Aptian Flysch in Central Tibet: Constraints on the Timing of Closure of the Bangong-Nujiang Tethyan Ocean

The timing of the closure of the Bangong-Nujiang Tethyan Ocean is highly controversial. An important reason for this is that the sedimentological work within the Bangong-Nujiang suture zone is not sufficient. In this study, based on the U-Pb zircon dating of turbiditic sandstone and tuff interlayers, we determine the existence of Aptian flysch (ca. 126-113 Ma) in the middle and western segments of the Bangong-Nujiang suture zone. Further analysis shows that the Aptian flysch was deposited in a trench environment. In space, from the Mabujia Co area in the western segment to the Kama area in the middle segment, the outcrop extent of the Aptian flysch spans nearly 300 km from east to west. These results indicate that the Bangong-Nujiang Tethyan Ocean had not fully closed by the end of Aptian time, and its oceanic slab was still subducting. Based on this new discovery, and the results of previous studies, we believe that the middle and western segments of the Bangong-Nujiang Tethyan Ocean closed between 113 and ca. 92 Ma nonmarine deposition of the Jingzhushan Formation, which lies in angular unconformity above the flysch.