Magnetotelluric 3-D full tensor inversion in the Dharwar craton, India: Mapping of subduction polarity and kimberlitic melt

Abstract Complex geological structures and processes that took place in the Dharwar craton formation make it difficult to understand the evolution history. 3-D magnetotelluric inversion is a challenging task for the imaging of sub-surface structures. Data at 40 stations in a gridded fashion are used in this study for inversion. A controversy exists regarding the subduction polarity between the eastern and western Dharwar craton. Based on the conductivity anomalies mapped in the sub-surface, the lithosphere can be divided into the shallower and deeper lithosphere. The study delineated several crustal and lithospheric upper mantle conductors. In the crustal region, several conductive features (~10 Ω-m) are imaged in the western part, central, and eastern part of the profile. A new finding of this 3-D study is a conductor in the eastern Dharwar craton in the depth range of 65–140 km. The base of this conductor shows the graphite diamond stability field and is correlated with the kimberlites/lamproites present in the region. An uppermost mantle conductor is present at the depth range of 80–200 km in the central part of the study area. Sulphides and carbon-rich fluids could be one cause of the conductors mapped in the crust. The low electrical resistivity imaged in the deeper lithosphere could be due to the refertilization of the mantle scar in the Cretaceous age by the passage of several hotspots. The lithospheric thickness estimated beneath the Dharwar craton in this study is more than 200 km. This study reveals geophysical evidence for the eastward subduction polarity in the Dharwar craton.