Physicochemical conditions of the formation of the Larino granite-gneiss dome (South Ural)
The Larino granite-gneiss dome is located on the border of the Aramil-Sukhtelya and Magnitogorsk megazones and is a two-headed anticlinal structure, the nuclear parts of which are composed of granitoids of the Pervomai and Larino massifs, and their framing - apovolcanic amphibolites, garnet-mica-tins, garnet-amphislans siliceous-carbonaceous schists of the Bulatovo Series (S1-D1bl). A series of concentric high-gradient zones of metamorphism are observed from granitoids to shales. Mineral parageneses of the amphibolite facies at a distance of several kilometers are replaced by associations of epidote-amphibolite and greenschist facies.It has been proven that granitoids belong to the granite-migmatite formation, are close to trondhjemites of the inner parts of the continents (granites, leucogranites) and continental margins (gneisized, migmatized granitoids) and were formed in intraplate and collisional geodynamic settings.Crystallization of granites took place at temperatures of 780-840°С and a pressure of 2.1-3.7 kbar, plagiogranites - 880-940°С and 2.9-3.3 kbar, which corresponds to the abyssal depth zone (7-11 km). For granitoids formed in the process of metasomatic granitization (gneissized and migmatized rocks), formation temperatures are noticeably lower - 650-680°С, and the pressure is higher - 6.6-7.0 kbar (almandine amphibolite facies).