Geochemistry and geochronology of acidic rocks in the Beishan region, NW China: Petrogenesis and tectonic implications

The dacites and granites from the Beishan region are characterized by highly-fractionated REE, enrichments in LILE, and depletion in Nb, Ta and Sr. The dacites contain zircons with ages ranging from 265 to 748Ma. These features suggest that they were probably derived from the older lower continental crust and were later on subjected to significant crustal assimilation. The rhyolites, diorites and diabases, all of which share similar geochemical features such as trace element patterns, zircon U-Pb ages of ~280Ma, positive εHf(t) and εNd(t), high initial (87Sr/86Sr)i and δ18O‰ values, were most likely derived from the juvenile crustal sources and subsequently experienced fractional crystallization and crustal contamination. These acidic igneous rocks (except dacites and granites) and coeval mafic-ultramafic intrusions form a bimodal igneous series. This implies that the Beishan region was a Late Paleozoic rift probably developed in association with the early Permian mantle plume activity in the Tarim Basin