Apatite(U-Th)/He and fission track dating and tectono-thermal history modeling were used to reconstruct the Meso-Cenozoic tectonic evolution of the Huangling paleo-uplift in the Middle Yangtze Block,South China.The te...Apatite(U-Th)/He and fission track dating and tectono-thermal history modeling were used to reconstruct the Meso-Cenozoic tectonic evolution of the Huangling paleo-uplift in the Middle Yangtze Block,South China.The tectono-thermal evolution showed different tectonic exhumation/subsidence processes in the tectonic evolution of the foreland basin.The apatite(U-Th)/He ages ranged from 31.3 to 77.8 Ma,recording the thermal events of the Cenozoic Himalayan movement and indicating progressive exhumation extending from the southeast to the northwest.The thermal information of the Mesozoic Yanshan movement period was recorded by the apatite fission track age with a pooled age of 93.8 to 147 Ma.The exhumation of the Huangling paleo-uplift began in the Late Jurassic.The tectono-thermal evolution was characterized by a rapid uplift during 140-115 Ma,subsidence during 115-60 Ma,a rapid uplift during 40-30 Ma,and a slow uplift from 30 Ma to the present.The western Hunan-Hubei Depression was exhumed in the Middle Jurassic,and the tectono-thermal evolution was characterized by a rapid uplift during 160-135 Ma,a slow uplift during 135-50 Ma,a rapid uplift during 50-25 Ma,and a slow uplift from 25 Ma to the present.This Cenozoic exhumation was a response to the far field effect of the eastward growth of the Tibetan Plateau.The Cretaceous basins exposed in the surrounding areas of the Huangling paleo-uplift(Zigui basin,Yichang slope,and Huaguoping synclinorium)are foreland basins formed by the bi-directional compression of the Qinling-Dabie orogenic belt and the Xuefengshan intracontinental deformation system.展开更多
The Ordos Basin(OB)in the western part of the North China Craton(NCC),was located at the jointed area of multi-plates and has recorded the Mesozoic tectonic characteristics.Its tectonic evolution in the Mesozoic is si...The Ordos Basin(OB)in the western part of the North China Craton(NCC),was located at the jointed area of multi-plates and has recorded the Mesozoic tectonic characteristics.Its tectonic evolution in the Mesozoic is significant to understand the tectonic transformation of the northern margin of the NCC.In this work,the detrital zircon and apatite(U-Th)/He chronological system were analyzed in the northern part of the OB,and have provided new evidence for the regional tectonic evolution.The(U-Th)/He chronological data states the weighted ages of 240‒235 Ma,141 Ma with the peak distribution of 244 Ma,219 Ma,173 Ma,147‒132 Ma.The thermal evolution,geochronological data,and regional unconformities have proved four stages of regional tectonic evolution for the OB and its surroundings in the Mesozoic:(1)The Late Permian-Early Triassic;(2)the Late Triassic-Early Jurassic;(3)the Late Jurassic-Early Cretaceous;(4)the Late Cretaceous-Early Paleogene.It is indicated that the multi-directional convergence from the surrounding tectonic units has controlled the Mesozoic tectonic evolution of the OB.Four-stage tectonic evolution reflected the activation or end of different plate movements and provided new time constraints for the regional tectonic evolution of the NCC in the Mesozoic.展开更多
The Bijigou intrusion is one of the largest and most well-differentiated Fe–Ti oxide-bearing layered intrusions in the Hannan massif located in the northwestern margin of the Yangtze Block,South China.Besides the min...The Bijigou intrusion is one of the largest and most well-differentiated Fe–Ti oxide-bearing layered intrusions in the Hannan massif located in the northwestern margin of the Yangtze Block,South China.Besides the mineralization-related mafic-ultramafic rocks,the intermediate-acid intrusive rocks are also exposed in the mining area,which is of great significance for the understanding the Neoproterozoic tectonic evolution of the Yangtze Block,but studies on these intermediate-acid rocks are scarce.The Bijigou mafic-ultramafic layered intrusion is surrounded by granite and cut by syenite veins.Here,we report new zircon U-Pb ages,Lu-Hf isotope composition and bulk rock geochemical data of the Bijigou syenite vein and wall-rock granite in the northwestern margin of the Yangtze Block.Laser ablation inductively coupled plasma mass spectrometry(LAICP-MS)zircon U-Pb dating results show that the Bijigou syenite vein and wall-rock granite formed at 770±3.5 Ma(MSWD=0.17,n=28)and 810±4 Ma(MSWD=0.84,n=26),respectively.The zirconεHf(t)values of the syenite veins range from+1.52 to+5.33(average of+3.05),combined with its high potassium contents,negative Nb–Ta anomalies and positive Pb anomalies,suggesting that they may have originated from mantle-derived basaltic magma,which was modified by materials from subducting oceanic slab.The zirconεHf(t)and T_(DM2)ages of the wall-rock granite range from+0.71 to+5.71(average+3.06)and 1344 to 1659 Ma(average 1519 Ma),respectively,indicating that the granite was produced by partial melting of juvenile crust.The geochemical characteristics of the Bijigou syenite and granite indicate that they were formed in a continental margin arc setting.Thus,combined with previous studies,it suggests that there was a major subduction system along the northwestern margin of the Yangtze Block during 824-720 Ma,and the magmatism in the Hannan massif was divided into two episodes:(1)early magmatism(824-790 Ma),such as the Bijigou,Hongmiaozhen and Huangguanzhen granitoids,was derived from partial melting of the juvenile or pre-existing crust in a continental arc setting;(2)later magmatism(789-718 Ma),including Bijigou syenite,Wudumen,Erliba and Zushidian granitoids,formed in a subduction-related back-arc extensional environment.The long-term subduction system along the northwestern margin of the Yangtze Block during 824-720 Ma suggests that the Yangtze Block was previously located at the periphery of the Rodinia supercontinent.展开更多
The Shuangwang Au deposit in the western Qinling Orogen is hosted by a WNW-ESE-trending breccia belt that is structurally controlled by the northern limb of the Yindonggou fold.Igneous rocks area in the deposit are pa...The Shuangwang Au deposit in the western Qinling Orogen is hosted by a WNW-ESE-trending breccia belt that is structurally controlled by the northern limb of the Yindonggou fold.Igneous rocks area in the deposit are part of the Xiba pluton,which comprises granodiorite and monzogranite that contains mafic microgranular envlaves(MMEs),and later mineralized granitic porphyry dikes.The mineralized granitic porphyry dikes were controlled by the same structures that controlled the ore bodies.Zircon LA-ICP-MS U-Pb dating yields ages of 220.0±1.9 Ma for the granodiorite,and 217.9±1.9 Ma for the granitic porphyry,which is consistent with the mineralization ages reported in previous studies(220-218 Ma).Together with the similarity of alteration mineral assemblages between ore and mineralized granitic porphyry,we suggest that the mineralization was controlled by structure and Xiba pluton.The geochemical data show that the granodiorite and granitic porphyry are subalkaline and the MMEs are alkaline in composition.All samples have similar chondrite-normalized rare earth element patterns with enrichment of light rare earth elements.The granodiorite and MMEs are depleted in Nb,Ta,Sr,P,and Ti and enriched in U,K,Pb,Zr,and Hf.The granitic porphyry is enriched in large-ion lithophile elements but depleted in high-field-strength elements.The granodiorite and MMEs have low whole-rockεNd(t)values(−10.90 to−2.32)and(^(87)Sr/^(86)Sr)i ratios(0.7000-0.7285),similar to coeval Triassic granites in the western Qinling Orogen.The(^(87)Sr/^(86)Sr)i ratios of the granitic porphyry have been affected by fluid metasomatism that results in higher(^(87)Sr/^(86)Sr)i values.The geochronological,geochemical,and isotopic evidence suggest that the Xiba pluton formed by partial melting of thickened lower crust that had been intruded by alkaline mafic magma,as documented by the MMEs,which were derived from a source metasomatized by subduction-related fluids.The granodioritic and granitic porphyry magmas were relatively oxidized(fayalite-magnetite-quartz[FMQ]to magnetite-hematite(MH)buffer conditions;zircon Ce^(4+)/Ce^(3+)=72-813;log(fO_(2))=−22 to−8).We propose that magma mixing between lower crust and mantle-derived mafic magma was triggered by the tectonic transition from a collisional to post-collision setting,which provided the metals,S,fluids,and increase in magma oxygen fugacity that enabled the formation of the Shuangwang Au deposit.Since the Late Triassic,the western Qinling Orogen evolved from a syn-collisional compressional to post-collisional extensional environment.The mineralization of the Shuangwang Au deposit involved early formation of a tectonic breccia in the compressional stage.Subsequently,hydrothermal fluids derived from a magma ascended,migrated,mixed,and precipitated ores in the tectonic breccia during the later extensional stage to form the Shuangwang Au deposit.展开更多
There is significant debate concerning the tectonic characteristics and evolutionary understanding of the South China Block(SCB)during the Early Mesozoic.One of the key points of contention is the tectonic-magmatic ac...There is significant debate concerning the tectonic characteristics and evolutionary understanding of the South China Block(SCB)during the Early Mesozoic.One of the key points of contention is the tectonic-magmatic activity during the Triassic and its dynamic mechanisms.However,research on the detailed chronology and tectonic settings of granite plutons in key regions remains insuffi-cient,limiting the understanding of the tectonic-magmatic dynamic mechanisms in the interior of SCB during the Triassic.In this contribution,we present whole-rock major and trace elemental data,Sr-Nd isotope data,LA-ICP-MS zircon U-Pb age dating,and Lu-Hf isotope data for granites of Dashenshan pluton in the Xiangzhong,northwest part of SCB.The results indicate that the Dashenshan granite has an emplacement age of 208.4-212.5 Ma,characterized by high SiO_(2),Na_(2)O,and K_(2)O contents and low MgO and CaO.The Dashenshan granite is enriched in light rare-earth elements with a significant negative Eu anomaly(averageδEu=0.42).It is also enriched in Rb,K,and Th and shows pronounced depletion in Nb,Ta,and Ti,classifying it as peraluminous calc-alkaline granite,specifically of the I-type.The zircon ε_(Hf(t)) values range from−8.39 to−4.4,with an average of−5.82,and the Sr-Nd isotopes are relatively enriched[ε_(Nd)(t)=−9.31 to−6.8].Combining these geochemical characteristics,it is revealed that the Dashenshan granite was derived from the partial melting of middle to upper crustal metamorphic basement materials under medium-to low-temperature conditions,with possible minor contributions from mantle-derived materials.Furthermore,it underwent fractional crystallization,including plagioclase differentiation.By integrating the geochemical features and spatial distribution of Triassic granites in SCB,this study suggests that the regional tectonic evolution of SCB during the Triassic was primarily controlled by the collision of the SCB with the Indochina Block and the North China Block.In Xiangzhong,the tectonic setting transitioned from syn-collisional compression to post-collisional extension during the Late Triassic.The Dashenshan pluton formed in a post-collisional extensional setting,resulting from the decompression melting of middle-to-upper crustal rocks.The upwelling of the asthenosphere and upward heat transfer likely played a significant role in the formation of the Dashenshan granitic magma.展开更多
