Geophysical and geological framework of the southern edge of the Parnaíba Basin, NE Brazil

Abstract

The application of geophysical techniques to highlight and characterize magnetic and gravity anomalies was carried out along a research area at the southern edge of the Parnaíba Basin. This study was conducted through qualitative and quantitative interpretations of magnetic and gravity data, supported by surface geological information, reflection seismic data, stratigraphic well data, field data, and magnetic susceptibility and density measurements of rock samples collected in outcrops. The study used the 3D magnetization vector inversion method, and 4 regional transects were performed for 2.5D modeling of magnetic and gravity data. The investigation revealed the configuration of the structural framework of the southern edge of the Parnaíba Basin. The characterization of magnetic anomalies allowed the definition of four main domains. Three magnetic zones were fragmented by depth, in the intervals of 20 km to 30 km, 5 km to 8 km and 0.5 km to 1 km, which demonstrate the association of magnetic anomalies with shallow and deep crustal structures. The magnetic susceptibility data show good correlation with the main structural discontinuities, and in particular with the Transbrasilian Zone. The results show that the maximum thickness of the sedimentary cover in the basin is approximately 2 km. No features associated with grabens or rifts were identified along the transects, and the presence of gravity and pseudo-gravity lows are closely related to less dense lithological units of the upper crust, such as granitic masses and supracrustal sequences. The reactivations of the Transbrasilian Zone during the Mesozoic generated deep structures in the crust that promoted the rise of basaltic rocks and the intrusion of kimberlitic bodies.