Magnetotelluric studies across the Kurduwadi gravity feature

Details Magnetotelluric studies across the Kurduwadi gravity feature Magnetotelluric studies across the Kurduwadi gravity feature

Jul 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992pepi...72...58g&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 72, Issue 1-2, p. 58-67.

Physics

5

Scientific paper

The Deccan traps have a predominantly negative Bougner anomaly with two prominent regions of gravity low along the Nasik-Koyna and Nasik-Kurduwadi lines. On the basis of these a rift zone was suggested along the Nasik-Kurduwadi region. This rift theory was not supported by later deep seismic sounding (DSS) studies. Subsequent gravity modelling studies indicated that the observed anomalies could be explained in terms of undulations in the crust-mantle boundary and the Conrad discontinuity. It was thus felt that the region should be reinvestigated to check for the rift valley using magnetotelluric (MT) techniques. A linear profile about 100 km long was identified for these studies. Magnetotelluric data were collected at 11 stations with an average station spacing of 8-15 km. The data at ten of these stations were found to be good for the purpose of analysis. The rotation of the impedance tensor showed a regional rotation angle of 60° east of north. With this rotation, the direction of the major resistivity is approximately perpendicular to the direction of gravity low as well as the west coast of the Indian peninsula. One-dimensional (1D) analysis at all stations showed a five-layered structure. A regional geoelectric cross-section is proposed using the 1D data. The influence of the west coast was studied using two-dimensional (2D) modelling techniques. The Deccan basalts were observed to be about 500 m thick, overlying the granitic upper crust. A mid-crustal conductor with a conductance of about 200 S was delineated at a depth of 12-18 km. This shows good agreement with the Conrad discontinuity reported from the DSS and gravity studies. The Moho discontinuity was not seen in the data presumably because it is not accompanied by any detectable change of electrical resistivity. The lithosphere-asthenosphere boundary is shallow, at a depth of about 80-100 km. The asthenosphere is not well formed as is evident from the large resistivities (50-100 ωm). Signature of sediments below the traps could not be found in the survey area.

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