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S. Ray ¹, P. K. Gangopadhyay ¹

Affiliations
1 Department of Geology, Prisidency College, Calcutta, IN

Abstract

Earlier studies on metamorphic zones in the metamorphic belts of Singhbhum, Manbhum and adjoining parts of Chhota Nagpur around longitude 86°E and between latitudes 22°45 Nand 23°40 N have been synthesised. Maps of Barrovian zones delineated by different workers in small areas have been coordinated into a regional zonal map.

Broad structural data of earlier workers plotted on the map depict that the pattern of extension of the zones over the whole region has a direct correlation with the plunges of the regional fold axes; higher grade zones occupy anticlinal cores with the lower grade ones succeeding them in the direction of the stratigraphic younging.

Granites, late syntectonic with tbe major folds on S" accompany most sillimanite zone outcrops. Andalusite occurs (i) across the chlorite to the kyanite zones along the southern fringes of the Dalma basic volcanics, and (ii) also sporadically. within sillimanite zone schists in association with sillimanite and kyanite.

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P. K. Gangopadhyay ¹, N. Chatterjee ¹

Affiliations
1 Department of Geology, Presidency College, Calcutta, IN

Abstract

The structural pattern of Delhi system of rocks around Dariba is dominated by open, asymmetrical folds which occur on both major and minor scales. A set of axial plane cleavages, which grades from discrete fractures to slaty cleavage, is consistently developed with the folds. The axial traces of the major fold range in trend from NNE-SSW to WNW-ESE. Although the fold axes vary both in direction and amount of plunge, the axial planes are consistently inclined westwards. The copper ore bodies which have been explored so far, occur in the eastern ridge of Dariba. Mineralisation is practically confined to phyllites ana schists. The lenticular ore bodies have been explored uptil now on the limbs of major overturned synformal fold in the eastern ridge. The axial plane cleavage has been observed to be the main structural plane controlling the distribution of the disseminated sulphides in the rock.

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P. K. Gangopadhyay ¹, S. K. Deb ¹, N. Chatterjee ¹

Affiliations
1 Department of Geology, Presidency College, Calcutta, IN

Abstract

No Abstract.

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P. K. Gangopadhyay ¹, D. Das ¹

Affiliations
1 Department of Geology, Presidency College, Calcutta, IN

Abstract

The Precambrian Delhi group of rocks in north-eastern Rajasthan is associated with a few granite bodies. Among these the Dadikar granite near Alwar city is intrusive into the Delhi metasediments. Both the granite and the Delhi rocks are deformed and recrystallised under the common plan. The Dadikar granite had been emplaced within an overall domal structural framework of the Delhi rocks. Any radiogenic age determination of this granite must be interpreted in the light of the field relationships between the granite and country rock.

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P. K. Gangopadhyay ¹, R. Sen ¹

Affiliations
1 Department of Geology, Presidency College, Calcutta, IN

Abstract

The Precambrian Delhi Group of rocks, which extend along a northeast-southwest belt in Rajasthan, disclose the presence of superimposed folds. A limited area around Kushalgarh in north eastern Rajasthan has been structurally studied in detail to establish the relative influence of the successive generations of folds which control the distribution of different units of the Delhi Group.

At Kushalgarh area a special interest is the study of superimposition of a late generation of fold on an earlier one. The structural pattern of the Delhi Group of rocks is shown to be dependent on the manner of such superimposition.

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P. K. Gangopadhyay ¹, T. K. Pyne ¹

Affiliations
1 Department of Geology, Presidency College, Calcutta, IN

Abstract

Selected specimens of quartzite belonging to the Precambrian Delhi Group, which bear evidence of one main phase of deformation and related recrystallisation, have been studied by the A. V. A. technique. The c-axes of quartz show preferred orientation patterns which are controlled by the spatial distribution of direction groups of quartz. Recognition of the direction groups and the manner of their distribution help to predict the inherently inhomogeneous nature of the microfabric and the likely pattern of symmetry.

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P. K. Gangopadhyay ¹, T. K. Pyne ¹

Affiliations
1 Department of Geology, Presidency College, Calcutta 700073, IN

Abstract

The Lalsot-Bayana hills in northeastern Rajasthan are dominated by the Delhi Group of rocks which are folded on a regional scale. In Lalsot hill region, extending from Chainpura in the north to Lalsot town in the south, a remarkable feature is the occurrence of unconformity between the Delhi Group and the underlying older rocks (Pre-Delhi).

Structural and lithostratigraphical mapping indicate that at Lalsot, the unconformity is a mistaken identity between two units of the same stratigraphical succession. Both the units belong to the Delhi Group and these have been renamed as 'Lalsot quartzite' and' Lalsot schist'. There is no evidence to suggest that the Lalsot schist was a metamorphosed unit prior to the onset of deformation and metamorphism.

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P. K. Gangopadhyay ¹, Amitava Lahiri ¹

Affiliations
1 Department of Geology, Presidency College, Calcutta 700 073, IN

Abstract

The lithostratigraphic units of the Delhi Supergroup are well exposed around Barr (26° 05': 74° 06'). Field, petrographic and geochemical observations from these units suggest that the lithofacies changes from lower arenaceous Alwar Group with basal polymictic conglomerate to the upper impure calcareous-cum-argillaceous Ajabgarh Group. The Barr conglomerate is truly a genuine sedimentary rock with assortment of pebbles and cobbles of quartzite, granite-gneiss, chert and mica schist. However, the conglomerate has been deformed along with other lithostratigraphic units of the Delhi Supergroup. Tectonically formed boudins can be distinguished from clastic pebbles and cobbles. The recognition of the sedimentary origin of the Barr conglomerate is useful in discussing the nature of Delhi-PreDelhi contact on the western flank of the 'Delhi synclinorium'.

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P. K. Gangopadhyay ¹, P. K. Das ¹

Affiliations
1 Ichapur, Ministry of Defence, IN

Abstract

Armour plates used in the fabrication of fighting vehicles are low alloy high strength steel hardened and tempered to predetermined level of hardness, high tensile strength and optimum ductility. This unique combination of material properties imparts antibullet properties to armour plates. Such steels have high carbon equivalent conducive to formation of crack during welding unless suitable welding procedure utilising correct welding consumable is selected.

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