Jurassic Trench basin of the Bangong-Nujiang Ocean in the Central Tibet: Record of clastic material mixing from Lhasa and Qiangtang terranes

Abstract

The early growth, subduction, and demise history of the oceans in the Tibetan Plateau remains a subject of significant controversy, particularly the evolution history of the Bangong-Nujiang Meso-Tethyan Ocean. Sedimentary records serve as faithful carriers of orogenic belt evolution. Here, we present a newly-discovered Jurassic deep-marine gravity-fan succession that is over 250 m thick. We employ multi-proxy, single-grain provenance analysis and forward modeling of sediment mixture on this sequence to reconstruct the Mesozoic Meso-Tethyan Ocean tectonic evolution in the Lunpola region. We find the detritus was deposited in a trench and was sourced from the accretionary wedge, island arc, and continent block. Through quantitative mixed modeling calculations of detrital zircon U-Pb ages, we found that the two detrital zircon samples from the Jienu Group obtained in this study indicated a source contribution of 73–79 % from the Qiangtang terrane, 10–17 % from the Lhasa terrane, and 10–11 % from the Tethyan Himalayan tectonic belt. This result directly proves that the Bangong-Nujiang Ocean was the ancient ocean between the Lhasa terrane and the Qiangtang terrane, rather than between the Himalayan terrane and the Qiangtang terrane during Jurassic.