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

A. S. Subrahmanyam ¹, S. Lakshminarayana ¹, D. V. Chandrasekhar ¹, K. S. R. Murthy ¹, T. C. S. Rao ¹

Affiliations
1 National Institute of Oceanography, Regional Centre, Visakhapatnam - 530 017, IN

Abstract

Detailed analysis of magnetic and bathymetric data over shelf and slope regions of Cauvery basin, east coast of India. between Mahabalipuram and Vedaranyam demarcated three major offshore lineaments trending N-S, NE-SW and E-W. The N-S lineation has been interpreted as due to dyke intrusions. NE-SW lineament reflects the offshore extension of a major basement depression, viz., the Pondicherry depression. E-W lineation, south of Porto Novo reveals a basement high suggesting the seaward extension of Kumbakonam ridge within the Pondicherry depression. The present analysis gives mosaic of a deep seated graben block flanked by rift related volcanic intrusives over the shelf region of the basin.

Keywords

Structure, Marine Geophysics, Cauvery Basin.

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K. S. R. Murthy ¹, M. M. Malleswara Rao ¹, K. Venkateswarlu ¹, A. S. Subrahmanyam ¹, S. Lakshminarayana ¹, T. C. S. Rao ¹

Affiliations
1 Regional Centre, National Institute of Oceanography, 176, Lawson's Bay Colony, Visakhapatnam-530017, IN

Abstract

Magnetic data of the eastern continental margin of India (ECMI) helped in demarcating the offshore extension of the granulite belts of east coast of India and their possible link to those of the East Antarctica. Short wavelength and high amplitude negative magnetic anomalies (200 to 1600 nT) are observed over the northern part of ECMI between Kakinada and Chilka lake and also off Madras shelf, the coastal regions of which are associated with granulite facies rocks . This part of the shelf is associated with structural lineaments with predominant NE-SW trends . In contrast, the offshore basins off Cauvery, Krishna - Godavari (K-G) and Mahanadi rivers are associated with subdued positive anomalies (less than 200 nT) indicating subsidence off these basins by heavy load of Phanerozoic/younger shelf sediments. Structural lineaments with NW-SE or W-E trends delineated over these basins are related to the offshore extension of these rift related Gondwana grabens. Similarity in the trends of the magnetic anomalies and the granulite facies on the east coast of India and their correlation with the granulite belt of Enderby Land of Antarctica supports the view that the entire region comprised of a single and stable block of granulite rocks prior to the fragmentation of the Gondwanaland. The study also suggests probable continuation of Mahanadi and Godavari grabens into East Antarctica.

Keywords

Marine Geophysics, Magnetic Anomalies, Eastern Ghat Granulite Belt, Enderby Land , Antarctica.

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