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

R. N. Singh ¹

Affiliations
1 National Geophysical Research Institute Hyderabad-500007, IN

Abstract

No Abstract.

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R. N. Singh ¹, K. R. Gupta ²

Affiliations
1 National Geophysical Research Institute, Hyderabad, IN
2 Department of Science and Technology, New Delhi, IN

Abstract

No Abstract.

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R. N. Singh ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN

Abstract

Erosion has been a dominant geological process. Erosion of the continental crust removes surface layers bringing hotter regions closer to the surface. Eroded surface layers also have larger radiogenic heat production. Effects of both these on the thermal evolution of crust have been earlier modelled analytically with the help of an advection-diffusion equation model. These processes lead to raising thermal gradient near the surface initially and decreasing later on ,depending on the rate of erosion. The changes in the thermal structure of the near surface region would lead to generation of thermal stresses, changes in the depth of brittle-ductile transition and lateral mass transport below this transition depth. Analytical models developed to quantify thermal effects due to erosion have been summarised and some numerical results, applicable to the south Indian region, are presented.

Keywords

Erosion, Thermal Models, Surface Stress, Lower Crustal Flow, Orogenic Complexity.

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R. N. Singh ¹, Ralph Thorpe ², D. Kristic ³

Affiliations
1 Geological Survey of India, Lohianagar, Patna - 800 020, IN
2 Geological Survey of Canada, Ontario, KIAOE 8, CA
3 Geospec Consultants Ltd., 4632, 151 Street, Edmonton, Alberta T6H5 N8, CA

Abstract

Pb isotope data were obtained for galena specimens from 5 sulphide occurrences within the Chotanagpur Gneissic Complex (CGC) in eastern Bihar, where the host rock occurs as enclaves within the CGC. Based on galena Pb isotope composition, an attempt has been made to suggest a Proterozoic event of sulphide mineralization related to Precambrian crustal evolution. An age range 1650 to 1700 Ma seems reasonable for the Bihar galena.

Keywords

Sulphides, Lead Isotopes, Actinolite-Tremolite Schist, Chotanagpur Gneissic Complex (CGC), Bihar.

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B. Ashalatha ¹, R. N. Singh ²

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500007, IN
2 National Environmental Engineering Research Institute, Nehru Marg, Nagpur - 440 020, IN

Abstract

The thermal structure of Carlsberg Ridge in the northwest Indian Qcean is discussed using the plate model with realistic thermal boundary condition at the ridge axis, which includes the effects of adiabatic cooling, magmatic crystallization and solidification. The elastic and brittle layer boundaries as predicted by the model are shallower when compared with results from earlier studies using gravity-bathymetry data across the ridge and seismicity at the axis of the ridge. In order to explain the observed anomalous structure, we consider hydrothermal circulation as resulting in additional heat loss. This is incorporated in the thermal model by presenting lower temperature in the shallow regions at the axis where fluid flows could occur. The resulting thermal structure explains the observed elastic thickness and brittle layer thickness.

Keywords

Carlsberg Ridge, Elastic Thickness, Thermal Structure, Plate Model, Hydrothermal Circulation.

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