Bitu ophiolite in eastern Tibet: The last piece of the jigsaw puzzle in the Paleotethyan regime along the eastern Cimmerian continental margin

Abstract

As part of the eastern Cimmerian continent, the Qiangtang terrane played an important role in the evolution of the Pangea supercontinent. Recent studies suggest the Qiangtang terrane be divided into two parts along the Longmu Co-Shuanghu Paleotethyan suture, which connected with the Changning-Menglian suture as the boundary of the Cimmerian continents from the Laurasia. However, this proposal has been challenged by the absence of ophiolite mélanges in 700-km length in eastern Tibet. To fill this gap, here we investigate an ophiolite mélange suite, named Bitu, in eastern Tibet. The mélange includes blocks of serpentinites, gabbros, basalts, and minor radiolarian-bearing cherts. Zircon UPb dating indicates that the gabbro crystallized at ~265 Ma and one basalt sample has zircon ages that cluster at ~426 Ma. Geochemical analysis shows that the mafic rocks have oceanic island basalt (OIB) or mid-ocean ridge basalt (MORB) characteristics. This indicates an expanded ocean from the Late Silurian to the Middle Triassic in eastern Tibet, comparable to that of other Paleotethyan sutures. Thus, based on regional comparison, we infer that the Longmu Co-Shuanghu, Bitu, and Changning-Menglian sutures represent the vanished Paleotethyan Ocean that spanned over ~4000 km between the eastern Cimmerian and the Laurasia continents. Reconstruction of the Paleozoic plate tectonics provides robust evidence for terrane correlation from Pamir to Southeast Asia. Moreover, the pre-Cenozoic plate configuration proposed by this study questions the suggestions of 400–500 km offset in the Cenozoic along the Karakorum-Jiali-Ailaoshan fault system based on the correlation of the Rushan-Pshart with the Bangong-Nujiang suture and the correlation of the Jinshajiang with the Dien Bien Phu suture.