The study area is situated in the Tianshan region,specifically within the eastern segment of the North Qilian Orogenic Belt(NQLOB).The NQLOB is a critical region for understanding oceanic closure and continental colli...The study area is situated in the Tianshan region,specifically within the eastern segment of the North Qilian Orogenic Belt(NQLOB).The NQLOB is a critical region for understanding oceanic closure and continental collision processes driven by the Shangdan Ocean subduction-exhumation,which was a segment of the Proto-Tethys Ocean during the Early Paleozoic.Despite significant research,the Early Paleozoic tectonic background and subduction-related orogenic processes,particularly in the eastern NQLOB,remain subjects of debate.This study presents significant petrographic,geochemical,and geochronologic insights into the metavolcanic rocks of the Chenjiahe Group in the eastern NQLOB.Petrographic analysis reveals that these metavolcanic rocks originated in a low-grade metamorphic setting.Zircon laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS)U-Pb dating yielded ages ranging between 449.7-443.4 Ma,indicating Late Ordovician formation.Geochemical signatures of felsic and intermediate rocks exhibit calc-alkaline to high-K calc-alkaline similarities,characterized by high light rare earth elements(LREEs),low heavy rare earth elements(HREEs),and moderate Eu anomalies,consistent with a continental arc setting.In contrast,basaltic rocks display tholeiitic features with elevated large-ion lithophile elements(LILEs),reduced high-field-strength elements(HFSEs),and weak Eu anomalies,suggesting an extensional environment.These findings imply that the metavolcanic rocks evolved in a continental arc-back-arc extension setting connected with the northward subduction and exhumation of the Huluhe back-arc oceanic basin.This process was likely triggered by the northward subduction and closure of the Shangdan Ocean,culminating in the Late Ordovician amalgamation of the Qilian Block and the southwestern North China Block.This study provides critical insight into the tectonic development of the NQLOB and the broader Proto-Tethys Ocean dynamics at the northern periphery of the Eastern Gondwana.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
基金supported by the National Nature Science Foundation of China (Grant Nos. 41872235, 42172236, and 41872233)Double First-Class University Construction Special Project of Shaanxi (Grant No. 300111240014)+1 种基金the Youth Innovation Team of Shaanxi Universitiesthe Fundamental Research Funds for the Central Universities of China (Grant Nos. 300102270202, 202110710062, 300103183081, 300108231154, S202410710285, and 300102274808)
文摘The study area is situated in the Tianshan region,specifically within the eastern segment of the North Qilian Orogenic Belt(NQLOB).The NQLOB is a critical region for understanding oceanic closure and continental collision processes driven by the Shangdan Ocean subduction-exhumation,which was a segment of the Proto-Tethys Ocean during the Early Paleozoic.Despite significant research,the Early Paleozoic tectonic background and subduction-related orogenic processes,particularly in the eastern NQLOB,remain subjects of debate.This study presents significant petrographic,geochemical,and geochronologic insights into the metavolcanic rocks of the Chenjiahe Group in the eastern NQLOB.Petrographic analysis reveals that these metavolcanic rocks originated in a low-grade metamorphic setting.Zircon laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS)U-Pb dating yielded ages ranging between 449.7-443.4 Ma,indicating Late Ordovician formation.Geochemical signatures of felsic and intermediate rocks exhibit calc-alkaline to high-K calc-alkaline similarities,characterized by high light rare earth elements(LREEs),low heavy rare earth elements(HREEs),and moderate Eu anomalies,consistent with a continental arc setting.In contrast,basaltic rocks display tholeiitic features with elevated large-ion lithophile elements(LILEs),reduced high-field-strength elements(HFSEs),and weak Eu anomalies,suggesting an extensional environment.These findings imply that the metavolcanic rocks evolved in a continental arc-back-arc extension setting connected with the northward subduction and exhumation of the Huluhe back-arc oceanic basin.This process was likely triggered by the northward subduction and closure of the Shangdan Ocean,culminating in the Late Ordovician amalgamation of the Qilian Block and the southwestern North China Block.This study provides critical insight into the tectonic development of the NQLOB and the broader Proto-Tethys Ocean dynamics at the northern periphery of the Eastern Gondwana.
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.
