PRESSURE, TEMPERATURE AND TIME CONSTRAINTS ON HIMALAYAN METAMORPHISM FROM EASTERN KASHMIR AND WESTERN ZANSKAR

Himalayan metamorphism in the Kashmir and Zanskar sector of the High Himalaya resulted from thrust- and fold-related crustal thickening within the Indian plate following the collision of India and Asia at c.50 Ma. Peak metamorphism, based on 40Ar/ 39Ar hornblende ages, occurred pre-30.7 ± 2.0 Ma at the top of the slab, and in the middle of the slab was pre-22 ± 1.0 Ma, probably 25-28 Ma. The lower structural levels in Zanskar record peak metamorphic conditions around 700-750°C and 8 kbar, reflecting depths of burial of 28-30 km. A new younger schistosity, which is not present in the higher structural levels, was developed under kyanite grade conditions. The regional distribution of high temperatures recorded by thermobarometry does not support the concept of additional heat being supplied by fractional heating along the Main Central thrust or magmatic heat resulting from anatexis. -from Author