NEW EVIDENCE OF ULTRAHIGH-PRESSURE METAMORPHISM IN THE MICA SCHISTS OF THE KULET AREA OF THE KOKCHETAV MASSIF (Northern Kazakhstan) Available to Purchase

Coesite was found for the first time in the garnet-mica schist of the Kulet area of the Kokchetav Massif. This fact indicates that the upper eclogite-bearing unit of the Kokchetav Massif was metamorphosed at pressures higher than 26 kbar. The estimated equilibrium temperatures for eclogites and garnet-amphibole-zoisitic and garnet-kyanite-biotite-amphibolic rocks show that the temperature of the high-pressure stage of metamorphism did not exceed 650 °C. Taking into account that the metamorphic rocks of the lower and upper tectonic units are coeval, the authors conclude that the Zerenda series is a tectonic mixture of fragments of the thinned continental crust of passive margin, submerged to different depths in the Lower Cambrian and rapidly (less than for a million years at the first stage) transported to the level corresponding to the amphibolite facies of metamorphism. The evidence is finding of kinetically unstable coesite in rocks differing in composition and grade of metamorphism.