Abstract
The east-west trending Palghat Gap across the Western Ghat hill ranges is a part of a well-defined low level landform along 10°45'N latitude in south India. The Nilgiri hills to the north and the Anai Malai-Palni hills to the south of the gap are marked by remnant plateau landforms representing a planation surface of Jurassic age. Field evidences are against block faulting and uplift of the hills to the north and south in post-Jurassic times to account for the elevation of the Jurassic surface and the evolution of a low level landform in between the hills. Results of recent studies do not support marine incursion in the gap area to carve out a low level landform.
It is put forward that crustal upwarp along an east-west axis coinciding with the Palghat Gap elevated the Jurassic surface; the brittle crustal rocks along the axis got ruptured by tensional stresses resulting from upwarping; and the ruptured rocks were eroded with comparative ease by fluviatile action. LANDSAT imagery (MSS Band 5 and 7) bears out the signature of an easterly flowing palaeo stream (Proto-Amaravati), which apparently dried up in post Mio-Pliocene times because of a change in the climatic pattern.
The upwarp of the continental crust is considered to be a natural response to correct the imbalance in equilibrium resulting from the erosion of crustal rocks and deposition of stupendous amounts of sediments in taphrogenic basins on the east coast. From the Plate tectonics angle, the elevation of the continental crust may be attributed to tremendous pressure exerted on the crust by vertical thermal plume activity related to Deccan trap volcanism.