In the context of complex tectonic evolution,due to the control of tectonic compression stress and faults on tectonic fractures,the formation and development of tectonic fractures in the T_3x~2 tight reservoirs presen...In the context of complex tectonic evolution,due to the control of tectonic compression stress and faults on tectonic fractures,the formation and development of tectonic fractures in the T_3x~2 tight reservoirs present significant variations across different tectonic segments in the Western Sichuan Foreland Basin.We clarified the control of differential tectonic evolution on the formation and development of tectonic fractures in different tectonic segments through field-based observations,core samples,image logging,as well as fluid inclusion petrography and temperature determinations of fracture-filling materials,combined with 2D balanced cross-section restoration.The study area primarily manifests two types of tectonic fractures in the tight reservoirs:orogen-related fractures(regional fractures)and fault-related fractures.The orientations of these fractures are predominantly E-W,nearly N-S,NE,and NW.Specifically,the northern segment area only shows the development of regional fractures,while the southern and middle segments exhibit the development of both regional and tectonic fractures.There are three phases of tectonic fractures in different tectonic segments,and their formation times are relatively consistent.The Mesozoic tectonic events had a significant impact on the northern and central segments,with the amount of tectonic shortening and the rate of stratigraphic shortening gradually decreasing from the northeast to the southwest.The compressional stress resulting from tectonic compression also decreases from the northeast to the southwest.As a result,the development of first-phase and second-phase tectonic shear fractures is more pronounced in the northern and middle segments compared to the southern segment.Under the significant control of faults,the development of N-S-and NE-oriented fault-related fractures is more pronounced in the southern segment,while the development of NE-oriented fault-related fractures is relatively higher in the middle segment.Overall,there is an increased density of fractures and an increasing trend in fracture scale from the northern to the middle and then to the southern segment.展开更多
The Yangtze Plate(YP)and the North China Plate(NCP)are key components of the East Asian continent,and their collision significantly influences the tectonic evolution of the eastern Asian continental margin.As the Sout...The Yangtze Plate(YP)and the North China Plate(NCP)are key components of the East Asian continent,and their collision significantly influences the tectonic evolution of the eastern Asian continental margin.As the South Yellow Sea is located at the convergence of these plates,it becomes a pivotal area for understanding the tectonic evolution of East Asia.The characteristics and provenance of clastic rocks of the Middle Permian-the Early Triassic were analyzed and the strata in the Central Uplift including the Qinglong Formation(T_(1)q)and Talung Formation(P_(3)d),consisting of various mudstones and sandstones,were anatomized.Results show that quartz and feldspar are the main diagenetic minerals,while illite and chlorite show signs of secondary alterations.Geochemical imprints indicate a gradual shift in provenance from ancient sedimentary and mafic igneous rocks to intermediate igneous rocks.In the meantime,the tectonic background transformed from continent to continental island arc from the Middle Permian to the Early Triassic.Therefore,we inferred that a soft collision between the North China Plate and the Yangtze Plate likely occurred during the Late Permian,resulted in intensified collision between two plates in the Early Triassic,and shaped the South Yellow Sea.This study provided valuable information on the timing of plate collisions in the South Yellow Sea.展开更多
0 INTRODUTION The Kuqa Depression,situated along the northern margin of the Tarim Basin,holds substantial geological significance due to its intricate sedimentary burial history,tectonic history,and the evolution of h...0 INTRODUTION The Kuqa Depression,situated along the northern margin of the Tarim Basin,holds substantial geological significance due to its intricate sedimentary burial history,tectonic history,and the evolution of hydrocarbon source rocks(Jiang et al.,2024;Zhang et al.,2023;Huang et al.,2019;Yang et al.,2017;Jia et al.,2003;Hendrix,2000).展开更多
The West Kunlun orogenic belt(WKOB) along the northern margin of the Tibetan Plateau is important for understanding the evolution of the Proto-and Paleo-Tethys oceans. Previous investigations have focused on the igneo...The West Kunlun orogenic belt(WKOB) along the northern margin of the Tibetan Plateau is important for understanding the evolution of the Proto-and Paleo-Tethys oceans. Previous investigations have focused on the igneous rocks and ophiolites distributed mostly along the Xinjiang-Tibet road and the China-Pakistan road, and have constructed a preliminary tectonic model for this orogenic belt. However, few studies have focused on the so-called Precambrian basement in this area. As a result, the tectonic affinity of the individual terranes of the WKOB and their detailed evolution process are uncertain. Here we report new field observations, zircon and monazite U-Pb ages of the "Precambrian basement" of the South Kunlun terrane(SKT) and the Tianshuihai terrane(TSHT), two major terranes in the WKOB. Based on new zircon U-Pb age data, the amphibolite-facies metamorphosed volcanosedimentary sequence within SKT was deposited during the late Neoproterozoic to Cambrian(600-500 Ma), and the flysch-affinity Tianshuihai Group, as the basement of the TSHT, was deposited during the late Neoproterozoic rather than Mesoproterozoic. The rock association of the volcano-sedimentary sequence within SKT suggests a large early Paleozoic accretionary wedge formed by the long-term lowangle southward subduction of the Proto-Tethys Ocean between Tarim and TSHT. The amphibolitefacies metamorphism in SKT occurred at ca. 440 Ma. This ca. 440 Ma metamorphism is genetically related to the closure of the Proto-Tethys Ocean between Tarim and the Tianshuihai terrane, which led to the assembly of Tarim to Eastern Gondwana and the final formation of the Gondwana. Since the late Paleozoic to early Mesozoic, the northward subduction of the Paleo-Tethys Ocean along the HongshihuQiaoertianshan belt produced the voluminous early Mesozoic arc-signature granites along the southern part of NKT-TSHT. The Paleo-Tethys ocean between TSHT and Karakorum closed at ca. 200 Ma, as demonstrated by the monazite age of the paragneiss in the Kangxiwa Group. Our study does not favor the existence of a Precambrian basement in SKT.展开更多
The Altun faulted Zone has been focused by lots of geologists for many years because it lies in a boundary area of several main tectonic units in the western China and is a geographically northern boundary line of Tib...The Altun faulted Zone has been focused by lots of geologists for many years because it lies in a boundary area of several main tectonic units in the western China and is a geographically northern boundary line of Tibet plateau.The latest achievements show that the Altun faulted zone is not only a Cenozoic strike\|slip faulted system but also an orogenic zone which underwent mutually subduction\|collision among paleo\|plates (or terrains) in its early stage and consists of geological bodies of different ages and tectonic environments. Based on the results of geological characteristics,petrology, geochemistry and isotopic dating, the Altun Orogenic Zone can be divided into four tectonic units and is considered to have undergone five stages during its tectonic evolution.The four tectonics units are :(1) Abei metamorphic block, which consists of Archean metamorphic complex of granulite facies;.(2) Hongliugou—Lapeiquan tectonic melange belt, which is composed of ophiolite blocks(belt), OIB blocks, pelagic silicalite, shallow\|bathyal sedimentary rock blocks and high\|pressure metamorphi c rock blocks. (3) Milanhe—Jinyanshan island\|arc block, which consists of mid\|uplifting belt and the south and north active margins. The uplifting belt is composed of metasandstone, marble, overlying thick stromatolite (Jinyanshan Group of Jixian System). Metamorphic rocks of 450Ma occur in both south and north hactive margin. Post\|collision bimodal volcanic rocks and A\|type granite occur in the middle and the north side.(4) Apa—Mangya tectonic melange belt, which consists of ophiolite(including ultramafic rocks, gabbro, plagiogranite and basalt) and flysch and eclogite of late Ordovician.展开更多
Okinawa Trough is a back-arc, initial marginal sea basin, located behind the Ryukyu Arc-Trench System. The formation and evolution of the Okinawa Trough is intimately related to the subduction process of the Philippin...Okinawa Trough is a back-arc, initial marginal sea basin, located behind the Ryukyu Arc-Trench System. The formation and evolution of the Okinawa Trough is intimately related to the subduction process of the Philippine Sea Plate beneath the Eurasian Plate since the late Miocene. The tectonic evolution of the trough is similar to other active back-arcs, such as the Mariana Trough and southern Lau Basin, all of which are experiencing the initial rifting and subsequent spreading process. This study reviews all petrologic and geochemical data of mafic volcanic lavas from the Okinawa Trough, Ryukyu Arc, and Philippine Sea Plate, combined with geophysical data to indicate the relationship between the subduction sources （input） and arc or back-arc magmas （output） in the Philippine Sea Plate-Ryukyu Arc-Okinawa Trough system （PROS）. The results obtained showed that several components were variably involved in the petrogenesis of the Oki-nawa Trough lavas：sub-continental lithospheric mantle underlying the Eurasian Plate, Indian mid-oceanic ridge basalt （MORB）-type mantle, and Pacific MORB-type mantle. The addition of shallow aqueous fluids and deep hydrous melts from subducted components with the characteristics of Indian MORB-type mantle into the mantle source of lavas variably modifies the primitive mantle wedge beneath the Ryukyu and sub-continental lithospheric mantle （SCLM） beneath the Okinawa Trough. In the northeastern end of the trough and arc, instead of Indian MORB-type mantle, Pacific MORB-type mantle dominates the magma source. Along the strike of the Ryukyu Arc and Okinawa Trough, the systematic variations in trace element ratios and isotopic compositions reflect the first-order effect of variable subduction input on the magma source. In general, petrologic data, combined with geophysical data, imply that the Okinawa Trough is experiencing the＂seafloor spreading＂process in the southwest segment,＂rift propagation＂process in the middle seg-ment, and＂crustal extension＂process in the northeast segment, and a nascent ocean basin occurs in the southwest segment.展开更多
