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

B. N. Singh ¹, O. P. Goel ¹, Mallickarjun Joshi ², J . W. Sheraton ³

Affiliations
1 Department of Geology, Kumaun University, Nainital 263 002, IN
2 Geology Laboratory, Department of Civil Engineering, Institute of Technology, Banaras University, Varanasi-221 005, IN
3 Australian Geological Survey Organisation, P. O. Box 378, Canberra City, A.C.T. 2601, AU

Abstract

Early Cambrian Champawat granitoids from Dhunaghat area, emplaced between medium-to high-grade metapelites of the Saryu Formation and low-grade melapelites of the Gumalikhet Formation of the Almora Group, show wide variations in their modal and chemical composition, ranging from granodiorite to granite. Biotite-rich mafic enclaves within the granitoids may represent restile, possibly modified by metasomatism. Chemical data for the calc-alkaline Champwat granitoids show some dcgree of fractional crystallization, although processes such as restite unmixing and different degree of melting may also have been important for the observed variation trends.

The Champwat intrusives are also characterized by enrichment of Y, Zr, Th, U, Nb, La, Ce, Pr and Nd and show affinities with "A"-type (anorogenic) granites.

Keywords

Geochemistry, Petrogenesis, Champawat graniloids, Almora Group, Dhunaghat, District Pithoragarh, Uttar Pradesh.

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B. N. Singh ¹, O. P. Goel ², Mallickarjun Joshi ¹, J. W. Sheraton ³

Affiliations
1 Geology Laboratory, Department of Civil Engineering, Institute of Technology, Banaras Hindu University, Varanasi - 221 005 (India), IN
2 Department of Geology, Kumaun University, Nainital - 263 002 (India), IN
3 Australian Geological Survey Organisation, P.O. Box 378, Canberra City, A.C.T. 2601 (Australia), AU

Abstract

The Precambrian Almora granite gneisses containing numerous schistose enclaves occuras thick and thin bands within the medium-grade Saryu metasediments of Almora Group. Petrography and major and trace element geochemistry of the granite gneisses indicate that they are strongly peraluminous, S-type granites, and were derived by partial meltingofthe meta-arkose/metapelites.

Keywords

Geochemistry, Granite, Dhunaghat, Uttar Pradesh.

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B. N. Singh ¹

Affiliations
1 Applied Geology Laboratory, Department of Civil Engineering, Institute of Technology, Banaras Hindu University, Varanasi -221 005, IN

Abstract

The Neoproterozoic mount Abu batholith comprises medium to coarse-grained, grey and pink porphyritic to non-porphyritic biotite granites. ChemicalIy and mineralogically, these are sub-aluminous and potash-rich granites. They are characterized by high SiO₂, Na₂O + K₂O, Fe/Mg, Rb, Nb, Zr, Y, Zn, Ga and Th, and low MgO, Fe₂O^t₃, CaO and Sr contents, and show close affinity to the A-type granites. High K/Rb, Rb/Sr, Ba/Sr and Ga/Al ratios of these granites are suggestive of crustal origin, which were most likely derived by low-degree partial melting of pre-existing depleted lower crustal source. The mount Abu granites were ernplaced at 650'-700°C at an assumed pressure of around 5 kb.

Keywords

Petrology, Geochemistry, A-type granite, Mount Abu granites, Rajasthan.

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Kamal Kant Sharma ¹, B. N. Singh ², S. Viswanathan ³, B. N. Singh ²

Affiliations
1 Government Postgraduate College, Sirohi - 307 001, IN
2 Department of Civil Engineering, Banaras Hindu University, Varanasi - 221 005, IN
3 Flat B-203, Block-B, United Avenue Apts., South End, 7-1-29, Ameerpet, Hyderabad - 500 016, IN

Abstract

No Abstract.

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B. N. Singh ¹, Mallickarjun Joshi ²

Affiliations
1 Geology Laboratory, Department of Civil Engineering, Institute of Technology, Banaras Hindu University, Varanasi- 221 005, IN
2 Department of Geology, Banaras Hindu University, Varanasi - 221 005, IN

Abstract

The occurrence of Malani rhyolites as dykes within the Mt. Abu batholith has been studied. The Mt. Abu rhyolitic dykes are peraluminous and of subalkaline nature. These are enriched in trace elements such as Rb, Nb, Zr, Y, Ga, Th and Zn, and depleted in Ba and Sr resulting in high K/Rb, Rb/Sr, Ba/Sr and Ga/AI ratios. The geochemical characters indicate Mt. Abu rhyoiitic dykes to be A-Type, within-Plate granites (WPG) with high SiO₂, Na₂O + K₂O and Fe/Mg. These rhyolites are likely to have formed in anorogenic Rift-Related setting and the volcanism may be correlated to early stages of Pan-African magmatic event (850-750 Ma).

Keywords

Rhyolite, Geochemistry, Mt. Abu Batholith, Rajasthan.

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