小笠原海嶺海溝側斜面および母島海山から採取された MORB 様玄武岩の多様性 ─伊豆・小笠原弧前弧域のテクトニクスの検討─

摘要: Geochemical compositions of the mid-ocean ridge basalt (MORB)-like basalts dredged from trench slope Ogasawara Ridge and Hahajima Seamount, southern Izu-Bonin fore arc are determined to obtain constraints on tectonic evolution in arc. The sample has a distinct enriched (E)-MORB chemistry unlike any other rocks previously sampled is moderate TiO2, low Zr/Nb, Ba light rare-earth elements. This could represent trapped remnant Philippine Sea plate which was built. On hand, two geochemical groups can be identified within Seamount basalts: Low-Ti type High-Ti basalts. characterized by depleted high-field strength (HFS) elements, lower 143Nd/144Nd ratio high Zr/Nb compared with Trace element isotopic similar normal (N)-MORB West Basin. In contrast, show an overall Jurassic Pacific N-MORB signature, marked HFS available MORB-like data that occur western side ones eastern seamount. signatures occurrences types suggest might compose uplifted ophiolitic massif Basin accreted piece subducting Plate, have been caused collision subduction Plateau Plate.