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

M. E. A. Mondal ¹, Syed M. Zainuddin ¹

Affiliations
1 Department of Geology, Aligarh Muslim University, Aligarh - 202002, IN

Abstract

The Bundelkhand massif comprises various types of granites. On the basis of field relations, three compositionally distinct granitic phases have been delineated. These are hornblende granite, biotite granite and leuco granite in stratigraphic sequence. The major elements variations against SiO₂, display smooth trends which should be expected for a composite massif evolved by fractionai crystallization. The variations of incompatible elements compared to the compatible elements suggest a partial melting process for the evolution of the massif.

Keywords

Petrogenesis, Geochemistry, Bundelkhand, Granites, Central India.

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M. E. A. Mondal ¹, R. Chandra ², T. Ahmad ³

Affiliations
1 Department of Geology, Aligarh Muslim University, Aligarh - 202 002, IN
2 Department of Geology, Bundelkhand University, Jhansi - 284 128, IN
3 Department of Geology, University of Delhi, Delhi - 110 007, IN

Abstract

Precambrian mafic magmatism of the Bundelkhand craton is represented by the mafic dyke swarms that have extensively traversed the gneisses and granitoids and metamorphosed mafic-ultramafic rocks associated with greenstone-gneiss, occurring as small linear isolated basins. The mafic dykes were emplaced (during ∼2.1 to ∼2.0 Ga) in three phases, two in NW-SE direction and the third in NE-SW direction, depicting episodic events subsequent to the stabilization of the craton (at ∼2.5 Ga). The former represent culmination of tectono-magmatic event in the Bundelkhand region. The mafic-ultramafic suite of rocks associated with greenstone-gneiss units, range in composition from basalt through basaltic-andesite to basaltic-komatiite. The basaltic-komatiites display remarkable geochemical similarity with boninites. The dykes are of varying compositions and are mostly low-Ti tholeiites and range from sub-alkaline basalt through basaltic andesite and dacite. They show enrichment of light rare earth elements (LREE) and large ion lithophile elements (LILE) and depletion of high field strength elements (HFSE). Incompatible trace elemental ratios indicate that crustal contamination alone cannot be the dominant process for the evolution of the dykes. Ti/Zr and Ti/Y ratios of the dykes reflect near primary chemical characteristics of the mantle sources. Large variations observed in Nb/La and La/Sm ratios possibly reflect varying influence of the crustal material and also some LREE-LILE enrichment processes. To explain the observed geochemical characteristics, it is proposed that the mantle source region was contaminated by sediments/crustal components probably via subduction processes. Geochemical characteristics of the dykes swarm probably reflects enriched mantle source characteristics followed by fractional crystallisation of the magma. Our study indicates important role of subduction processes in the evolution of the Precambrian crust and subcontinental lithosphere in the Bundelkhand and neighbouring shield and Himalayan areas.

Keywords

Precambrian Mafic Dykes, Bundelkhand Craton, Enriched Mantle Sources, Crustal Contamination, Subduction Processes.

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Salam Ranjeeta Devi ¹, M. E. A. Mondal ¹

Affiliations
1 Department of Geology, AMU, Aligarh - 20202, IN

Abstract

Sandstones of sub-flysch Oligocene Barail Group and molasse Miocene Surma Group of the Surma-Barak basin (Manipur, India), developed with uplift of the Himalaya and the Indo-Burma range, are fine to medium grained and have high quartz and lithic contents relative to feldspar. Barail Group of sandstone is moderately mature both in terms of texture and composition, whereas Surma Group of sandstone is immature texturally and compositionally. Barail and Surma sandstones are sublitharenite and litharenite. The provenance of sandstone of the Barail Group is "quartzose recycled orogen" and "cratonic interior", whereas that of the Surma Group is "quartzose recycled orogen" and "transitional recycled orogen". The detritus of sandstone are mostly derived from collision-suture fold belt. Diverse lithic fragments of shale, siltstone, slate, chert, phyllite, quartzite and quartz-mica schist with few plutonic and volcanic igneous rocks suggest their derivation from a complex assemblage of sedimentary, metasedimentary and low-medium grade metamorphic source with minor plutonic and volcanic rock contribution. Petrographic studies also suggest the prevalence of humid and semi-humid climate for Barail and Surma sandstone. Modal plots on the QpLvrnLms and LmLvLs diagram indicate that the Barail and the Surma sandstones were derived from the Collision suture and Fold Thrust belt source. Tectonic activity is the dominant factor controlling the nature and composition of the sandstone of this Surma-Barak basin.

Keywords

Surma-Barak Basin, Indo-Burma, Provenance Evolution, Petrographic Analysis, Barail and Surma Sandstone.

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M. Masroor Alam ¹, M. E. A. Mondal ², A. H. M. Ahmad ²

Affiliations
1 Department of Civil Engineering, Aligarh Muslim University, Aligarh - 202 002, IN
2 Department of Geology, Aligarh Muslim University, Aligarh - 202 002, IN

Abstract

This study mainly deals with the sandstone lithofacies and petrofacies of Jahaj-Govindpura Formation of the Raialo Group, rich in volcaniclastics, exposed near Hathori village. These cross and planar bedded sandstones are medium grained poorly sorted, and are cemented mainly by iron oxide, carbonate and by matrix rich in phyllosilicates and vitrofelsitic material. The sandstone petrofacies arc rich in detrital modes suggestive of metamorphic source terrain as well as juvenile volcanic 1ithic fragments with textual and mineralogical characteristics typical of neo-volcanic source which was very near to the basin. The underlying clastics of Raialo Group and the overlying formations represented by the Alwar and Ajabgarh Groups of the Jahaj-Govindpura volcanics respectively, do not have a notable amount of volcanic lithics. This suggests that the volcanism was intrabasinal, took place for a shorter time period and was not vety explosive. While the sedimentation continued in this basin, detritus from the highs exposing the BGC and Aravalli Supergroup of rocks in SE and SW were mixed with intrabasinal volcaniclastics. These volcanic highs then may have been carapaced by younger sediments which were deposited in linear rift zones and were eroded from an "Accreted Basement Provenance" comprising Banded Gneissic Complex and Aravalli Supergroup in a short time span.

Keywords

Syn-Depositional Volcanism, Sandstone, Lithofacies, Petrofacies, Tectonic Setting, Bayana Basin, Aravalli-Delhi Fold Belt, Rajasthan.

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V. K. Sibal ¹, S. V. Rajui ¹, M. E. A. Mondal ², M. Nauroz Ahmad ¹

Affiliations
1 Directorate General of Hydrocarbons, New Delhi 110 001, IN
2 Department of Geology, Aligarh Muslim University, Aligarh 202002, IN

Abstract

No Abstract.

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M. E. A. Mondal ¹

Affiliations
1 Department of Geology, Aligarh Muslim University, Aligarh - 202 002, IN

Abstract

No Abstract.

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