The Changning - Menglian belt , located between the Baoshan - Gengma massif and the Simao - Lincang massif in Western Yunnan , preserves the complete record of a suture zone and the most continuous record of deep wate...The Changning - Menglian belt , located between the Baoshan - Gengma massif and the Simao - Lincang massif in Western Yunnan , preserves the complete record of a suture zone and the most continuous record of deep water sedimentation , representing the main branch of the Palaeo - Tethys polyisland ocean in the Hercynian - Indo-sinian stage .This belt could be further subdivided into three tectono - lithofacies zones . In the east zone , terrigenous elastics , argillaceous ,marl-argillaceous and silicate sedi-ments lie on the metamorphosed Early Palaeozoic base ment in concealed unconformity , representing deep water sediments on a passive continental margin . The central zone , although the basement rocks are absent from outcropping here , includes a contemporary complex of various sedimentary types , among them one type is of deep ocean sediments represented by radiolarian bedded chert , appearing from at least early Early Devonian to the Middle Triassic . Another type includes pure carbonates of the Early Carboniferous to the Late Permian , a type of shallow water carbonate platform on seamount or oceanic plateau within an ocean basin . In the west zone , the Permo - Carboniferous terrigenous elastics , argillaceous and silicate sediments appear again -representing the passive continental slope sedimentation in the east of the Baoshan - Gengma massif .As the Permo-Carboniferous rock types,sedimentary environments and palaeontological characters of the east and west zones are quite similar , we hold that these two zones were originally formed all on the eastern continental slope of the Baoshan - Gengma massif , and were separated due to eastward thrust later in the Indosinian orogeny . Intense thrust compacting also resulted in tectonic melange in the central zone , which is displayed by shallow water carbonates overlapping on or embedded in deep water volcanics . In the Lancangjiang belt , the Permo - Carboniferous are very complicated in sedimentary types which include island arc volcanics , deep water turbidites, silicolites and shallow water carbonates , representing the active continental margin in the west of the Simao massif. Whether there existed by Early Permi an, a Lincang magma tic arc still awaits further evidence . From the Late Permian,both the Changning-Meng-lian belt and the Lancangjiang belt experienced important sedimentary and volanic events which took place contemporaneously or penecontemporaneously but with different characters . Evidence for the Lincang magmatic arc began to be apparent , and the turbidite deep water basin in the Lancangjiang belt closed . Nevertheless , the Palaeo - Tethys oceanic basin , represented by the Changning - Menglian suture zone , existed until the Mid-dle Triassic . In the Late Triassic . massifs of Baoshan -Gengma ,Simao - Lincang ,collided and aggregated ,resulting in the disappearance of the Palaeo - Tethys ocean .展开更多
Mesozoic multi-stage tectono-magmatic events produced widely distributed granitoids in the South China Block. Huangshadong(HSD) is located in south-eastern South China Block, where closely spaced hot springs accompany...Mesozoic multi-stage tectono-magmatic events produced widely distributed granitoids in the South China Block. Huangshadong(HSD) is located in south-eastern South China Block, where closely spaced hot springs accompany outcrops of Mesozoic granites. New data on whole-rock geochemistry, zircon U-Pb geochronology, and zircon Lu-Hf isotopes are presented, to study the petrogenesis and tectonic evolution of the granites, and to explore the relationship between granites and geothermal anomalies. Zircon U-Pb isotopes display three periods of granites in the HSD area: Indosinian(ca. 253 Ma, G4) muscovite-bearing monzonitic granite, early Yanshanian(ca. 175–155 Ma, G5 and G3) monzonitic granite and granodiorite, and late Yanshanian(ca. 140 Ma, G1 and G2) biotite monzonitic granite. In petrogenetic type, granites of the three periods are I-type granite. Among them, G1, G2, G3, and G4 are characterized by high fractionation, with high values of SiO2, alkalis, Ga/Al, and Rb/Sr, and depletion in Sr, Ba, Zr, Nb, Ti, REEs, with low(La/Yb)N, Nb/Ta, and Zr/Hf ratios and negative Eu anomalies. In terms of tectonic setting, 253 Ma G4 may be the product of partial melting of the ancient lower crust under post-orogenic extensional tectonics, as the closure of the Paleo-Tethys Ocean resulted in an intracontinental orogeny. At 175 Ma, the subduction of the Pacific Plate became the dominant tectonic system, and low-angle subduction of the Paleo-Pacific Plate facilitated partial melting of the subducted oceanic crust and basement to generate the hornblende-bearing I-type granodiorite. As the dip angle of the subducting plate increased, the continental arc tectonic setting was transformed to back-arc extension, inducing intense partial melting of the lower crust at ca. 158 Ma and resulting in the most frequent granitic magmatic activity in the South China hinterland. When slab foundering occurred at ca. 140 Ma, underplating of mantle-derived magmas caused melting of the continental crust, generating extensive highly fractionated granites in HSD. Combining the granitic evolution of HSD and adjacent areas and radioactive heat production rates, it is suggested that highly fractionated granites are connected to the enrichments in U and Th with magma evolution. The high radioactive heat derived from the Yanshanian granites is an important part of the crustal heat, which contributes significantly to the terrestrial heat flow. Drilling ZK8 reveals deep, ca. 140 Ma granite, which implies the heat source of the geothermal anomalies is mainly the concealed Yanshanian granites, combining the granite distribution on the surface.展开更多
The Yangjiang-Yitongdong Fault (YJF) is an important NW-trending regional fault, which divides the Zhujiang (Pearl) River Mouth Basin (ZRMB) into western and eastern segments. In Cenozoic, the northern continental mar...The Yangjiang-Yitongdong Fault (YJF) is an important NW-trending regional fault, which divides the Zhujiang (Pearl) River Mouth Basin (ZRMB) into western and eastern segments. In Cenozoic, the northern continental margin of the South China Sea (SCS) underwent continental rifting, breakup, seafloor spreading and thermal subsidence processes, and the Cenozoic activities of YJF is one part of this series of complex processes. Two long NW-trending multichannel seismic profiles located on both sides of the YJF extending from the continental shelf to Continent-Ocean Boundary (COB) were used to study the tectonic and sedimentary characteristics of western ZRMB. Using the 2D-Move software and back-stripping method, we constructed the balance cross-section model and calculated the fault activity rate. Through the comprehensive consideration of tectonic position, tectonic evolution history, featured structure, and stress analysis, we deduced the activity history of the YJF in Cenozoic. The results showed that the YJF can be divided into two segments by the central uplift belt. From 65 Ma to 32 Ma, the YJF was in sinistral motion as a whole, inherited the preexisting sinistral motion of Mesozoic YJF, in which, the southern part of YJF was mainly in extension activity, controlling the formation and evolution of Yunkai Low Uplift, coupled with slight sinistral motion. From 32 Ma to 23.8 Ma, the sinistral motion in northern part of YJF continued, while the sinistral motion in southern part began to stop or shifted to a slightly dextral motion. After 23.8 Ma, the dextral motion in southern part of YJF continued, while the sinistral motion in northern part of YJF gradually stopped, or shifted to the slightly dextral motion. The shift of the YJF strike-slip direction may be related to the magmatic underplating in continent-ocean transition, southeastern ZRMB. According to the analysis of tectonic activity intensity and rift sedimentary structure, the activities of YJF in Cenozoic played a regulating role in the rift extension process of ZRMB.展开更多
The authors introduced two kinds of newly found soft-sediment deformation-synsedimentary extension structure and syn-sedimentary compression structure, and discuss their origins and constraints on basin tectonic evolu...The authors introduced two kinds of newly found soft-sediment deformation-synsedimentary extension structure and syn-sedimentary compression structure, and discuss their origins and constraints on basin tectonic evolution. One representative of the syn-sedimentary extension structure is syn-sedimentary boudinage structure, while the typical example of the syn-sedimentary compression structure is compression sand pillows or compression wrinkles. The former shows NW-SE-trendlng contemporaneous extension events related to earthquakes in the rift basin near a famous Fe-Nb-REE deposit in northern China during the Early Paleozoic （or Mesoproterozoic as proposed by some researches）, while the latter indicates NE-SW-trending contemporaneous compression activities related to earthquakes in the Middle Triassic in the Nanpanjiang remnant basin covering south Guizhou, northwestern Guangxi and eastern Yunnan in southwestern China. The syn-sedimentary boudinage structure was found in an earthquake slump block in the lower part of the Early Paleozoic Sailinhudong Group, 20 km to the southeast of Bayan Obo, Inner Mongolia, north of China. The slump block is composed of two kinds of very thin layers-pale-gray micrite （microcrystalline limestone） of 1-2 cm thick interbedded with gray muddy micrite layers with the similar thickness. Almost every thin muddy micrite layer was cut into imbricate blocks or boudins by abundant tiny contemporaneous faults, while the interbedded micrite remain in continuity. Boudins form as a response to layer-parallel extension （and/or layer-perpendicular flattening） of stiff layers enveloped top and bottom by mechanically soft layers. In this case, the imbricate blocks cut by the tiny contemporaneous faults are the result of abrupt horizontal extension of the crust in the SE-NW direction accompanied with earthquakes. Thus, the rock block is, in fact, a kind of seismites. The syn-sedimentary boudins indicate that there was at least a strong earthquake belt on the southeast side of the basin during the early stage of the Sailinhudong Group. This may be a good constraint on the tectonic evolution of the Bayan Obo area during the Early Paleozoic time. The syn-sedimentary compression structure was found in the Middle Triassic flysch in the Nanpanjiang Basin. The typical structures are compression sand pillows and compression wrinkles. Both of them were found on the bottoms of sand units and the top surface of the underlying mud units. In other words, the structures were found only in the interfaces between the graded sand layer and the underlying mud layer of the flysch. A deformation experiment with dough was conducted, showing that the tectonic deformation must have been instantaneous one accompanied by earthquakes. The compression sand pillows or wrinkles showed uniform directions along the bottoms of the sand layer in the flysch, revealing contemporaneous horizontal compression during the time between deposition and diagenesis of the related beds. The Nanpanjiang Basin was affected, in general, with SSW-NNE compression during the Middle Triassic, according to the syn-sedimentary compression structure. The two kinds of syn-sedimentary tectonic deformation also indicate that the related basins belong to a rift basin and a remnant basin, respectively, in the model of Wilson Cycle.展开更多
