Geodynamic factors of metamorphism and their modeling: Review and analysisof the problem

Deep geodynamic (tectonic and magmatic) activity disturbs matter and temper ature balance established previously in the Earth's crust; this results in metamorphism of the rocks. Five types of metamorphism can be recognized: co ntact, in low-pressure high-temperature belts, burial (subsidence), Archean , and collisional. These types are different in thermodynamic conditions, p aleogeothermal gradients, and metamorphism duration. They are usually assoc iated with each other. These associations are not casual and reflect certai n tectonic regularities in the crust evolution. Magmatic intrusions are con sidered the most important elements of an additional heat supply into the E arth's crust. In the absence of attendant magmatism, rock temperatures duri ng the burial metamorphism in the Phanerozoic usually did not exceed those typical of prehnite-pumpellyite subfacies/facies, and, rarely, greenschist facies. The collisional metamorphism caused by the subduction or superimpos ed load manifested itself at nonestablished thermal equilibrium owing to th e rapid setting and subsequent rapid exhumation of crustal blacks and erosi on. At present, determination of P-T-t-trends without invoking supplementar y information can be used only for approximate evaluation of tectonic situa tions and elucidation of the types (causes) of metamorphism.