Геохимия летучих компонентов в процессах метаморфизма и гранитизации. Часть 2. Гранитизированные породы Ольхонского комплекса (Западное Прибайкальестатья
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Аннотация:The distribution of H-2, CH4, CO, CO2, H2O, F, and B was inspected in cross sections of migmatized rocks (gneiss-migmatite-granite profiles) in the granulite and amphibolite metamorphic zones. These two types of metamorphism in the Ol'khon Complex were determined to have been associated with two distinct styles of migmatization. The early granulite metamorphism under a total pressure of 8-9 kbar, at temperatures above 800degreesC, high carbon dioxide partial pressures, and an insignificant decompression was accompanied by plagiomigmatization, with the X-CO2 and Na activity increasing by the end of this process. The second stage of amphibolite metamorphism proceeded at a decreasing temperature and pressure, under the effect of H-2-rich fluid. Its oxidation increased the activities of H2O, K2O, and SiO2 as the mole fractions of other gases decreased and resulted in potassium feldspar-rich migmatites. Both migmatization styles ended with the local melting of plagioclase and potassium-feldspar granites as the sums of volatile components decreased. Different amounts of fluid components in distinct parts of the metamorphic complex, with identical tendencies of the migmatization process, testify to the limited inflow of volatile components within individual tectonic slabs and confirm the earlier conclusion about the local development of melting chambers and the strong dependence of the composition of migmatization products (particularly their trace-element chemistry) on the composition of the migmatized. protolithic rocks.