Review Article: Recent Marine Geological Research in the Mariana and Izu-Bonin Island Arcs

Over the last decade models of the structure, composition, and evolutionary processes of the Mariana and lzu-Bonin island arc systems of the western Pacific have been changed profoundly by an interdisciplinary and multinational approach to studying the details of these regions. The standard marine geological studies have been superseded by detailed sea-floor mapping, sea-floor observations using submersibles, and deep-ocean drilling efforts. The increased level of effort is the result of discoveries of new geological phenomena in these regions and the desire to approach the study of ancient convergent margin terrains exposed on land in the light of the resultant insights. The new discoveries include active eruption of serpentine muds forming large volcano-like seamounts in the Mariana forearc, recent protrusion of serpentinite debris flows from faultdissected horsts of metamorphosed supra-subduction zone mantle also in the Mariana forearc, similar ancient seamounts in the Izu-Bonin forearc region, evidence of recent forearc rifting, petrogenetically complex arc volcanoes situated within the backarc basin setting in both the Mariana and lzu-Bonin systems, the occurrence in close proximity to one another of magmas generated from different sources (the deep arc source and the shallower backarc basin basalt source) in neovolcanic zones of the incipient rifting portions of the Mariana and Izu-Bonin backarc rifts, and a variety of unique hydrothermal systems and fauna associated both with the arc volcanoes and with the active backarc spreading centers