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

C. V. R. K. Prasad ¹, V. Damodara Reddy ¹

Affiliations
1 Department of Geology, Sri Venkateswara University, Tirupati, IN

Abstract

The magnetic studies on the ferruginous sandstone samples from the Kaverisamudram area and the metamorphosed shales from Beduduru area of Cuddapah basin are presented here along with the results from the dykes near Tirupati. From a comparison of these results with those obtained from other Precambrian formations of India, it is found that the Bijawars are equivalent to Cuddapahs. The results from the metamorphosed shales have indicated that the igneous activity in Cuddapah basin was contemporaneous with sedimentation. This igneous activity is also found to be contemporaneous with one of the intrusive phases of the Tirupati area.

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V. Damodara Reddy ¹, C. V. R. K. Prasad ¹

Affiliations
1 Department of Geology, S. V. University, Tirupati-517502, IN

Abstract

Results of the palaeomagnetic studies on five dykes intruding the Archaean schists from the Nundydroog mine (lat. 12°57', long. 78°15") of the Kolar Gold Fields are reported. Three dykes have given consistent and stable directions after cleaning in an alternating field of 150-200 oe. The virtual geomagnetic poles (VGP's) of these dykes are 47°N, 163°W; 50°N 36°W; and 45°N, 30°W. A Precambrian polar wandering curve for India is drawn taking into consideration radiometric ages and the palaeomagnetic data, available from the formations other than the dykes. Based on this polar wandering curve the ages of the dykes are interpreted. It is suggested that these dykes occupy the fractures which were probably formed during Precambrian times, due to an East-West compressive stress. Continental drift in Precambrian era is indicated.

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N. Subba Reddy ¹, C. V. R. K. Prasad ¹

Affiliations
1 Department of Geology, S. V. University, Tirupati-517 502, IN

Abstract

Magnetite-quartzites of Tamil Nadu associated with pyroxene granulites and gneisses occur in the Precambrian high grade granulite terrain. A study of distribution of ferride group of trace elements in separated magnetites suggests that the magnetite-quartzites and pyroxene granulites may have differrent modes of origin-metasedimentary and metavolcanic respectively. However, a volcano-sedimentary process for the magnetite-quartzites may have to be considered in view of the close association of metavolcanics.

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C. V. R. K. Prasad ¹, N. Subba Reddy ¹, B. F. Windley ²

Affiliations
1 Department of Geology, Sri Venkateswara University, Tirupati 517 502, Andhra Pradesh, IN
2 Department of Geology, The University, Leicester LEI 7RH, GB

Abstract

In Archaean granulite-gneiss belts there are banded iron formations (BIF) less than 20m thick which are weakly banded magnetite quartzites occurring in a supracrustal sequence of quartzites, mica schists, marbles and metavolcanic amphibolites. This sequence forms stratigraphic markers within voluminous intrusive tonalitic to trondbjemitic gneisses. These rocks are highly folded and metamorphosed to high amphibolite or granulite facies at 7-12 kb pressure in the lower Archaean crust. Such iron formations are well represented in Tamil Nadu, Southern Karnataka, Kerala and Andhra Pradesh in South India; in Hebei Province in China; Kola Peninsula, Stanovoy Range, and Ukraine in USSR; Kambui schists of Sierra Leone; Nimba series of Liberia; Limpopo belt of southern Africa; Imataca complex of Venezuela; Uivak gneisses of Labrador; and Amitsoq gneisses of West Greenland. They are obviously different in type and environment from the Proterozoic Superior type of BIF; it is shown here how they are different from the Archaean Algoma type of BIF. They were deposited in a quartzite-pelite-carbonate association and they lack the silicate-carbopate-sulphide facies of the Algoma-type which, in contrast, was deposited with a greywacke-flyschconglomerate- shale association in subsiding basins (Greenstone belts). Because they are dissimilar to the Algoma-type of BIF in both their sedimentary facies and tectonic environment (the granulite-gneiss belts are not highly metamorphosed greenstone belts), they should be given a separate status and we tentatively suggest they be termed the Tamil Nadu type.

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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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N. Subba Reddy ¹, C. V. R. K. Prasad ¹, V. Balaram ²

Affiliations
1 Department of Geology, S. V. University, Tirupati - 517 502, IN
2 National Geophysical Research Institute, Hyderabad - 500 007, IN

Abstract

Rare Earth Element (REE) distribution in 10 samples of Precambrian BIF of granulite gneiss belts of Tami! Nadu suggest that the BIP derived their constitutents of iron and silica from hydrothermal source. The BIP thus formed were metamorphosed to granulite fades metamorphism along with the associated volcanogenic products and sediments.

Keywords

Geochemistry, Iron Formation, Granulites, Tamil Nadu.

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V. Pulla Reddy ¹, N. Subba Reddy ², C. V. R. K. Prasad ²

Affiliations
1 ONGC, Nazira-785 685, Assam, IN
2 Department of Geology, Sri Venkateswara University, Tirupati-517502, IN

Abstract

Quartzites occurring at different stratigraphic levels in the Proterozoic Cuddapah Group are studied for petrography, chemistry and grain size distribution for purposes of comparison and determination of the environment of deposition. It is indicated that these formations were laid down in a beach environment and that they were subjected to tectonic disturbances before the Srisailam sediments were deposited. This resulted in the less mature nature of the Srisailam quartzites compared to all other quartzites underlying it.

Keywords

Sedimentary Geology, Quartzites, Cuddapah Group, Proterozoic.

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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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N. Subba Reddy ¹, N. Darga Reddy ¹, C. V. R. K. Prasad ¹

Affiliations
1 Department of Geology, Sri Venkateswara University, Tirupati - 517 502, IN

Abstract

Two hundred and ninety samples of Banded Magnetite Quartzites from Archaean granulitegneiss terrain and greenstone belts of Southern India are investigated for magnetic granillometry. It is suggested that these mainly contain MD grains with a combination of SD or CD grains. The granulometry and other magnetic properties of samples from the two regions are similar.

Keywords

Geophysics, Magnetic Properties, BMQ, Granulite Terrain, Greenstone Belts.

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