Lithosphere structures of the Parnaiba Basin and adjacent provinces revealed by deep magnetotelluric imaging

Magnetotelluric (MT) data from 49 broadband and 23 long period stations, covering periods between 10(-3) and 10(4)s, were measured along a NNW-SSE profile of approximately 470 km, crossing the Parnaiba Basin, Borborema Province and Sao Francisco Craton in northeastern Brazil. The geotectonic scenario of the study region comprehends a complex structural framework formed during the Brasiliano orogenic collage. The MT data were processed to obtain the impedance tensor estimates for each MT site using a robust technique and then followed by a dimensional analysis via both the rotational invariants (WAL invariants) of the magnetotelluric tensor and the phase tensor. The two approaches indicated a three-dimensional nature of the region, allowing to proceed to 3D inversion, despite the data distribution along a profile. Several inversion trials of the full impedance tensor, tipper and tipper combined with impedance tensor resulted in a final 3D resistivity model, which suggests a division of the profile into three major zones. A sub horizontal resistive crustal block, interpreted as being part of the Parnaiba block, characterizes the western zone. A mosaic of resistive and conductive zones, which integrates the extended fold belt of the Borborema Province, composes the central zone. In the interface between the central and the eastern zones, there is a sub vertical conductive region limiting two resistive blocks, interpreted as a suture zone. This suture divides tectonic provinces and is supposed to be related with a Neoproterozoic collisional system. The 3D MT imaging recovered the structural framework under the Parnaiba Basin and marked the main lineaments. The paper suggests a distinct tectonic evolution for the complex assemblage of blocks in Northeast Brazil.