Late quaternary tectonic evolution of Dun in fault bend/propagated fold system, Garhwal Sub-Himalaya

摘要

Two distinct styles and amplitudes of folding occur in Dun. In the northern part, the overturned Santaurgarh anticline with both limbs dipping steep to moderate was developed as fault propagated fold over the Santaurgarh Thrust (ST). The uplifted hanging wall of the ST constituted the dissected Siwalik,. and the down-faulted footwall formed the pedimented Siwalik. To the South in the frontal range, the Siwalik strata were folded into Mohand anticline as fault-bend fold over the Himalayan Frontal Thrust (HFT). The uplifted terraces on the fore-limb of the anticline resulted due to displacement on the HFT in Holocene. The Bhauwala Thrust, Majhaun Fault and Asan Fault were formed as out-of-sequence thrusts within the Main Boundary Thrust-HFT wedge of folded Siwalik and overlying Dun gravels subsequent to ST. Extrapolation of earlier published OSL age data and our observations suggest initiation of HFT between 500 and 100 Ka; the ST was initiated in post-500 Ka and continued to propagate till post-40 Ka. The Bhauwala Thrust was developed between 29 and 20 Ka, and the Asan fault post-dated 10 Ka.