Metamorphic mineral reactions and mineral paragenesis in the rocks of the Meyeri tectonic zone (the south-eastern part of the Fennoscandian shield, Russia)

Abstract

Mineral reactions were studied in metamorphic rocks from the Meyeri tectonic zone, and the P–T path of the development of this structure was calculated. According to the P–T path, the Proterozoic granulite complex of the Svecofennian Belt was thrust onto low-temperature rocks of the Archean Karelian Craton’s margin. Relict staurolite and other minerals preserved as inclusions in the garnet porphyroblasts made it possible to identify P–T parameters of the pre-peak stage of metamorphism using the compositions of the relict minerals. The temperature on the prograde trend of metamorphism was 500–600°C at a pressure of about 5 kbar. The peak metamorphic conditions of the Meyeri tectonic zone are estimated at T 700°C and P ~ 7 kbar. The post-peak stage began with a decompressional P–T path at the aforementioned temperatures, with a change from granulite hypersthene-containing paragenesis to lower-temperature amphibole-containing ones. The subsequent metamorphic retrogression was characterized by the development of numerous hydrous minerals as a result of the activation of fluids in the shear zone. The P–T path of the tectonic zone is clockwise and reflects the exhumation of the Svecofennian granulite complex during the orogenic events.