Provenance and tectonic settings of Permian turbidites from the Beishan Mountains, NW China: Implications for the Late Paleozoic accretionary tectonics of the southern Altaids

Abstract The Beishan orogenic belt, which connects the Tianshan suture on the west and Solonker suture on the east, contains key evidence for the termination time of the southern Altaids. Critical for evaluating different controversial tectonic models are Permian marine volcaniclastic arenites in the Liuyuan and Heishankou areas, which are dominated by greywackes and lenticular pebbly litharenites that contain grading, groove marks, and erosional bases, which provide evidence of turbidity action. Sandstones from the Liuyuan section are dominated by angular basaltic, andesitic, and feldspar fragments, but sandstones from the Heishankou section mainly consist of andesitic and felsic volcanic fragments. These relations suggest derivation from two different sources. Major element compositions suggest that the source rocks of the Heishankou litharenites were more SiO 2 -rich than those at Liuyuan. Sandstones at Heishankou are characterized by lower Ni–Co–Cr–V and slightly higher Th and La contents than those at Liuyuan. This indicates that the litharenites in the Liuyuan and Heishankou areas were derived from intermediate-mafic and intermediate-felsic source rocks, respectively. Tectonic setting discrimination plots suggest that the Liuyuan sandstones were deposited as detritus from an oceanic island arc, but the Heishankou sediments from an Andean continental margin. Our petrological and geochemical data from these two types of Permian turbidites suggest that an arc-continent collision took place in the Early Permian, and this is consistent with the Permian termination of the southern Altaids.