In active rift basins, tectonism is extremely important for sequence stratigraphic patterns, affecting both the sequence architecture and internal makeup. Sequence stratigraphic framework of a Paleogene rift successio...In active rift basins, tectonism is extremely important for sequence stratigraphic patterns, affecting both the sequence architecture and internal makeup. Sequence stratigraphic framework of a Paleogene rift succession in Qiongdongnan Basin, northern South China Sea, was built using seismic profiles, complemented by well logs and cores. One first-order and three second-order sequences were identified on the basis of basin-scale unconformities, and seven third-order sequences are defined by unconformities along the basin margins and correlative conformities within the central basin. Through unconformity analysis and backstripping procedure, the Paleogene synrift tectonic evolution of deep- water area of Qiongdongnan Basin was proved to be episodic, which can be divided into rifting stage-I, rifting stage-II and rifting stage-III. Episodic rifting resulted in the formation of various types of struc- tural slope break belts, which controlled different architectures and internal makeup of sequences. This study enhances the understanding of the control of tectonic evolution on sequence stratigraphic pat- terns and establishes relevant patterns in a typical rift basin, and further proposes the favorable sand- stone reservoirs developing in different sequence stratigraphic patterns, which will be pretty helpful for subtle pool exploration in deepwater area of petroliferous basins.展开更多
The Ordos Basin is one of the most important oil and gas basins in China. Based on surface outcrop, key exploratory wells and seismic reflection data and by using the technology of ＂prototype basin recovery＂, seismi...The Ordos Basin is one of the most important oil and gas basins in China. Based on surface outcrop, key exploratory wells and seismic reflection data and by using the technology of ＂prototype basin recovery＂, seismic profile ＂layer flattening＂ and ＂restoration of balanced section＂, and other methods, the sedimentary boundary, structure and the evolution history of the Tianhuan depression on the western margin of the Ordos Basin are reestablished. The following results have been obtained. （1） The west boundary of the Late Triassic Ordos Basin was far beyond the scope of the current basin. The basin is connected with the Late Triassic Hexi Corridor Basin, and its western margin did not have tectonic characteristics of a foreland basin. （2） The Tianhuan depression was first formed in the Late Jurassic. At the late stage it was impacted by the late Yanshanian and Himalayan tectonic movement and the depression axis gradually moved eastwards to the present location with a cumulative migration distance of -30 km. （3） Eastward migration of the depression axis caused adjustment and even destruction of the originally formed oil and gas reservoirs, so that oil and gas remigrated and aggregated, resulting in secondary structural reservoirs formed at high positions on the western flank of the depression.展开更多
The Qarhan Salt Lake area is the Quaternary depocenter of the Qaidam Basin, and carries thick lacustrine sediments, as well as rich potassium and magnesium salt deposits. The abundant resources and thick sediments in ...The Qarhan Salt Lake area is the Quaternary depocenter of the Qaidam Basin, and carries thick lacustrine sediments, as well as rich potassium and magnesium salt deposits. The abundant resources and thick sediments in this lake provide an ideal place for the study of biogas formation and preservation, salt lake evolution, and the uplift of the Tibetan Plateau. In this study, we attempt to construct a paleomagnetic and ^(230)Th age model and to obtain information on tectonic activity and salt lake evolution through detailed studies on a 1300-m-long drill core(15DZK01) from the northwestern margin of the Qarhan Salt Lake area(Dongling Lake). Based on gypsum ^(230)Th dating, the age of the uppermost clastic deposit was calculated to be around 0.052 Ma. The polarity sequence consist of 13 pairs of normal and reversed zones,which can be correlated with subchrons C2r.1r-C1n of the geomagnetic polarity timescale(GPTS 2012)(from ~2.070 Ma to ~0.052 Ma). Sedimentary characteristics indicate that Dongling Lake witnessed freshwater environment between ~ 2.070 Ma and 1.546 Ma. During this period, the sedimentary record reflects primarily lakeshore, shallow-water and swamp environments, representing favourable conditions for the formation of hydrocarbon source rocks. Between 1.546 Ma and ~ 0.052 Ma, the Dongling Lake was in sulphate deposition stage, which contrasts with the central Qarhan Salt Lake area, where this stage did not occur in the meantime. During this stage, Dongling Lake was in a shallow saltwater lake environment, but several periods of reduced salinity occurred during this stage. During the late Pleistocene at ~0.052 Ma, the Dongling Lake experienced uplift due to tectonic activity, and saltwater migrated through the Sanhu Fault to the central Qarhan Salt Lake area, resulting in the absence of halite deposition stage. The residual saline water was concentrated into magnesium-rich brine due to the lack of freshwater, and few potassium salt deposits occur in the Dongling Lake area.展开更多
Because of its rich oil and gas resources and the special tectonic location of the Liaohe Western Sag （the Tanlu Fault traverses the sag）, Bohai Bay Basin, a detailed study of its strike-slip tectonics is significan...Because of its rich oil and gas resources and the special tectonic location of the Liaohe Western Sag （the Tanlu Fault traverses the sag）, Bohai Bay Basin, a detailed study of its strike-slip tectonics is significant in revealing the sag＇s tectonic evolution, its control on hydrocarbon accumulation, and the activity history of the northern section of the Tanlu Fault in the Cenozoic. Through systematic structure analysis of 3D seismic data of the Liaohe Western Sag, combined with balanced section analysis, a variety of structural features in relation to right-lateral strike-slip faults, such as echelon normal faults, ＂comb＂ structure, ＂flower＂ structure,＂interpretable＂ and ＂buried＂ strike-slip faults have been revealed exist in the Liaohe Western Sag. According to the research in this paper, the complex structural phenomena in the Liaohe Western Sag could be reasonably interpreted as right-lateral strike-slip activity and the strike-slip activities of the Liaohe Western Sag began in the early Oligocene. The activity was weak at the beginning （E3s1-2）, then strengthened gradually and reached its strongest level in the late Oligocene （E3d1）. In the Miocene, the strike-slip activity was low and then strengthened significantly once again from the Pliocene to the present. It is speculated that the entire northern section of the Tanlu Fault has had a similar evolution history since the Oligocene.展开更多
The early Mesozoic marked an important transition from collisional orogeny to post-orogenic extension at the northern margin of the North China Craton(NCC). In this study, we undertook zircon U-Pb dating and whole-roc...The early Mesozoic marked an important transition from collisional orogeny to post-orogenic extension at the northern margin of the North China Craton(NCC). In this study, we undertook zircon U-Pb dating and whole-rock majorand trace-element geochemical analyses of early Mesozoic granitic rocks in the Chifeng area to establish their geochronological framework, petrogenesis, and implications for the tectonic evolution of the eastern Central Asia Orogenic Belt(CAOB). Zircon U-Pb dating results show that these rocks were emplaced in three stages during the Triassic:(1) syenogranites during 250-248 Ma,(2) granodiorites during 244-243 Ma, and(3) monzogranites and granodiorites during 232-230 Ma. These Triassic granitoids belong to the high-K calc-alkaline series and are evolved I-type granites. They have high SiO2 and low Mg O contents with enrichments in light rare-earth elements, Zr, Hf, Rb, Th, and U, and depletions in Ba, Nb, Ta, Sr, and Eu. These geochemical data indicate that the granitoids were derived from partial melting of a lower-crustal source under relatively low-pressure conditions and subsequently underwent extensive fractional crystallization. Considering both the geochemical data and regional geological information, we propose that the 250-248 Ma syenogranites were emplaced in an extensional environment linked to slab break-off after closure of the Paleo-Asian Ocean(PAO) along the Solonker-Xra Moron-Changchun suture zone. The 244-243 Ma granodiorites were formed in a compressional orogenic setting during collision between the Erguna-Xing’an-Songliao composite block and the NCC. The 232-230 Ma granodiorites and monzogranites were emplaced during the transition from compressional orogeny to post-orogenic extension. Overall, the early Mesozoic tectonic evolution of the Chifeng area can be divided into three main stages:(1) closure of the Paleo-Asian Ocean and extension related to slab break-off during the Early Triassic;(2) continuous collisional compression during the Middle Triassic after closure of the PAO;and(3) post-orogenic extension during the Late Triassic, most probably due to lithospheric delamination after amalgamation of the Erguna-Xing’an-Songliao composite block and the NCC.展开更多
基金funded by the National Natural Science Foundation of China(U2244208,42302138)China Postdoctoral Science Foundation(No.2020M733869)Science Foundation of China University of Petroleum,Beijing(No.2462023XKBH003).
