Tectonic affinity of the Wusushan Group in the central segment of the Qilian orogen

Abstract：Based on an analysis of the characteristics of the rock association and geochemistry of volcanic rocks of the Wusushan Group, combined with a comparative study of the regional geological setting of the neighboring regions, the authors discuss the environment and tectonic affinity and implications of the Wusushan Group in the southwest of Lanzhou in the Qilian orogen. The Wusushan Group is a rock association consisting mainly of intermediate and intermediate-basic volcanic rocks and dacite with small amounts of pyroclastic rocks and ordinary sedimentary rocks, which formed in the Mid-Late Ordovician and underwent low greenschist facies metamorphism. Geochemical characteristics of different types of volcanic rocks show that the rocks formed in an island arc or forearc tectonic setting. By analyzing the characteristics of the rock association and geochemistry of volcanic rocks of the Wusushan Group and comparing these characteristics with those of the Lajishan tectonic belt and North Qilian orogen, it is preliminarily thought that the Wusushan Group is probably not the eastward extension of the Lajishan tectonic belt but the structural remnants of the extension of the island arc belt at the southern margin of the North Qilian Mountains southwest of Lanzhou. The redefinition of the tectonic affinity of the Wusushan Group is of great significance for solving the eastward extension of the Qilian orogen, understanding the intersection relation between the Qilian orogen and Qinling orogen and establishing the tectonic framework of the east-central segment of the Qilian orogen.