METAMORPHIC EVOLUTION OF HIGH-ALUMINA METAPELITES NEAR THE PANIMBA OVERTHRUST (YENISEI RANGE): MINERAL ASSOCIATIONS, PT-CONDITIONS, AND TECTONIC MODEL

Abstract

An attempt is made to study pressure-heterogeneous high-alumina metapelites of andalusite-sillimanite and kyanite-sillimanite fades series for clearing up the PT-evolution of metamorphism related to thrusting tectonics. As a result of detailed research with the use of geothennobarometry and THERMOCALC-based analysis of mineral equilibria, PT-conditions were estimated and PT-paths of evolution were plotted for moderate and elevated pressures. The obtained data on the change of PT-conditions of metamorphism suggest that the kyanite substitution for andalusite and other mineral transformations were caused by an increase in pressure under low geothermal gradient, described by a model for tectonic thickening of the crust in the zone of the Panimba overthrust. The absence of a marked increase in temperature on thrusting is explained by specific behavior of stationary geotherms for different kinds of rocks that have different thermophysical and heat-producing properties.