文摘Apatite(U-Th)/He and fission track dating and tectono-thermal history modeling were used to reconstruct the Meso-Cenozoic tectonic evolution of the Huangling paleo-uplift in the Middle Yangtze Block,South China.The tectono-thermal evolution showed different tectonic exhumation/subsidence processes in the tectonic evolution of the foreland basin.The apatite(U-Th)/He ages ranged from 31.3 to 77.8 Ma,recording the thermal events of the Cenozoic Himalayan movement and indicating progressive exhumation extending from the southeast to the northwest.The thermal information of the Mesozoic Yanshan movement period was recorded by the apatite fission track age with a pooled age of 93.8 to 147 Ma.The exhumation of the Huangling paleo-uplift began in the Late Jurassic.The tectono-thermal evolution was characterized by a rapid uplift during 140-115 Ma,subsidence during 115-60 Ma,a rapid uplift during 40-30 Ma,and a slow uplift from 30 Ma to the present.The western Hunan-Hubei Depression was exhumed in the Middle Jurassic,and the tectono-thermal evolution was characterized by a rapid uplift during 160-135 Ma,a slow uplift during 135-50 Ma,a rapid uplift during 50-25 Ma,and a slow uplift from 25 Ma to the present.This Cenozoic exhumation was a response to the far field effect of the eastward growth of the Tibetan Plateau.The Cretaceous basins exposed in the surrounding areas of the Huangling paleo-uplift(Zigui basin,Yichang slope,and Huaguoping synclinorium)are foreland basins formed by the bi-directional compression of the Qinling-Dabie orogenic belt and the Xuefengshan intracontinental deformation system.
基金This study was jointly supported by the Science&Technology Fundamental Resources Investigation Program(2022FY101800)National Science Foundation(92162212)+1 种基金the project from the Key Laboratory of Tectonics and Petroleum Resources(China University of Geosciences,Wuhan)(TPR-2022-22)the International Geoscience Programme(IGCP-675)。
文摘The Ordos Basin(OB)in the western part of the North China Craton(NCC),was located at the jointed area of multi-plates and has recorded the Mesozoic tectonic characteristics.Its tectonic evolution in the Mesozoic is significant to understand the tectonic transformation of the northern margin of the NCC.In this work,the detrital zircon and apatite(U-Th)/He chronological system were analyzed in the northern part of the OB,and have provided new evidence for the regional tectonic evolution.The(U-Th)/He chronological data states the weighted ages of 240‒235 Ma,141 Ma with the peak distribution of 244 Ma,219 Ma,173 Ma,147‒132 Ma.The thermal evolution,geochronological data,and regional unconformities have proved four stages of regional tectonic evolution for the OB and its surroundings in the Mesozoic:(1)The Late Permian-Early Triassic;(2)the Late Triassic-Early Jurassic;(3)the Late Jurassic-Early Cretaceous;(4)the Late Cretaceous-Early Paleogene.It is indicated that the multi-directional convergence from the surrounding tectonic units has controlled the Mesozoic tectonic evolution of the OB.Four-stage tectonic evolution reflected the activation or end of different plate movements and provided new time constraints for the regional tectonic evolution of the NCC in the Mesozoic.
基金jointly supported financially by the National Natural Science Foundation of China(No.41603040)the Natural Science Basic Research Plan in Shaanxi Province of China(No.2023-JC-YB-239)Fundamental Research Funds for the Central Universities(S202310710204)。
文摘The Bijigou intrusion is one of the largest and most well-differentiated Fe–Ti oxide-bearing layered intrusions in the Hannan massif located in the northwestern margin of the Yangtze Block,South China.Besides the mineralization-related mafic-ultramafic rocks,the intermediate-acid intrusive rocks are also exposed in the mining area,which is of great significance for the understanding the Neoproterozoic tectonic evolution of the Yangtze Block,but studies on these intermediate-acid rocks are scarce.The Bijigou mafic-ultramafic layered intrusion is surrounded by granite and cut by syenite veins.Here,we report new zircon U-Pb ages,Lu-Hf isotope composition and bulk rock geochemical data of the Bijigou syenite vein and wall-rock granite in the northwestern margin of the Yangtze Block.Laser ablation inductively coupled plasma mass spectrometry(LAICP-MS)zircon U-Pb dating results show that the Bijigou syenite vein and wall-rock granite formed at 770±3.5 Ma(MSWD=0.17,n=28)and 810±4 Ma(MSWD=0.84,n=26),respectively.The zirconεHf(t)values of the syenite veins range from+1.52 to+5.33(average of+3.05),combined with its high potassium contents,negative Nb–Ta anomalies and positive Pb anomalies,suggesting that they may have originated from mantle-derived basaltic magma,which was modified by materials from subducting oceanic slab.The zirconεHf(t)and T_(DM2)ages of the wall-rock granite range from+0.71 to+5.71(average+3.06)and 1344 to 1659 Ma(average 1519 Ma),respectively,indicating that the granite was produced by partial melting of juvenile crust.The geochemical characteristics of the Bijigou syenite and granite indicate that they were formed in a continental margin arc setting.Thus,combined with previous studies,it suggests that there was a major subduction system along the northwestern margin of the Yangtze Block during 824-720 Ma,and the magmatism in the Hannan massif was divided into two episodes:(1)early magmatism(824-790 Ma),such as the Bijigou,Hongmiaozhen and Huangguanzhen granitoids,was derived from partial melting of the juvenile or pre-existing crust in a continental arc setting;(2)later magmatism(789-718 Ma),including Bijigou syenite,Wudumen,Erliba and Zushidian granitoids,formed in a subduction-related back-arc extensional environment.The long-term subduction system along the northwestern margin of the Yangtze Block during 824-720 Ma suggests that the Yangtze Block was previously located at the periphery of the Rodinia supercontinent.
基金supported by the Natural Science Foundation of Shaanxi Province(2023-JC-YB-222)National Natural Science Foundation of China(41872219)+1 种基金Opening Foundation of Key Laboratory of Mineral Resources Evaluation in Northeast Asia,Ministry of Natural Resources(DBY-KF-19-12)Research on metallogenic structure and metallogenic structural plane of Shuangwang gold deposit(220227220347,220227230756).
文摘The Shuangwang Au deposit in the western Qinling Orogen is hosted by a WNW-ESE-trending breccia belt that is structurally controlled by the northern limb of the Yindonggou fold.Igneous rocks area in the deposit are part of the Xiba pluton,which comprises granodiorite and monzogranite that contains mafic microgranular envlaves(MMEs),and later mineralized granitic porphyry dikes.The mineralized granitic porphyry dikes were controlled by the same structures that controlled the ore bodies.Zircon LA-ICP-MS U-Pb dating yields ages of 220.0±1.9 Ma for the granodiorite,and 217.9±1.9 Ma for the granitic porphyry,which is consistent with the mineralization ages reported in previous studies(220-218 Ma).Together with the similarity of alteration mineral assemblages between ore and mineralized granitic porphyry,we suggest that the mineralization was controlled by structure and Xiba pluton.The geochemical data show that the granodiorite and granitic porphyry are subalkaline and the MMEs are alkaline in composition.All samples have similar chondrite-normalized rare earth element patterns with enrichment of light rare earth elements.The granodiorite and MMEs are depleted in Nb,Ta,Sr,P,and Ti and enriched in U,K,Pb,Zr,and Hf.The granitic porphyry is enriched in large-ion lithophile elements but depleted in high-field-strength elements.The granodiorite and MMEs have low whole-rockεNd(t)values(−10.90 to−2.32)and(^(87)Sr/^(86)Sr)i ratios(0.7000-0.7285),similar to coeval Triassic granites in the western Qinling Orogen.The(^(87)Sr/^(86)Sr)i ratios of the granitic porphyry have been affected by fluid metasomatism that results in higher(^(87)Sr/^(86)Sr)i values.The geochronological,geochemical,and isotopic evidence suggest that the Xiba pluton formed by partial melting of thickened lower crust that had been intruded by alkaline mafic magma,as documented by the MMEs,which were derived from a source metasomatized by subduction-related fluids.The granodioritic and granitic porphyry magmas were relatively oxidized(fayalite-magnetite-quartz[FMQ]to magnetite-hematite(MH)buffer conditions;zircon Ce^(4+)/Ce^(3+)=72-813;log(fO_(2))=−22 to−8).We propose that magma mixing between lower crust and mantle-derived mafic magma was triggered by the tectonic transition from a collisional to post-collision setting,which provided the metals,S,fluids,and increase in magma oxygen fugacity that enabled the formation of the Shuangwang Au deposit.Since the Late Triassic,the western Qinling Orogen evolved from a syn-collisional compressional to post-collisional extensional environment.The mineralization of the Shuangwang Au deposit involved early formation of a tectonic breccia in the compressional stage.Subsequently,hydrothermal fluids derived from a magma ascended,migrated,mixed,and precipitated ores in the tectonic breccia during the later extensional stage to form the Shuangwang Au deposit.
基金supported financially by the Research Foundation of the Department of Natural Resources of Hunan Province(20230135DZ)the Provincial Natural Science Foundation of Hunan(2024JJ7080)+1 种基金the Scientific Research Fund of Hunan Provincial Education Department(23C0320)Hunan Provincial College Student Innovation and Entrepreneurship Training Project(S202311527014).
