CONTRIBUTION OF SHEAR DEFORMATION TO ROCK METAMORPHISM

Abstract

Numerous independent observations contradict the hitherto accepted notions as to the contribution that shear-induced metamorphism makes to the overall metamorphic process. The authors attempt to review this, based primarily on data from high metamorphic gradient regions. One group of observations that the authors rely on consists of data on the geological structure of typical zones of high-gradient regional metamorphism. It is shown that chemical conversions and phase transitions in rocks take place under specific pressure and temperature conditions, whose evolution is governed by tectonic movements. In tectonic processes, the total pressure in the lithosphere is comprised of the lithostatic pressure and the pressure generated by the viscous flow of lithospheric matter. Correction for nonlithostatic pressure increment opens up a new approach to determining the conditions under which high-gradient metamorphic zones were generated.