Deep Resistivity Structure of Basalt‐Covered Central Part of Paraná Basin, Brazil, From Joint 3‐D MT and GDS Data Imaging

The deep structure beneath the basalt‐covered sediments of Paraná basin is not well understood. Magnetotelluric (MT) broadband (1,000 to 0.001 Hz) data recorded at 296 selected stations along three new survey lines were first inverted in three dimensions to reveal the local scale resistivity structure of the central part of the basin where there are three deep exploration wells with resistivity logs for model validation. The 3‐D MT inversion model correctly identified the resistive (>100 Ωm) flood basalts and postvolcanic cover layer, the underlying electrically conductive (~10 Ωm) sediments, and the highly resistive (>1,000 Ωm) crystalline basement at the well locations and provides a reliable average crustal resistivity structure consisting of ~20–24 km thick highly resistive upper crust and ~20 km thick conductive lower crust above a resistive mantle. Subsequent basin‐scale joint inversion of highest quality MT data sets (261 stations) and geomagnetic depth sounding array data imaged two prominent subparallel belts of N‐S and NNE‐SSW trending steep conductors in the deep crust and upper mantle, one located directly beneath the present‐day axis of thickest sedimentary deposits in the basin and another near the coastal location where dolerite dyke swarms intrude the outcropping Precambrian basement. Other roughly orthogonal bands (E‐W to NW‐SE) of linear crustal conductors radiate from these two main belts. The resulting networks of steep conductors at upper to midcrustal level seem to mark the fossil plumbing system of Paraná magmatic province and are interpreted as preexisting shear zones exploited by the voluminous Early Cretaceous magmatism in the region. Plain Language Summary Data from new magnetotelluric survey have been modeled to reveal the widespread occurrence of low resistivity materials (most likely sediments) beneath thick basalt cover in the top 6 km of this basin. The model also shows that the basic lithospheric structure consists of ~20–24 km thick upper crust of high resistivity, ~20 km thick lower crust of low to moderate resistivity, and upper mantle of high resistivity. These are dissected by steep zones of low resistivity interpreted as mineralized shear zones or fossil conduits for the voluminous Early Cretaceous magma in the region. Using combined magnetotelluric and legacy geomagnetic depth sounding data, an anomalous ~500‐km‐wide block of high resistivity is imaged in the upper mantle down to about 250‐km depth beneath the basin