12:00 〜 14:00
[R8P-10] Deformation microstructures and slip systems developed in olivine from the Petit-spot peridotite xenoliths: Insights on deformation mechanisms and anisotropy of upper mantle
キーワード：petit-spot, olivine deformation, mantle deformation, seismic anisotropy
Petit-spot is small knoll (~1 km3 volume) occurring on the ocean floor and is considered to be formed as a result of plate flexure along outer rise. The presently studied peridotite xenoliths were obtained from petit-spot volcanic fields (Sites A and B) placed in the offshore of northern Japan during scientific cruises of YK20-14S and YK21-07S, using deep-submergence research vehicle Shinkai6500. The peridotite xenoliths are included in vesicular alkaline basalts. The peridotites are harzburgitic to lherzolitic in modal composition. The forsterite number (Mg/(Mg + Fe) atomic ratio × 100) of the olivine ranges from 91 to 92, and the pyroxenes are enstatite or diopside in composition. The olivines show minor reaction only in the boundaries with the host basalt, suggesting the preservation of pristine mantle microstructures. Additionally, the olivine grains show development of sub-grain boundaries, however distinct foliation and lineation are not prominently observed. Elucidating the deformation fabric of the olivine is a challenge as the individual xenoliths are unoriented and do not have distinct foliation or lineation. Hence to determine the active slip systems we have used Electron Backscatter Diffraction (EBSD) analysis to determine the slip system of individual sub-grain boundaries developed in each olivine grains for the samples and attempted to infer the overall slip system developed in the analyzed samples. We present these results and infer the possible deformation conditions for the peridotite xenoliths from the petit-spot volcanoes. Additionally, the results also provide us insights on the seismic anisotropy of the lithospheric mantle in the northwestern Pacific region.