The elusive crustal resistive boundary beneath the Deccan Volcanic Province and the western Dharwar craton, India

Abstract

The electrical properties of the boundary beneath the Deccan Volcanic Province and the western Dharwar craton are imaged by using the magnetotelluric method. The magnetotelluric study was carried out along a 150km long WNW-ESE profile from Belgaum (in the Deccan Volcanic Province) to Haveri (in the western Dharwar craton). Data from 19 magnetotelluric stations spaced 10-15km apart were used. The dominant regional geo-electric strike direction obtained is N20ºE. Two-dimensional (2-D) inversion is done by using the non-linear conjugate gradient scheme for both apparent resistivity and phase. The 2-D resistivity model shows a high electrical resistivity character (>10,000ohm·m) in the western Dharwar craton. Two conductive anomalies are mapped in the crustal region. In the WNW side of the profile, a conductive feature (~200ohm·m) is imaged in the mid-lower crust and, in the central part of the profile another conductive feature is mapped in the lower crust. The robustness of conductive features is tested using linear and non-linear sensitivity analyses. The conductor mapped in the WNW part of the profile is considered as a deep-seated fault representing a boundary or a rift related feature beneath the Deccan Volcanic Province and the western Dharwar craton. A zone of enhanced conductivity (<50ohm·m) at an approximate depth of 10-30km may represent the presence of the rift in the region. This conducting feature on the Western side of the E-W trending Kaladgi Basin can be interpreted as the extension of the Kaladgi Basin further west. A wellcorrelated geological cross-section is also derived to interpret the resistive features mapped in this study. The electrical resistivity nature of the crust is compared with other regions of the world.