文摘There is significant debate concerning the tectonic characteristics and evolutionary understanding of the South China Block(SCB)during the Early Mesozoic.One of the key points of contention is the tectonic-magmatic activity during the Triassic and its dynamic mechanisms.However,research on the detailed chronology and tectonic settings of granite plutons in key regions remains insuffi-cient,limiting the understanding of the tectonic-magmatic dynamic mechanisms in the interior of SCB during the Triassic.In this contribution,we present whole-rock major and trace elemental data,Sr-Nd isotope data,LA-ICP-MS zircon U-Pb age dating,and Lu-Hf isotope data for granites of Dashenshan pluton in the Xiangzhong,northwest part of SCB.The results indicate that the Dashenshan granite has an emplacement age of 208.4-212.5 Ma,characterized by high SiO_(2),Na_(2)O,and K_(2)O contents and low MgO and CaO.The Dashenshan granite is enriched in light rare-earth elements with a significant negative Eu anomaly(averageδEu=0.42).It is also enriched in Rb,K,and Th and shows pronounced depletion in Nb,Ta,and Ti,classifying it as peraluminous calc-alkaline granite,specifically of the I-type.The zircon ε_(Hf(t)) values range from−8.39 to−4.4,with an average of−5.82,and the Sr-Nd isotopes are relatively enriched[ε_(Nd)(t)=−9.31 to−6.8].Combining these geochemical characteristics,it is revealed that the Dashenshan granite was derived from the partial melting of middle to upper crustal metamorphic basement materials under medium-to low-temperature conditions,with possible minor contributions from mantle-derived materials.Furthermore,it underwent fractional crystallization,including plagioclase differentiation.By integrating the geochemical features and spatial distribution of Triassic granites in SCB,this study suggests that the regional tectonic evolution of SCB during the Triassic was primarily controlled by the collision of the SCB with the Indochina Block and the North China Block.In Xiangzhong,the tectonic setting transitioned from syn-collisional compression to post-collisional extension during the Late Triassic.The Dashenshan pluton formed in a post-collisional extensional setting,resulting from the decompression melting of middle-to-upper crustal rocks.The upwelling of the asthenosphere and upward heat transfer likely played a significant role in the formation of the Dashenshan granitic magma.
基金financially supported by the National Natural Science Foundation of China(No.42402171)the China Postdoctoral Science Foundation(No.2023MD744255)+6 种基金the Natural Science Basic Research Program of Shaanxi(No.2024JC-YBQN-0353)the Scientific Research Program Funded by Shaanxi Provincial Education Department(No.23JK0600)the Shaanxi Postdoctoral Science Foundation(No.2023BSHEDZZ324)the project of Theory of Hydrocarbon Enrichment under Multi-Spheric Interactions of the Earth(No.THEMSIE04010107)the Key Research and Development Program of Shaanxi(No.2021KW-10)the Innovation Capability Support Program of Shaanxi(No.2022PT-08)the SINOPEC CCUS Fund Project(No.33550000-22ZC0613-0326)。
文摘In the context of complex tectonic evolution,due to the control of tectonic compression stress and faults on tectonic fractures,the formation and development of tectonic fractures in the T_3x~2 tight reservoirs present significant variations across different tectonic segments in the Western Sichuan Foreland Basin.We clarified the control of differential tectonic evolution on the formation and development of tectonic fractures in different tectonic segments through field-based observations,core samples,image logging,as well as fluid inclusion petrography and temperature determinations of fracture-filling materials,combined with 2D balanced cross-section restoration.The study area primarily manifests two types of tectonic fractures in the tight reservoirs:orogen-related fractures(regional fractures)and fault-related fractures.The orientations of these fractures are predominantly E-W,nearly N-S,NE,and NW.Specifically,the northern segment area only shows the development of regional fractures,while the southern and middle segments exhibit the development of both regional and tectonic fractures.There are three phases of tectonic fractures in different tectonic segments,and their formation times are relatively consistent.The Mesozoic tectonic events had a significant impact on the northern and central segments,with the amount of tectonic shortening and the rate of stratigraphic shortening gradually decreasing from the northeast to the southwest.The compressional stress resulting from tectonic compression also decreases from the northeast to the southwest.As a result,the development of first-phase and second-phase tectonic shear fractures is more pronounced in the northern and middle segments compared to the southern segment.Under the significant control of faults,the development of N-S-and NE-oriented fault-related fractures is more pronounced in the southern segment,while the development of NE-oriented fault-related fractures is relatively higher in the middle segment.Overall,there is an increased density of fractures and an increasing trend in fracture scale from the northern to the middle and then to the southern segment.
基金Supported by the National Natural Science Foundation of China(No.U 2344221)。
文摘The Yangtze Plate(YP)and the North China Plate(NCP)are key components of the East Asian continent,and their collision significantly influences the tectonic evolution of the eastern Asian continental margin.As the South Yellow Sea is located at the convergence of these plates,it becomes a pivotal area for understanding the tectonic evolution of East Asia.The characteristics and provenance of clastic rocks of the Middle Permian-the Early Triassic were analyzed and the strata in the Central Uplift including the Qinglong Formation(T_(1)q)and Talung Formation(P_(3)d),consisting of various mudstones and sandstones,were anatomized.Results show that quartz and feldspar are the main diagenetic minerals,while illite and chlorite show signs of secondary alterations.Geochemical imprints indicate a gradual shift in provenance from ancient sedimentary and mafic igneous rocks to intermediate igneous rocks.In the meantime,the tectonic background transformed from continent to continental island arc from the Middle Permian to the Early Triassic.Therefore,we inferred that a soft collision between the North China Plate and the Yangtze Plate likely occurred during the Late Permian,resulted in intensified collision between two plates in the Early Triassic,and shaped the South Yellow Sea.This study provided valuable information on the timing of plate collisions in the South Yellow Sea.
基金supported by the National Key Research and Development Project(No.2019YFA0708601)the National Natural Science Foundation of China(No.4231101056)the Chinese Academy of Geological Sciences Basic Research Fund(No.JKYZD202402)。
文摘0 INTRODUTION The Kuqa Depression,situated along the northern margin of the Tarim Basin,holds substantial geological significance due to its intricate sedimentary burial history,tectonic history,and the evolution of hydrocarbon source rocks(Jiang et al.,2024;Zhang et al.,2023;Huang et al.,2019;Yang et al.,2017;Jia et al.,2003;Hendrix,2000).
基金funded by the National 305 Project of China (2018A03004-1, 2015BAB05B01-02)the Fundamental Research Fund for Central Universities(B16020127)
文摘The West Kunlun orogenic belt(WKOB) along the northern margin of the Tibetan Plateau is important for understanding the evolution of the Proto-and Paleo-Tethys oceans. Previous investigations have focused on the igneous rocks and ophiolites distributed mostly along the Xinjiang-Tibet road and the China-Pakistan road, and have constructed a preliminary tectonic model for this orogenic belt. However, few studies have focused on the so-called Precambrian basement in this area. As a result, the tectonic affinity of the individual terranes of the WKOB and their detailed evolution process are uncertain. Here we report new field observations, zircon and monazite U-Pb ages of the "Precambrian basement" of the South Kunlun terrane(SKT) and the Tianshuihai terrane(TSHT), two major terranes in the WKOB. Based on new zircon U-Pb age data, the amphibolite-facies metamorphosed volcanosedimentary sequence within SKT was deposited during the late Neoproterozoic to Cambrian(600-500 Ma), and the flysch-affinity Tianshuihai Group, as the basement of the TSHT, was deposited during the late Neoproterozoic rather than Mesoproterozoic. The rock association of the volcano-sedimentary sequence within SKT suggests a large early Paleozoic accretionary wedge formed by the long-term lowangle southward subduction of the Proto-Tethys Ocean between Tarim and TSHT. The amphibolitefacies metamorphism in SKT occurred at ca. 440 Ma. This ca. 440 Ma metamorphism is genetically related to the closure of the Proto-Tethys Ocean between Tarim and the Tianshuihai terrane, which led to the assembly of Tarim to Eastern Gondwana and the final formation of the Gondwana. Since the late Paleozoic to early Mesozoic, the northward subduction of the Paleo-Tethys Ocean along the HongshihuQiaoertianshan belt produced the voluminous early Mesozoic arc-signature granites along the southern part of NKT-TSHT. The Paleo-Tethys ocean between TSHT and Karakorum closed at ca. 200 Ma, as demonstrated by the monazite age of the paragneiss in the Kangxiwa Group. Our study does not favor the existence of a Precambrian basement in SKT.
文摘The Altun faulted Zone has been focused by lots of geologists for many years because it lies in a boundary area of several main tectonic units in the western China and is a geographically northern boundary line of Tibet plateau.The latest achievements show that the Altun faulted zone is not only a Cenozoic strike\|slip faulted system but also an orogenic zone which underwent mutually subduction\|collision among paleo\|plates (or terrains) in its early stage and consists of geological bodies of different ages and tectonic environments. Based on the results of geological characteristics,petrology, geochemistry and isotopic dating, the Altun Orogenic Zone can be divided into four tectonic units and is considered to have undergone five stages during its tectonic evolution.The four tectonics units are :(1) Abei metamorphic block, which consists of Archean metamorphic complex of granulite facies;.(2) Hongliugou—Lapeiquan tectonic melange belt, which is composed of ophiolite blocks(belt), OIB blocks, pelagic silicalite, shallow\|bathyal sedimentary rock blocks and high\|pressure metamorphi c rock blocks. (3) Milanhe—Jinyanshan island\|arc block, which consists of mid\|uplifting belt and the south and north active margins. The uplifting belt is composed of metasandstone, marble, overlying thick stromatolite (Jinyanshan Group of Jixian System). Metamorphic rocks of 450Ma occur in both south and north hactive margin. Post\|collision bimodal volcanic rocks and A\|type granite occur in the middle and the north side.(4) Apa—Mangya tectonic melange belt, which consists of ophiolite(including ultramafic rocks, gabbro, plagiogranite and basalt) and flysch and eclogite of late Ordovician.
