Petrostructural analysis of olivine in ultramafic and mafic different formation types оf the Kansky blockof East Sayan

On the territory оf the Kansky block among metamorphosed sedimentary and volcanic rocks numerous ultramafic and maficultramaficbodies were found, which were classified into four formational types and grouped in four sets: restite - idarsky duniteharzburgite;and magmatic - kingashsky dunite-vehrlite-picrite, talazhinsky plagiodunite-troctolite-gabbro-anorthosite and kulibinskyperidotite-pyroxenite-gabbro. The purpose of this study was to identify the petrostructural features of olivine in the ultramafic and maficrocks of different formation types. The proposed petrostructural research allowed reconstructing the thermodynamic conditions ofcrystallization of olivine and its subsequent deformation both in magmatic and restite formations. The analysis of petrostructuralpatterns of olivines in magmatic ultramafic and mafic rocks of talazhinsky, kulibinsky and kingashsky complexes suggests that theyformed as a result of magmatic crystallization of melt and subsequent imposed plastic deformations. The formation of olivinepetrostructure in magmatic ultramafites and mafites could occur in the conditions of falling temperature, slow speed and low stressunder the structural control of external stress field in the situation of laminar flow of the magmatic fluids in the magmatic camera, not insteady-state conditions, under which isotropic petrostructural patterns in gravitational sedimentation of crystals are formed. Thefollowing imposed dynamic loads contributed to the complication of petrostructural patterns and plastic deformations of olivine. Thecharacter of petrostructural patterns of olivines in restite ultramafites of idarsky complex reflects the conditions of their plasticdeformations in the process of moves in the earths crust. Ultramafites of idarsky complex, according to the petrostructural analysis ofolivine, underwent metamorphic changes in the conditions of regional metamorphism in the temperature regime (500-850°С) and lowvoltage (1020 MPa) to form granoblastic structures. During subsequent deformation in the dynamically active areas they were subjectedto intensive plastic flow in the mode of preserving the temperature range (500-850°С) and increasing voltage (100-200 MPa) withincreasing the strain rate, which contributed to their intensive syn-tectonic recrystallization.

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