On the basis of the synthetic studies of geology and geochemistry, an ophiolitic tectonic melange waa discovered in Sanligang-Sanyang area, the western part of Xiangfan-Guangji fault, the south margin of the Qinling O...On the basis of the synthetic studies of geology and geochemistry, an ophiolitic tectonic melange waa discovered in Sanligang-Sanyang area, the western part of Xiangfan-Guangji fault, the south margin of the Qinling Orogenic Belt. It is composed of different tectonic blocks with different lithological features and ages, mainly including the Huashan ophiolite blocks, Xiaofu Island-arc volcanic blocks, pelagic sediments, fore-arc volcanic-sedimentary system, and the massif of the basement and the covering strata of the Yangtze Block. These massifs were emplaced in the western part of Xiangfan-Guangji fault, the boundary between the Qinling Orogenic Belt and Yangtze Block, contacting each other by a shear zone or chaotic matrix. The characteristics of geochemistry indicate that the bash of the Huashan ophiolite are similar to mid-oceanic ridge basalts (MORB) formed in an initial oceanic baain, and the Xiaofu volcanic rocks are formed in a tectonic setting of island arc. The ophiolitic tectonic melange is the fragments of subduction wedge, which implies that there has been an oceanic basin between Qinling Block and Yangtze Block.展开更多
the Qinling Mountains in central China are a joint orogenic zone between the Sino-Korean (or North China) and the Yangtze (or South China) craton blocks, the two major tectonic units of eastern Asia. On the end time o...the Qinling Mountains in central China are a joint orogenic zone between the Sino-Korean (or North China) and the Yangtze (or South China) craton blocks, the two major tectonic units of eastern Asia. On the end time of the main orogenic stage in this orogenic展开更多
Late Early Paleozoic mafic-ultramafic dykes and volcanic rocks from the South Qinling belt are char- acterized by εNd( t ) = +3.28― +5.02, (87Sr/86Sr)i= 0.70341― 0.70555, (206Pb/204Pb)i = 17.256― 18.993, (207Pb/20...Late Early Paleozoic mafic-ultramafic dykes and volcanic rocks from the South Qinling belt are char- acterized by εNd( t ) = +3.28― +5.02, (87Sr/86Sr)i= 0.70341― 0.70555, (206Pb/204Pb)i = 17.256― 18.993, (207Pb/204Pb)i= 15.505―15.642, (208Pb/204Pb)i=37.125―38.968, ?8/4=21.18―774.43, ?7/4=8.11―18.82. These charac- teristics suggest that they derived from a Middle Neoproterozoic mantle with isotopic compositions of mixed HIMU, EMII and minor EMI components. We interpret that these rocks were melting products of depleted mantle modified by subducted ancient oceanic crust and continental margin sediments along the northern margin of Yangtze block during Early Neoproterozoic.展开更多
The Qinling Orogenic Belt is divided commonly by the Fengxian-Taibai strike-slip shear zone and the Huicheng Basin into the East and West Qinling mountains, which show significant geological differences after the Indo...The Qinling Orogenic Belt is divided commonly by the Fengxian-Taibai strike-slip shear zone and the Huicheng Basin into the East and West Qinling mountains, which show significant geological differences after the Indosinian orogeny. The Fengxian-Taibai fault zone and the Meso-Cenozoic Huicheng Basin, situated at the boundary of the East and West Qinling, provide a natural laboratory for tectonic analysis and sedimentological study of intracontinental tectonic evolution of the Qin- ling Orogenic Belt. In order to explain the dynamic development of the Huicheng Basin and elucidate its post-orogenic tecton- ic evolution at the junction of the East and West Qinling, we studied the geometry and kinematics of fault zones between the blocks of West Qinling, as well as the sedimentary fill history of the Huicheng Basin. First, we found that after the collisional orogeny in the Late Triassic, post-orogenic extensional collapse occurred in the Early and Middle Jurassic within the Qinling Orogenic Belt, resulting in a series of rift basins. Second, in the Late Jurassic and Early Cretaceous, a NE-SW compressive stress field caused large-scale sinistral strike-slip faults in the Qinling Orogenic Belt, causing intracontinental escape tectonics at the junction of the East and West Qinling, including eastward finite escape of the East Qinling micro-plate and southwest lateral escape of the Bikou Terrane. Meanwhile, the strike-slip-related Early Cretaceous sedimentary basin was formed with a fight-order echelon arrangement in sinistral shear zones along the southern margin of the Huicheng fault. Overall during the Mesozoic, the Huicheng Basin and surrounding areas experienced four tectonic evolutionary stages, including extensional rift basin development in the Early and Middle Jurassic, intense compressive uplift in the Late Jurassic, formation of a strike-slip extensional basin in the Early Cretaceous, and compressive uplift in the Late Cretaceous.展开更多
