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

T. Seshunarayana ¹, P. Senthil Kumar ¹, V. Sampath Rao ¹, D. Mysaih ¹, K. Satish Kumar ¹, P. Pavan Kishore ¹

Affiliations
1 National Geophysical Research Institute, Uppal Road, Hyderabad-500007, IN

Abstract

Delineation of shear zones and fracture systems in hard rock areas is essential in locating potential groundwater zones. The Mu1tichannel Analysis of Surface Waves (MASW) is a new developing seismic geophysical technique, which has now been widely used in imaging shallow subsurface, in terms of shear wave velocity. We test its potentiality in Hyderabad granite terrain, at Wailapally watershed, for delineating shear zones and fractures in a shallow granite basement covered with thin weathering and alluvium cover. Surface wave data were obtained at three sites using 24 channel seismograph, and were used to model the shear wave velocity of the subsurface. The study clearly demarcates the bedrock depths, shear zones or faults, fractures, weathering and soi1 covers in the shallow subsurface up to a depth of -30 m, the results are also in good agreement with the surface geological observations. Therefore, the MASW is an excellent geophysical tool that can clearly demarcate the shallow structures favorable for groundwater in hard rock areas.

Keywords

Surface Waves, Shear Zones, Fractures, Granite, Groundwater, Wallapally, Hyderabad, Andhra Pradesh.

Full Text

     

P. Senthil kumar ¹, G. Parthasarathy ¹, S. Das Sharma ¹, R. Srinivasan ¹, P. Krishnamurthy ²

Affiliations
1 National Geophysical Research Institute, Uppal Road, Hyderabad-500 007, IN
2 Atomic Minerals Directorate for Exploration and Research, AMD Complex, Begumpet, Hyderabad-500 01 6, IN

Abstract

Carbonate veins up to few metres thick have been recognised in the E-W striking Salem-Attur deep fault zone which represents the eastern extention of the Moyar fault in the southern granulite terrane of India. X-ray diffraction, FTIR spectroscopy and chemical analyses show calcite, ankerite, siderite and benstonite as dominant minerals besides minor apatite and green biotite. Whole rock compositions show enrichment of light REE, Ba, Sr and Nb. C and 0 isotopic data determined for calcite (δ¹³C= -4.9 to -5.1%0 V-PDB and δ¹⁸0 = 9 to 9.2%0 V-SMOW) points to a mantle origin. The chemical characteristics therefore suggest that the carbonate veins have carbonatitic affinity. The FTIR spectra provide evidence for presence of H₂0 and CH₄ in addition to CO₂ in the carbonate minerals of these veins.

Keywords

Ferrocarbonatites, Benstonite, FTIR Spectroscopy, X-Ray Diffraction, Geochemistry, Isotopes, Tamil Nadu.

Full Text