^(2)(averaging 2.32×10^(-3)μm^(2)).Vertically,there are five types of coal rock gas accumulation and dissipation combinations,among which the coal rock-mudstone gas accumulation combination and the coal rock-limestone gas accumulation combination are the most important,with good sealing conditions and high peak values of total hydrocarbon in gas logging.A model of coal rock gas accumulation has been constructed,which includes widespread distribution of medium-to-high rank coal rocks continually generating gas,matrix pores and cleats/fractures in coal rocks acting as large-scale reservoir spaces,tight cap rocks providing sealing,source-reservoir integration,and five types of efficient enrichment patterns(lateral pinchout complex,lenses,low-amplitude structures,nose-like structures,and lithologically self-sealing).According to the geological characteristics of coal rock gas,the Benxi Formation is divided into 8 plays,and the estimated coal rock gas resources with a buried depth of more than 2000 m are more than 12.33×10^(12)m^(3).The above understandings guide the deployment of risk exploration.Two wells drilled accordingly obtained an industrial gas flow,driving the further deployment of exploratory and appraisal wells.Substantial breakthroughs have been achieved,with the possible reserves over a trillion cubic meters and the proved reserves over a hundred billion cubic meters,which is of great significance for the reserves increase and efficient development of natural gas in China.
基金supported by the China Geological Survey (Nos. 1212010510507, 1212010811005, 1212011220448)the Fundamental Research Funds for the Central Universities, China University of Geosciences, Wuhan (No. CUGL150816)
文摘Geochronological and geochemical analyses were performed on K-feldspar granites and monzonitic granites from the Xilinhot area, Inner Mongolia, China. Zircon U/Pb ages indicate that the two types granites were emplaced during the Lower Carboniferous. The K-feldspar granites （332 Ma） have the typical A-type granite characteristics of a post-collision setting. The monzonitic granites have an emplacement age of 323 Ma. Zircon tHf values of the former range from ＋12.8 to ＋14.2, with an av- erage TDM2 of 453 Ma. The latter have lower zircon ~Hf values, ranging from ＋5.4 to ＋10.7, with an av- erage TDM2 of 798 Ma. The strong, positive ~nf values of the zircon indicate that both sets of samples are from a juvenile crust formed in an oceanic crust subduction stage, although the monzonitic granite may have undergone a hybridization of crustal materials. These results indicate a younger post orogenic event. The Paleo-Asian Ocean had closed before the Early Carboniferous and the Xilinhot area started its post-orogenic evolution with an extensional tectonic environment durin~ the Early Carboniferous.
基金jointly supported by the Projects from China (Nos. U1701641, 41506050, 2016ZT06N331 and 2017M612794)
文摘Volcanic rocks in the Bangxi-Chenxing tectonic zone provide important carries for better understanding the Late Paleozoic tectonic evolution in Hainan and its temporal-spatial pattern of the eastern Paleotethyan evolution. This paper presents a set of new geochronological and geochemical data on the andesitic and dacitic rocks along the Bangxi-Chenxing tectonic zone in central Hainan. The rep- resentative andesitic and dacitic samples yield similar zircon U-Pb ages of 353^-3 and 351^-7 Ma, respec- tively, being of Early Carboniferous origin. These volcanic rocks are characterized by low TiO2 and high A1203 contents and are enriched in LILEs and LREEs but depletion in HFSEs, along with negative fNd（t） Values of =1.4-- -4.7 and high STSr/S6Sr（i） ratios of 0.707 2-0.710 1. Geochemical signatures suggest that the andesitic and dacitic samples might originate from a metasomatized wedge modified by the slab-derived component in a continental arc setting. In combination with the available data, it is pro- posed for the development of a Carboniferous continental arc in response to the eastern Paleotethyan evolution. The Bangxi-Chenxing tectonic zone might westerly link with the Jinshajiang-Ailaoshan-Song Ma suture zone, constituting an assemblage boundary between the South China and Indochina blocks.
基金financially supported by the National Natural Science Foundation of China (Grant Nos.40703012,41030314)Geological Survey of China (Grant Nos.1212011120332,DD20160123-05)Chinese Ministry of Science and Technology (Grant 2012FY120100)
文摘We present zircon ages and geochemical data for the Hongshishan Carboniferous Alaskan-type mafic–ultramafic complex exposed in the Beishan area along the Sino–Mongolian boundary, southern margin of the Central Asian Orogenic Belt. This complex mainly consists of dunite,harzburgite, lherzolite, wehrlite, and gabbro, which intrudes Early Carboniferous volcanic rocks and reveals a zoned structure. Zircons of a gabbro sample yielded a 206Pb/238 U age of 357 ± 4 Ma, reflecting the time of Early Carboniferous magmatism. Zircon ages were also obtained for an andesite(322 ± 3 Ma) and a basaltic andesite(304 ± 2 Ma).High initial Nd isotope whole-rock values suggest that the Hongshishan gabbro [e_(Nd(t))= +9.6-+10.2] and basalt[eNd(t)= +10.0-+10.8] were derived from a depleted mantle source. Slightly lower eNd(t)values for the ultramafic rocks [eNd(t)= +8.5-+8.7] suggest some interaction of the parental magma with the continental crust. In contrast, the Late Carboniferous Quershan samples in this area represent subduction-related arc volcanic rocks with Adakite-like compositions. The early Carboniferous Hongshishan Alaskan-type complex was interpreted to represent the remnants of a magma chamber that crystallized at the base of a mature island arc, whereas the Quershan island arc volcanic rockssuggest the resurrection of the subduction process after arccontinent collision and uplift of the roots of the arc.
