The Early Precambrian metamorphic events in Eastern Sarmatia

Four metamorphic events were identified in the Early Precambrian history of the Eastern Sarmatia. The oldest Mesoarchaean (?) ultrahigh temperature (UHT) metamorphism at 900-1000 °C and 10-12 kbar occurred in the Kursk and Azov domains. Although attempts to constrain accurately the age of metamorphism failed, they provided evidence for the existence of the early Mesoarchaean ultra-hot orogen in the central part of the Archaean core of the Eastern Sarmatia. The 2.82 Ga metamorphism, widespread within the Eastern Sarmatia, finished the formation of the ancient Mesoarchaean basement. The granulite facies metamorphism at ∼750 °C and ∼5 kbar is confined to zones composed of gneisses and migmatites, while the epidote-amphibolite and amphibolite facies metamorphism occurred within preserved fragments of greenstone belts. The Palaeoproterozoic low-pressure metamorphism occured at 2.07 Ga in all Palaeoproterozoic structures under P-T conditions ranging from 350 °C at 2 kbar to 750 °C at 5 kbar. The metamorphic event was caused by a collision between the Volga-Uralia segment and Sarmatia at ca. 2.1 Ga. The youngest high-T granulite metamorphism at 850 °C and 5.5 kbar (2.04 Ga) recorded in the Bryansk domain likely reflects a thermal effect related to magmatic event that preceeded the main episode of the Osnitsk-Mikashevichi volcano-plutonic belt formation at the active margin of Sarmatia at 1.96-2.00 Ga.