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Russian Geology and Geophysics

2001 year, number 3

SILICA-ALKALINE METASOMATISM AND GRANITOID MAGMATISM IN THE MAJOR SAYAN FAULT ZONE

V. B. Savel'eva
Keywords: Metamorphism, metasomatism, granites, East Siberia, Major Sayan Fault
Pages: 409-426

Abstract

We have studied endogenic processes in the southeastern part of the Major Sayan Fault zone at the boundary of the Siberian Platform and Sayan-Baikal folded region. This is a zone of repeated occurrence of deformations, silica-alkaline metasomatism, and granite formation, which proceeded under moderate pressures no higher than 5.5-6 kbar. Some silica-alkaline metasomatites replacing each other with time include products of high-temperature granitization and quartz-albite-microcline (±magnetite, biotite, riebeckite, aegerine-augite) metasomatites and albitites. Early granitization took place under normal alkalinity with participation of rather reduced fluids, and postmagmatic fluid systems are carbon-enriched. Quartz-albite-microcline metasomatites formed at elevated alkalinity and F and f(O2) activity. There is a clear difference between granitoids of the early tectonometamorphic cycles and the latest granites of the stage of marginal-suture activity, which are characterized by elevated concentrations of Nb, Y, Be, Sn, Pb, Th, and U.