浙东早白垩世火山岩组合的地球化学及其成因研究

The comparison studies of major elements and trace elements of early Cretaceous intermediate-bearing volcanic rock assemblage and bimodal volcanic rock assemblage in eastern Zhejiang suggest that the geochemical characteristics of intermediate volcanic rocks are obviously controlled by those of coexisted basalts and rhyolites. The plots of trace elements of these volcanic rocks testify that intermediate volcanic rocks were generated by mixing of basaltic magma and rhyolitic magma. Intermediate-bearing volcanic rock assemblage and bimodal volcanic rock assemblage have similar characteristics of major elements and different characteristics of trace elements. Based on the early Cretaceous tectonic setting in the coastal area of southeast China which was changing from compression to extension, and the different diffusion rate of trace elements during magma mixing, a genetic model for early Cretaceous volcanic rock assemblages in eastern Zhejiang is proposed. If basaltic magma and rhyolitic magma coexisted only for a short time in lower crust before eruption, then they had no time to exchange their major elements except for some trace elements, they formed bimodal volcanic rock assemblage. If basaltic magma and rhyolitic magma coexisted in lower crust for a long period of time, and they had enough time to exchange their major elements except for trace elements, then intermediate magma can be generated at the interface of the magmas. A typical andesitic magma can be produced by further composition exchanges, forming intermediate-bearing volcanic rock assemblage.