Early Permian post-collisional high-K granitoids from Liuyuan area in southern Beishan orogen, NW China: Petrogenesis and tectonic implications

Abstract

Early Permian magmatism is one of the most important tectonothermal events in the Central Asian Orogenic Belt (CAOB). Early Permian granitic magmatism has been recognized from southern Beishan, NW China and they were emplaced between 275Ma and 279Ma according to LA-ICPMS zircon U–Pb dating. They are mainly metaluminous I-type and belong to the high-K calc-alkaline and shoshonitic series. The granitoids have calc-alkalic and alkali-calcic features. Their Sri values range from 0.7028 to 0.7047, εNd(t) values from −2.5 to +1.2 with Nd model ages (TDM) of 1.06–1.25Ga, suggesting a mixed magma source of juvenile material with old continental crust. Furthermore, some granitoids have weak heterogeneous zircon εHf(t) values (−1.7 to +9.6) and Hf model ages (TDM2=0.84–1.57Ga) that are also indicative of juvenile components with a small involvement of old continental crust. Based on geochemical and isotopic features, these high-K granitoids were derived from melting of heterogeneous crustal sources or through mixing of old continental crust with juvenile components and minor AFC (assimilation and fractional crystallization). The juvenile components probably originated from underplated basaltic magmas in response to asthenospheric upwelling. These Early Permian high-K calc-alkaline granitoids in the southern Beishan orogen were probably emplaced in a post-collisional extensional setting and suggest vertical continental crustal growth in the southern CAOB, which is the same or similar to most granitoids in CAOB. This study provides new evidence for determining the post-accretionary evolution of the southern CAOB.