Geochemistry of Plastic Deformed Olivine from Ophiolite Peridotites and Dunites of Kraka Massifs (Southern Urals).

Rock-forming olivines from mantle ultramafic rocks of Kraka massifs have been studied by several methods, including microstructural analysis, scanning electron microscopy, and LA-ICP-MS. In all studied peridotite and dunite samples, olivine demonstrates a distinct crystallographic preferred orientation (CPO) due to the rock formation under high-temperature plastic flow conditions. Olivine from wallrock dunites at podiform chromitite deposits is substantially depleted in Al, as compared to olivine from peridotites and thin dunite veinlets in the dunite–peridotite complex. Olivine aggregates from primary dunites contain numerous newly formed high-Al Cr-spinel segregations as thin needles and rods, turning into morphologically more complicated forms as they become larger. They are interpreted as resulting from such processes as segregation of trace elements, coalescence, and spheroidization of newly formed Cr-spinel grains induced by plastic deformation of olivine. [ABSTRACT FROM AUTHOR]