Metamorphic zoning of the Tongulak mountain range, Altai; mathematical modeling

The Tongulak metamorphic complex lies in southeastern Gorny Altai, in the Bashkaus-Kubadru interfluve. Four zones have been recognized in its composition: chloritic (on the periphery), cordieritic, sillimanitic, and staurolite-free. The metamorphic zoning is symmetrical, with a general width of 13-15 km. Conditions of metamorphism are estimated to have been 500-700 degrees C and 3.5-5 kbar. To understand the mechanism of formation of metamorphic zoning from geological and mineralogical data, a two-dimensional mathematical model has been developed simulating the thermal action of a deep-seated magmatic body upon the host rocks. The simulation was carried out in a flat region 30 by 40 km in size corresponding to the vertical section of the Earth's crust. The structure and the observed distribution of temperatures within the Tongulak complex are best described by the model for heat source in the form of a shallow magmatic body with the wedge-like roof whose side faces dip at 45 degrees to the horizon.