The garnet amphibolites from the newly identified Wanhe ophiolitic mélange in the Changning-Menglian suture zone(CMSZ)provide a probe to elucidate the evolution of the Triassic Palaeo-Tethys.An integrated petrolo...The garnet amphibolites from the newly identified Wanhe ophiolitic mélange in the Changning-Menglian suture zone(CMSZ)provide a probe to elucidate the evolution of the Triassic Palaeo-Tethys.An integrated petrologic,phase equilibria modeling and geochronological study of the garnet amphibolites,southeast Tibetan Plateau,shows that the garnet amphibolites have a peak mineral assemblage of garnet,glaucophane,lawsonite,chlorite,rutile,phengite and quartz,and a clockwise P-T path with a prograde segment from blueschist-facies to eclogite-facies with a peak-metamorphic P-T conditions of 2000–2100 MPa and 495–515℃,indicating a cold geothermal gradient of about 240–260℃/GPa.Theretrograde metamorphic P-T path is characterized by nearly isothermal decompression to lower amphibolite-facies and subsequent cooling to greenschist-facies.The metamorphic zircons have fractionated HREE patterns and significant negative Eu anomalies,and therefore the obtained zircon U-Pb age of 231±1.5 Ma is interpreted to be the timing of the amphibolite facies metamorphism occurrence.The present study probably indicates that the garnet amphibolites in the Wanhe ophiolitic mélange was the retrograded highpressure eclogite-facies blueschist,instead of the previously proposed eclogites,and the garnet amphibolites recorded the subduction and exhumation process of the Palaeo-Tethys Oceanic crust in the Triassic.展开更多
The foramtion and evolution of collisional orogen is a prominent feature along convergent plate margins,and is generally a complex process.This article presents an integrated study of zircon genesis,U-Pb age and Lu-Hf...The foramtion and evolution of collisional orogen is a prominent feature along convergent plate margins,and is generally a complex process.This article presents an integrated study of zircon genesis,U-Pb age and Lu-Hf isotope composition as well as geological characteristics for the western Dabie orogen to constrain its multi-stage evolution history.The results suggest that the formation of oceanic crust in the Huwan area was constrained at ca.400―430 Ma,which was slightly later than the collision of the northern Qinling with the North China Block.It formed in a marginal basin in the northern margin of the Yangtze Block.The peak metamorphism of eclogite in the Huwan area occurred at ca.310 Ma,and the timing of the initial exhumation of oceanic eclogite was about 270 Ma.The high to ultrahigh pressure(HP-UHP)metamorphic rocks in the Xinxian and the Hong'an metamorphic zones have the same ages and natures as those of the HP-UHP metamorphic rocks in the other Dabie-Sulu terrains,and also have experienced multi-stage exhumation,and thus can be taken as a coherent part of the Dabie-Sulu orogen.Therefore,the Qinling-Dabie-Sulu orogen is a typical multi-stage continental collision orogen,with an amalgamation process extending more than 200 Ma.展开更多
基金supported by the National Natural Science Foundation of China(41802071,41773026 and 41303028)the Geological Survey of China-Nepal railway(202008000000180117).
文摘The garnet amphibolites from the newly identified Wanhe ophiolitic mélange in the Changning-Menglian suture zone(CMSZ)provide a probe to elucidate the evolution of the Triassic Palaeo-Tethys.An integrated petrologic,phase equilibria modeling and geochronological study of the garnet amphibolites,southeast Tibetan Plateau,shows that the garnet amphibolites have a peak mineral assemblage of garnet,glaucophane,lawsonite,chlorite,rutile,phengite and quartz,and a clockwise P-T path with a prograde segment from blueschist-facies to eclogite-facies with a peak-metamorphic P-T conditions of 2000–2100 MPa and 495–515℃,indicating a cold geothermal gradient of about 240–260℃/GPa.Theretrograde metamorphic P-T path is characterized by nearly isothermal decompression to lower amphibolite-facies and subsequent cooling to greenschist-facies.The metamorphic zircons have fractionated HREE patterns and significant negative Eu anomalies,and therefore the obtained zircon U-Pb age of 231±1.5 Ma is interpreted to be the timing of the amphibolite facies metamorphism occurrence.The present study probably indicates that the garnet amphibolites in the Wanhe ophiolitic mélange was the retrograded highpressure eclogite-facies blueschist,instead of the previously proposed eclogites,and the garnet amphibolites recorded the subduction and exhumation process of the Palaeo-Tethys Oceanic crust in the Triassic.
基金Supported by the National Basic Research Program of China(Grant No.2009CB825000)National Natural Science Foundation of China(Grant Nos.40873043,40821061,90714010 and 40772042)+1 种基金Ministry of Education of China(Grant Nos.IRT0441,B07039 and NCET-06-0659)Foundation of the State Key Laboratory of Continental Dynamics,Northwest University
文摘The foramtion and evolution of collisional orogen is a prominent feature along convergent plate margins,and is generally a complex process.This article presents an integrated study of zircon genesis,U-Pb age and Lu-Hf isotope composition as well as geological characteristics for the western Dabie orogen to constrain its multi-stage evolution history.The results suggest that the formation of oceanic crust in the Huwan area was constrained at ca.400―430 Ma,which was slightly later than the collision of the northern Qinling with the North China Block.It formed in a marginal basin in the northern margin of the Yangtze Block.The peak metamorphism of eclogite in the Huwan area occurred at ca.310 Ma,and the timing of the initial exhumation of oceanic eclogite was about 270 Ma.The high to ultrahigh pressure(HP-UHP)metamorphic rocks in the Xinxian and the Hong'an metamorphic zones have the same ages and natures as those of the HP-UHP metamorphic rocks in the other Dabie-Sulu terrains,and also have experienced multi-stage exhumation,and thus can be taken as a coherent part of the Dabie-Sulu orogen.Therefore,the Qinling-Dabie-Sulu orogen is a typical multi-stage continental collision orogen,with an amalgamation process extending more than 200 Ma.
