Causes, Geodynamic Factors and Models of Metamorphism

This chapter considers numerical model-based relationships between metamorphism and geodynamics, discusses tectonomagmatic causes and controls of metamorphism, and makes attempt to link the geological types of metamorphism to the specific Р-Т conditions and Р-Т-t paths. Three categories of metamorphism are distinguished based on the magnitude of the heat flux: (1) metamorphism induced by a thermal gradient close to the average continental values (metamorphism associated with crustal subsidence, in depressions during continental rifting, metamorphism caused by tectonic stacking in orogeny, and metamorphism associated with Archean crust formation), (2) by a higher thermal gradient caused by the supply of additional heat by magmatic intrusions (contact metamorphism, medium-pressure zonal metamorphism) and diapirism, (3) by a lower thermal gradient during the collision of lithospheric plates and crustal blocks (metamorphism associated with overthrusting, underthrusting and subduction). Different types of metamorphism are manifested in different geodynamic regimes over different time scales and can be correlated with a specific combination of metamorphic facies. Interpretation of geodynamic and magmatic causes of different types of metamorphism using thermomechanical numerical models accounting for variable rates and mechanisms of subsidence and exhumation can be used to solve many geodynamical problems. Analysis of the problem reveals that metamorphism is a consequence and an indicator of geodynamics.