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

K. Soman ¹, N. G. K. Nair ², V. N. Golubyev ³, M. M. Arakelyan ³

Affiliations
1 Department of Geology, Friendship University, Moscow, RU
2 Centre for Earth Science Studies, Trivandrum 695010, IN
3 IGEM, Academy of Sciences, Moscow, USSR, RU

Abstract

K/Ar mica age of chrysoberyl-bearing pegmatites from four localities of Trivandrum district, Kerala ranges from 445 to 474 m.y., with a mean around 460 m.y. There is a close agreement between the ages of the concordant and cross-cutting pegmatites, between muscovite and biotite ages, as also between various size fractions. Chrysoberyl occurs within feldspars in association with quartz and muscovite. Since the formation of chrysoberyl-quartz association requires a higher pressure or temperature, the reported age would indicate the time of emplacement of the chrysoberyl-bearing pegmatites at the closing phase of a major tectonomagmatic event. It is interesting to note that these pegmatites of south-western India are younger compared to those of other localities viz., Rajasthan, Bihar. Nellore and Mysore.

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N. G. K Nair ¹, K. Soman ¹, M. Santosh ¹, M. M. Arakelyants ², V. N. Golubyev ²

Affiliations
1 Centre for Earth Science Studies, Trivandrum 695010, IN
2 IGEM, Academy of Sciences, Moscow, USSR, RU

Abstract

Biotite separates from three granite plutons in the Northern part of the Kerala region, namely, Kalpatta. Ambalavayal and Thaluru yield K-Ar ages of 512±20 m.y., 560±30 m.y. and 710±20 m y. respectively. The age data are comparable with those reported for similar granitic intrusives of the south Indian region.

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K. Soman ¹, K. G. Thara ¹, M. M. Arakelyants ², V. N. Golubyev ³

Affiliations
1 Centre for Earth Science Studies, Trivandrum 695031, IN
2 IGEM, Academy of Sciences, Moscow 109017, RU
3 IGEM, Academy of Sciences, Moscow 109017, IN

Abstract

Of the three styles of deformation recognised in the Palghat Gap area, the D₃ period is conspicuous with a major pegmatite emplacement phase, associated with the migmatization event. Dating of mica from pegmatites belonging to this stage (both concordant and cross-cutting) has yielded ages ranging from 484 to 512 m.y. The pegmatite emplacement is suggested to be towards the closing stage of a retrogressive metamorphic event, associated with crustal uplift in the Palghat Gap region, which laid the tectonic frame-work for the formation of the gap later.

Keywords

Geochronology, Palghat Gap, Pegmatites, Kerala.

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