Cenxi Permian basalts are the late Palaeozoic island-arc type basalts first found in South China. REE and trace element characteristics and distribution patterns show that this volcanic formation, which has been isoto...Cenxi Permian basalts are the late Palaeozoic island-arc type basalts first found in South China. REE and trace element characteristics and distribution patterns show that this volcanic formation, which has been isotopically dated at 261 MaB.P. by the 39Ar/ 40Ar method, is of an active continental marginal island arc type, and that the tectonic environment at that time was an island-arc marginal sea or minor ocean basin related with the paleo-Tethyan tectonic belt in western Guangdong-eastern Guangxi.展开更多
High/ultrahigh-pressure(HP/UHP)metamorphic complexes,such as eclogite and blueschist,are generally regarded as significant signature of paleo-subduction zones and paleo-suture zones.Glaucophane eclogites have been rec...High/ultrahigh-pressure(HP/UHP)metamorphic complexes,such as eclogite and blueschist,are generally regarded as significant signature of paleo-subduction zones and paleo-suture zones.Glaucophane eclogites have been recently identified within the Lancang Group characterized by accretionary mélange in the Changning-Menglian suture zone,at Bangbing in the Shuangjiang area of southeastern Tibetan Plateau.The authors report the result of petrological,mineralogical and metamorphism investigations of these rocks,and discuss their tectonic implications.The eclogites are located within the Suyi blueschist belt and occur as tectonic lenses in coarse-grained garnet muscovite schists.The major mineral assemblage of the eclogites includes garnet,omphacite,glaucophane,phengite,clinozoisite and rutile.Eclogitic garnet contains numerous inclusions,such as omphacite,glaucophane,rutile,and quartz with radial cracks around.Glaucophane and clinozoisite in the matrix have apparent optical and compositional zonation.Four stages of metamorphic evolution can be determined:The prograde blueschist facies(M_(1)),the peak eclogite facies(M_(2)),the decompression blueschist facies(M_(3))and retrograde greenschist facies(M_(4)).Using the Grt-Omp-Phn geothermobarometer,a peak eclogite facies metamorphic P-T condition of 3000–3270 MPa and 617–658℃ was determined,which is typical of low-temperature ultrahigh-pressure metamorphism.The comparison of the geological characteristics of the Bangbing glaucophane eclogites and the Mengku lawsonite-bearing retrograde eclogites indicates that two suites of eclogites may have formed from significantly different depths or localities to create the tectonic mélange in a subduction channel during subduction of the Triassic Changning-Menglian Ocean.The discovery of the Bangbing glaucophane eclogites may represent a new oceanic HP/UHP metamorphic belt in the Changning-Menglian suture zone.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
The granites of ambiguous geodynamic mechanism in the Qin-Fang tectonic belt(SW China)were studied in detail based on petrological,element geochemical,zircon U-Pb geochronological,and Hf isotopic data.LA-ICPMS U-Pb an...The granites of ambiguous geodynamic mechanism in the Qin-Fang tectonic belt(SW China)were studied in detail based on petrological,element geochemical,zircon U-Pb geochronological,and Hf isotopic data.LA-ICPMS U-Pb analyses on zircon yield ages of 248-245 Ma for the granites from the Qin-Fang tectonic belt.The geochemical data show that they are high-K,calc-alkaline,and peraluminous series.Their ε_(Hf)(t)values are from -14.01 to -7.75 with two-stage model ages of 1.74-1.43 Ga.These data,integrated with low Al_(2)O_(3)/TiO_(2),Rb/Sr,Rb/Ba,and(Na_(2)O+K_(2)O)/(FeO^(T)+MgO+TiO_(2))ratios,and high CaO/Na_(2)O ratios for the granite,suggest an origin from psammite source which was contaminated by mantle-derived components.These observations,in combination with the age data and stratigraphic records in the Jinshajiang,Ailaoshan,and Hainan Island areas suggest that the granites were formed in a post-collision tectonic setting.The Qin-Fang tectonic belt was likely a branched ocean basin of the eastern Paleo-Tethys.展开更多
文摘Cenxi Permian basalts are the late Palaeozoic island-arc type basalts first found in South China. REE and trace element characteristics and distribution patterns show that this volcanic formation, which has been isotopically dated at 261 MaB.P. by the 39Ar/ 40Ar method, is of an active continental marginal island arc type, and that the tectonic environment at that time was an island-arc marginal sea or minor ocean basin related with the paleo-Tethyan tectonic belt in western Guangdong-eastern Guangxi.
