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

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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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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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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