DECIPHERING BASINAL RECORDS OF INTRAOCEANIC ARC EVOLUTION: CORE IS KEY

The history of intraoceanic magmatic arcs, from their birth to their demise, is recorded in the fragmental volcanic debris shed into associated marine basins. There are several potential sedimentary deposit-generating mechanisms in arc-proximal submarine apron to distal deep-marine settings: 1) primary ash falls; 2) volcanic-eruption-generated flows; 3) volcano-sector-collapse-generated flows; 4) seismic-shock-generated flows; 5) hurricane/typhoon-generated flows; 6) debris flows and slumps generated by fault movement; and 7) syndepositional magmatism. Larger-scale submarine deposit geometries and associated facies are related to the generating mechanisms: ash drape, submarine volcanic apron, submarine fan, channel fill, and slump to debris-flow sheets/blankets that taper away from the volcanic center. Another potential control on sediment input is eustasy, which determines the areal extent of arc edifice exposure and erosion. We illustrate some of the products of these processes using ocean drilling cores recovered in the Izu-Bonin system on Ocean Drilling Program Leg 126 and on Ocean Discovery Program Expedition 351 (Site U1438). In combination, these drilling expeditions recovered a nearly complete record of Izu-Bonin arc sedimentation including coeval Oligocene forearc/backarc successions and, at Site U1438, an Eocene sedimentary record extending back to arc inception. These cores offer unprecedented insight into intraoceanic arc evolution.