Abstract
We discussed the chemical compositions of rhyolites from three distinct tectonic settings: the continental rift from Ethiopia; the early Miocene continental arc of Japan; and the Izu oceanic island arc. The comparison revealed distinct chemical differences between continental rift and oceanic island arc, but rhyolites from Miocene continental arc heralding the Japan Sea opening resemble those from Ethiopia except for some subduction-zone signatures. This implies that fractional crystallization processes were dominant in the rift-related rhyolites both from continental rift and continental arc regardless of the nature of underlying crust, whereas the oceanic island arc rhyolites may form through partial melting of young, mafic crust.
