Quantitative study of textures and micro- structures of olivine- rich achondrites as indication for cumulate formation and early solid-state deformation in asteroids.

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Based on our unpredicted finding of solid state plastic deformation during our work on diogenites (Tkalcec et al. 2013), which will have several far reaching consequences on the thermal history, chemical and structural equilibration in the early stages of asteroid and protoplanet formation, we propose to perform a comprehensive quantitative structural and textural study of a sub-type of unbreciated, ureilites showing a well defined crystal lattice orientation.A characterization and quantification of the micro and nano structural inventory of this rock type will be performed. This enables to unravel details of the thermal and structural evolution and the effective deformation mechanism. A combination of electron backscatter diffraction (EBSD) and large area transmission electron microscopic (TEM) will be applied in order to measure details of the crystallographic preferred orientation and relate them to texture forming processes like crystallization, compaction, shock effects and deformation mechanism. These processes are essential for the understanding of planetary differentiation, mantle mingling or mixing and initial cooling of asteroids and planetary embryos.Ureilites are ideal candidates for this attempt as they represent the second most common type of achondrites, resemble olivine-rich mantle rocks and the fast cooling from their initial conditions preserve most of the original fabric and microstructure.