Paleozoic cherts from the Mianl and the Erlangping ophiolite zones of the Qinling orogenic belt are characterized by low Si/Al ratios (52.14-683.52 in the Mianle cherts, 12.29-58.62 in the Erlangping cherts), Fe2O3 (0...Paleozoic cherts from the Mianl and the Erlangping ophiolite zones of the Qinling orogenic belt are characterized by low Si/Al ratios (52.14-683.52 in the Mianle cherts, 12.29-58.62 in the Erlangping cherts), Fe2O3 (0.01-0.35 and 0.02-1.24) and high Al2O3/(Al2O3+Fe2O3) ratios (0.82-0.99 and 0.83-0.99). The negative correlation between Si2O and Al2O3 in the cherts reflects the important role of terrigenous components. The Erlangping cherts have Lan/Cen=0.9-1.15 and Ce/Ce*=0.95-1.15 with low contents of V, Ni and Cu, consistent with those of cherts forming on the continental margin. In contrast, the Ce/Ce* ratios of the Mianle cherts range from 0.71 to 1.18 and Lan/Cen from 0.88 to 1.43 with slightly high V, Ni and Cu, which are similar to cherts found in the mid-ocean ridges and pelagic basins. Combined with the features of basic lavas associated with the cherts, it is suggested that during the Paleozoic, when the back-arc basin represented by the Erlangping ophiolite commenced shrinking in size in the mid-Ordovician, the southern Qinling was still in an extensional regime and finally grew into a new limited oceanic basin in the early Carboniferous.展开更多
The Hejiazhuang pluton is located in the South Qinling Tectonic Belt （SQTB） in the north side of the MianxianLueyang Su ture Zone, and consists dominantly of granodiorites. LAICPMS zircon UPb dating and LuHf isotopi...The Hejiazhuang pluton is located in the South Qinling Tectonic Belt （SQTB） in the north side of the MianxianLueyang Su ture Zone, and consists dominantly of granodiorites. LAICPMS zircon UPb dating and LuHf isotopic analyses reveal that these granodiorites of the Hejiazhaung pluton emplaced at 248 Ma, and show a large variation in zircon eHt（t） values from 4.8 to 8.8. These granodiorite samples are attributed to highK to midK calcalkaline series, and characterized by high SiO2 （66.6±70.0%）, A1203 （15.04±16.10%） and Na20 （3.74±4.33%） concentrations, with high Mg# （54.2±61.7）. All samples have high Sr （627±751 ppm）, Cr （553±73 ppm） and Ni （17.2182 ppm）, but low Y （5.42-8.41 ppm） and Yb （0.59-0.74 ppm） concentrations with high Sr/Y ratios （84.90±120.66）. They also display highly fractionated REE patterns with （La/Yb）N ratios of 18.93-4.0 and positive Eu anomalies （0＂Eu=1.102.22） in the chondritenormalized REE patterns. In the primitive mantle normalized spidergrams, these samples exhibit enrichment in LILEs but depletion in Nb, Ta, P and Ti. These geochemical fea tures indicate that the granodioritic magma of the Hejiazhuang pluton was derived from the partial melting of hybrid sources comprising the subducted oceanic slab and sediments, and the melts were polluted by the mantle wedge materials during their ascent. The emplacement ages and petrogenesis of the Hejiazhuang pluton prove that the initial subduction of the Mianlue oceanic crust occurred at 248 Ma ago, and the SQTB was still under subduction tectonic setting in the Early Triassic.展开更多
The North Qinling Orogenic Belt(NQOB)is a composite orogenic belt in central China.It started evolving during the Meso-Neoproterozoic period and underwent multiple stages of plate subduction and collision before enter...The North Qinling Orogenic Belt(NQOB)is a composite orogenic belt in central China.It started evolving during the Meso-Neoproterozoic period and underwent multiple stages of plate subduction and collision before entering intra-continental orogeny in the Late Triassic.The Meso-Cenozoic intra-continental orogeny and tectonic evolution had different responses in various terranes of the belt,with the tectonic evolution of the middle part of the belt being particularly controversial.The granites distributed in the Dayu and Kuyu areas in the middle part of the NQOB can provide an important window for revealing the geodynamic mechanisms of the NQOB.The main lithology of Dayu and Kuyu granites is biotite monzogranite,and the zircon U-Pb dating yielded intrusive ages of 151.3±3.4 Ma and 147.7±1.5 Ma,respectively.The dates suggest that the biotite monzogranite were formed at the end of the Late Jurassic.The whole-rock geochemistry analysis shows that