Early Eocene magmatism following subduction initiation along the Bonin forearc: An up-to-date model

Recent investigations of core samples taken from the Izu-Bonin-Mariana fore-arc region (IODP Expedition 352) have revealed a wealth of information on the effects of subduction initiation in what is now preserved in the western Pacific. Based on new glass analyses, we show that: primitive forearc basalt melts likely assimilated a large amount of altered oceanic crust prior to eruption, off-axis basalts in the same core are distinguished by separate trace element characteristics, low-Si boninite compositions are consistent with derivation from a forearc basalt residue fluxed by percolating slab melts, and high-Si boninites are formed from the most highly depleted mantle in the presence of multiple subducted components. When contextualized by studies published over the last 2 years, the entire magmatic history of the Bonin fore-arc region may be synthesized as one of progressive infiltration and melting of depleted mantle by compositionally variable slab components.