越南北部地區晚二疊紀至早三疊紀岩漿活動研究

Abstract

The intraplate Song Hien-An Chau system zone together with the Song Da (Black River), Phan Si Pan uplift and Tu Le Basin are major Permian-Triassic geological structures in northern Vietnam. These are believed to dislocate from western China following the India-Eurasian collision. Permian-Triassic magmatism in these structures has been interpreted to relate to Emeishan ‘mantle plume’- derived large igneous province (LIP). Permian volcanic rocks, including picrites, flood basalts and silicic volcanic rocks, crop out in the Song Da district, northern Vietnam. They occur as a~300-km-long belt emanating from the southernmost part of the Emeishan large igneous province, SW China. The belt represents a detached part from the province and was displaced ~600 km southeastward along the Ailao Shan-Red River shear zone during the mid-Tertiary in response to the India–Eurasia collision. We report here geochemical and Sr–Nd isotopic data on the Song Da volcanic rocks to decipher the petrogenetic processes responsible for their formation. The picrites show evidence of olivine fractionation and formed from high-Mg magmas (MgO = 20–25 wt.%) originated from depleted mantle peridotites from the Emeishan plume head. The plume head is characterized by