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

K. C. Sahu ¹, A. M. Nair ²

Affiliations
1 Indian Institute of Technology, Powai, Bombay 400076, IN
2 Centre of Earth Sciences Studies, Trivandram, IN

Abstract

Chemical study on clean chromites reveals enrichment of chromium and iron due to alteration. Physico-chemical properties show that alteration has enhanced the cell-edge, reflectivity and specific gravity but reduced the microhardness of the mineral. The reemplacement and subsequent instability of tectonic conditions might be the ultimate cause for the shift of Byrapur chromites from aluminian to ferrian field of composition.

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A. M. Nair ¹, Narayanaswamy ¹

Affiliations
1 Centre for Earth Science Studies, Trivandrum, IN

Abstract

Comparative morphometric analysis of zircons from sediments and charnockite-quartzo-feldspathic gneiss-pegmatite rock units along the Manimala river valley in Kottayam and Alleppey districts of Kerala has brought to light a unimodal-bimodal size frequency distribution of zircons transported via a major meander near Komalam in Alleppey district. The slope variation in the up-mid (meander)-downstream zircons is 25°28' to 30°17'. The trapping of heavy minerals (0.002%-0.004%) by the meander has also affected the anticipated coastward enrichment of zircons. RMA plots for the rocks reveal the self-nucleated origin of zircons and the dispersion of trend lines suggests phases of zircon crystallization. Heavy minerals released from the rocks as revealed from zircon morphometry, are not carried through to the coast. Nevertheless, the coastward enrichment of Cu-Pb-Zn concentration indicates a steady flow right up to the coast of only the fine sediment fraction with these absorbed elements.

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R. Parthasarathy ¹, A. V. Murali ¹, M. Sankar Das ¹, A. M. Nair ², Narayanaswamy ²

Affiliations
1 Analytical Chemistry Division, BARC, Bombay 400085, IN
2 Geosciences Division, Centre for Earth Science Studies, Trivandrum, Kerala 695010, IN

Abstract

Zircon separates from a few whole rocks and sediments along with the parent sources have been analysed for Zr, Hf, Se, REE, Th and U concentrations by the neutron activation analysis technique. The major, minor and trace analyses of rock samples and their modal analyses are also presented. The chondritic normalised REE patterns of rock samples show positive Eu anomalies, while the zircon samples show negative Eu anomalies. The data have been used to explain the genetical relationship among the rocks under study. This study supports the hypothesis proposed from this laboratory that the detrital zircons of Kerala beach are time integrated cumulates from the whole-rocks of this region. The scandium data indicate the paragenetic sequence of crystallization of zircons in relation to cpx and magnetite.

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