Abstract

Recent geological and geophysical surveys in the Izu-Bonin-Mariana forearc have revealed the occurrence on the seafloor of oceanic crust generated in the initial stages of subduction and the earliest stage of island arc formation. The earliest magmatism after subduction initiation generated forearc basalts, and subsequently, boninitic and tholeiitic to calc-alkaline lavas were produced. Collectively, these rocks make up the extrusive sequence of the Izu-Bonin-Mariana forearc oceanic crust. This volcanic stratigraphy and its time-progressive development are analogous to those documented from many suprasubduction zone ophiolites. Most suprasubduction zone ophiolites may be on-land fragments of forearc oceanic crust, produced during the initiation of subduction and the early stages of island arc development.

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