Diachronous closure of the Shuanghu Paleo-Tethys Ocean: Constraints from the Late Triassic Tanggula arc-related volcanism in the East Qiangtang subterrane, Central Tibet

The tectonic evolution of the Shuanghu Paleo-Tethys Ocean is an important but poorly understood issue in the geology of the Tibetan Plateau and Tethys. Here we present a new and detailed petrological, geochronological, major and trace elemental, Sr-Nd-Hf isotopic dataset for the Late Triassic Tanggula volcanic sequence in the East Qjangtang subterrane, central Tibet, which, together with previously published data, would provide critical constraints on the evolution of the Shuanghu Paleo-Tethys Ocean. The volcanic sequence is constituted by two nearly concentric belts, namely the outer belt of rhyolites and the inner belt of granite-porphyries. LA-ICP-MS zircon U-Pb dating indicates that the granite-porphyries formed at ca. 221 Ma, later than the rhyolites by ca. 15 Myr. They are characterized by enrichments in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), with significant negative anomalies at Nb, Ta, and Ti but positive anomalies at Th, U, and Pb. Isotopic compositions exhibit enrichment signatures, with epsilon(Hf)(t) values ranging from -14.1 to -5.7 and epsilon(Nd)(t) values from -8.84 to -7.06. Geochemical characteristics indicate that these volcanic rocks were formed by progressive melting of the subducted sediments accumulated on the Shuanghu Paleo-Tethys Ocean floor, which originated from the weathered Paleozoic continental crust in the Qjangtang Terrane. Combined with the geological background, we further propose that the eastern Tanggula-Changdu segment of the Shuanghu Paleo-Tethys Ocean was still northward subducting at ca. 221 Ma. The Shuanghu Paleo-Tethys Ocean has an diachronous closing process where the eastern Tanggula-Changdu segment closed later than the western Gangma Co-Shuanghu segment by >20 Myr. (C) 2019 Elsevier B.V. All rights reserved.