LATE CENOZOIC-QUATERNARY THERMO-TECTONIC HISTORY OF HIGHER HIMALAYAN CRYSTALLINE (HHC) IN KISHTWAR-PADAR-ZANSKAR REGION, NW HIMALAYA - EVIDENCE FROM FISSION-TRACK AGES

Fission Track Fl ages of apatite and zircon from the Higher Himalayan Crystalline (HHC), SE - Jammu and Kashmir along Chenab-Suru-Doda river s and their tributaries provide constraints on the cooling (<250 degre es C) and exhumation history of these rocks. FT ages of apatite/zircon versus the topographic elevations of the host samples from different traverses provide linear relationships, indicating differential and se cular nature od exhumation in the Himalaya. The HHC belt is exhumed at a rate of about 0.27 mm/a during Middle to Late Miocene. However, reg ional exhumation rate near the base along the Main Central Thrust and in central parts of the HHC from FT apatite ages is faster up to 0.35 mm/a since Late Miocene. Exhumation has considerably slowed down to 0. 11 mm/a along its northern boundary and 0.02 mm/a along the Zanskar Sh earZone. No apparent faster exhumation is discernible either along thr ee MCT or the Zanskar ShearZone (ZSZ). On the other hand, three large fold structures namely the Suru Dome, the Chisoti Dome and the Kishtwa r antiformal window have indicated very young and fast exhumation of 0 .33 mm/a, 1.1 mm/a and 3.6 mm/a respectively during the last 1 to 5 Ma .