Geochronology of high-pressure granulite in the Amdo,Qinghai-Tibet Plateau

This paper reports the results of LA-ICP-MS U-Pb dating of the zircon in newly discovered high-pressure granulite,and the Ar-Ar isotopic dating of biotite in granitic gneiss of the surrounding rock of high-pressure granulite on Nyainrong microcontinent.There are two types of zircon in high-pressure granulites,the first type is a core-edge microstructure,the zircon residualed cores with typical features of magmatic zircon,zircon U-Pb age is 541±8Ma～834±11Ma;the second zircon with typical structural characteristics of the causes metamorphic zircon,zircon U-Pb age is 179.0±1.7Ma.In granite gneiss the biotite Ar-Ar plateau age of 166.7±1.1Ma.Age data show both granulite and its surrounding are with the Pan-African age information,granulite protolith experienced a Late Proterozoic-Early Paleozoic orogeny,and in the Early-Middle Jurassic occurred peak high-pressure metamorphic role in transformation,the metamorphic event may be related to a major role in collision which occurred in Bangong Co-Nujiang River suture zone in region it may represent the Nyainrong microcontinent and Qiangnan plate put together.With the Early-Middle Jurassic magmatism,granulite and its surrounding rapidly exhumation,exhumation of the time span is about 13Myr and at about 166.7Ma uplift to shallow parts of the crust or near the surface.