Paragenesis and petrogenesis of a corundum-bearing marble at Hunza /Kashmir/

摘要: A calcite-marble containing gem-quality ruby is exposed in the Hunza Valley, northwestern part of Karakoram mountains, Pakistan zone Kashmir. The marble forms concordant intercalations within sillimanite- and garnet-bearing biotite-plagioclase gneisses mica schists. metamorphic sequence cut by discordant aplite pegmatite dikes. following mineral assemblages are recognized marble: 1) Calcite+corundum+phlogopite±margarite±sheridanite±Al-rich pargasite±anorthite (An 96.7), 2) calcite+spinel±corundum+phlogopite+sheridanite. Microprobe analyses given for essential minerals including corundum (ruby) three different colour varieties spinel. On basis recent experimental data, especially system CaO - Al2O3 SiO2 H2O -CO2 (and related subsystems), we assume that, during regional metamorphism, temperatures about 600 – 620°C a water vapour pressure 6 kb were realized area. gas phase must have contained roughly 20 mole-% CO2. Thus total fluid may reached 7 kb. Presumably, increased northwest direction, perhaps up to 700°C. estimated P-T conditions consistent with geothermal gradient 25°C/km.