Upper Mantle beneath Oceanic Island Arcs

点击翻译按钮获取中文摘要

The aim of this study was to image the uppermantle heterogeneity beneath an oceanic island arc system using ocean bottom seismographic recordings of teleseismic events by conventional instrumants and by newly developed long-period long-term instrument, amd to geologically interpret the results. We have imaged the low-Q zone above the subducting slab in the Izu-Ogasawara src system and a deep aseismic subducting plate beneath the Solomons arc system using conventional instrumants. The subducting aseismic slab was detected by using teleseismic P-wave traveltime relativeresidual patterns. However, the predominant frequencies of 1 Hz or less are beyond the useful range of conventional OBS(ocean bottom seismograph), so that we developed a new OBS equipped with 1-Hz sensor and 4 GB data capacity for about 3-month recording. We have not yet acquired data with this system yet.The Izu-Ogasawara oceanic arc crust was interpreted to have been produced in an early stage of subduction when relatively hot environement existed. This environment produced Boninites with ample water content and it is interpreted that the re-melting of the lower crust formed the granitic crust.