the granites in the study areas are characterized by slightly high SiO_(2)(64.50-68.88 wt%)and high Al_(2)O_(3)(15.12-16.24 wt%)and Na_(2)O(3.55-3.80 wt%)contents.They are also enriched in light rare earth elements,large ion lithophile elements(e.g.,Ba,K,La,Pb and Sr),and depleted in high field strength elements(HFSEs)(e.g.,Ta,Nb,P and Ti).Additionally,the granites have weakly negative-slightly positive Eu anomalies(δEu=0.91-1.19).Zircon Lu-Hf isotopic analysis showedε_(Hf)(t)=-6.1--3.8,and the two-stage model age is T_(2DM(crust))=1.5-1.6 Ga.The granites in the study areas are analyzed as weak peraluminous high-K calc-alkaline I-type granites.They formed by partial melting of the thickened ancient lower crust,accompanied by the addition of minor mantle-derived materials.During magma ascent,they experienced fractional crystallization,with residual garnet and amphibole for a certain proportion in the magma source region.Comprehensive the geotectonic data suggest that the end of the Late Jurassic granite magmatism in the Dayu and Kuyu areas represents a compression-extension展开更多
The West Qinling Orogen(WQO)is located in the western part of the Qinling Orogen and in the transition zone of Qilian Orogen,Songpan-Garze Orogen and Yangtze Block,and also the key position of Triassic collision oroge...The West Qinling Orogen(WQO)is located in the western part of the Qinling Orogen and in the transition zone of Qilian Orogen,Songpan-Garze Orogen and Yangtze Block,and also the key position of Triassic collision orogenic event.The study of the Early Triassic strata in the WQO is contributed to analyze the closure process of the paleo-Tethys.We conducted LA-ICP-MS U-Pb dating studies on detrital zircons to determine the provenance,depositional age,and tectonic setting of the Early Triassic Longwuhe Formation in the Lintan area of the WQO.The results show that the majority of the detrital zircons in the Longwuhe Formation are mainly magmatic origin and have characteristic of crust source zircon.The lowest limit of sedimentation of the Longwuhe Formation is constrained to the Early Triassic,with the youngest detrital zircon age of 253±3 Ma.The ages can be divided into five age groups:3346–1636 Ma,with two peak ages of ca.2495 and ca.1885 Ma;1585–1010 Ma,with a peak age at ca.1084 Ma;992–554 Ma,with a peak age at ca.939 Ma;521–421 Ma,with a peak age at ca.445 Ma;418–253 Ma,with a peak age at ca.280 Ma.Apparently,the sources of the Longwuhe Formation include the northern margin of the WQO,the Qilian Orogen(QLO)and the basement of the southern margin of the North China Block(NCB),of which the ancient basement of the southern margin of the NCB is the main source area of the Longwuhe Formation.Combined with previous studies,we propose that the Longwuhe Formation was formed in a fore-arc basin,which is related to the closure of the A’nyemaqen-Mianlüe Ocean from the Early Permian to Early–Middle Triassic due to the northward subduction-collision of the Yangtze Block(YZB).This also indicates that the A’nyemaqen-Mianlüe Ocean has flat subduction characteristics.展开更多
Based on a large number of newly added deep well data in recent years,the subsidence of the Ordos Basin in the Mid-Late Triassic is systematically studied,and it is proposed that the Ordos Basin experienced two import...Based on a large number of newly added deep well data in recent years,the subsidence of the Ordos Basin in the Mid-Late Triassic is systematically studied,and it is proposed that the Ordos Basin experienced two important subsidence events during this depositional period.Through contrastive analysis of the two stages of tectonic subsidence,including stratigraphic characteristics,lithology combination,location of catchment area and sedimentary evolution,it is proposed that both of them are responses to the Indosinian Qinling tectonic activity on the edge of the craton basin.The early subsidence occurred in the Chang 10 Member was featured by high amplitude,large debris supply and fast deposition rate,with coarse debris filling and rapid subsidence accompanied by rapid accumulation,resulting in strata thickness increasing from northeast to southwest in wedge-shape.The subsidence center was located in Huanxian–Zhenyuan–Qingyang–Zhengning areas of southwestern basin with the strata thickness of 800–1300 m.The subsidence center deviating from the depocenter developed multiple catchment areas,until then,unified lake basin has not been formed yet.Under the combined action of subsidence and Carnian heavy rainfall event during the deposition period of Chang 7 Member,a large deep-water depression was formed with slow deposition rate,and the subsidence center coincided with the depocenter basically in the Mahuangshan–Huachi–Huangling areas.The deep-water sediments were 120–320 m thick in the subsidence center,characterized by fine grain.There are differences in the mechanism between the two stages of subsidence.The early one was the response to the northward subduction of the MianLüe Ocean and intense depression under compression in Qinling during Mid-Triassic.The later subsidence is controlled by the weak extensional tectonic environment of the post-collision stage during Late Triassic.展开更多