基金The National Natural Science Foundation of China under contract Nos 41322036,41230960,40906034,41276003 and 41176058China Ocean Mineral Resources R&D Association(COMRA)under contract No.DY125-12-R-05
文摘Okinawa Trough is a back-arc, initial marginal sea basin, located behind the Ryukyu Arc-Trench System. The formation and evolution of the Okinawa Trough is intimately related to the subduction process of the Philippine Sea Plate beneath the Eurasian Plate since the late Miocene. The tectonic evolution of the trough is similar to other active back-arcs, such as the Mariana Trough and southern Lau Basin, all of which are experiencing the initial rifting and subsequent spreading process. This study reviews all petrologic and geochemical data of mafic volcanic lavas from the Okinawa Trough, Ryukyu Arc, and Philippine Sea Plate, combined with geophysical data to indicate the relationship between the subduction sources （input） and arc or back-arc magmas （output） in the Philippine Sea Plate-Ryukyu Arc-Okinawa Trough system （PROS）. The results obtained showed that several components were variably involved in the petrogenesis of the Oki-nawa Trough lavas：sub-continental lithospheric mantle underlying the Eurasian Plate, Indian mid-oceanic ridge basalt （MORB）-type mantle, and Pacific MORB-type mantle. The addition of shallow aqueous fluids and deep hydrous melts from subducted components with the characteristics of Indian MORB-type mantle into the mantle source of lavas variably modifies the primitive mantle wedge beneath the Ryukyu and sub-continental lithospheric mantle （SCLM） beneath the Okinawa Trough. In the northeastern end of the trough and arc, instead of Indian MORB-type mantle, Pacific MORB-type mantle dominates the magma source. Along the strike of the Ryukyu Arc and Okinawa Trough, the systematic variations in trace element ratios and isotopic compositions reflect the first-order effect of variable subduction input on the magma source. In general, petrologic data, combined with geophysical data, imply that the Okinawa Trough is experiencing the＂seafloor spreading＂process in the southwest segment,＂rift propagation＂process in the middle seg-ment, and＂crustal extension＂process in the northeast segment, and a nascent ocean basin occurs in the southwest segment.
文摘The Changning - Menglian belt , located between the Baoshan - Gengma massif and the Simao - Lincang massif in Western Yunnan , preserves the complete record of a suture zone and the most continuous record of deep water sedimentation , representing the main branch of the Palaeo - Tethys polyisland ocean in the Hercynian - Indo-sinian stage .This belt could be further subdivided into three tectono - lithofacies zones . In the east zone , terrigenous elastics , argillaceous ,marl-argillaceous and silicate sedi-ments lie on the metamorphosed Early Palaeozoic base ment in concealed unconformity , representing deep water sediments on a passive continental margin . The central zone , although the basement rocks are absent from outcropping here , includes a contemporary complex of various sedimentary types , among them one type is of deep ocean sediments represented by radiolarian bedded chert , appearing from at least early Early Devonian to the Middle Triassic . Another type includes pure carbonates of the Early Carboniferous to the Late Permian , a type of shallow water carbonate platform on seamount or oceanic plateau within an ocean basin . In the west zone , the Permo - Carboniferous terrigenous elastics , argillaceous and silicate sediments appear again -representing the passive continental slope sedimentation in the east of the Baoshan - Gengma massif .As the Permo-Carboniferous rock types,sedimentary environments and palaeontological characters of the east and west zones are quite similar , we hold that these two zones were originally formed all on the eastern continental slope of the Baoshan - Gengma massif , and were separated due to eastward thrust later in the Indosinian orogeny . Intense thrust compacting also resulted in tectonic melange in the central zone , which is displayed by shallow water carbonates overlapping on or embedded in deep water volcanics . In the Lancangjiang belt , the Permo - Carboniferous are very complicated in sedimentary types which include island arc volcanics , deep water turbidites, silicolites and shallow water carbonates , representing the active continental margin in the west of the Simao massif. Whether there existed by Early Permi an, a Lincang magma tic arc still awaits further evidence . From the Late Permian,both the Changning-Meng-lian belt and the Lancangjiang belt experienced important sedimentary and volanic events which took place contemporaneously or penecontemporaneously but with different characters . Evidence for the Lincang magmatic arc began to be apparent , and the turbidite deep water basin in the Lancangjiang belt closed . Nevertheless , the Palaeo - Tethys oceanic basin , represented by the Changning - Menglian suture zone , existed until the Mid-dle Triassic . In the Late Triassic . massifs of Baoshan -Gengma ,Simao - Lincang ,collided and aggregated ,resulting in the disappearance of the Palaeo - Tethys ocean .
基金financially supported by the China Geological Survey(No.1212011220014)
文摘Mesozoic multi-stage tectono-magmatic events produced widely distributed granitoids in the South China Block. Huangshadong(HSD) is located in south-eastern South China Block, where closely spaced hot springs accompany outcrops of Mesozoic granites. New data on whole-rock geochemistry, zircon U-Pb geochronology, and zircon Lu-Hf isotopes are presented, to study the petrogenesis and tectonic evolution of the granites, and to explore the relationship between granites and geothermal anomalies. Zircon U-Pb isotopes display three periods of granites in the HSD area: Indosinian(ca. 253 Ma, G4) muscovite-bearing monzonitic granite, early Yanshanian(ca. 175–155 Ma, G5 and G3) monzonitic granite and granodiorite, and late Yanshanian(ca. 140 Ma, G1 and G2) biotite monzonitic granite. In petrogenetic type, granites of the three periods are I-type granite. Among them, G1, G2, G3, and G4 are characterized by high fractionation, with high values of SiO2, alkalis, Ga/Al, and Rb/Sr, and depletion in Sr, Ba, Zr, Nb, Ti, REEs, with low(La/Yb)N, Nb/Ta, and Zr/Hf ratios and negative Eu anomalies. In terms of tectonic setting, 253 Ma G4 may be the product of partial melting of the ancient lower crust under post-orogenic extensional tectonics, as the closure of the Paleo-Tethys Ocean resulted in an intracontinental orogeny. At 175 Ma, the subduction of the Pacific Plate became the dominant tectonic system, and low-angle subduction of the Paleo-Pacific Plate facilitated partial melting of the subducted oceanic crust and basement to generate the hornblende-bearing I-type granodiorite. As the dip angle of the subducting plate increased, the continental arc tectonic setting was transformed to back-arc extension, inducing intense partial melting of the lower crust at ca. 158 Ma and resulting in the most frequent granitic magmatic activity in the South China hinterland. When slab foundering occurred at ca. 140 Ma, underplating of mantle-derived magmas caused melting of the continental crust, generating extensive highly fractionated granites in HSD. Combining the granitic evolution of HSD and adjacent areas and radioactive heat production rates, it is suggested that highly fractionated granites are connected to the enrichments in U and Th with magma evolution. The high radioactive heat derived from the Yanshanian granites is an important part of the crustal heat, which contributes significantly to the terrestrial heat flow. Drilling ZK8 reveals deep, ca. 140 Ma granite, which implies the heat source of the geothermal anomalies is mainly the concealed Yanshanian granites, combining the granite distribution on the surface.
基金The National Natural Science Foundation of China under contract Nos 41776072,41476039,41674092 and 41676045the Geotectonic Evolution of China and Compilation of International Asian Geotectonic Map under contract No.DD20190364the Marine Basic Geological Survey Project under contract No.DD20190627
文摘The Yangjiang-Yitongdong Fault (YJF) is an important NW-trending regional fault, which divides the Zhujiang (Pearl) River Mouth Basin (ZRMB) into western and eastern segments. In Cenozoic, the northern continental margin of the South China Sea (SCS) underwent continental rifting, breakup, seafloor spreading and thermal subsidence processes, and the Cenozoic activities of YJF is one part of this series of complex processes. Two long NW-trending multichannel seismic profiles located on both sides of the YJF extending from the continental shelf to Continent-Ocean Boundary (COB) were used to study the tectonic and sedimentary characteristics of western ZRMB. Using the 2D-Move software and back-stripping method, we constructed the balance cross-section model and calculated the fault activity rate. Through the comprehensive consideration of tectonic position, tectonic evolution history, featured structure, and stress analysis, we deduced the activity history of the YJF in Cenozoic. The results showed that the YJF can be divided into two segments by the central uplift belt. From 65 Ma to 32 Ma, the YJF was in sinistral motion as a whole, inherited the preexisting sinistral motion of Mesozoic YJF, in which, the southern part of YJF was mainly in extension activity, controlling the formation and evolution of Yunkai Low Uplift, coupled with slight sinistral motion. From 32 Ma to 23.8 Ma, the sinistral motion in northern part of YJF continued, while the sinistral motion in southern part began to stop or shifted to a slightly dextral motion. After 23.8 Ma, the dextral motion in southern part of YJF continued, while the sinistral motion in northern part of YJF gradually stopped, or shifted to the slightly dextral motion. The shift of the YJF strike-slip direction may be related to the magmatic underplating in continent-ocean transition, southeastern ZRMB. According to the analysis of tectonic activity intensity and rift sedimentary structure, the activities of YJF in Cenozoic played a regulating role in the rift extension process of ZRMB.
基金This paper was sponsored by the National Natural Science Foundation of China(grant No.40272049)Doctor Research Foundation of China University of Petroleum(Project No.Y020109).