基金supported by the National Natural Science Foundation of China(92055314 and 41602091)the geological survey project of China Geological Survey(DD20160016).
文摘High/ultrahigh-pressure(HP/UHP)metamorphic complexes,such as eclogite and blueschist,are generally regarded as significant signature of paleo-subduction zones and paleo-suture zones.Glaucophane eclogites have been recently identified within the Lancang Group characterized by accretionary mélange in the Changning-Menglian suture zone,at Bangbing in the Shuangjiang area of southeastern Tibetan Plateau.The authors report the result of petrological,mineralogical and metamorphism investigations of these rocks,and discuss their tectonic implications.The eclogites are located within the Suyi blueschist belt and occur as tectonic lenses in coarse-grained garnet muscovite schists.The major mineral assemblage of the eclogites includes garnet,omphacite,glaucophane,phengite,clinozoisite and rutile.Eclogitic garnet contains numerous inclusions,such as omphacite,glaucophane,rutile,and quartz with radial cracks around.Glaucophane and clinozoisite in the matrix have apparent optical and compositional zonation.Four stages of metamorphic evolution can be determined:The prograde blueschist facies(M_(1)),the peak eclogite facies(M_(2)),the decompression blueschist facies(M_(3))and retrograde greenschist facies(M_(4)).Using the Grt-Omp-Phn geothermobarometer,a peak eclogite facies metamorphic P-T condition of 3000–3270 MPa and 617–658℃ was determined,which is typical of low-temperature ultrahigh-pressure metamorphism.The comparison of the geological characteristics of the Bangbing glaucophane eclogites and the Mengku lawsonite-bearing retrograde eclogites indicates that two suites of eclogites may have formed from significantly different depths or localities to create the tectonic mélange in a subduction channel during subduction of the Triassic Changning-Menglian Ocean.The discovery of the Bangbing glaucophane eclogites may represent a new oceanic HP/UHP metamorphic belt in the Changning-Menglian suture zone.
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financially supported by the National Natural Science Foundation of China(No.42372102)the Guangxi Natural Science Foundation Program(Nos.2017GXNSFAA198209 and 2022GXNSFAA035620)the Guangxi Key R&D Program(No.AB22035045).
文摘The granites of ambiguous geodynamic mechanism in the Qin-Fang tectonic belt(SW China)were studied in detail based on petrological,element geochemical,zircon U-Pb geochronological,and Hf isotopic data.LA-ICPMS U-Pb analyses on zircon yield ages of 248-245 Ma for the granites from the Qin-Fang tectonic belt.The geochemical data show that they are high-K,calc-alkaline,and peraluminous series.Their ε_(Hf)(t)values are from -14.01 to -7.75 with two-stage model ages of 1.74-1.43 Ga.These data,integrated with low Al_(2)O_(3)/TiO_(2),Rb/Sr,Rb/Ba,and(Na_(2)O+K_(2)O)/(FeO^(T)+MgO+TiO_(2))ratios,and high CaO/Na_(2)O ratios for the granite,suggest an origin from psammite source which was contaminated by mantle-derived components.These observations,in combination with the age data and stratigraphic records in the Jinshajiang,Ailaoshan,and Hainan Island areas suggest that the granites were formed in a post-collision tectonic setting.The Qin-Fang tectonic belt was likely a branched ocean basin of the eastern Paleo-Tethys.
