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M. V. Ramana ¹, V. Subrahmanyam ¹, L. V. Subba Raju ¹

Affiliations
1 National Institute of Oceanography, Dona Paula, Goa 403 004, IN

Abstract

Total magnetic field intensity measurements along two parallel NW-SE tracks from the Direction Bank to the Kori Bank show correlatable magnetic anomalies. High frequency positive anomalies observed northwest of Kathiawar coast terminating at about 21°N are interpreted due to the magnetic basement i.e, basalts at a depth of about 2 km. A low amplitude negative anomaly observed around 21°N (between 69°E and 70°E) may be due to the westward extension of the Narmada-Son lineament. Absence of significant anomalies south of these high frequency anomalies may be due to thin Traps or greater thickness of sediments. High amplitude and broad wavelength negative anomaly observed off Bombay (l9°N, 71.5°E) is interpreted as due to contact or faulting of Precambrian formations and Deccan Traps.

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L. V. Subba Raju ¹, K. S. Krishna ¹

Affiliations
1 National Institute of Oceanography, Dona Paula, Goa - 403 004, IN

Abstract

Complete descriptions and basic facts of nine gravity stations of Marmugao harbour are presented. They exhibit a maximum Bouguer difference of 2.12 mGal in an overall distance of about 2 km. Keeping in view the limited amount of data, certain broad and tentative conclusions regarding crustal structure are drawn.

Keywords

Gravity Stations, Crustal Thickness, Goa.

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V. Subrahmanyam ¹, M. V. Ramana ¹, L. V. Subba Raju ¹

Affiliations
1 National Institute of Oceanography, Dona Pau]a, Goa 403 004, IN

Abstract

Geophysical studies of the southwestern continental margin revealed significant surface and subsurface topographic highs (ridges) trending NNW-SSE to NW-SE beyond the shelf break. Residual magnetic anomaly map depicts prominent NNW-SSE, NW-SE and E-W trends. The magnetic anomaly map also reveals three different provinces, A, B and C, based on magnetic signatures, confined to inner shelf, outer shelf and lower shelf. A prominent E-W trending structural Jineament with a NW-SE trending offset is observed cutting across the inner shelf and the lower shelf. Model studies of the geopotential data over the topographic rise indicate about 18 km thick mafic basement of continental origin at a shallow depth (∼800 m). The gravity model studies indicate a thick consolidated sediment layer deposited over the horst and grabenlike features within the granitic layer. The occurrence of ridges parallel to the shelf edge shows the similarity of the western Indian continental margin with the other typical and extensively studied passive margins.

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