MODELLING HEAT GENERATION DURING FRICTION AND VISCOPLASTIC DEFORMATION BASED ON THE EXAMPLE OF THE YENISEI SHEAR ZONE (EASTERN SIBERIA)

Abstract

Deviations of the РТ parameters from the background values, corresponding to the lithostatic pressure and the standard geotherm characteristic of the neighboring crustal blocks of the Yenisei Ridge, were recorded by geothermobarometry in the zones of dislocation metamorphism of the Yenisei regional shear zone (Eastern Siberia). To explain the reason for large deviations from metamorphic conditions for shear and collision, we worked out 3D and 2D thermomechanical numerical models. The paper presents two- and three-dimensional models of dissipative heating during friction and visco-plastic deformations. The modelling results are compared with geological observations on the metamorphic grade and the scale of deformations of the Yenisei regional shear zone. A detailed consideration is being given to the ratio of heat released during friction at the contact of shear fault blocks, or during viscous deformations of the rheologically layered zone of tectonic flow and blastomylonitization. Estimates of the magnitude of dissipative heating are obtained for typical parameters of shear zones. The model of viscous deformation of a shear zone of finite width, taking into account the rheological layering of the crust, predicts dissipative heating by 200–310 °C at strain rates of 2–4 cm/year. The model of obduction of the tectonic plate with a thrusting velocity of 5 cm/year yields estimates of frictional heating of rocks at the contact of blocks no higher than 130–190 °C. The characteristic time period of the stationary dissipative regime formation is 6–8 million years. Dissipative heating could be a heat source for the metamorphic complexes of the Yenisei regional shear zone, though melting conditions of metapelite were not attained.