R5: Extraterrestrial materials

[R5-02] Crystallographic orientation analysis of olivine in dunitic achondrites: Magmatic crystallization and deformation in protoplanets

*Takashi Mikouchi¹, Atsushi Takenouchi², Akira Yamaguchi³, Masahiro Yasutake⁴, Anthony J. Irving⁵ (1. Univ. of Tokyo, 2. Kyoto Univ., 3. NIPR, 4. JASRI, 5. Univ. of Washington)

Keywords:Dunitic achondrite, Olivine, Crystallographic preferred orientation (CPO), Electron back-scatter diffraction (EBSD)

We analyzed olivine CPO of 11 brachinites and 3 ungrouped dunitic achondrites using EBSD. Nearly half of the samples analyzed exhibited olivine CPO either on b, c, b+c axes, suggesting diverse formation mechanism of dunitic rocks in protoplanets. It is known rheological deformation can concentrate olivine b axis. NWA 6077 ungrouped achondrite might have formed by this process in the interior of a protoplanet because its geochemistry suggests a residual origin after chondritic partial melting.