Arc-continent collision during culmination of Proto-Tethyan Ocean closure in the Central Qilian belt, NE Tibetan Plateau

Abstract

Abstract Accurate lithostratigraphy framework of the Central Qilian belt is key to understand subduction-collision of the Proto-Tethyan Ocean in the NE Tibetan Plateau. The Dongchagou and the Moshigou formations share similar detrital zircon age populations with youngest age peak at ca. 1.15–1.21 Ga, which is consistent with the granitoid gneiss of the Liujiatai Formation. In combination with rock assemblages, metamorphic facies, and associated oldest granitoid plutons, we revised Precambrian lithostratigraphy of the Central Qilian belt as the >1.2 Ga Huangyuan Group and the ca. 1200–930 Ma Huangzhong Group in this study. The former is the same as the Liujiatai Formation, whereas the later includes the Dongchagou and Moshigou formations. Siliciclastic turbidites of the Qingshipo Formation gradually pass upward into carbonates of the Huashishan Group, we therefore ascribe them to the Huashishan Group. This group unconformably overlies the Precambrian basement of the Central Qilian belt and consists of continental slope to coastal plain deposits with a bi-direction of the S- and N-ward paleocurrent. These sediments contain abundant metamorphic, magmatic, and minor ophiolitic detritus with main age populations of ca. 910 Ma, ca. 487 Ma, and ca. 447 Ma detrital zircons, probably derived from the Central and South Qilian belts. The basement of the Huangzhong Group experienced 440– 430 Ma continent-continent collision-related metamorphism and deformation. These results and regional geology demonstrate that the Huashishan Group was formed by arc-continent collision deposition during culmination of the Proto-Tethyan Ocean closure in the Qilian orogenic belt, NE Tibetan Plateau.