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Venkateswarlu, N.
- Delineation of Faults, Using Deep Seismic Sounding Refraction Data, West Bengal Basin
Authors
1 National Geophysical Research Institute, Hyderabad-500 007, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 45, No 1 (1995), Pagination: 97-106Abstract
A systematic analysis of refraction data obtained in West BengaI basin, has been carried out to bring into focus the utility of the seismic refraction data in delineating fault zones. The study clearly points out the different conspicuous signatures present in the refraction travel time data, associated with the shallower fault zones affecting the top sedirnentry column and the crystalline basement.Keywords
Seismology, Geophysics, Structure, West Bengal.
- Nagaur-Jhalawar Geotransect Across the Delhi/Aravalli Fold Belt in Northwest India
Authors
1 National Geophysical Research Institute, Hyderabad-500007, IN
2 National Geophysical Research Institute, Hyderabad-500007
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 52, No 2 (1998), Pagination: 153-161Abstract
Lithological, gravity, magnetic, and seismic data within 100 Km corridor of the 400 km long seismic reflection profile are compiled to constitute the NW-SE Nagaur-Jhalawar Geotransect. The transect sequentially cuts across the Neo-Proterozoic Marwar Basin (MB) on the northwest, the Palaeo/Mesoproterozoic Delhi Fold Belt (DFB), the middle/late Archaean Bhilwara Gneissic Complex (BGC) and the MesolNeoproterozoic to early Palaeozoic Vindhyan Basin (VB) at the southeast. The BGC and DFB belts show polyphase deformation and metamorphism.
The BGC within the transect, consists of Sandmata Granulite Complex, followed by amphibolite facies Mangalwar Complex and Greenschist facies Hindoli/Sawar groups. The BGC show evidence of crustal reworking at c.3.0 Ga. The DFB is represented by amphibolite facies metavolcanic-metasedimentary shallow marine sequences and is tectonically highly disturbed. The DFB deposits (c. 2.0 - 1.5 Ga.) were subjected to tectonic deformation during Delhi orogeny (c. 1.5 Ga.), which is marked by syntectonic granitic plutonism. Both, the BGC and OFB also appear to have been affected by Neoproterozoic thermal events and granitic plutonism. The Neoproterozoic MB consists of clayevaporite sequences of shallow oscillatory basin deposits.
Seismic, gravitylmagnetic and magneto-telluric techniques could delineate a number of shallow to deep faults, intrusive bodies and a high conductivity zone. The total magnetic intensity shows a regional increase towards southeast. The Bouguer anomaly values show a steep rise of upto 80 mGal towards the boundary of OFB and BGC. Based on the seismic studies, doubling of the crust under the OFB and vertical intrusion of high density material under the BGC are inferred. The upper crust is, in general, transparent in its reflectivity while the lower crustal reflectivity is high in the transect area, except in the BGC and the VB. A thrust boundary, dipping NW, is present at the eastern margin of the BGC and could be traced up to 30 km depth. The Moho is at a depth of 36-38 km under the MB. Multiple Moho reflections are identified in the DFB crust, the deepest being at 45-50 km depth. In some part of the BGC the Moho can not be identified but in parts it is traced at about 50 km depth, with southeast up dip, before becoming subhorizontal at depth of 41-42 km. It becomes shallower to about 30 km depth at the SE end under the VB.