Thermo-chemical evolution of mantle wedge during the incipient stage of the Izu-Ogasawara-Mariana subduction zone

Abstract

We present the genetic conditions of the Eocene magmas from the Ogasawara (Bonin) Ridge and discuss the thermo-chemical structure of the mantle wedge beneath the Ogasawara region during the incipient stages of the IBM arc. After the FAB (forearc basalt) activity, depleted harzburgite upwelled from deeper asthenosphere to <1 GPa, suffering flux melting to generate the high-Si boninite magma (48-46 Ma). By 45 Ma, asthenosphere began circulating in the wedge. As a result, magma composition changed from high-Si boninite through low-Si boninite to arc tholeiite and calc-alkaline magmas.