Geochemical characteristics and genesis of the granitic gneisses from the southeastern Dabie Mountains

The granitic gneisses from the ultrahigh-pressure (UHP) metamorphic terrain of the southeastern Dabie Mountains encompass two types: monzonitic granit ic gneiss and alkali-feldspar granitic gneiss, which are characterized by r ich alkalis, poor CaO, high FeO/MgO, particularly high Ba, Rb, Th, Ta, REE (except Eu), Ga, Nb and Zn, and low Sr, Eu, Cr, Co and Ni. The gneisses, pa rticularly the alkali-feldspar granitic gneiss, have typical chemical chara cteristics of A-type granites. They resulted from partial melting of crusta l materials existing in the rift zone along the northern margin of the Sout h China block during the Neoproterozoic. These gneisses might not have unde rgone UHP metamorphism during the late Triassic, but were involved into UHP rocks by the tectonic mixing process and kept the exhumation message of th e UHP rocks from the middle and upper crust.