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

S. Saravanan ¹, G. Thimmi Chetty ¹, S. Ramanathan ¹

Affiliations
1 Department of Geology, Presidency College, Madras, IN

Abstract

No Abstract.

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S. Saravanan ¹, S. Ramanathan ¹

Affiliations
1 Department of Geology, Presidency College, Madras, IN

Abstract

No Abstract.

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S. Saravanan ¹, R. Ramasamy ²

Affiliations
1 18, Natesan Salai, Madras, 600 083, IN
2 Tamil Nadu State Department of Geology and Mining, Madras 600 032, IN

Abstract

Shonkinite occurring in the carbonatite complex of Tiruppattur, Tamil Nadu is essentially composed of equal proportions of anorthoclase and augite with accessories of olivine, hastingsite, biotite, apatite and magnetite. The carbonatite complex comprises alkaline rocks emplaced in two adjacent structural basins of Sevvattur and Jogipatti. The chemical composition of shonkinite is intermediate between melanocratic rocks, alkali syenites and soda-rich alkali syenites of the Sevvattur structural basin and highly potassic alkaline rocks of the Jogipaui structural basin. Both these basins constitute the carbonatite complex of Tiruppattur. The study of geochemistry of clinopyroxenes in the co-magmatic alkaline series of the carbonatite complex reveals that both the groups of alkaline rocks were derived from shonkinitic parent magma by convection current aided differentiation and fractionation of mafic cumulates with intermittent immiscible separations of carbonate and silicate liquids.

Keywords

Alkaline rocks. Clinopyroxene, Geochemistry, Tiruppattur, Tamil Nadu.

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S. Saravanan ¹, S. Ramanathan ¹

Affiliations
1 Department of Geology, Presidency College, Madras, IN

Abstract

The plagioclase - pyroxene - garnet rocks, occurring in the Manalur area, have been designated as 'meta-anorthosite' by Murthy (1959). The authors however, consider them as a member of meta-sedimentary group of Archaeans which have resulted from the metamorphism of calcareous sediments of varying compositions. Since there is a general misconception among some of the Indian petrologists, who consider these metasedimentary calcareous members as 'anorthosites', it is proposed to deal with these rock types, in order to show that they have no association with anorthosites, which are one of the members of the layered complex.

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