GEODYNAMIC FACTORS OF METAMORPHISM AND THEIR MODELING: REVIEW AND ANALYSIS OF THE PROBLEM

Abstract

Deep geodynamic (tectonic and magmatic) activity disturbs matter and temperature balance established previously in the Earth's crust; this results in metamorphism of the rocks. Five types of metamorphism can be recognized: contact, in low-pressure high-temperature belts, burial (subsidence), Archean, and collisional. These types are different in thermodynamic conditions, paleogeothermal gradients, and metamorphism duration. They are usually associated with each other. These associations are not casual and reflect certain tectonic regularities in the crust evolution. Magmatic intrusions are considered the most important elements of an additional heat supply into the Earth's crust. In the absence of attendant magmatism, rock temperatures during 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 superimposed load manifested itself at nonestablished thermal equilibrium owing to the rapid setting and subsequent rapid exhumation of crustal blocks and erosion. At present, determination of P-T-t-trends without invoking supplementary information can be used only for approximate evaluation of tectonic situations and elucidation of the types (causes) of metamorphism.