Plastically deformed ultramafites of the Ergaksky chromite-bearing massif (Western Sayan)

Abstract

Dunites and harzburgites of Ergaksky massif constantly show signs of plastic deformation of olivine and enstatite as inhomogeneous extinction, bands of plastic fracture and sintectonic recrystallization. At level of the upper mantle dunites and harzburgites have undergone plastic deformation by translational sliding in olivine at high temperature and low speed. As a result, ultramafic with medium-grained, meso-granular texture formed. In the process of movement in the Earth’s crust plastic deformation occurs mostly as sintectonic recrystallization at subordinate role of translational sliding in conditions of decreasing temperatures and growing speed of plastic flow. This has contributed to the formation of porphyroclastic textures, while translational sliding promoted the distortion of crystal structure and the emergence of non-homogeneous extinction and bands of plastic fracture. Olivinites appeared as a result of secondary recrystallization of annealing under influence of high-temperature fluids on ultramafites.