Spatial and volumetric distribution of Quaternary volcanoes and growth rate of the Izu-Bonin Arc A trial for the volume estimation by bathymetry -

The Izu-Bonin Arc (IBA), one of an oceanic island arc that was formed by the subduction of the Pacific Plate under the Philippine Sea Plate, which lies south of Japanese Islands from Izu Peninsula down to Iwo-jima island connecting to the Mariana arc. The IBA forms an arcuate structure with its length of almost 1200 km and width of maximum 400 km in the northern segment and is grown up by the magmatic accretion due to the subduction of Pacific and North New Guinea Plates since Eocene Time. The IBA is not a simple and a single arc and is morphologically divided into three segments, North, Central and South, respectively by two major tectonic lines, Aogashima Tectonic Line (ATL) and Sofugan Tectonic Line (STL) based on various kind of geophysical parameters. We report here volcano spacing and volume of volcanic materials of the Quaternary volcanoes (2Ma >) of the IBA based on a new and a high resolution bathymetric map. The volcano spacing along the volcanic front of the IBA has a paired interval in the North Segment and a short regular interval at the northern part and a long interval at the southern part of the South Segment. The Central Segment has no regular spacing. The estimated volume of the volcanic materials has maximum peak on the volcanic front and decreases toward backarc region. The regular spacing in the Southern Segment reflects a little reaction between crust and melts which rise from the upper mantle by a kind of Rayleigh-Taylor Instability. However, melts react with thick crust causes bimodal and caldera forming volcanism both in Central and North segments. The spacing and volume in relation to the other geophysical parameters demonstrate that the IBA has the different evolving stages, from south to north due to the different duration of magma formation that had been caused by partial melting of the mantle wedge mantle by the addition of fluids from the subducting Pacific and North New Guinea Plates since the Eocene time. The growth rate of IBM is higher than that of ordinary island arc but one order lower than that of LIPs such as Ontong java Plateau.