The Late Triassic witnessed significant collisional orogenic events in the Qinling orogenic belt,accompanied by magma underplating and tectonic deformation.These processes potentially resulted in substantial crustal t...The Late Triassic witnessed significant collisional orogenic events in the Qinling orogenic belt,accompanied by magma underplating and tectonic deformation.These processes potentially resulted in substantial crustal thickening and uplift of the Qinling orogen.However,due to the absence of igneous rock records from this period in the eastern section of the Qinling orogen,the changes in crustal thickness during this orogenic process have not been thoroughly investigated.A series of foreland basins emerged during the Early Mesozoic to the south of the East Qinling orogenic belt.These basins have preserved clastic sedimentary rocks derived from the uplift and erosion of the orogenic belt.These sedimentary records serve as crucial records to reconstruct the evolutionary history of the Qinling orogen.To further clarify the collisional orogenic process of the Qinling orogenic belt,this study conducted in situ volcanic lithic fragment geochemistry,detrital zircon U-Pb chronology and trace element composition analysis on the sandstones of the Lower Jurassic Tongzhuyuan Formation in the Zigui Basin.The results suggest that the sandstones,which exhibit a significant abundance of volcanic lithic fragments,has a characteristic detrital zircon age group of 250–200 Ma,indicating a major provenance from the Triassic volcanic rocks.Combined with regional correlation and paleocurrent analysis,the detrital zircon U-Pb age data show that the source area of volcanic rocks should be in the Qinling orogenic belt to the north of the basin.This interpretation is further supported by the Triassic granitic rocks exposed in the western part of the orogenic belt,representing the magmatism during the Triassic collisional orogenesis in the Qinling orogen.Based on the co-varying relationships between present-day crust thickness with the chemical compositions of granite rocks and zircons,the La/Yb ratio of volcanic lithic fragments in the Tongzhuyuan Formation and the Eu/Eu*ratio of detrital zircons with Triassic ages indicate that the Qinling展开更多
The Shangdan suture zone(SDZ)in the Qinling orogenic belt(QOB)is a key to understanding the East Asia tectonic evolution.The SDZ gives information about convergent processes between the North China Block(NCB)and South...The Shangdan suture zone(SDZ)in the Qinling orogenic belt(QOB)is a key to understanding the East Asia tectonic evolution.The SDZ gives information about convergent processes between the North China Block(NCB)and South China Block(SCB).In the Late Mesozoic,several shear zones evolved along the SDZ boundary that helps us comprehend the collisional deformation between the NCB and SCB,which was neglected in previous studies.These shear zones play an essential role in the tectonic evolution of the East Asia continents.This study focuses on the deformation and geochronology of two shear zones distributed along the SDZ,identified in the Shaliangzi and Maanqiao areas.The shear sense indicators and kinematic vorticity numbers(0.54–0.90)suggest these shear zones have sinistral shear and sub-simple shear deformation kinematics.The quartz’s dynamic recrystallization and c-axis fabric analysis in the Maanqiao shear zone(MSZ)revealed that the MSZ experienced deformation under green-schist facies conditions at∼400–500℃.The Shaliangzi shear zone deformed under amphibolite facies at∼500–700℃.The^(40)Ar/^(39)Ar(muscovite-biotite)dating of samples provided a plateau age of 121–123 Ma.Together with previously published data,our results concluded that QOB was dominated by compressional tectonics during the Late Early Cretaceous.Moreover,we suggested that the Siberian Block moved back to the south and Lhasa-Qiantang-Indochina Block to the north,which promoted intra-continental compressional tectonics.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 49773187, 49732080).
