METAMORPHIC AND DEFORMATION TEMPERATURE TRENDS IN THE HIMALAYAN THRUST BELT IN EASTERNMOST BHUTAN: PRELIMINARY INSIGHTS FROM RSCM THERMOMETRY AND QUARTZ PETROFABRICS
Rocks 22 km below the MCT yield an RSCM temperature of ~190±30 °C and contain non-recrystallized quartz. Rocks between 21-17 km below the MCT yield opening angles that correspond to temperatures of ~350±50 °C and quartz recrystallization textures consistent with temperatures of ~350-450 °C. Between ~17-2 km below the MCT, RSCM temperatures range from ~470 to 570 °C, which overlap with quartz opening angle (~450-520 °C) and recrystallization texture (~450-550 °C) estimates. Between 2 km below and 5 km above the MCT, RSCM temperatures increase upward from ~470 °C to ~550-650 °C, and apparent quartz recrystallization temperatures increase upward from ~450-550 °C to ~550-750 °C. Between 5-10 km above the MCT, RSCM temperatures decrease upward from ~630-680 °C to ~500-550 °C, and apparent quartz recrystallization temperatures decrease from ~550-750 °C to ~450-550 °C.
In summary, temperatures increase sharply at 17 km below the MCT, then remain relatively constant between 17-2 km below the MCT. A trend of apparent inverted temperature is defined across the MCT zone, with the highest temperatures located 5 km above the MCT. An apparent upright temperature gradient is defined between 5-10 km above the MCT. Additional temperature data, fabric analyses, metamorphic pressures, and finite strain data will be collected to further define these preliminary trends.