Thermodynamic conditions of granitization and metamorphism of rocks in the northwestern part of the Ukrainian shield

Abstract

The article examines the RT conditions of the formation of granites of the Sheremetyevo and Zhytomyr complexes and the metamorphism of rocks of the Teteriv series of the Volyn megablock of the Ukrainian Shield, the role of fluids in granitization. According to thermodynamic modeling, the appearance of granites is a link in the redistribution of heat and matter in the plume process. This proves the analysis of all known geological and petrological data. During the accumulation of the primary volcanogenic-sedimentary stratum, magmatic melts formed in the mantle’s melting centers located at different depths appeared many times. The formation of the melting layer in the crust is caused by conductive heating caused by its sublayering by ultrabasic melts. Temperatures of the melting point at a depth of 15 km exceed 650 °C. An increase in the gradient above it from 20 to 35 °C/km causes metamorphism, and the influx of melts and solutions through deformation zones ¾ metasomatic transformations and the formation of migmatites. Where the upper part of the thermal asthenosphere is brought to the surface, you can see unmoved granites. At the intersection of several permeable zones (faults), granite massifs are formed, in which quartz-feldspar rocks crystallize. It is shown that the modern surface was on the border of metamorphosed rocks and the melting center in the Proterozoic time. Such a location does not contradict the existence of Archean rocks at greater depths — the level of thermal asthenosphere that produces granites.