Dynamic Component of Pressure during Metamorphism in a Thrust Zone

In the southeastern fragment of the Raabe-Ladoga suture zone in Russia, within the Meyeri tectonic zone, increased pressures ("overpressure") were revealed, caused by structural-metamorphic transformations of rocks during collisional interaction of allochthonous and autochthonous blocks. It is assumed that tectonic interaction of the rigid crustal block of the Archean basement of the Karelian craton (autochthon) and the Proterozoic granulite block of the Svecofemian belt (allochthon) controls the conditions for the formation of superlithostatic pressure anomalies. Methods of mineral geobarometry and numerical thermomechanical modeling in the rocks of the thrust zone recorded pressures up to 9–11 kbar, while lithostatic pressure not exceeding 4–6 kbar. The obtained results allow us to consider that the nature of the local superlithostatic pressure up to 7–9 kbar, established by mineral geobarometers and numerical thermomechanical modeling, can be explained by the tectonic interaction of blocks with heterogeneous physical and mechanical properties, and not reflect the error of the applied mineral geobarometry instruments.