Abstract

• A new unit composed of felsic and mafic granulitic rocks are exposed in the study area. Granulite (Latin granulum, a little grain) is a name first introduced by petrographers. Such a rock is characterized by a mineral assemblage that was developed under high-grade metamorphic conditions. Granulites were observed around Mogok and Momeik area. The writer will try to draw some comparisons between felsic and mafic granulite of the study area with reference to the theoretical definitions by some authors and websites. The study area is situated in the remote area between Mogok Township, Mandalay Region and Momeik Township, Shan State (North), on either side of Mogok-Momeik motor road. The study area, which is a segment of the Mogok Metamorphic Belt, is mainly composed of metamorphic rocks and granitic and syenitic intrusions. Taking the metamorphic rock units of the study area into consideration, granulite rock is fairly exposed and it is associated with both sillimanite-garnet-biotite gneiss and interbedded with marble and calc-silicate rocks. Granulite unit is intruded by syenitic and granitic rock. Granulite can be subdivided into two distinct units based on pyroxene percentage (< and > 30); felsic granulite (<30) (sapphirine-hypersthene-garnet-biotite granulite) and mafic granulite (>30) (pyroxene granulite), respectively. Petrochemically, sillimanite-garnet-biotite gneisses in the study area have reached granulite facies (730-810 ºC 6.5-9.3 kbar), characterized by the mineral assemblages and petrochemical results from EPMA and XRF. The P-T condition of granulite rocks in the study area should probably be the same as and/ or greater than the P-T condition of the high-grade gneiss of the study area, according to the mineral assemblages: orthopyroxene alkali feldspar biotite chlorite plagioclase garnet quartz rutile sillimanite sapphirine opaque hercynite sillimanite sericite zircon ilmenite of felsic granulite and mineral assemblages clinopyroxene biotite plagioclase (andesine) alkali feldspar quartz perthite orthopyroxene sphene opaque chalcedony antigorite of mafic granulite.