Petrology, geothermobarometry and geochemistry of granulite facies wall rocks and hosting gneiss of gemstone deposits from the Mogok area (Myanmar)

•PT-estimates were accomplished for the formation of marble-hosted ruby-spinel-deposits in the Mogok area of the Mogok Metamorphic Belt (MMB) of Myanmar. Application of conventional thermobarometry on host rocks of the deposit yields granulite facies conditions of 756–792 °C at 7.4–7.6 kbar. These PT-conditions are reproduced by Theriak-Domino modelling within the error of both methods at water activities of 0.34–0.4. Alkaline, strongly SiO2-undersaturated metadykes cut through the marble deposits. These unique rocks, which now form garnet-nepheline gneisses and clinopyroxene-clinoamphibole gneisses, also experienced high-grade metamorphic conditions. Their protoliths are subduction-related magmatic rocks, which intruded the marble sequences.