Detrital zircon provenance constraints on the final closure of the middle segment of the Paleo-Asian Ocean

The main site and timing of the final closure of the middle segment of the Paleo-Asian Ocean (PAO) has been an issue of hot debate, which hampers us from better understanding the late-stage tectonic evolution of the Central Asian Orogenic Belt (CAOB). Synthesizing the available geological records for the ophiolitic melanges in the Beishan Orogenic Belt (BOB), we regard the Liuyuan ophiolitic melange as the main site of the final closure of the middle segment of the PAO. To determine the final closure time of the middle segment of the PAO, this study mainly applied field-based, systematic zircon U-Pb-Hf isotopic analyses for the Carboniferous and Permian sedimentary successions on the northern and southern sides of the Liuyuan ophiolitic melange. Our results indicate that the late Carboniferous sedimentary successions north of the Liuyuan melange consisting mainly of interbedded sandstone and siltstone with minor conglomerate show primarily affinity with a local, single source, i.e. the constituent units of the BOB north of the Liuyuan melange. They were closely associated with the northward subduction of the middle segment of the PAO. By contrast, the unconformably overlying Permian clastic deposition on both sides of the Liuyuan ophiolitic melange shows comparable lithology that fines from a thick sequence of conglomerate at the base to thin-bedded turbidite sequences up section. These Permian units were probably deposited in a progressively deepening basin within an extensional post-collision regime after the disappearance of the middle segment of the PAO. All the <274-261 Ma sandstones on both sides of the Liuyuan ophiolitic melange were derived from commingling source regions on both sides of the Liuyuan melange, as supported by comparable, diagnostic ages and epsilon(Hf)(t) values between the studied detrital zircons and coeval magmatic zircons from the BOB and north Tarim. Such a marked transition from a single, local provenance in the late Carboniferous to commingling provenances at ca. 274-261 Ma indicates the final closure of the middle segment of the PAO prior to the end of the early Permian. In conjunction with available data for the eastern and western segments of the PAO, we establish the eastward-younging, scissor-like closure for the whole PAO during mid Carboniferous to Early Triassic time. (C) 2019 Published by Elsevier B.V. on behalf of International Association for Gondwana Research.