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

Sukanta Dey ¹, R. Gajapathi Rao ², D. Veerabhaskar ¹, Anjan Chaki ¹, Tapan Kumar Baidya ³

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Begumpet, Hyderabad - 500 016, IN
2 Atomic Minerals Directorate for Exploration and Research, Madhavadhara, Visakhapatnam - 530 018, IN
3 Atomic Minerals Directorate for Exploration and Research, Department of Geological Sciences, Jadavpur University, Kolkata - 700 032, IN

Abstract

Shales of the Proterozoic Kaladgi Supergroup, occupying the intracratonic Kaladgi-Badami Basin in the Dharwar craton, are analyzed for mineralogical as well as major and trace element compositions. Field setting and elemental ratios, critical to provenance, indicate (1) major contribution from highly weathered Archaean silicic source rocks like Peninsular Gneiss and Closepet Granite, (2) the shales lack any systematic time-dependent variation of composition and (3) they record normal weathering history. Compared to the middle Archaean cratonic shales of the Dharwar craton, the Kaladgi shales are enriched in K₂O, Th, La, Ce and Yb and depleted in MgO, Cr and Ni suggesting secular change in the Cpper crustal composition towards more felsic nature. The middle Archaean shales document acid leaching as an important weathering process, whereas the Kaladgi shales reflect intense weathering of the source similar to that of present day warm humid climate. In contrast to the extreme variability of the middle Archaean shales, the Kaladgi shales show smaller compositional variation suggesting development of Iarger platformal environment suitable for repeated recycling and efficient mixing. During late Archaean crustal growth, emplacement of juvenile granites into the crust and subsequent intracrustal melting has transferred huge amount of incompatible elements into the upper continental crust. The effect of ths change is clearly imprinted in the evolved composition of the Kaladgi shales.

Keywords

Shale, Geochemistry, Proterozoic, Kaladgi Supergroup, Palaeoweathering, Upper Crustal Composition.

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Sukantadey ¹, R. Gajapathi Rao ¹, R. A. Gorikhan ¹, D. Veerabhaskar ¹, Sunil Kumar ¹, Mary K. Kumar ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Bangalore - 560 072, IN

Abstract

The late Archaean Closepet Granite of the Gudur-Guledagudda area consists of equigranular pink and grey biotite granites, and porphyntic pink biotite granodionte to quartz-monzodionte. The granitoids exhibit intrusive relation with the Hungund-Kushtagi schist belt at places. The equigranular granites show limited range of major oxide compositions and compared to the porphyntic granodionte and quartz-monzodionte, are enriched in Si0₂, K₂0 and Rb but depleted in Al₂0₃, FeO, Fe₂0₃, CaO, MgO, P₂0₅, Sr, Ba, Y, Nb and REE. The granitoids fall near the boundary between peraluminous and metaluminous granitoids with the A/CNK ratios around one Fractionated LREE and flat HREE patterns and a negative Eu anomaly characterize all the samples Field evidences indicate mainly post-kinematic nature of the granitoids. The equigranular granites appear to be minimum melt derived from anatexis of Peninsular Gneiss without fractional crystallization. The porphyntic granodionte and quartz-monzodionte represent non-minimum melt derived from a different source enriched in REE Geochemical signatures indicate that the Closepet Granite of Gudur-Guledagudda area is the product of melting at shallower level compared to the southern Closepet Granite.

Keywords

Petrography, Geochemistry, Northern Closepet Granite, Gudur-Guledagudda Area, Karnataka.

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R. Gajapathi Rao ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Nagarabhavi, Bangalore - 560 072, IN

Abstract

No Abstract.

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Sukanta Dey ¹, R. Gajapathi Rao ¹, Sunil Kumar ¹, D. Veerabhaskar ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Nagarabhavi, Bangalore - 560 072, IN

Abstract

The Neoproterozoic Badami Group of the Kaladgi-Badami basin consists of an undisturbed sequence of sandstone, shale and limestone exposed in the northern districts of Karnataka and adjoining parts of Maharashtra (Viswanathiah, 1977; Jayaprakash et al. 1987). The sequence unconformably overlies Archaean granitoids, schists and the Mesoproterozoic Bagalkot Group of sediments. The environment of deposition of the Badami Group has been interpreted as shallow marine (Sathyanarayan, 1994). This note presents some field evidences around Khanapur village, Bagalkot district revealing the nature of palaeo-coas tal morphology during the deposition of Cave Temple arenite (CTa), the main sandstone member of the Badami Group.

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