An Early Permian (ca. 280Ma) silicic igneous province in the Alxa Block, NW China: A magmatic flare-up triggered by a mantle-plume?
Abstract Silicic igneous provinces have important implications for geodynamic processes. In this study, we show that the predominantly Early Permian (ca. 280 Ma) granitoids in the Alxa Block correspond to an important silicic igneous province with areal distribution in Northwest (NW) China. We present zircon U–Pb age and Hf–O isotopic, and whole-rock geochemical and Sr–Nd isotopic data for the newly identified I- and A-type granites and high Sr/Y granodiorites in the Bayannuoergong batholith, and gabbros, diorites and quartz diorites in the Bijiertai Complex, Alxa Block. The I-type monzogranites, granodiorites and A-type granites of the Bayannuoergong batholith were probably generated by mixing between crust- and mantle-derived magmas, partial melting of a thickened eclogitic lower crust and underplated mantle-derived mafic rocks, respectively. The gabbros, quartz diorites and diorites of the Bijiertai Complex were likely generated by partial melting of the lithospheric mantle, differentiation from basaltic magmas and partial melting of the middle crust, respectively. Despite pronounced geochemical and isotopic heterogeneity of these rocks, new SIMS and LA–ICP-MS U–Pb zircon dating indicates that they were formed over a very short time interval at ca. 280 Ma. Thus, the mantle, lower crust and middle crust underwent widespread melting at this time. Given that these magmatic rocks have no spatial or temporal zonation, and were probably formed in an extensional setting, we suggest that the ca. 280 Ma Tarim mantle plume in NW China may have triggered the magmatic flare-up of the Alxa silicic igneous province.