Late Mesozoic tectonic evolution of the central Bangong–Nujiang Suture Zone, central Tibetan Plateau

Abstract

ABSTRACT The Bangong–Nujiang Suture Zone (BNSZ), located in the central Tibetan Plateau, experienced a Late Mesozoic transition from oceanic closure to continent–continent collision. Based on sandstone-composition analyses, U-Pb detrital-zircon dating and structural observations, we determined that this transition occurred coeval with the accretion of the Lhasa Terrane to Eurasia. According to our newly observed stratigraphic and geochronological data, we conclude the following: (1) the Upper Triassic-Lower Jurassic Muggar Gangri Group was mainly derived from the Qiangtang Terrane; (2) the Shamuluo Formation composed of Upper Jurassic-Lower Cretaceous shallow marine strata was sourced from both the Qiangtang Terrane and recycled Muggar Gangri Group; (3) the Lower Cretaceous (~125–110 Ma) Duoni Formation shows both Lhasa and Qiangtang detrital zircon fingerprints, indicating closure of the Bangong–Nujiang Ocean at ~120 Ma; and (4) the Upper Cretaceous Abushan Formation is a suite of intramontane molasse deposited after the Qiangtang–Lhasa collision. Therefore, these sedimentary strata record the transition from oceanic closure to continent–continent collision from 125 to 90 Ma within the central BNSZ. Moreover, based on relationships among strata distributions and thrust locations, we propose that thrust movements propagated southward during this transition and controlled sedimentary basin deposition. The Late Mesozoic tectonic transition within the BNSZ occurred well before the India-Asia collision and hence profoundly influenced the Cenozoic formation of the Tibetan Plateau.