The credit of introducing this theory goes to Hary Hess (1960), R.S. Dietz (Global Tectonics, 1961), W.J. Morgan and Le Pichon (Sea Floor Spreading and Continental Drift, 1968). According to this theory about 70-65 million years ago there was an extensive geosynclines in the place of the Himalayas called die Tethys Sea. It was bordered by the Asian plate in die notion and die Indian plate in the south.
Tethys Sea began to contract in size due to the converging movement of die two plates. About 60- 30 million years ago the Indian plate came very close to the Asian plate and it started subducting under the latter. This caused lateral compression due to which the sediments of the Tethys were squeezed and folded into three parallel ranges of die Himalayas about 30-20 million years ago. It has been estimated that this convergence has caused a crustal shortening of about 500 km in the Himalayan region and is compensated by sea floor spreading along the oceanic ridge in die Indian Ocean region. Since the northward movement of the Indian plate is still continuing the height of the Himalayan peaks is increasing.
While the Plate Tectonic theory finds highest number of supporters amongst the academic world there is no dead of such scholars who doubt its efficacy to explain die upheaval of the Himalayas. Crawford thinks that “the origin of the Himalaya is misunderstood.
The ‘Gondwanaland plate’ or shield reached as far as the Tien Shan and not only up to die Himalaya. The Himalayas are in Tracontinental Mountains; they are not due to continental collision. They are a heap of fractured material in the middle of the Indo-Tibetan plate. India and Tibet formed part of the same plate or crustal section.
The southern half rose and the northern were submerged in Phanerozoic times. That the height of die Himalayas is related to the movement of the Gondwanaland is medical” (A.R. Crawford, 1974, pp. 369-380). Seismic observations do not give any positive support to the under thrusting of the Indian plate below the Asian plate. There arc. However, some indications of dipping of the India plate towards he north (Chaudhary, Srivastavaand Rao, 1974, pp. 481-491).
The direction of movement deduced from the rocks exposed at the surface is towards the south in the Himalayan Are, towards the west in the Burmese Arc and towards the cast in the Baluchistan Arc. This very well supports the northerly movement of the Indian shield (Krishnan, 1982, p. 69). Gupta (1974).
On the basis of scismological observations, has concluded that “Indian and Asian plates have underthrust into the upper mantle forming a V-shaped pocket of intermediate focus earthquakes (H.K. Gupta, 1974. pp. 465-479). R.N. Srivastava (1973) is of opinion that ‘the pattern of crustal scismicity observed in the region (India-Tibet-Nepal border) as well as in Tibet has been associated with ‘Hat tectonics’ recently proposed for continent-continent collision.’
M.N. Qureshy-Qureshy’s analysis of the available geophysical data about the Himalaya suggested that vertical movements have played a primary part in the elevation of the Himalayas. ‘Large positive isostatic anomalies over the Middle Himalaya and large crustal thickness reaching 80 km in places are interpreted to be mainly due to thickening of a basalt layeron incorporation of heavy material moving from depth in the crust.’ Density anomalies calculated (by Schwidcrski, 1967) from satellite data also indicate upward movement of matter from the mantle under the Himalaya and Central Asian mountains. This view is also supported by the discovery of basic material in deep bore holes in the Ganga basin and along major faults in Assam area.