文摘On the basis of the synthetic studies of geology and geochemistry, an ophiolitic tectonic melange waa discovered in Sanligang-Sanyang area, the western part of Xiangfan-Guangji fault, the south margin of the Qinling Orogenic Belt. It is composed of different tectonic blocks with different lithological features and ages, mainly including the Huashan ophiolite blocks, Xiaofu Island-arc volcanic blocks, pelagic sediments, fore-arc volcanic-sedimentary system, and the massif of the basement and the covering strata of the Yangtze Block. These massifs were emplaced in the western part of Xiangfan-Guangji fault, the boundary between the Qinling Orogenic Belt and Yangtze Block, contacting each other by a shear zone or chaotic matrix. The characteristics of geochemistry indicate that the bash of the Huashan ophiolite are similar to mid-oceanic ridge basalts (MORB) formed in an initial oceanic baain, and the Xiaofu volcanic rocks are formed in a tectonic setting of island arc. The ophiolitic tectonic melange is the fragments of subduction wedge, which implies that there has been an oceanic basin between Qinling Block and Yangtze Block.
文摘the Qinling Mountains in central China are a joint orogenic zone between the Sino-Korean (or North China) and the Yangtze (or South China) craton blocks, the two major tectonic units of eastern Asia. On the end time of the main orogenic stage in this orogenic
基金Supported jointly by the National Natural Science Foundation of China (Grant Nos. 40372039, 40521001)Ministry of Education of China (Grant Nos. IRT0441 and B07039)the State Key Laboratory of Geological Progresses and Mineral Re-sources (Grant No. MGMR2002-27)
文摘Late Early Paleozoic mafic-ultramafic dykes and volcanic rocks from the South Qinling belt are char- acterized by εNd( t ) = +3.28― +5.02, (87Sr/86Sr)i= 0.70341― 0.70555, (206Pb/204Pb)i = 17.256― 18.993, (207Pb/204Pb)i= 15.505―15.642, (208Pb/204Pb)i=37.125―38.968, ?8/4=21.18―774.43, ?7/4=8.11―18.82. These charac- teristics suggest that they derived from a Middle Neoproterozoic mantle with isotopic compositions of mixed HIMU, EMII and minor EMI components. We interpret that these rocks were melting products of depleted mantle modified by subducted ancient oceanic crust and continental margin sediments along the northern margin of Yangtze block during Early Neoproterozoic.
基金supported by National Natural Science Foundation of China(Grant Nos.40802051&41190074)MOST Special Fund from the State Key Laboratory of Continental DynamicsNorthwest University
文摘The Qinling Orogenic Belt is divided commonly by the Fengxian-Taibai strike-slip shear zone and the Huicheng Basin into the East and West Qinling mountains, which show significant geological differences after the Indosinian orogeny. The Fengxian-Taibai fault zone and the Meso-Cenozoic Huicheng Basin, situated at the boundary of the East and West Qinling, provide a natural laboratory for tectonic analysis and sedimentological study of intracontinental tectonic evolution of the Qin- ling Orogenic Belt. In order to explain the dynamic development of the Huicheng Basin and elucidate its post-orogenic tecton- ic evolution at the junction of the East and West Qinling, we studied the geometry and kinematics of fault zones between the blocks of West Qinling, as well as the sedimentary fill history of the Huicheng Basin. First, we found that after the collisional orogeny in the Late Triassic, post-orogenic extensional collapse occurred in the Early and Middle Jurassic within the Qinling Orogenic Belt, resulting in a series of rift basins. Second, in the Late Jurassic and Early Cretaceous, a NE-SW compressive stress field caused large-scale sinistral strike-slip faults in the Qinling Orogenic Belt, causing intracontinental escape tectonics at the junction of the East and West Qinling, including eastward finite escape of the East Qinling micro-plate and southwest lateral escape of the Bikou Terrane. Meanwhile, the strike-slip-related Early Cretaceous sedimentary basin was formed with a fight-order echelon arrangement in sinistral shear zones along the southern margin of the Huicheng fault. Overall during the Mesozoic, the Huicheng Basin and surrounding areas experienced four tectonic evolutionary stages, including extensional rift basin development in the Early and Middle Jurassic, intense compressive uplift in the Late Jurassic, formation of a strike-slip extensional basin in the Early Cretaceous, and compressive uplift in the Late Cretaceous.
