Carboniferous bimodal volcanic rocks and their plate tectonic setting, Hainan Island

The Carboniferous volcanic rocks in western Hainan Island consist of a series of oceanic tholeiite and rhyoporphyrite, showing bimodal nature. Similar geochemical characters, in terms of abundances and relative ratios of incompatible elements and REE and the REE patterns, between the basalt and continental rift-associated tholeiite indicate the occurrence of Late Paleozoic rifting in the area. The basaltic magma, with a low degree of evolution, was originated from deep mantle, showing contamination by low crustal material. The rhyolite is thought to be formed from partial melting of the continental crust caused by higher thermal flow in a rift environment rather than from fractional crystallization of a basaltic magma.