Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Abstract

Deep Seismic Sounding (DSS) studies carried out for the first time in the syntaxial bend of the Himalaya in Kashmir region during 1974 and 1975 have revealed the deep crustal and upper mantle structure in the region of the great Himalaya Karakorum-Pamir ranges. The Moho which is at a depth of about 45 km near Sopur changes rapidly to 54 km depth in the region of Wular lake from where it continues to go still deeper towards NNE, attaining a depth of about 64 km near Kanzalwan. Then there is a deep fault displacing Moho to a depth of 76 km, which then rises to about 62 km under the Nangaparbat shot point. Similarly the Moho, along profile 2, is found to be at a depth of about 53 km in the region about 10 km NNW of Tral going still deeper towards NNW and attaining a depth of about 64 km in the region about 17km NE of Srinagar. Further NNW, in the region of Kanzalwan, there seems to be some flattening of the Moho boundary which is at a depth of about 70km. Beyond Kanzalwan both the profiles 1 and 2, reveal a change in the dip direction on the Moho boundary which then starts rising up towards Nangaparbat. This updip of the Moho boundary in the region between Kanzalwan and Nangaparbat is an indication of the upwarp of the Moho in this region, which could be responsible for the uplift of the Nangaparbat massif. The crustal block in the Kashmir Himalayan region between Sopur and Kanzalwan and between Tral and Kanzalwan appears to be bounded by two large-angle deep-faults which extend down almost to the Moho boundary.

A number of deep reflections have been recorded along profile 3 indicating deep reflecting boundary at a depth of about 140km extending right from beneath Nangaparbat to the great Pamir ranges which is inferred as representing the top of the asthenospheric layer.

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Abstract

Deep Seismic Sounding (DSS) studies were initiated for the first time in India under a 3-year Indo-Soviet collaboration agreement starting 1972, along a 600km long roughly ENE-WSW profile which lies near 14°N latitude, extending from Kavali on the east coast of India to Udipi on the west coast.

A crustal section is depicted along the Kavali-Udipi profile, showing a large number of reflectors from about 2 km to about 50 km depth. The 600 km long section consists of 17 major blocks, besides a few smaller ones. It is cut up by 15 major deep faults and two major low angle thrusts. In addition there are 5 faults/thrusts extending to intermediate depths. The geological evolution of this part of the shield probably began in Early Proterozoic with the formation of the Dharwar geosyncline between Parnapalle and Agumbe, This was divided into two parts by the uplift of the block where Closepet granites are now exposed. The Dharwars in the eastern part are now almost completely eroded, exposing their basement. The Moho here is at an average depth of 35-36 km, going down to 38 km below Dharmavaram. In the western part, where there is a large thickness of Dharwars still present, Moho is more or less flat at a depth of 38 km, going down to 41 km below Holalkere and rising about 36 km below Chennagiri, The basement of the schist belt here varies from 4 to 7 km in depth.

The Cuddapahs must have been deposited starting near Parnapalle eastward due to en-echelon type faulting. Moho goes down from 34km below Parnapalle to 40 km below Duttaluru. The block between Maidukuru and Malepadu subsided later to create a fresh depression in which the Kurnools were deposited. In general, the basement of the Cuddapahs is at a depth of 8-10 km. The Cuddapahs, on their eastern margin, have been subjected to a major low angle thrust.

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