基金This project was jointly supported by the NationalNatural Science Foundation of China (Grant Nos. 40372039,40032010-C, 40133020 and 49732080)the Foundations of Senior Visiting Scholarship of Colleges in Western areas and Backbone Teacher of Ministry of Education, China (Grant No. 2000-143).
文摘Paleozoic cherts from the Mianl and the Erlangping ophiolite zones of the Qinling orogenic belt are characterized by low Si/Al ratios (52.14-683.52 in the Mianle cherts, 12.29-58.62 in the Erlangping cherts), Fe2O3 (0.01-0.35 and 0.02-1.24) and high Al2O3/(Al2O3+Fe2O3) ratios (0.82-0.99 and 0.83-0.99). The negative correlation between Si2O and Al2O3 in the cherts reflects the important role of terrigenous components. The Erlangping cherts have Lan/Cen=0.9-1.15 and Ce/Ce*=0.95-1.15 with low contents of V, Ni and Cu, consistent with those of cherts forming on the continental margin. In contrast, the Ce/Ce* ratios of the Mianle cherts range from 0.71 to 1.18 and Lan/Cen from 0.88 to 1.43 with slightly high V, Ni and Cu, which are similar to cherts found in the mid-ocean ridges and pelagic basins. Combined with the features of basic lavas associated with the cherts, it is suggested that during the Paleozoic, when the back-arc basin represented by the Erlangping ophiolite commenced shrinking in size in the mid-Ordovician, the southern Qinling was still in an extensional regime and finally grew into a new limited oceanic basin in the early Carboniferous.
基金supported by National Key Technology R&D Program(Grant Nos.2011BAB04B05,2006BAB01A11)National Natural Science Foundation of China(Grant Nos.41072143,41072169)
文摘The Hejiazhuang pluton is located in the South Qinling Tectonic Belt （SQTB） in the north side of the MianxianLueyang Su ture Zone, and consists dominantly of granodiorites. LAICPMS zircon UPb dating and LuHf isotopic analyses reveal that these granodiorites of the Hejiazhaung pluton emplaced at 248 Ma, and show a large variation in zircon eHt（t） values from 4.8 to 8.8. These granodiorite samples are attributed to highK to midK calcalkaline series, and characterized by high SiO2 （66.6±70.0%）, A1203 （15.04±16.10%） and Na20 （3.74±4.33%） concentrations, with high Mg# （54.2±61.7）. All samples have high Sr （627±751 ppm）, Cr （553±73 ppm） and Ni （17.2182 ppm）, but low Y （5.42-8.41 ppm） and Yb （0.59-0.74 ppm） concentrations with high Sr/Y ratios （84.90±120.66）. They also display highly fractionated REE patterns with （La/Yb）N ratios of 18.93-4.0 and positive Eu anomalies （0＂Eu=1.102.22） in the chondritenormalized REE patterns. In the primitive mantle normalized spidergrams, these samples exhibit enrichment in LILEs but depletion in Nb, Ta, P and Ti. These geochemical fea tures indicate that the granodioritic magma of the Hejiazhuang pluton was derived from the partial melting of hybrid sources comprising the subducted oceanic slab and sediments, and the melts were polluted by the mantle wedge materials during their ascent. The emplacement ages and petrogenesis of the Hejiazhuang pluton prove that the initial subduction of the Mianlue oceanic crust occurred at 248 Ma ago, and the SQTB was still under subduction tectonic setting in the Early Triassic.
