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

Abstract

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.

3D inversion of MT data in Misiones and Corrientes, NE Argentina

“…Although structures outside of the data area should be interpreted with caution, this conductor is robust, since it appeared in every inversion we run, using different initial models and parameters, and was also suggested by the induction arrows behavior in this part of the profile, where they point northwestwards. In Brazil, other MT and GDS studies conducted by PADILHA et al (2015) and MAURYA et al (2018) have shown a similar conductive lineament continuing to the northeast, from the Argentina-Brazilian border on. In Brazil it is close to the basin depocenter, coincident to areas where the basalt layer is thicker.…”

“…In Brazil it is close to the basin depocenter, coincident to areas where the basalt layer is thicker. Maurya et al (2018) have proposed a deflection of this conductive lineament to the east at latitude ~28S, towards the Torre Syncline. Our inverted model suggests another possibility, that it continues directly into Argentina.…”

Estimating Geomagnetically Induced Currents in Southern Brazil Using 3‐D Earth Resistivity Model

“…In this case, the modeled geoelectric values should be considered lower estimates of potential real values. However, within the basin, MT surveys (e.g., Maurya et al., 2018; Padilha et al., 2015) show that the volcanic‐sedimentary package is quite homogeneous in terms of electrical resistivity, approaching a 1‐D situation. Variations in the geoelectric field occur mainly in the crystalline basement under the basin and are correctly represented in the model.…”

Synthesizing Seemingly Contradictory Seismic and Magnetotelluric Observations in the Southeastern United States to Image Physical Properties of the Lithosphere

“…Although much MT work has been completed in the areas of Brazil and India that were affected by these recent flood-basalt events (e.g., Danda et al, 2017;Maurya et al, 2018;Padilha et al, 2015;Patro & Egbert, 2011), all studies so far have focused on crustal and uppermost mantle structures (even though resolvable resistive structures in some cases do extend deeper, beyond the putative depth resolution limit), and there are few three-dimensional inversion results from these areas. Current MT results are insufficient to make a clear comparison between MT-derived and seismic-derived estimates of thermal lithosphere properties in those regions.…”

“…Current MT results are insufficient to make a clear comparison between MT-derived and seismic-derived estimates of thermal lithosphere properties in those regions. Although much MT work has been completed in the areas of Brazil and India that were affected by these recent flood-basalt events (e.g., Danda et al, 2017;Maurya et al, 2018;Padilha et al, 2015;Patro & Egbert, 2011), all studies so far have focused on crustal and uppermost mantle structures (even though resolvable resistive structures in some cases do extend deeper, beyond the putative depth resolution limit), and there are few three-dimensional inversion results from these areas. Further work in these regions, as well as in other regions affected by CAMP magmatism (specifically the margins of Europe, Africa, and northeastern North America) is clearly warranted to see if similar apparent discrepancies between seismic and MT observations are found.…”