HR: 0800h
AN: T21A-0505    [Abstracts]
TI: A Early Paleozoic HP/UHP metamorphic belt truncated by the Altyn Tagh fault in NW China­GPetrological and geochronological constaints
AU: * Zhang, J
EM: zjx66@yeah.net
AF: Institute of Geology,CAGS, 26 Baiwanzhuang, Beijing, 100037 China
AU: Yang, J
EM: yangjsui@ccsd.org.cn
AF: Institute of Geology,CAGS, 26 Baiwanzhuang, Beijing, 100037 China
AU: Chris, M
EM: cgm@pang.stanford.edu
AF: Department of Geological and Environmental Sciences, Stanford University, Stanford, Stanford, 94305-2115 United States
AB: The Altyn Tagh and North Qaidam Mountains at the northern margin of Qinghai-Tibet plateau are separated by the Altyn Tagh sinistral strike-slip fault, which is one of the largest strike-slip fault systems in the world and was considered as the key element in the escape tectonics model for Euraisa-India continent-continent collision. In recent years, the eclogites, HP granulite and garnet peridotites were recognized in the Altyn Tagh and the North Qaidam Monutains (NQD), respectively. They occur as lens or boundins within quratzofeldspathic gneisses or pelitic gneisses characterized by amphibolite-facies parageneses. Along NQD, eclogites occur in the the Yuka, Xitieshan and Dulan area, respectively. Garnet peridotite lenses occur within quartzofeldspathic gneisses in the Luliangshan between Xitieshan and Yuka. Some UHP metamorphic evidences, such as quartz pseudomorphs after coesite from eclogites, coesite inclusions in zircons from the host paragneisses as well as unusual exsolution textures in ompacites, have been recognized. Zircon U-Pb and Sm-Nd isochron ages from the eclogites gave ages of 450-500Ma for eclogite-facies metamorphism. These eclogites and associated rocks constitute an early Paleozoic HP/UHP metamorphic belt which extends from the Dulan in the east to the Altyn Tagh fault to the west along the NQD. To the northwest of the Altyn Tagh fault, eclogites and HP granulite-garnet peridotite associations were discovered respectively in the Jianggelesayi and Bashiwake area. Polycrystalline quartz inclusions within eclogite garnets, P-T estimates (P = 2.8-3.0 GPa, T = 780-820 ,aC) and unusual exsolution textures suggest UHP conditions of eclogite formation. Petrological data gave peak metamorphic conditions of P = 1.9-2.7 GPa, T = 870-1050 ,aC for HP granulite-garnet peridotite associations. Zircon U-Pb and Sm-Nd isochron analyses from the eclogites, HP granulites and garnet peridotites indicate HP/UHP ages of around 500 Ma The similarity of age, occurrence, and P-T conditions of the NQD and Altyn Tagh HP/UHP rocks suggests that the Altyn Tagh is the northwestward extension of the NQD metamorphic belt, formed by early Paleozoic subduction and collision of the Qaidam and Qilian blocks, and subsequently offset by left-lateral slip on the Altyn Tagh fault. This situation might be similar to the Dabie-Sulu HP-UHP metamorphic zone in eastern China, which was split into Dabie and Sulu regions by the sinistral Tanlu strike-slip fault.
DE: 3600 MINERALOGY AND PETROLOGY (replaces
DE: 3660 Metamorphic petrology
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting