Japan Geoscience Union Meeting 2019

Presentation information

[J] Poster

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

[S-CG54] Rheology, fracture and friction in Earth and planetary sciences

Tue. May 28, 2019 3:30 PM - 5:00 PM Poster Hall (International Exhibition Hall8, Makuhari Messe)

convener:Miki Tasaka(Shimane 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), Hidemi Ishibashi(Faculty of Science, Shizuoka University)

[SCG54-P08] Microstructural & petrological analysis of peridotite xenolith in Noyama-dake, Shimane prefecture ~ implication of plastic deformation during Japan sea opening

*Miki Tasaka1, Shunsuke Inagawa1 (1.Shimane University)

Keywords:peridotite xenolith, Japan sea opening

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

The microstructure of peridotites is classified into three types, including (1) coarse-grained equigranular texture (~ 1mm), (2) fine-grained texture (~50 um), and (3) large- and fine-grained fractured texture. Based on electron backscattered diffraction (EBSD) analysis, the olivine crystals in (1) coarse-grained equigranular texture and (2) fine-grained texture have a crystallographic preferred orientation (CPO), indicating plastic deformation with various stress condition. Straight cracks are observed in large olivine grains in (3) large- and fine-grained fractured texture. Basaltic melt and fine-grained olivine aggregates with CPO intrude in these cracks. These features indicate that large- and fine-grained fractured texture results from brittle-ductile deformation during volcanic eruption.

Based on electron probe micro analyzer (EPMA), (1) coarse-grained equigranular texture has origin of residual mantle, whereas (2) fine-grained texture and (3) large- and fine-grained fractured textures are originated from cumulus mantle. Two pyroxene geothermometer 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).