Crustal architecture across the Mahanadi Shear Zone in the Northern EGMB region: Insights from Mohr Circle and Phase Tensor Analysis
摘要
The Eastern Ghats Mobile Belt (EGMB) is a tectonically reworked terrane characterized by complex lithospheric architecture shaped by multiple orogenic events. Understanding the dimensionality of Magnetotelluric (MT) data is essential for comprehensive resistivity modelling and reliable geological interpretation. In this study, broadband MT data acquired along a profile crossing the northern EGMB were analysed using the Mohr circle approach, complemented by phase tensor and skewness evaluations. The Mohr circle method, through its representation of impedance tensor invariants, provides a powerful tool for assessing frequency dependent dimensionality, anisotropy, and noise-affected data. At higher frequencies, the Mohr circles display consistent alignment, reflecting a dominantly 1D/2D resistivity structure associated with shallow subsurface. With increasing period towards intermediate to lower frequencies, the increasing divergence of the Mohr circle arms reflects a growing influence of three-dimensional effects concentrated around the Mahanadi Shear Zone (MSZ) and the Angul-Dhenkanal Shear Zone (ADSZ), major E-W trending crustal-scale structures, along with enhanced electrical anisotropy at depth. Phase tensor analysis further corroborates the above interpretation, showing ellipses filled with low skew values dominating at short periods, while elongated ellipses with high skew angles emerge at longer periods, indicating crustal deformation. Skewness values remain below 0.3 across much of the profile, consistent with 2D structures, but exceed this threshold at the intermediate to lower frequencies, pointing to 3D effects. Integration of these dimensionality diagnostics reveals that the subsurface beneath the profile is structurally complex, with 2D responses transitioning into strong 3D signatures near major tectonic contacts and shear zones. Collectively, the contrasting responses of MT stations (3, 4 and 7, 8) in the proximity to the shear zones highlight pronounced lateral variability in subsurface electrical properties along the profile.
Research highlightsMohr circle-based dimensionality analysis of MT data. A comparison of the dimensionality patterns from Phase tensor, skew analyses, and Mohr circles. Pronounced lateral heterogeneity near the Mahanadi and Angul–Dhenkanal shear zones. Role of Shear zones in lateral electrical heterogeneity and crustal architecture.