基金substantially supported by the National Nature Science Foundation of China(Grant No.41872220)。
文摘The North Qinling Orogenic Belt(NQOB)is a composite orogenic belt in central China.It started evolving during the Meso-Neoproterozoic period and underwent multiple stages of plate subduction and collision before entering intra-continental orogeny in the Late Triassic.The Meso-Cenozoic intra-continental orogeny and tectonic evolution had different responses in various terranes of the belt,with the tectonic evolution of the middle part of the belt being particularly controversial.The granites distributed in the Dayu and Kuyu areas in the middle part of the NQOB can provide an important window for revealing the geodynamic mechanisms of the NQOB.The main lithology of Dayu and Kuyu granites is biotite monzogranite,and the zircon U-Pb dating yielded intrusive ages of 151.3±3.4 Ma and 147.7±1.5 Ma,respectively.The dates suggest that the biotite monzogranite were formed at the end of the Late Jurassic.The whole-rock geochemistry analysis shows that the granites in the study areas are characterized by slightly high SiO_(2)(64.50-68.88 wt%)and high Al_(2)O_(3)(15.12-16.24 wt%)and Na_(2)O(3.55-3.80 wt%)contents.They are also enriched in light rare earth elements,large ion lithophile elements(e.g.,Ba,K,La,Pb and Sr),and depleted in high field strength elements(HFSEs)(e.g.,Ta,Nb,P and Ti).Additionally,the granites have weakly negative-slightly positive Eu anomalies(δEu=0.91-1.19).Zircon Lu-Hf isotopic analysis showedε_(Hf)(t)=-6.1--3.8,and the two-stage model age is T_(2DM(crust))=1.5-1.6 Ga.The granites in the study areas are analyzed as weak peraluminous high-K calc-alkaline I-type granites.They formed by partial melting of the thickened ancient lower crust,accompanied by the addition of minor mantle-derived materials.During magma ascent,they experienced fractional crystallization,with residual garnet and amphibole for a certain proportion in the magma source region.Comprehensive the geotectonic data suggest that the end of the Late Jurassic granite magmatism in the Dayu and Kuyu areas represents a compression-extension
基金supported financially by the National Nature Sciences Foundation of China(Nos.41872235,42172236,41872233,42072267,41802234,41602229 and 41502191)China Scholarship Council(No.201806565026)+3 种基金Natural Science Basic Research Plan in Shaanxi Province of China(Nos.2019JM-312,2019JQ-090 and 2019JQ-209)China Geological Survey(Nos.12120114041201 and DD2016007901)China Postdoctoral Science Foundation(No.2016M592726)the Fundamental Research Funds for the Central Universities of China(Nos.300102270202,300103120009,202110710062,300103183081,300104282717,300102279204 and 201810710233).
文摘The West Qinling Orogen(WQO)is located in the western part of the Qinling Orogen and in the transition zone of Qilian Orogen,Songpan-Garze Orogen and Yangtze Block,and also the key position of Triassic collision orogenic event.The study of the Early Triassic strata in the WQO is contributed to analyze the closure process of the paleo-Tethys.We conducted LA-ICP-MS U-Pb dating studies on detrital zircons to determine the provenance,depositional age,and tectonic setting of the Early Triassic Longwuhe Formation in the Lintan area of the WQO.The results show that the majority of the detrital zircons in the Longwuhe Formation are mainly magmatic origin and have characteristic of crust source zircon.The lowest limit of sedimentation of the Longwuhe Formation is constrained to the Early Triassic,with the youngest detrital zircon age of 253±3 Ma.The ages can be divided into five age groups:3346–1636 Ma,with two peak ages of ca.2495 and ca.1885 Ma;1585–1010 Ma,with a peak age at ca.1084 Ma;992–554 Ma,with a peak age at ca.939 Ma;521–421 Ma,with a peak age at ca.445 Ma;418–253 Ma,with a peak age at ca.280 Ma.Apparently,the sources of the Longwuhe Formation include the northern margin of the WQO,the Qilian Orogen(QLO)and the basement of the southern margin of the North China Block(NCB),of which the ancient basement of the southern margin of the NCB is the main source area of the Longwuhe Formation.Combined with previous studies,we propose that the Longwuhe Formation was formed in a fore-arc basin,which is related to the closure of the A’nyemaqen-Mianlüe Ocean from the Early Permian to Early–Middle Triassic due to the northward subduction-collision of the Yangtze Block(YZB).This also indicates that the A’nyemaqen-Mianlüe Ocean has flat subduction characteristics.
基金Supported by the National Science and Technology Major Project(2017ZX05001)CNPC Science and Technology Project(2021DJ22).
