Early Jurassic metamorphism and anatectic melting of the eastern Lhasa terrane
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    Abstract:

    The Lhasa terrane located on the southern Tibetan Plateau not only records the Mesozoic subduction of the NeoTethyan oceanic lithosphere and subsequent Cenozoic continental collision between India and Asian plates, but also the Late Paleozoic- Early Mesozoic amalgamation of the southernnorthern Lhasa subterranes. This study carried out petrology and zircon U- Pb chronology analysis of schist and veins in the Dongjiu area of the eastern Lhasa terrane. The results show that the schist experienced peak high amphibolitefacies metamorphism and partial melting, then retrograde mediumpressure amphibolitefacies metamorphism and later retrograde metamorphism of cooling and decompression. Schist records peak mineral assemblage, including Ky+Grt+Bt+Pl+Ilm+Qz, while the retrograde mineral assemblages are Grt+Sil+Crd+Bt+Pl+Ilm+Qz and Crd+Bt+Ms+Chl+Pl+Ilm+Qz, respectively. Phase equilibrium simulation shows that the peakmetamorphic conditions are 0. 9 GPa and 720℃, and retrograde conditions are 0. 59GPa and 670℃, and then 0. 12 GPa and 480℃. The garnetbearing felsic vein has significant Eu positive anomaly (δEu=3. 57), suggesting that it was the products of plagioclase cumulation. Zircon UPb dating suggests tht the Dongjiu schist and vein underwent metamorphism and partial melting at the Early Jurassic of 181 and 195 Ma respectively. With the published results, we suggest that the Dongjiu highgrade metamorphic rocks contain two tectonic blocks and expereniced the similar metamorphism at early Jurassic period. They were the products of collision of the southernnorthern Lhasa subterranes.

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DONG Xin, ZHANG Zeming, TIAN Zuolin, LI Bing.2019. Early Jurassic metamorphism and anatectic melting of the eastern Lhasa terrane[J]. Acta Geologica Sinica,93(10):2446-2462

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History
  • Received:August 04,2019
  • Revised:August 19,2019
  • Adopted:August 29,2019
  • Online: August 29,2019
  • Published: