Major geochemical characteristics of bimodal volcanic rocks in different geochemical environments.

The latest achievements on bimodal volcanic rocks are reviewed in this pape r. It is suggested that bimodal volcanic rocks can occur in highly contrast ing geodynamic environments, such as continental rifts, oceanic islands, co ntinental-breakup setting, incipient back-are spreading, post-orogenic exte nsional setting, intra-oceanic arcs and mature islands/active continental m argins, etc. Rhyolites can be mainly generated in two ways. First, coeval b asalts and rhyolites may share a common mantle-derived parent, while the rh yolites are evolved from basaltic magmas with a small rhyolite/basalt volum e ratio, and both of them have similar geochemical characteristics. Alterna tively, rhyolites and basalts may have totally unrelated sources, the rhyol ite are derived from anatexis of the crust. The exposed rhyolite is predomi nant relative to basalt and the rhyolite and basalt often have dinstinctive geochemical characteristics.