基金supported by a grant to the senior author from Faculty of Sciences, Ferdowsi University of Mashhad
文摘Geochemical analysis of sandstones from the Sardar Formation （from two stratigraphic successions） in east-central Iran were used for identification of geochemical characterization of sandstones, provenance and tectonic setting. Sandstones in the two lithostratigraphic successions have similar chemical compositions suggesting a common provenance. Bulk-rock geochemistry analysis of Carboniferous sandstones from Sardar Formation indicates that they are mainly quartz dominated and are classified as quartzarenites, sublitharenites and subarkoses, derived from acid igneous to intermediate igneous rocks. Discrimination function analysis indicates that the sandstones of Sardar Formation were derived from quartzose sedimentary provenance in a recycled orogenic setting. Also, major and trace elements in sandstones of Sardar Formation （e.g., K2O/Na2O vs. SiO2 ） indicate deposition in a stable passive continental margin （PM）. Chemical index of alteration （CIA） for these rocks （65%） suggests a moderate to relatively high degree of weathering in the source area.
基金This study is supported by a grant （No. 40572014） from National Science Foundation of China （NFSC）.
文摘Phylloid algae arc important rcef-builders in the late Carboniferous. This paper focuses on the paleoecology of phylloid algae in the Late Carboniferous on well-exposed reefs in Ziyun County, Guizhou Province. Phylloid algae growing closely packed arc attached via holdfast or similar structure to substrate. They were growing in environments such as shallow water, photic zone and below the wave base with medium energy currents. They have a variety of morphological forms, such as single cup-shaped, cabbage-shaped and clustering cup-shaped. The thalli arc of certain tenacity and intensity. In the areas dominated by phylloid algae, other marine orgam＇sms arc relatively scarce. Obviously, phylloid algae arc stronger competitors for living space than other co-occurring organisms.
基金supported by the National Key Research and Development Program of China (No. 2016YFC0601003)the National Natural Science Foundation of China (Nos. 41903031,41421002)+1 种基金the China Postdoctoral Science Foundation (No. 2019M652431)the National Basic Research Program of China (No. 2014CB440801)
文摘This paper presents new LA-ICP-MS zircon U-Pb geochronology,whole-rock major and trace element geochemistry,and Sr-Nd isotopes systematically on porphyritic granitic and K-feldspar granitic intrusions from the Dananhu belt,eastern Tianshan orogenic belt(ETOB).Zircon U-Pb dating indicates that the porphyritic granitic and K-feldspar granitic plutons were formed at 357±3 and 311±3 Ma,respectively.The porphyritic granites show geochemical and isotopic characteristics(high Si O2,low Mg O and Mg^#,depleted Sr-Nd isotopic values(about 0.7034 and 6.13,respectively),with Nb/Ta(13.3–14.7)and Zr/Hf(31.0–33.9)ratios)similar to those of the crustal-derived magmas.The above characteristics suggest they were probably originated from juvenile lower crustal materials.The K-feldspar granites also have high Si O2,low Mg O and Mg^#,depleted Sr-Nd isotopic values(0.7033–0.7046 and 4.41–5.67,respectively).But some trace elements contents vary widely,with variable Nb/Ta(12.7–22.7),Zr/Hf(21.3–36.1)and Nb/La(0.38–1.07)ratios,indicating that the K-feldspar granites were formed by partial melting of juvenile lower crustal materials with old crustal materials.Combined with previous data on Carboniferous granitoids in the Dananhu belt,we infer that all the Carboniferous granitic plutons in the Dananhu belt were most likely emplaced in an island arc environment(Dananhu arc).Subsequently,a tectonic transition from oceanic subduction to post-collisional extension probably occurred in the ETOB.
基金supported by the China Postdoctoral Science Foundation
文摘Carboniferous source rocks identified by drilling in Santanghu （三塘湖） Basin were evaluated for their source potential, employing organic geochemistry and RockEval pyrolysis. The organic matter origin and depositional environment of these samples were also determined through biomarker analysis. Most of the Carboniferous source rocks in Santanghu Basin are characterised by high values of total organic carbon （TOC） content and high extractable organic matter content and hydrocarbon yields, indicating that they are organicrich source rocks with high oil generative potential. The organic matter is predominantly Type I and Type II kerogen with a minor contribution of Type III kerogen, as demonstrated by its pyrolysis parameters and carbon isotope values. According to Ro （%） and T max values, most of the studied samples are at earlyto middle-thermal mature stage; only a few of the samples are at a highly mature stage （past peak oil generation）. The biomarker analysis reveals a dominance of algal/bacterial organic matter input, with a minor contribution of land plant material. Pr/Ph ratio supports a suboxic depositional condition, consistent with a neritic or marine-continental alternating environment proposed by predecessor.
