Bazuru Article Tools Print this article. Muthuswami Memorial Lecture C. Nallamalai fold belt is demarcated from the undeformed western sub-basins by the prominent fault lineament called the Rudravaram Line along which cleavage begins to develop in the Cuddapah sediments, which become intensely deformed towards the boundary thrust in the east. Karanth Endowment Lecture T.

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Dalziel, The reorganization of Rodinia is thought to have been responsible for the formation of Gondwana e. Rogers et al. It is in this context that the locations of Proterozoic kimberlites and lamproites in the pre-Cretaceous Gondwana fit assume significance.

A number of kimberlites and lamproites were emplaced during the Proterozoic in the Eastern Dharwar Craton and Cuddapah Basin of the southern Indian shield Fig. Known kimberlite occurrences in the Dharwar Craton are confined to an area immediately west of the Cuddapah Basin Fig. The kimberlites and lamproites of the Indian sub-continent offer a rare opportunity to investigate Proterozoic tectono-magmatic processes operating when southern India formed a part of the Gondwana supercontinent.

Current understanding of the petrogenesis of kimberlites and lamproites has been strongly influenced by studies of examples from South Africa e.

Jaques et al. Gibson et al. Beard et al. This work complements these recent studies and sheds further insight into the genesis of, and genetic relationship between, kimberlites and lamproites. Geological map of the Cuddapah Basin and surrounding areas after Nagaraja Rao et al.

The evolution of the Indian shield was initially suggested to have started around Archaean nuclei that developed into three cratons Dharwar, Singhbhum and Aravalli; Naqvi et al. Subsequent studies revealed additional tectonic sutures, and the Indian shield is now subdivided into seven cratons e. Although the nature of the cratonic boundaries remains unresolved see Mahadevan, , there is a consensus that the Indian shield has been a single lithospheric unit since mid-Proterozoic times e. The Dharwar Craton mainly comprises schists and gneisses that have undergone greenschist- to granulite-facies metamorphism Rollinson et al.

The Eastern Ghat orogeny affected the Eastern Dharwar Craton, resulting in a narrow, highly deformed granulite-facies belt extending from Madras in the south to near Calcutta in the north.

This belt may extend into Eastern Antarctica e. Chetty, The basin is crescent shaped, covers an area of 44 km2 and shows increasing metamorphic grade from west to east, attributed to the Eastern Ghat orogeny. A marked angular unconformity separates sediments of the older Cuddapah Supergroup from the Kurnool Group.

Intrusive and extrusive rocks are present throughout much of the Cuddapah Supergroup, and extensive lava flows, ash beds and sills occur along the SW fringes of the Cuddapah Basin Reddy, ; Anand et al. Additional intrusives include lamproites at Chelima and Zangamarajupalle , rare alkali syenites and granitoid domes.

The crust beneath the Cuddapah Basin is 40—50 km thick Kaila et al. The thermal structure of the Dharwar lithosphere is considered identical to cratons in Africa, Australia and South America Gupta, Evidence for the existence of a thickened Proterozoic Indian lithosphere comes from studies of mantle-derived xenoliths from a kimberlite from the Dharwar Craton [Pipe 3 from Lattavaram in the Anantapur cluster Fig.

Thermobarometry of garnet peridotites from this pipe suggests that the mid-Proterozoic lithosphere was at least km thick see below.

The Archaean basement surrounding the basin is intruded by an extensive swarm of dolerite dykes, which trend ENE—WSW but do not intrude the basin sediments. Radiometric age determinations are of variable precision but suggest that at least three major episodes of dyke emplacement occurred at — Ma, — Ma and — Ma together with a minor younger event at Ma Murthy et al.

Some north—south-trending mafic dykes, at the northern end of the Cuddapah Basin, are of basaltic komatiite affinity and were emplaced between and Ma Mallikharjuna Rao et al. The freshest possible surface samples, augmented by drill-core samples, were used in this study. The major petrographic features of the studied rocks are summarized in Table 2.

Table 2: Petrography of kimberlites and lamproites of the Dharwar Craton Pipe details.



Akisar The early sediments of the basin are interspersed with basic volcanics and sills. Gupta Gold Medal L. The basin extends for a length of about km along the arcuate eastern margin with a mean width of km, and is the second largest Purana basin of Penninsular India, after the great Vindhayan basin. How to cite item. Karanth Endowment Lecture T. This site is best viewed using current versions of Firefox v. Email the author Login required.





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