Upper crustal structures of the southeast edge of Parnaiba basin using 3D magnetotelluric data imaging

Abstract

In this study, broadband magnetotelluric (MT) data are acquired from 101 stations in the southeastern edge of the Parnaiba basin in NE Brazil. The MT stations are distributed in 10 semi-parallel profiles, with NW-SE orientation. In order to characterize the internal structure of this area, we propose a geoelectric resistivity model by applying the three-dimensional (3D) inversion of this data. In this way, the time series of the horizontal electric and magnetic fields are processed using a robust technique to evaluate the impedance tensor. The dimensionality analysis that was performed indicates a predominant 3D behavior, and the full tensor components were inverted. The preferred model verified the presence of low-resistivity areas located in the upper crust. The interpretation of these areas is in relation to geodynamic events that happened in the three domains of the Borborema Province: northern, central, and southern. The low-resistivity region located in the northern domain shows that there is an association with graphite precipitation, as defined by the metamorphism in the western zone of the Seridó belt. We propose that the conductive region in the central domain is explained by the reactivation of the Pernambuco shear zone. In the southern domain, it was associated with serpentinization processes by the hydration of mafic and ultramafic rocks from the Brejo Seco complex in the context of subduction in the Neoproterozoic. In addition, the 3D resistivity model revealed the graben-like structures with predominate NE-SW direction observed in previous works. Likewise, upper crust discontinuities were shown to be associated with the Senador Pompeu and Pernambuco shear zones, which were defined previously using aerogravimetric and aeromagnetic data.