文摘Based on a large number of newly added deep well data in recent years,the subsidence of the Ordos Basin in the Mid-Late Triassic is systematically studied,and it is proposed that the Ordos Basin experienced two important subsidence events during this depositional period.Through contrastive analysis of the two stages of tectonic subsidence,including stratigraphic characteristics,lithology combination,location of catchment area and sedimentary evolution,it is proposed that both of them are responses to the Indosinian Qinling tectonic activity on the edge of the craton basin.The early subsidence occurred in the Chang 10 Member was featured by high amplitude,large debris supply and fast deposition rate,with coarse debris filling and rapid subsidence accompanied by rapid accumulation,resulting in strata thickness increasing from northeast to southwest in wedge-shape.The subsidence center was located in Huanxian–Zhenyuan–Qingyang–Zhengning areas of southwestern basin with the strata thickness of 800–1300 m.The subsidence center deviating from the depocenter developed multiple catchment areas,until then,unified lake basin has not been formed yet.Under the combined action of subsidence and Carnian heavy rainfall event during the deposition period of Chang 7 Member,a large deep-water depression was formed with slow deposition rate,and the subsidence center coincided with the depocenter basically in the Mahuangshan–Huachi–Huangling areas.The deep-water sediments were 120–320 m thick in the subsidence center,characterized by fine grain.There are differences in the mechanism between the two stages of subsidence.The early one was the response to the northward subduction of the MianLüe Ocean and intense depression under compression in Qinling during Mid-Triassic.The later subsidence is controlled by the weak extensional tectonic environment of the post-collision stage during Late Triassic.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.41888101,42102121,42122015)the China Geological Survey Project(Grant Nos.DD20230008,DD20221656)Guizhou Provincial Science and Technology Projects(Grant No.ZK[2022]General 081).
文摘The Late Triassic witnessed significant collisional orogenic events in the Qinling orogenic belt,accompanied by magma underplating and tectonic deformation.These processes potentially resulted in substantial crustal thickening and uplift of the Qinling orogen.However,due to the absence of igneous rock records from this period in the eastern section of the Qinling orogen,the changes in crustal thickness during this orogenic process have not been thoroughly investigated.A series of foreland basins emerged during the Early Mesozoic to the south of the East Qinling orogenic belt.These basins have preserved clastic sedimentary rocks derived from the uplift and erosion of the orogenic belt.These sedimentary records serve as crucial records to reconstruct the evolutionary history of the Qinling orogen.To further clarify the collisional orogenic process of the Qinling orogenic belt,this study conducted in situ volcanic lithic fragment geochemistry,detrital zircon U-Pb chronology and trace element composition analysis on the sandstones of the Lower Jurassic Tongzhuyuan Formation in the Zigui Basin.The results suggest that the sandstones,which exhibit a significant abundance of volcanic lithic fragments,has a characteristic detrital zircon age group of 250–200 Ma,indicating a major provenance from the Triassic volcanic rocks.Combined with regional correlation and paleocurrent analysis,the detrital zircon U-Pb age data show that the source area of volcanic rocks should be in the Qinling orogenic belt to the north of the basin.This interpretation is further supported by the Triassic granitic rocks exposed in the western part of the orogenic belt,representing the magmatism during the Triassic collisional orogenesis in the Qinling orogen.Based on the co-varying relationships between present-day crust thickness with the chemical compositions of granite rocks and zircons,the La/Yb ratio of volcanic lithic fragments in the Tongzhuyuan Formation and the Eu/Eu*ratio of detrital zircons with Triassic ages indicate that the Qinling
基金the National Natural Science Foundation of China who provided necessary financial support for this study(Nos.41872218,41572179,and 41372204)the State Key Laboratory of Continental Dynamics,Northwest University,Xi’an for providing a special fund to accomplish this study.
文摘The Shangdan suture zone(SDZ)in the Qinling orogenic belt(QOB)is a key to understanding the East Asia tectonic evolution.The SDZ gives information about convergent processes between the North China Block(NCB)and South China Block(SCB).In the Late Mesozoic,several shear zones evolved along the SDZ boundary that helps us comprehend the collisional deformation between the NCB and SCB,which was neglected in previous studies.These shear zones play an essential role in the tectonic evolution of the East Asia continents.This study focuses on the deformation and geochronology of two shear zones distributed along the SDZ,identified in the Shaliangzi and Maanqiao areas.The shear sense indicators and kinematic vorticity numbers(0.54–0.90)suggest these shear zones have sinistral shear and sub-simple shear deformation kinematics.The quartz’s dynamic recrystallization and c-axis fabric analysis in the Maanqiao shear zone(MSZ)revealed that the MSZ experienced deformation under green-schist facies conditions at∼400–500℃.The Shaliangzi shear zone deformed under amphibolite facies at∼500–700℃.The^(40)Ar/^(39)Ar(muscovite-biotite)dating of samples provided a plateau age of 121–123 Ma.Together with previously published data,our results concluded that QOB was dominated by compressional tectonics during the Late Early Cretaceous.Moreover,we suggested that the Siberian Block moved back to the south and Lhasa-Qiantang-Indochina Block to the north,which promoted intra-continental compressional tectonics.
