Geochemistry,petrogenesis and tectonic implication of Early Cretaceous A-type rhyolites in Hailar Basin,NE China

Early Cretaceous A-type rhyolites of the Shangkuli Formation in the Hailar Basin of NE China exhibit geochemical characteristics of high silicon, alkali, Fe/Mg, Ga/Al, Zr, Pb, HFSEs, and REE contents but low Ca, Ba, Sr and Eu, which meet the criteria of typical reduced A-type granite.The A-type rhyolites are most probably derived from magmatic underplating and partial melting of quartz-feldspathic lower crust, with the lithospheric mantle material involved, due to the extensional deformation of the Erguna-Hulun Fault.Although the A-type rhyolites show A1-type trace elements characteristics, they were formed in a post-orogenic extension-al background together with the coeval widespread bimodal volcanic rocks, metamorphic core complexes, vol-canic fault basins and metallogenic province in the Sino-Russia-Mongolia border tract.This extension event was related to the collapse of thickened region of the continental crust after the closure of the Mongol-Okhotsk Ocean.