Petrogenesis of Permian A‐Type and I‐Type Felsic Rocks in the Southern Beishan Orogenic Collage and Geodynamic Implications

ABSTRACT The specific closure timing of the Paleo‐Asian Ocean (PAO) and the triggering mechanism of Late Palaeozoic tectonic‐magmatic activities in the Beishan Orogenic Collage (BOC), Central Asian Orogenic Belt, remain subjects of debate. In order to solve these issues, this study carries out systematic research for the felsic igneous rocks (i.e., Yin'aoxia rhyolites, Yin'aoxia and Qiaowan granitoids) from the southern BOC. Zircon U–Pb dating for six studied samples reveal their formation ages of Early Permian (288.1 ± 2.2 Ma to 274.9 ± 1.7 Ma). The Yin'aoxia rhyolites are classified as A 2 ‐type rhyolites and characterized by high values of SiO 2 , Al 2 O 3 , Na 2 O and Th/Nb but low values of Mg # , Cr and Ni, suggesting that they were formed by melting of crustal materials. The Yin'aoxia and Qiaowan granitoids are identified as I‐type granitoids. The low ratios of Nb/Ta and Nd/Th, negative to positive values of εHf(t) and εNd(t) and existence of mafic enclaves indicate that the I‐type granitoids were derived from lower continental crust melting triggered by mantle melts injection. The features of whole‐rock and zircon geochemical compositions as well as regional geology are obviously unmatched with the Late Palaeozoic tectonic mechanisms of mantle plume, intracontinental rifting, subduction‐related processes or lithosphere delamination in the southern BOC, but conform to the model of slab break‐off. The data in this study supports that the branch of PAO in southern BOC closed in the earliest Permian, leading to slab break‐off and widespread Late Palaeozoic magmatic emplacement.