PETROGENESIS OF S-TYPE GRANITOID MAGMATISM ON THE MARGIN OF THE TUVA-MONGOLIAN MASSIF (WESTERN SANGILEN, SOUTHEASTERN TUVA): SETTINGS, AGE, AND FORMATION STAGES

This study integrates the isotope-geochronological (zircon U-Pb dating), petrogeochemical and structural-petrological data, as well as the data on garnet composition and fluid inclusions in leucogranite quartz, to characterize S-type granitoid magmatism on the margin of the Tuva-Mongolian massif (Western Sangilen, Southeastern Tuva). The S-type granites form small garnet-, garnet-cordierite-bearing granite and leucogranite vein bodies. Their formation occurred during two stages of tectono-magmatic activity. The first stage (517±3 Ma) relates to the initiation of a tectonic zone and is characterized by migmatization and garnet-cordierite granite formation at T=730–790 °C and P=5.3 kbar. The second stage (490–483 Ma) of local extension involved repeated heating to ~680 °C, which led to rheomorphism of the Early Cambrian migmatite-granites. The leucogranite veins (480±6 Ma) represent neosomes of migmatites, formed at T=760–830 °C via low-degree melting (