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S. A. Chore ¹, M. Mohanty ¹

Affiliations
1 Geological Survey of India, 1-Bhutan Unit, Samtse; 2-Operation Orissa, Nayapalli, Bhubaneswar-751012, IN

Abstract

At least three formations in Punagarh Group and two in Sindreth Group are identifiable on the basis of varied lithoassemblages. The geochemical parametres of the mafic (mainly pillowed) and felsic volcanics suggest that their effusion is linked to the deep seated fractures responsible for the formation of intracratonic grabens. The association of bimodal volcanics and coarse clastics in linear grabens suggest the development of retroarc basins as a consequence of subduction of South Delhi Oceanic-transitional crust under the western Marwar continental crust. The Trans-Aravalli region in Rajasthan contains Neoproterozoic sequences of Punagarh and Sindreth groups occurring in isolated linear basins.

Keywords

Stratigraphy, Tectonics, Aravalli, Neoproterozoic, Rajasthan.

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S. Sinha-Roy ¹, M. Mohanty ¹, G. Malhotra ¹, V. P. Sharma ¹, D. W. Joshi ¹

Affiliations
1 Geological Survey of India, 15-16 Jhalana Dungri, Jaipur 302 004, IN

Abstract

The Proterozoic sequences of South-Central Rajasthan are contained in the Lower to Middle Proterozoic Aravalli and Middle to Upper Proterozoic Delhi fold belts. The stratigraphic relations within these fold belts as well as the basement-cover relations are beset with several problems. The conglomerate horizons have been studied to address some of these problems. Based on the conglomerate horizons, representing erosional unconformities, the Aravalli Supergroup has been sub-divided into three groups and the Delhi Supergroup of the South Delhi fold belt into two groups with constituent formations. These horizons are also useful in identifying three stages of basin evolution for the Aravalli fold belt. The Middle Aravalli Conglomerate is the most prominent representing mid-Aravalli hiatus, and corresponding to the Debari Transgressive Stage which followed the Delwara Rifting Stage in the Lower Aravalli in a system of ensialic distensional tectonics where triple-junctions and pull-apart basins are formed. The Upper Aravalli has been the Jharol Ocean Opening Stage, the oceanic/transitional crust having been consumed at a median ultramafic suture line during the formation of the Aravalli fold belt. The South Delhi fold belt has also multi-stage development history with the Barr Conglomerate representing the base of the youngest Delhi sequence.

Keywords

Proterozoic, Conglomerate, Aravalli Fold Belt, Delhi Fold Belt, Rajasthan, Basin Evolution.

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M. Mohanty ¹, K. C. Sahoo ¹

Affiliations
1 Geological Survey of India Operation Orissa Nayapalli , Unit-8 Bhubaneswar - 751 012, IN

Abstract

No Abstract.

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M. Mohanty ¹

Affiliations
1 Geological Survey of India, Bhubaneswar, IN

Abstract

No Abstract.

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M. Mohanty ¹

Affiliations
1 Geological Survey of India, Bhubaneswar, IN

Abstract

No Abstract.

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M. Mohanty ¹, P. K. Panda ², B. K. Mohanty ¹

Affiliations
1 Geological Survey of India, Laitumkrah, Shillong-793003, IN
2 Geological Survey of India, Laitumkrah, Bhubaneswar-751012, IN

Abstract

A large segment of the southcentral part of the Eastern Indian Craton proximal to the contact of the Eastern Ghats Mobile belt is occupied by the Pal Laharha gneiss. Spatially associated with the lithoensemble of greenstone belts. This segment is a zone of high strain traversed by regional faults. The granite gneiss is mainly represented by stromatic migmatite having supracrustal rocks constituting the immobile components. Three different varieties of granite VIZ (i) fine to medium grained mesocratic, horriblende-magnetite bearing granite, (ii) banded, pink, leucocratic granitic gneiss, and (iii) muscovite-biotite±garnet bearing medium to coarse grained granitic gneiss have been identified in this segment.

The granitic gneiss has a granite to monzogranite range of composition and compares well with anorogenic, metalummous A-type granite (A/CNK<1). Highly fractionated REE, LREE enrichment, flat HREE pattern and a -ve Eu-Anomaly characterize the granites. From field, petrographic and geochemical attributes, it is suggested that the Pal Laharha granitic gneiss does not form a discrete plutonic body. It possibly evolved by the synkinematic mid-crustal anatexis of the supracrustal sequences now occuring either as megaenclaves or as immobile components.

Keywords

Greenstones, Stromatic Migmatite, Immobile Component, Eastern Indian Craton, Orissa.

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M. Mohanty , K. C. Sahoo

Abstract

No Abstract.

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Abhishek Kumar Shukla ¹, Parasuram Behera ¹, K. Basavaraja ¹, M. Mohanty ¹

Affiliations
1 Geological Survey of India, Vasudha Bhavan, Kumarswamy Layout, Bengaluru 560 078, IN

Abstract

Parallel to the Krishna river course, a set of ENE to WSW trending brittle-ductile shear zones affecting the Neoarchaean pink porphyritic granite remains athwart to the NW-SE tectonic fabric of the Eastern Dharwar Craton (EDC) in Raichur and Gulbarga districts, Karnataka, India. These zones are not only manifested by intense mylonitization, brecciation and fracturing, but also witness several episodes of mafic and felsic intrusions. At Machanur, Raichur district a 5 km long and 400 m wide shear zone hosts copper, gold and REE mineralization both in specularite-rich hydrothermal veins and as disseminations within the dolerite dykes. The mineralization is associated with well-developed zones of hydrothermal alteration in the form of propylitization, carbonatization, epidotization and silicification with patches of strong iron-staining and fracture-filled iron solution dominantly in the foot wall side. Due to similarity with many iron oxide- copper-gold-type deposits, this prospect in Machanur is interpreted as iron oxide-copper-gold-type mineralization.

Keywords

Brittle–Ductile, Hydrothermal Alteration, Ore Deposits, Mineralization, Shear Zones.

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