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

S. M. Karisiddaiah ¹

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

Abstract

Petrographic study indicates that the nucleus of nodules is generally composed of clay, volcanic glass, basalt fragments, and earlier nodules. Polished sections indicate typical collomorphic globular segregations and partly crystalline oxides of todorokite. Scanning electron micrographs indicate that they are made up of small and large botryoids; and occasional platelets of todorokite, within cavities formed due to post depositional recrystallization. X-ray diffraction patterns do not show any peaks of todorokite due to poor crystallinity, while δ-MnO₂ is seen in all the nodules studied. The nodules analysed show: Mn 15.01-21.40%, Fe 10.07-20.10%, Cu 0.07-0.32%, Ni 0.32-0.57%, Co 0.07-0-21%, and also have a Mn/Fe ratio less than 2. The nodules are of hydrogenetic, secondary origin, source being volcanogenic.

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H. N. Siddiquie ¹, S. M. Karisiddaiah ¹, V. Subrahmanyam ¹

Affiliations
1 National lnstitute of Oceanography, Dona Paula, Goa 403004, IN

Abstract

The total magnetic intensity map of the area shows that the inner shelf to a depth of 50m is marked by a zone of magnetic closures. The occurrence of offshore ortho-amphibolites and the qualitative interpretation of the magnetic map indicate the extension of onshore rocks (or the amphibolites and associated rocks of Precambrian (?) and intrusions of Deccan Trap age) under a thin cover of sediments to the offshore to a depth of about 50 m.

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S. M. Karisiddaiah ¹, S. D. Iyer ¹

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

Abstract

Rocks dredged in the vicinity of the 79°E fracture zone, in the Central Indian Basin, are sub-alkaline basalts, which are regarded as precursors to spilites. The Minerals identified are mainly albitic plagioclase, augite, olivine, and less of chlorite, epidote and opaques. The oxide variation plots indicate a mid-ocean ridge basalt trend for the samples, which have been spilitised to varying degrees. It is suggested that the basalts formed as a result of a fissure type of eruption along the fracture zone. Subsequently, some of the basalts were spilitised probably due to hydrothermal solution, possibly the result of tectonic activity along the fracture zone.

Keywords

Basalts, Spilitisation, Fracture Zone, Central Indian Basin, Petrology.

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S. M. Karisiddaiah ¹

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

Abstract

No Abstract.

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