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Rao, C. K.
- Electrical Conductance Map for Saurashtra Region, Gujarat, India
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Authors
Affiliations
1 Indian Institute of Geomagnetism, Panvel, Navi Mumbai 410 218, IN
1 Indian Institute of Geomagnetism, Panvel, Navi Mumbai 410 218, IN
Source
Current Science, Vol 114, No 10 (2018), Pagination: 2175-2181Abstract
In the present study, we have deployed 35 fluxgate magnetometers and 20 long-period magnetotelluric sites to derive the electrical conductivity distribution of Saurashtra region, Gujarat, India. Geomagnetic field variations (X-north–south, Y-east–west and Z-vertically downward components) recorded at the above sites are investigated to obtain single-station vertical field transfer functions. Maps of induction arrows suggest that the offshore basins are more conducting than inland basins of the region. Thin sheet modelling of the induction features suggests that the anomalous behaviour is strongly influenced by the offshore and shelf edge sedimentary basins that contain thick depo centres of Mesozoic sediments. Jamnagar, Ulva and Mesozoic sedimentary basins on land are also reflected as high conductivity anomalies that could be related to the presence of carbonate/shale sediments. Release of carbon (in the form of thin films) due to thermal activity of Reunion hotspot on carbonate rich sediments may give rise to high conductivity anomalies.Keywords
Carbon Films, Induction Arrows, Thermal Activity, Thin Sheet Modelling.Full Text
References
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- Magnetotelluric Study to Characterize Sediment Thickness Across Kachchh and Cambay Rift Basins, Western India
Abstract Views :177 |
PDF Views:72
Authors
Nagarjuna Danda
1,
C. K. Rao
1
Affiliations
1 Dr K. S. Krishnan Geomagnetic Research Laboratory, Indian Institute of Geomagnetism, Allahabad - 221 505, IN
1 Dr K. S. Krishnan Geomagnetic Research Laboratory, Indian Institute of Geomagnetism, Allahabad - 221 505, IN
Source
Current Science, Vol 116, No 2 (2019), Pagination: 299-304Abstract
The Kachchh and Cambay rift basins are two pericon-tinental rift basins at the western continental margin of India (WCMI), which evolved during different stages of the Mesozoic era. Magnetotelluric measure-ments were carried out at 68 stations along four east–west trending profiles across these basins with an aim to infer basement configuration and sediment thickness. The data were analysed for galvanic distortions and decomposed into transverse electric (TE) and transverse magnetic (TM)-modes by rotating the im-pedance tensor into corresponding geoelectric strike directions of the four profiles. The decomposed data responses were then inverted using a nonlinear conjugate gradient algorithm. The top conductive layers (∼2500–7500 S) across the Kachchh and Cambay rift basins indicate the presence of Cenozoic sediments and Deccan traps, which corroborates the results of earlier geophysical studies across these basins. The sediment thickness is low across Diyodar and Tharad ridges compared to the Sanchore, Patan and Mehsana sub-basins. A high conductive zone near Mehsana may support the evidence for the presence of Mesozoic sediments beneath traps as inferred from a deep seis-mic sounding (DSS) study. Even though the Oil and Natural Gas Corporation Limited (ONGC) drilled wells and DSS study reported the presence of Mesozo-ic sediments beneath the traps near Tharad ridge, their presence here is not clear from this study. Igne-ous intrusives and a Precambrian Aravalli–Delhi fold belt are delineated on either side of the Cambay rift basin. The electrical resistivity variations across these basins lead to the inference that the subsurface struc-ture is highly heterogeneous in nature due to faults within the rift basins.Keywords
Cambay Rift, Deccan Traps, Kachchh Rift, Magnetotellurics, Sediment Thickness.Full Text
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