Upper Riphean Age of Kyanite-Sillimanite Metamorphism in the Transangarian Yenisei Ridge: Evidence from ~(40)Ar/~(39)Ar Data

摘要

Medium-pressure metamorphism is locally typical for the Transangarian part of the Yenisei Ridge, near thrusts of the Tatar deep fault zone. As a result, progressive replacement of andalusite by kyanite and the formation of new mineral associations and deformation textures are registered. Among the general peculiarities of collision metamorphism are low thickness of zoned medium-pressure metamorphism (from 2.5 to 7 km) and gradual increase of total pressure with approach to thrusts from 4.5-5 to 6.5-8 kbar at a poor development of thermal zonation that provides evidence for very low geothermal gradient (up to 12℃/km).