Deciphering Fine Electrical Conductivity Structures in the Crust From MT Data Using the Equivalent Conductivity Formula

Abstract

AbstractFine structures in the lower crust sounded by seismic reflection can be formed in various geological processes and their electrical resistivity properties can provide significant insights into the geodynamic processes of the lithosphere. The magnetotelluric (MT) method is popular for imaging the electrical resistivity structure of the lithosphere; however, it lacks high resolution to resolve the small heterogeneities in deep crust. To recover the fine electrical resistivity structures, we propose a strategy based on their equivalent resistivity that defines the relationship between the fine structures and the inverted bulk resistivities. Thus, we first formulated the equivalent resistivity for a 3‐D laminated structure with >95% accuracy. In this strategy, the bulk resistivity inverted from MT data is used to retrieve the fine resistivity structures, for which the corresponding equivalent resistivities should match with the inverted resistivities. The strategy was tested to demonstrate its feasibility for analyzing the electrical property and the cause of lamellae in the lower crust of the Basin and Range Province. From the bulk resistivities of 1‐D anisotropic inversion, we retrieved the resistivity of lamellae that was in the range of 0.15–0.3  and coincident with the resistivity of silicate melts, implying that the lamellae are probably magma chambers with >50% melt fraction, which is also supported by seismic and geological evidences. Our case study demonstrated that this strategy based on equivalence can be successfully used to recover the fine resistivity structures from MT data.