Post-collisional Southeastern Beishan granites: Geochemistry, geochronology, Sr–Nd–Hf isotopes and their implications for tectonic evolution

Abstract

Bandaoshan granites are exposed in the Southeastern Beishan area, in the central part of the Central Asia Orogenic Belt (CAOB). LA-ICP-MS U–Pb zircon dating indicates that Bandaoshan granites were emplaced into Precambrian basement at 285±4Ma and their geochemistry indicates that they are alkali-rich potassium-high granites. Initial εNd values (−4.3 to −2.7) and εHf values (−2.7 to +0.7) suggest that Bandaoshan granites were derived from mantle-derived melt and an upper continental crustal or sedimentary component. The latter plays a significant role in their genesis. In combination with regional geology, the Early Permian Bandaoshan pluton is interpreted to form in a post-collisional environment. In the Southeastern Beishan area Late Carboniferous Qiaowan granites, Early Permian Yin’aoxia granites and Middle Permian Xijianquanzi granites are also considered as post-collisional granites, and together with Bandaoshan granites indicate that the region was in a post-collisional stage from the end of Late Carboniferous to Middle Permian.