THERMOMECHANICAL MODEL OF MELTING DURING HEAT DISSIPATION AS A POSSIBLE FORMATION MECHANISM FOR THE POSOLNAYA MASSIF OF GRANITOIDS OF THE SOUTH YENISEI RIDGE

The paper presents the results of 3D numerical thermomechanical modeling of the formation mechanism for the Posolnaya massif of granitoids in the Posolnaya-Kuzeeva tectonic zone of the South Yenisei Ridge. A mathematical numerical model has been proposed for the massif formation due to heat dissipation during shear deformations in the Posolnaya-Kuzeeva tectonic zone. The modeling was carried out in a 3D formulation by solving the Navier-Stokes equations using the ANSYS Fluent software package. Versions of the structural model of the Posolnaya-Kuzeeva tectonic zone have been considered in relation to the width of an active horizontal shear zone and composition of the crustal rocks (metamorphic protolith) from the tectonic zone. The model of dissipative heating and melting in a 20 km-wide shear zone reproduces the actually observed shape of the Posolnaya massif. The dependence between the height of magma ascent and the rheological properties of crustal rocks has been determined. It has been shown that dissipative heat release during the deformation of rocks, exhibiting the rheological properties of wet granite, results in melting and diapiric ascent of felsic magma from the base of the granite-gneiss layer (45 km) to a depth of 9–11 km. In a crustal model described by the rheological properties of felsic granulite, melting occurs "in situ" in a larger volume, but without further ascent of the magmatic mass. Shear rate is shown to be a key parameter for the efficiency of dissipative heating. A threshold shear rate for the most efficient melting and magmatism under dissipative conditions has been estimated at 4 cm/yr (and higher).