文摘The authors introduced two kinds of newly found soft-sediment deformation-synsedimentary extension structure and syn-sedimentary compression structure, and discuss their origins and constraints on basin tectonic evolution. One representative of the syn-sedimentary extension structure is syn-sedimentary boudinage structure, while the typical example of the syn-sedimentary compression structure is compression sand pillows or compression wrinkles. The former shows NW-SE-trendlng contemporaneous extension events related to earthquakes in the rift basin near a famous Fe-Nb-REE deposit in northern China during the Early Paleozoic （or Mesoproterozoic as proposed by some researches）, while the latter indicates NE-SW-trending contemporaneous compression activities related to earthquakes in the Middle Triassic in the Nanpanjiang remnant basin covering south Guizhou, northwestern Guangxi and eastern Yunnan in southwestern China. The syn-sedimentary boudinage structure was found in an earthquake slump block in the lower part of the Early Paleozoic Sailinhudong Group, 20 km to the southeast of Bayan Obo, Inner Mongolia, north of China. The slump block is composed of two kinds of very thin layers-pale-gray micrite （microcrystalline limestone） of 1-2 cm thick interbedded with gray muddy micrite layers with the similar thickness. Almost every thin muddy micrite layer was cut into imbricate blocks or boudins by abundant tiny contemporaneous faults, while the interbedded micrite remain in continuity. Boudins form as a response to layer-parallel extension （and/or layer-perpendicular flattening） of stiff layers enveloped top and bottom by mechanically soft layers. In this case, the imbricate blocks cut by the tiny contemporaneous faults are the result of abrupt horizontal extension of the crust in the SE-NW direction accompanied with earthquakes. Thus, the rock block is, in fact, a kind of seismites. The syn-sedimentary boudins indicate that there was at least a strong earthquake belt on the southeast side of the basin during the early stage of the Sailinhudong Group. This may be a good constraint on the tectonic evolution of the Bayan Obo area during the Early Paleozoic time. The syn-sedimentary compression structure was found in the Middle Triassic flysch in the Nanpanjiang Basin. The typical structures are compression sand pillows and compression wrinkles. Both of them were found on the bottoms of sand units and the top surface of the underlying mud units. In other words, the structures were found only in the interfaces between the graded sand layer and the underlying mud layer of the flysch. A deformation experiment with dough was conducted, showing that the tectonic deformation must have been instantaneous one accompanied by earthquakes. The compression sand pillows or wrinkles showed uniform directions along the bottoms of the sand layer in the flysch, revealing contemporaneous horizontal compression during the time between deposition and diagenesis of the related beds. The Nanpanjiang Basin was affected, in general, with SSW-NNE compression during the Middle Triassic, according to the syn-sedimentary compression structure. The two kinds of syn-sedimentary tectonic deformation also indicate that the related basins belong to a rift basin and a remnant basin, respectively, in the model of Wilson Cycle.
基金supported by the National Science Foundation of China (NSFC) (Nos. 41272122, 41202074 and 41172123)the Major National Science and Technology Programs in the "Twelfth Five-Year" Plan of China (No. 2011ZX05009-002-02)+1 种基金the Open Research Program Foundation of Teaching Laboratory of China University of Geosciencesthe Foundation of Key Laboratory of Tectonics and Petroleum Resources (China University of Geosciences) of Ministry of Education (No. TPR-2013-14)
文摘In active rift basins, tectonism is extremely important for sequence stratigraphic patterns, affecting both the sequence architecture and internal makeup. Sequence stratigraphic framework of a Paleogene rift succession in Qiongdongnan Basin, northern South China Sea, was built using seismic profiles, complemented by well logs and cores. One first-order and three second-order sequences were identified on the basis of basin-scale unconformities, and seven third-order sequences are defined by unconformities along the basin margins and correlative conformities within the central basin. Through unconformity analysis and backstripping procedure, the Paleogene synrift tectonic evolution of deep- water area of Qiongdongnan Basin was proved to be episodic, which can be divided into rifting stage-I, rifting stage-II and rifting stage-III. Episodic rifting resulted in the formation of various types of struc- tural slope break belts, which controlled different architectures and internal makeup of sequences. This study enhances the understanding of the control of tectonic evolution on sequence stratigraphic pat- terns and establishes relevant patterns in a typical rift basin, and further proposes the favorable sand- stone reservoirs developing in different sequence stratigraphic patterns, which will be pretty helpful for subtle pool exploration in deepwater area of petroliferous basins.
文摘The Ordos Basin is one of the most important oil and gas basins in China. Based on surface outcrop, key exploratory wells and seismic reflection data and by using the technology of ＂prototype basin recovery＂, seismic profile ＂layer flattening＂ and ＂restoration of balanced section＂, and other methods, the sedimentary boundary, structure and the evolution history of the Tianhuan depression on the western margin of the Ordos Basin are reestablished. The following results have been obtained. （1） The west boundary of the Late Triassic Ordos Basin was far beyond the scope of the current basin. The basin is connected with the Late Triassic Hexi Corridor Basin, and its western margin did not have tectonic characteristics of a foreland basin. （2） The Tianhuan depression was first formed in the Late Jurassic. At the late stage it was impacted by the late Yanshanian and Himalayan tectonic movement and the depression axis gradually moved eastwards to the present location with a cumulative migration distance of -30 km. （3） Eastward migration of the depression axis caused adjustment and even destruction of the originally formed oil and gas reservoirs, so that oil and gas remigrated and aggregated, resulting in secondary structural reservoirs formed at high positions on the western flank of the depression.
基金co-supported by the Geological Survey Project of China(Grant No. 1212331413023)the National Natural Science Foundation of China(Grant No. U1407207)
文摘The Qarhan Salt Lake area is the Quaternary depocenter of the Qaidam Basin, and carries thick lacustrine sediments, as well as rich potassium and magnesium salt deposits. The abundant resources and thick sediments in this lake provide an ideal place for the study of biogas formation and preservation, salt lake evolution, and the uplift of the Tibetan Plateau. In this study, we attempt to construct a paleomagnetic and ^(230)Th age model and to obtain information on tectonic activity and salt lake evolution through detailed studies on a 1300-m-long drill core(15DZK01) from the northwestern margin of the Qarhan Salt Lake area(Dongling Lake). Based on gypsum ^(230)Th dating, the age of the uppermost clastic deposit was calculated to be around 0.052 Ma. The polarity sequence consist of 13 pairs of normal and reversed zones,which can be correlated with subchrons C2r.1r-C1n of the geomagnetic polarity timescale(GPTS 2012)(from ~2.070 Ma to ~0.052 Ma). Sedimentary characteristics indicate that Dongling Lake witnessed freshwater environment between ~ 2.070 Ma and 1.546 Ma. During this period, the sedimentary record reflects primarily lakeshore, shallow-water and swamp environments, representing favourable conditions for the formation of hydrocarbon source rocks. Between 1.546 Ma and ~ 0.052 Ma, the Dongling Lake was in sulphate deposition stage, which contrasts with the central Qarhan Salt Lake area, where this stage did not occur in the meantime. During this stage, Dongling Lake was in a shallow saltwater lake environment, but several periods of reduced salinity occurred during this stage. During the late Pleistocene at ~0.052 Ma, the Dongling Lake experienced uplift due to tectonic activity, and saltwater migrated through the Sanhu Fault to the central Qarhan Salt Lake area, resulting in the absence of halite deposition stage. The residual saline water was concentrated into magnesium-rich brine due to the lack of freshwater, and few potassium salt deposits occur in the Dongling Lake area.
基金National Natural Science Foundation (40772086)Common advanced projects of CNPC oil and gas exploration (07-01C-01-04)
文摘Because of its rich oil and gas resources and the special tectonic location of the Liaohe Western Sag （the Tanlu Fault traverses the sag）, Bohai Bay Basin, a detailed study of its strike-slip tectonics is significant in revealing the sag＇s tectonic evolution, its control on hydrocarbon accumulation, and the activity history of the northern section of the Tanlu Fault in the Cenozoic. Through systematic structure analysis of 3D seismic data of the Liaohe Western Sag, combined with balanced section analysis, a variety of structural features in relation to right-lateral strike-slip faults, such as echelon normal faults, ＂comb＂ structure, ＂flower＂ structure,＂interpretable＂ and ＂buried＂ strike-slip faults have been revealed exist in the Liaohe Western Sag. According to the research in this paper, the complex structural phenomena in the Liaohe Western Sag could be reasonably interpreted as right-lateral strike-slip activity and the strike-slip activities of the Liaohe Western Sag began in the early Oligocene. The activity was weak at the beginning （E3s1-2）, then strengthened gradually and reached its strongest level in the late Oligocene （E3d1）. In the Miocene, the strike-slip activity was low and then strengthened significantly once again from the Pliocene to the present. It is speculated that the entire northern section of the Tanlu Fault has had a similar evolution history since the Oligocene.
基金financially supported by the National Key Research and Development Program (Grant Nos. 2018YFC0603804)the China Geological Survey (Grants DD20190042, DD20190039 and DD20160048-05)
文摘The early Mesozoic marked an important transition from collisional orogeny to post-orogenic extension at the northern margin of the North China Craton(NCC). In this study, we undertook zircon U-Pb dating and whole-rock majorand trace-element geochemical analyses of early Mesozoic granitic rocks in the Chifeng area to establish their geochronological framework, petrogenesis, and implications for the tectonic evolution of the eastern Central Asia Orogenic Belt(CAOB). Zircon U-Pb dating results show that these rocks were emplaced in three stages during the Triassic:(1) syenogranites during 250-248 Ma,(2) granodiorites during 244-243 Ma, and(3) monzogranites and granodiorites during 232-230 Ma. These Triassic granitoids belong to the high-K calc-alkaline series and are evolved I-type granites. They have high SiO2 and low Mg O contents with enrichments in light rare-earth elements, Zr, Hf, Rb, Th, and U, and depletions in Ba, Nb, Ta, Sr, and Eu. These geochemical data indicate that the granitoids were derived from partial melting of a lower-crustal source under relatively low-pressure conditions and subsequently underwent extensive fractional crystallization. Considering both the geochemical data and regional geological information, we propose that the 250-248 Ma syenogranites were emplaced in an extensional environment linked to slab break-off after closure of the Paleo-Asian Ocean(PAO) along the Solonker-Xra Moron-Changchun suture zone. The 244-243 Ma granodiorites were formed in a compressional orogenic setting during collision between the Erguna-Xing’an-Songliao composite block and the NCC. The 232-230 Ma granodiorites and monzogranites were emplaced during the transition from compressional orogeny to post-orogenic extension. Overall, the early Mesozoic tectonic evolution of the Chifeng area can be divided into three main stages:(1) closure of the Paleo-Asian Ocean and extension related to slab break-off during the Early Triassic;(2) continuous collisional compression during the Middle Triassic after closure of the PAO;and(3) post-orogenic extension during the Late Triassic, most probably due to lithospheric delamination after amalgamation of the Erguna-Xing’an-Songliao composite block and the NCC.
