2-D versus 3-D Magnetotelluric Data Interpretation: A case study from the Dharwar craton, India

The resistivity structure of the lithosphere in the Dharwar craton is imaged using 17 magnetotelluric stations along a ~280 km long profile with an inter-station spacing of ~15 km. Since the adjacent two profiles have shown 2-D nature, initially 2-D inversion is carried out. But the resulting structures are completely different. WALDIM dimensionality analysis shows the 3-D nature of the subsurface structures for most of the frequencies beneath the given profile. 3-D inversion was done by using the WSINV3DMT inversion code. 3-D modelling results imaged several conductors in the crust and uppermost mantle region. The lithosphere can be divided into shallow and deeper lithospheres based on the conductivity anomalies present in the model. In the crustal region, vertical conductive features (~10 Ω-m) are present in the western and central part of the profile. A new finding of this 3-D study is the presence of an uppermost mantle conductor at the depth range of 100–200 km. The electrical properties of the conductors are comparable with the northward situated adjacent profiles conductors. The conductors present in the crust are due to sulphides and carbon-rich fluids. The low electrical resistivity in the deeper lithosphere is due to the refertilization of the mantle scar in the Cretaceous age by the passage of several hotspots. The conductor could be interpreted in the terms of the melt present in the region. In general, 2-D interpretation of 3-D magnetotelluric data acts as a guide to geological interpretation, but not in this case of the Dharwar craton. The concluding remark is that the 3-D image of the single profile data gives a better understanding of the subsurface structures as compared to 2-D inversion results. •MT method is used to image the structures in the Dharwar craton (DC)•Crustal conductors are associated with sulphides and carbon-rich fluids•Imaged an upper mantle conductor in the depth range of 100–200 km•Mantle conductors represent Cretaceous refertilization of mantle scar•2-D interpretation of MT data acquired over 3-D structures is sometimes misleading