JpGU-AGU Joint Meeting 2020

Presentation information

[J] Poster

S (Solid Earth Sciences ) » S-CG Complex & General

[S-CG69] Rheology, fracture and friction in Earth and planetary sciences

convener:Miki Tasaka(Shizuoka University), Osamu Kuwano(Japan Agency for Marine-Earth Science and Technology), Ichiko Shimizu(Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University), Shintaro Azuma(Department of Earth and Planetary Sciences, School of Science, Tokyo Institute of Technology)

[SCG69-P10] Microstructural analyses of peridotite xenoliths in Shimane prefecture ~ implications for plastic deformation during Japan Sea opening

*Miki Tasaka1, Hiroyuki Oma2, Shunsuke Inagawa2 (1.Shizuoka University, 2.Shimane University)

Keywords:ultramafic xenoliths, EBSD, Japan Sea opening

A number of Cenozoic ultramafic xenoliths are located on the southwest Japan arc. In this study, we conducted microstructural analyses using peridotite xenoliths in Noyama-dake and Kawashimo, Shimane prefecture. The microstructural results imply that these textures are formed by plastic deformation during Japan Sea opening (~15 Ma) with various stress conditions before volcanic eruption (~7 Ma).

The microstructure of peridotites is classified into 2 types, including (1) coarse-grained equigranular texture (~ 1mm), (2) large- and fine-grained combined texture. Based on electron backscattered diffraction (EBSD) analysis, the olivine crystals in (1) coarse-grained equigranular texture have a crystallographic preferred orientation (CPO) with (010)[100] slip systems, indicating plastic deformation during mantle flow. In (2) large- and fine-grained combined texture, large grains have kink band with slip direction (001)[100] or (100)[001]. Further nine-grained aggregates have similar CPOs indicating the fine grains are recrystallized by one large grain.

Based on electron probe micro analyzer (EPMA), both (1) coarse-grained equigranular texture and (2) large- and fine-grained combined texture have origin of residual mantle. Two pyroxene geothermometer (Wells, 1977) indicates that the rock has equilibrium temperature T ~ 1200C, resulting from high temperature at the pressure of spinel stability field (P ~ 1 to 2 GPa). Based on these results, we will discuss the deformation history of the ultramafic xenoliths.