Evolving Permian magmatism associated with arc migration in the southern Beishan Orogenic Collage, Central Asian Orogenic Belt, NW China

Abstract

Abstract The Beishan Orogen contains the youngest suture in the Central Asian Orogenic Belt and is vital to understanding its terminal collision history and closure of the last vestiges of the Palaeo-Asian Ocean. Multidisciplinary evidence is provided for a close temporal and spatial linkage between the Liuyuan Complex back-arc ophiolite and the Ganquan Complex arc rocks. The Ganquan Complex mainly comprises felsic volcanic and volcaniclastic rocks and is divided into a lower and upper sequence, both of which exhibit arc-like geochemical signatures and have magmatic zircons characterized by mantle-like δ 18 O values. Their U–Pb zircon ages range between 295 and 286 Ma and between 283 and 281 Ma, with corresponding ε Hf values varying from −4.2 to +1.9 and from +1.3 to +7.6, respectively, indicating a more juvenile magma source over time. The increase of juvenile isotopic signatures in the Ganquan Complex rocks is attributed to arc-trench migration, which progressively removed the arc from influences of an old arc basement contaminant and led to back-arc spreading and formation of the Liuyuan ophiolite. Cessation of the multi-phase Ganquan arc system at c. 280 Ma coincided with the accretion of the continental Baidunzi Complex in the south.