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

K. V. Subbarao ¹, V. V. Reddy ¹, G. R. Reddy ², R. N. Sukheswala ³

Affiliations
1 Indian Insntute of Technology, Powai, Bombay-400076, IN
2 Bhabha Atomic Research Center, Trombay, Bombay-400085, IN
3 St. Xavier's College, Bombay-400 001, IN

Abstract

No Abstract.

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K. V. Subbarao ¹, V. V. Reddy ¹, G. R. Reddy ², R. Hekinian ³

Affiliations
1 Indian Institute of Technology, Powai, Bombay-400076, IN
2 Bhabha Atomic Research Centre, Trombay, Bombay-400085, IN
3 Centre Oceanologique de Bretagne, 29-273 Brest, FR

Abstract

Rare earth element (REE) analysis for fresh glass and crystalline basalts from the FAMOUS area along the Rift Valley at about 36°N in Atlantic Ocean lying close to the triple junction of North American, Eurasian and African plates, are presented. These rocks display light rare earth element (LREE) patterns with (La/Sm)_e.f. ratios ranging between 0.56-0.84 similar to spreading mid-oceanic ridge rocks, suggesting the definite presence of large ion lithophile element (LILE) depleted mantle source in this area. White and Bryan (1977) report the presence of LREE enriched basalts from the FAMOUS area which perhaps resulted due to the effect of the Azores mantle plume. Thus, geochemically the FAMOUS area represents a transitional zone-a mixture of mantle plume and LILE depleted normal ridge.

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A. V. Murali ¹, P. B. Pawaskar ¹, G. R. Reddy ¹, K. V. Subbarao ², V. N. Vasudev ³, M. Sankar Das ¹

Affiliations
1 Analytical Chemistry Division, Bhabha Atomic Research Centre, Trombay, Bombay-400085, IN
2 Geology Department, Indian lnstitute of Technology, Powai, Bombay-400 076, IN
3 Chitradurga Copper Company, 16, Ali Asker Road, Bangalore-560052, IN

Abstract

No Abstract.

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P. K. Seccombe ¹, K. V. Subbarao ², J. N. Pawar ²

Affiliations
1 Department of Geology, University of Newcastle, Newcastle, N. S. W. 2308, AU
2 Indian Institute of Technology, Powai, Bombay 400076, IN

Abstract

Mineralisation at Ingaldhal, Kamataka State, comprises massive vein and disseminated sulphides within deformed Archaean metasedimentary rocks and metabasaltic rocks of tholeiitic affinity. Seven sulphur isotope ratio determinations on sulphide minerals separated from ore samples yield a narrow distribution of δ³⁴S values around the meteoritic mean (range -0.9 to +0.4 per mil; mean -0.2 per mil) values which arc similar to Archaean volcanogenic ores elsewhere.

The source of sulphur is considered to be magmatic, with possible contribution from Archaean seawater. The stockwork and massive nature of the Ingaldhal ores, their Cu-Fe content, poorly developed metal zoning and basic volcanic association in a submarine setting point strongly to subsurface and sea-floor sulphide accumulation from sulphur- and metal-bearing fluids of volcanic origin. The sulphur isotope data support this view.

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K. V. Subbarao ¹

Affiliations
1 I.I.T., Bombay, IN

Abstract

No Abstract.

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M. Sreenivasa Rao ¹, N. Ramasubba Reddy ², K. V. Subbarao ¹, C. V. R. K. Prasad ², C. Radhakrishnamurty ³

Affiliations
1 Department of Earth Sciences, Indian Institute of Technology, Bombay 400076, IN
2 Department of Geology, Sri Venkateswara University, Tirupati 517502, IN
3 Tata Institute of Fundamental Research, Bombay 400005, IN

Abstract

Field investigations of a 666 m thick Deccan volcanic sequence north of the River Narmada (Khalghat-Mhow traverse; 60 km) showed the presence of 21 flows, while a 549 m thick southern section comprises of 28 flows (Mandaleswar-Pipaljopa traverse: 110 km). The lava sequences essentially consist of PI and/or Pyx phyric to aphyric basalts with glassy vesicular - amygdular tops/flow breccia.

