Granulite facies paragneisses from the middle segment of the Mogok metamorphic belt, central Myanmar

Abstract

The Mogok metamorphic belt in central Myanmar is composed mainly of high–temperature paragneisses, marbles, calc–silicate rocks, and granitoids. The garnet–biotite–plagioclase–sillimanite–quartz and garnet–cordierite–sillimanite–biotite–quartz assemblages and their partial systems suggest pressure–temperature (P–T) conditions of 0.60–0.79 GPa/800–860 °C and 0.65 GPa/820 °C, respectively, for the peak metamorphic stage, and 0.40 GPa/620 °C for the exhumation stage. Ti–in–biotite and Zr–in–rutile geothermometers also indicate metamorphic equilibrium under upper amphibolite– and granulite facies conditions. Comparison of these estimates with previously described P–T conditions suggests that (1) the metamorphic conditions of the Mogok metamorphic belt vary from the lower amphibolite– to granulite facies, (2) metamorphic grade seems to increase from east to west perpendicular to the north–trending extensional direction of the Mogok belt, (3) granulite facies rocks are widespread in the middle segment of the Mogok belt, and (4) the granulite facies rocks were locally re–equilibrated at lower amphibolite facies conditions during the exhumation.