Dynamic Component of Pressure during Metamorphism in a Thrust Zone

Elevated pressure (overpressure) was revealed in the southeastern fragment of the Raahe–Ladoga suture zone in Russia, within the Meyeri tectonic zone. It was caused by structural metamorphic transformations of rocks during collisional interaction of allochthonous and autochthonous blocks. It was supposed that tectonic interaction between the rigid crustal block of the Archean basement of the Karelian craton (autochthon) and the Proterozoic granulite block of the Svecofennian belt (allochthon) provided conditions for the formation of superlithostatic pressure anomalies. Mineral geobarometry and numerical thermomechanical modeling indicated pressures up to 9–11 kbar at a lithostatic pressure of 4–6 kbar. Based on the obtained results, it was argued that the nature of the local superlithostatic pressure (up to 7–9 kbar) established by mineral geobarometry and numerical thermomechanical modeling can be explained by tectonic interaction of blocks with heterogeneous physical and mechanical properties rather than by the errors of the applied mineral geobarometry tools.