On the basis of selected major and trace elements (Si, K, Ti, P, Ba, Sr, Zr), the Khalghat section is divided into three formations. The lowermost Narmada Formation is characterized by lower K, Ba, Sr, Ba/Ti, Ba/Sr and Ba/Zr than the succeeding Manpur Formation. The uppermost Mhow Formation is highly depleted in K, Ba, Sr compared to the two lower formations. Chemically, a four-unit informal stratigraphy has been adopted for the Mandaleswar section. The lower three may be correlated with the Narmada, Manpur and Mhow Fms of the Khalghat section and the upper one is labelled the Satpura Formation. Each formation is defined as a set of flows characterized by one or more chemical types such as 'primitive' and' evolved' ones.

The palaeomagnetic results of the Khalghat section demonstrate that the lower 254m pile of flows belongs to normal polarity (N) ('Narmada Normal Epoch') overlain by 412 m thick flows with reversed polarity (R) ('Malwa Reversed Epoch'). Interestingly, on the southern side of the river, about 21 m thick N flows are overlain by 476 m R flows, which in turn are capped by 52m thick N flows ('Satpura Normal Epoch') resulting in an unambiguous NRN sequence in the Deccan basalt province. It appears that the northern side of the Narmada River has been thrown up relative to the southern side. Based on the correlation of the magnetic reversals in the Deccan as well as marine magnetic anomalies, it seems likely that the normally magnetized older Rajmahal traps (about 100 MA) of eastern India form the base of the Deccan basalts.

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K. V. Subbarao ¹, S. Pathak ¹

Affiliations
1 Department of Earth Sciences, Indian Institute of Technology, Powai, Bombay-400 076, IN

Abstract

No Abstract.

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K. V. Subbarao ¹

Affiliations
1 Dept. of Earth Sciences, Indian Institute of Technology, Powai, Bombay 400 076, IN

Abstract

A critical petrographic investigation together with magnetic studies such as the variation of susceptibility with temperature and hysteresis have been carried out on basalt samples drilled across a dyke and a columnar sill from the Deccan Traps. In the case of columnar basalts, not much variation has been found in the grain size but display increase in shattering of the grains towards the edge of the column. In contrast, the dyke samples are tachylitic at the edge grading to fine-grained basalt in the middle.

The magnetic hysteresis studies indicate an increase of single-domain (SO) mineral grains from the margin to the centre of the columnar basalt. Low temperature susceptibility studies clearly indicate Ihe presence of some multidomain (MD) componcnt of pure magnctite in the cdge samples where as it is barely noticeahle in the s.1l1lple from the cenlre. Samples from the dyke show systematic variations of rhe magnetic parameters. These magnetic variations can be undcrstood in terms of titanomagnctite composition and domain states of thc grains among samples from across the dyke.

Keywords

Deccan Traps, Dyke, Sill; Petrology, Maharashtra.

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K. V. SubbaRao ¹, M. J. Le Bas ², B. Bhaskar Rao ¹

Affiliations
1 Department of Earth Sciences, Indian Institute of Technology, Powai, Bombay 400 076, IN
2 Department of Geology, University of Leicester, Leicester LEI 7RH, GB

Abstract

New whole-rock rare earth element (REE) data for the metacarbonate rocks interbedded with schists at Vinjamur in the Nellore Schist Belt of Andhra Pradesh, show low total REE contents (Σ9-128 ppm) that are inconsistent with an igneous carbonatitic origin but which correspond more closely with a sedimentary limestone origin. The REE data of these rocks however, do not give absolute discrimination between marbles of meta-limestone and metacarbonatite origin. Micro-probe analytical data give better discrimination, and the chemical compositions of the calcite, micas, amphibole, plagioclase, apatite, monazite and staurolite in the Vinjamur marbles give strong and consistent evidence of a metamorphosed sedimentary rather than an igneous origin.

