Magnetotelluric imaging of the Parnaíba Basin: Implications to the West Gondwana formation

Abstract

The Parnaíba Basin, in northeastern Brazil, is one of the most significant intracratonic basins on the South American platform. Its formation, driven by vertical thermal and mechanical processes has been extensively studied, however, the internal structural configuration remains subject of debate. Magnetotellurics (MT) is a geophysical method that provides information about the geo-electric internal distribution. As part of the multi-physics Parnaíba Basin Analysis Project (PBAP), 218 broadband and 37 long-period MT stations were deployed along an E-W transect profile of $\sim 1400\mathrm{km}$. The MT data were inverted to produce 3-D resistivity models. Lateral resistivity variations were identified along the profile and interpreted as the amalgamation of the three blocks, from west to east: Amazonian Craton, Parnaíba block, and Borborema Province. Within each block, the models reveal differentiated geoelectric behaviours. The Amazonian Craton exhibits a high-conductivity domain associated with the replacement of a delaminated lithosphere. The Parnaíba block comprises two distinct tectonic domains: the resistive Grajaú block and the conductive Teresina block. Their resistivity contrast is associated with magmatic activity, which is more intense in Teresina. However, Cretaceous extensional events related to the opening of the South Atlantic may have also influenced it. In the Borborema Province, resistive and conductive signatures at lower crustal depth are identified, providing evidence of collisional events associated with its formation in the Neoproterozoic. These deep resistivity models provide new evidence for the crustal amalgamation of the Parnaíba Basin and offer insights into the tectonic processes that shaped Western Gondwana.