The geochemistry and zircon U-Pb dating for the metamorphic volcanic rocks in Nimu area，Tibet

Located in the south of the Gangdise magmatic arc, Nimu area occurred a set of metamorphic volcanic rocks mainly composed of amphibolite and amphibole-bearing plagioclase gneiss. Previously, they are believed to be the late Paleozoic crystalline basement rocks of the Lhasa block. By detailed geological survey and studies on mineral associations, geochemistry, and zircon U-Pb dating, the authors believe these metamorphic volcanic rocks were the accretion complex related to the subduction of the New Tethys Ocean in the late Jurassic. Following their formation, these arc-type volcanic rocks then experienced the mid-pressure amphibolite facies metamorphism in the late Cretaceous and the high-temperature contact metamorphism in the Eocene. Mineral chemistry shows that hornblendes in the rocks are mainly magnesium hornblendes and the paragenetic feldspars are mainly labradorites. The geochemistry of the rocks shows that Al₂O₃ is in rich and TiO₂ is in poor, and LILEs such as Rb, Sr, Ba are in rich and HFSEs such as Nb, Ta, Ti are in poor, comparatively. The LA-ICP-MS U-Pb dating of zircons from the metamorphic volcanic rocks shows an age from 151.4±1.6Ma to 150.7±1.4Ma, which indicate that the studied rocks are originally the product of the northward subduction of the New Tethys Ocean in the late Jurassic.