METAMORPHIC TRANSFORMATIONS OF ROCKS IN THE CENTRAL PART OF THE PRIMORSKY FAULT. WESTERN BAIKALIA

Abstract

In this paper we compare metamorphic transformations in acid and mafic rocks in a zone of intense tectonic movements. The object of study is the exhumed part of damage zone of Primorsky fault – main collision suture, which connects the Siberian Craton and the Olkhon Terrane. The studied area is located near the Khorga River. Collected metamorphic rock samples are represented by both acid (plagiogranitegneiss) and mafic (amphibole-biotite plagiogneisses) rocks. The samples present two different parent rocks contacting each other but differ in chemical composition. The formation of identical metamorphic minerals belonging to the groups of garnet and epidote is noted in both types of rocks. Mineral formation was associated with high-pressure regional metamorphism and possibly with later collision. Studying chemical composition of rock-forming minerals has allowed to determine the P-T condition of metamorphism in these rocks via the method of multimineral thermobarometry. It was established that conditions of early metamorphism retain in amphibole-biotite plagiogneiss. Early metamorphism is characterized by high-pressure amphibolite facies of medium temperature next to eclogite facies. In plagiogranitegneisses were found conditions of later metamorphism that formed rocks at the same pressure but at a lower temperature in the paragonite-kyanite-zoisite subfacies of the eclogite facies next to the greenschist facies. Minerals formed in the early metamorphism are poorly preserved.