As the important component of the eastern Tethys tectonic region,the Jinsha River-Ailao Mountain suture zone is often considered to be an ophiolitic mé1ange belt.However,the P-T-t path and chronological framework...As the important component of the eastern Tethys tectonic region,the Jinsha River-Ailao Mountain suture zone is often considered to be an ophiolitic mé1ange belt.However,the P-T-t path and chronological framework of the metamorphic evolution in the collisional orogenetic process of this zone are still poorly understood owing to the lack of metamorphism research of symbolic high-pressure rocks.During a regional geological survey on a scale of 1:50000 in Gonjo County,Tibet Autonomous Region involved in this paper,(retrograde)eclogites lenses of different scales were found in Jinsha River suture zone,eastern Tibet for the first time.The(retrograde)eclogites can be divided into garnet-albite-chlorite-actinolite schists and eclogites according to retrograde degrees.The mainly mineral components of eclogites include garnet(45%-50%),clinopyroxene(about 25%),and hornblende(5%-10%)primarily,and biotite,quartz,rutile,and muscovite secondarily.According to the data of electron probe micro analysis(EPMA),clinopyroxenes feature high content of Na2O(5.6%-6%)and corresponding jadeite(Jd)molecules of 37%-44%,and they fall within the omphacite region in Quad-Jd-Ae diagram.The temperature and pressure of the metamorphism at peak are P≈2.2-2.34 GPa and T≈622-688℃respectively as measured with geobarometry Grt-Omp-Phe and geothermometer Grt-Omp.This will provide a new reference for the understanding of Paleo-Tethyan evolution.In this paper,two samples of eclogites were chosen for LA-ICP-MS zircon U-Pb dating and their 206pb/238U ages obtained are 240±3 Ma and 244±1 Ma respectively.Furthermore,the zircons feature extremely low Th/U ratio(<0.01),extremely low content ofNb,Ta,and HREE,and invisible negative Eu anomaly.Therefore,the genesis of the zircons shall be eclogites-facies metamorphism,indicating that the 240-245 Ma determined in this paper shall be the age of eclogites-facies metamorphism and may represent the westward subduction-collision epoch of Paleo-Tethys Ocean located between Zhongza Block and Qamdo Block.展开更多
Omphacite grains from UHP eclogite of the Dabie Mountains in eastern China are elongated and show strong lattice preferred orientations (LPOs). Observations by the transmission electron microscopy (TEM) identified not...Omphacite grains from UHP eclogite of the Dabie Mountains in eastern China are elongated and show strong lattice preferred orientations (LPOs). Observations by the transmission electron microscopy (TEM) identified not only structures of plastic deformation occurring as free dislocation, dislocation loops and dislocation walls, but also bubbles of water present in the deformed omphacite. The bubbles attach to the dislocation loops which are often connected to one another via a common bubble. Using infrared spectroscopy (IR), two types of hydrous components are identified as hydroxyl and free-water in the omphacite. An analysis of deformation mechanism of microstructure in omphacite suggests that the mineral deformed plastically under UHP metamorphic conditions by dislocation creep through hydrolitic weakening.展开更多
The mineral inclusions in accessory minerals of the country gneisses have been studied in order to interpret relation between eclogites and their country gneissic rocks. Omphacite inclusions have been identified in ti...The mineral inclusions in accessory minerals of the country gneisses have been studied in order to interpret relation between eclogites and their country gneissic rocks. Omphacite inclusions have been identified in titanite and zircon, which indicates that the present mineral assemblages of country gneisses are the last retrograded assemblages and eclogites and their country gneissic rocks probably have a same metamorphic history.展开更多
基金This research was jointly funded by National Natural Science Foundation of China(41773026)geological survey project of China Geological Survey(DD20190053).
文摘As the important component of the eastern Tethys tectonic region,the Jinsha River-Ailao Mountain suture zone is often considered to be an ophiolitic mé1ange belt.However,the P-T-t path and chronological framework of the metamorphic evolution in the collisional orogenetic process of this zone are still poorly understood owing to the lack of metamorphism research of symbolic high-pressure rocks.During a regional geological survey on a scale of 1:50000 in Gonjo County,Tibet Autonomous Region involved in this paper,(retrograde)eclogites lenses of different scales were found in Jinsha River suture zone,eastern Tibet for the first time.The(retrograde)eclogites can be divided into garnet-albite-chlorite-actinolite schists and eclogites according to retrograde degrees.The mainly mineral components of eclogites include garnet(45%-50%),clinopyroxene(about 25%),and hornblende(5%-10%)primarily,and biotite,quartz,rutile,and muscovite secondarily.According to the data of electron probe micro analysis(EPMA),clinopyroxenes feature high content of Na2O(5.6%-6%)and corresponding jadeite(Jd)molecules of 37%-44%,and they fall within the omphacite region in Quad-Jd-Ae diagram.The temperature and pressure of the metamorphism at peak are P≈2.2-2.34 GPa and T≈622-688℃respectively as measured with geobarometry Grt-Omp-Phe and geothermometer Grt-Omp.This will provide a new reference for the understanding of Paleo-Tethyan evolution.In this paper,two samples of eclogites were chosen for LA-ICP-MS zircon U-Pb dating and their 206pb/238U ages obtained are 240±3 Ma and 244±1 Ma respectively.Furthermore,the zircons feature extremely low Th/U ratio(<0.01),extremely low content ofNb,Ta,and HREE,and invisible negative Eu anomaly.Therefore,the genesis of the zircons shall be eclogites-facies metamorphism,indicating that the 240-245 Ma determined in this paper shall be the age of eclogites-facies metamorphism and may represent the westward subduction-collision epoch of Paleo-Tethys Ocean located between Zhongza Block and Qamdo Block.
基金funded by the Ministry of Science and Technology of China(No.G19990755-01)the National Natural Science Foundation of China,Postdoctoral Science Foundation of China,the Chinese Academy of Sciences Wong K.C.Post-doctoral Research Award Fund and the State Key Laboratory of Mineral Deposits,Nanjing University
文摘Omphacite grains from UHP eclogite of the Dabie Mountains in eastern China are elongated and show strong lattice preferred orientations (LPOs). Observations by the transmission electron microscopy (TEM) identified not only structures of plastic deformation occurring as free dislocation, dislocation loops and dislocation walls, but also bubbles of water present in the deformed omphacite. The bubbles attach to the dislocation loops which are often connected to one another via a common bubble. Using infrared spectroscopy (IR), two types of hydrous components are identified as hydroxyl and free-water in the omphacite. An analysis of deformation mechanism of microstructure in omphacite suggests that the mineral deformed plastically under UHP metamorphic conditions by dislocation creep through hydrolitic weakening.
文摘The mineral inclusions in accessory minerals of the country gneisses have been studied in order to interpret relation between eclogites and their country gneissic rocks. Omphacite inclusions have been identified in titanite and zircon, which indicates that the present mineral assemblages of country gneisses are the last retrograded assemblages and eclogites and their country gneissic rocks probably have a same metamorphic history.
