Microstructural features of ophiolitic chromitites in the Kraka massif, Southern Urals. I. Banded disseminated ores

Saveliev D. E., Shilovskykh V. V., Sergeeva S. N.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2020. V. 149. N 5. P. 59-81

https://doi.org/10.31857/S086960552005007X

Language: Russian

Abstract

The microstructure and composition of accessory chrome spinels and chromites from disseminated ores located in dunites near the boundary of mantle tectonites and rocks of the gabbroid complex (petrological paleo-Moho) were studied. Studies using backscattered electron diffraction (EBSD) have revealed microstructural heterogeneity of individuals, expressed in a domain (subgrain) structure, which is caused by plastic deformation and the associated processes of recrystallization. Using the study of accessory Cr-spinels as an example, it is shown that the formation and growth of new grains is possible synkinematically in the solid state due to the segregation of aluminum and chromium from rock-forming silicates. The observed microstructural features of chromitites indicate the interplay on the genesis of ores of two processes: 1) a decrease in the size of grains by glide and dynamic recrystallization, and 2) the growth of recrystallized grains and their aggregation (coalescence).

Keywords: chromitite, ophiolite, chromian spinel, plastic deformation, recrystallization, ultramafic rocks, Kraka, Southern Urals