文摘
A ca. 600 m-long, 0.5x2013;20 m-wide NWx2013;SE trending granite dike crosscuts the high pressurex2013;low temperature (HPx2013;LT) Tianshan metamorphic belt, the foliation of which is parallel to the main ENE regional trend in the Chinese South Tianshan Orogen. It is mainly composed of plagioclase, K-feldspar, quartz, muscovite, biotite and secondary chlorite, while fluorite, zircon and xenotime occur as accessories. The immediate country rock is a quartzx2013;biotitex2013;plagioclase schist, which grades several tens of meters away from the granite dike into a chloritex2013;micax2013;albite schist. The latter schist is intimately intercalated with blueschist layers and boudins. The A/CNK value of the granite dike samples varies from 1.15 to 1.27 indicating a strongly peraluminous composition. CaO/Na2O ranges from 0.06 to 0.17 and Al2O3/TiO2 from 240 to 525, similar to the ratios of strongly peraluminous (SP) granites exposed in x2018;high-pressurex2019; collision zones such as the Himalayas. A zircon Ux2013;Pb age of 285 Ma was obtained for the granite dike, thus constraining the upper limit for the age of HPx2013;LT metamorphism. The petrological and geochemical data suggest that the SP leucogranite dike intruded during the exhumation of overthickened crust in the post-collisional setting between the Yili (x2013;Central Tianshan) and Tarim blocks. The dataset presented here in conjunction with previously published data corroborate that the HPx2013;LT metamorphism must have occurred earlier than the Permian in the Tianshan Orogen. Therefore, the collision between the Yili (x2013;Central Tianshan) and Tarim blocks and the final amalgamation of the Southwestern Altaids must have been terminated in Late Paleozoic and not in Triassic times as previously suggested.