Keywords

Carbonatites, Vinjamur, Nellore Schist Belt, Andhra Pradesh.

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R. Shankar ¹, K. V. Subbarao ², V. Kolla ³

Affiliations
1 Department of Marine Geology, Mangalore University, Mangalagangotri 574 199, IN
2 Department of Earth Sciences, Indian Institute of Technology, Powai, Bombay 400 076,, IN
3 ELF Aquitaine Petroleum, 1000 Louisiana, Houston, Texas 77002, US

Abstract

A wide variety of processes such as volcanic activity, submarine and continental weathering, aeolian transport and authigenesis can account for the magnetic susceptibility of the deep Arabian Sea sediments. Preliminary studies of the magnetic fraction indicate that it is predominantly composed of pseudo-single domain and viscous magnetite. It is found that magnetic susceptibility can be used to estimate the approximate iron content of marine sediments.

Keywords

Magnetic Susceptibility, Marine Geology, Arabian Sea.

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M. R. Goutham ¹, K. Raghubabu ², C. V. R. K. Prasad ³, K. V. Subbarao ⁴, V. Damodara Reddy ²

Affiliations
1 Department of Geophysics, Osmania University, Hyderabad - 500 007, IN
2 Department of Geology, Sri Venkateswara University, Tirupati - 517 502, IN
3 "Amararama" Venkataratnam Street, Suryaraopet, Vijayawada - 520 002, IN
4 Centre for Earth and Space Sciences, University of Hyderabad, Hyderabad - 500 046, IN

Abstract

The Proterozoic Cuddapah Supergroup is predominantly of normal magnetization but has a reversely magnetized level coinciding with the Srisailam Quartzite at the top of the succession. The Kurnool Group overlies the Cuddapah Supergroup with an unconformity and we present palaeomagnetic results from the Kurnool Group members comprising the Banganapalli Quartzite and the Narji Limestone. The Neoproterozoic Banganapalli Quartzite carries stable normal and reverse magnetizations suggesting a geomagnetic field reversal at the time of its formation. The Narji Limestone is normally magnetized. A similar magnetization to that in the Banganapalli Quartzite is reported -1000km away in the Baghain Sandstone of the Vindhyan Supergroup. A possible correlation is made between Cuddapah Supergroup and Kurnool Group with the Vindhyan Supergroup. Based on palaeomagnetic poles, palaeolatitudes, palaeoclimatic and structural evidence it is suggested that India and Australia collided possibly during Neo-Proterozoic times in an attempt to form larger Gondwana.

Keywords

Palaeomagnetism, Reversal of Poles, Magnetostratigraphy, Gondwana Evolution, Cuddapah Supergroup, Kurnool Group, Andhra Pradesh.

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K. V. Subbarao ¹, Arun Agarwal ¹, chaitan Baru ²

Affiliations
1 University of Hyderabad, Hyderabad - 500 046, IN
2 University of California, San Diego 9500 Gilman Drive, MC 0505 La Jolla, CA - 92093, US

Abstract

No Abstract.

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K. V. Subbarao ¹

Affiliations
1 Centre for Earth and Space Sciences University of Hyderabad, Gachibowli, Hyderabad - 500 046, IN

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K. V. Subbarao ¹

Affiliations
1 Indian Institute of Technology, Mumbai and University of Hyderabad, IN

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K. V. SubbaRao ¹, S. Viswanadhan ¹

Affiliations
1 IIT, Bombay, Powai Mumbai - 400 076, IN

Abstract

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Richa Sahu ¹, Anil Kumar ², K. V. Subbarao ¹, J. N. Walsh ³, T. K. Biswal ¹

Affiliations
1 Indian Institute of Technology, Mumbai - 400 076., IN
2 National Geophysical ,Research Laboratory, Hyderabad - 500 007., IN
3 Royal Holloway, University of London, Egham, Surrey TW20 OEX, GB

Abstract

No Abstract.

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K. V. Subbarao ¹

Affiliations
1 Indian Institute of Technology, Mumbai, IN

Abstract

No Abstract.

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