Integração de dados geofísicos (magnetometria, gravimetria e magnetotelúrico) na Borda Nordeste da Bacia do Parnaíba, NW do Estado do Ceará, Brasil

Abstract

An integrated study of geophysical data (magnetic, gravity and magnetotelluric) was undertaken in the northeast edge of Parnaíba Basin, NW Ceará. The development of the basin suffered tectonic reactivation of major faults associated with the north part of Transbrasiliano Lineament, known locally as Sobral-Pedro II Shear Zone (SPIISZ), and has two gravimetric low interpreted as grabens in previous work. Qualitative and quantitative interpretations of geophysical data were performed in order to understanding tectonostratigraphy relationships involving the northeast part of Parnaíba Basin based on main geophysical lineaments, geometry and depth of sources. The results show structural lineaments partitioning characterized by lineaments in the 1st NE -SW order direction and 2nd EW and NW-SE order directions. The depth of the magnetic and gravity sources was estimated using 2D Euler deconvolution from NW-SE geophysical profile, perpendicular to Brasiliano shear zones and two gravimetric lows. Outcropping rock density measurements and geophysical information from previous work in the area were integrated to constrain modeling. The magnetic and gravity profiles of the northeast edge of Parnaíba basin estimated sources up to 5 km depth. The Café-Ipueiras shear zone and SPIISZ that is not marked on the surface appear much pronounced in the various maps and subsurface geophysical models. Another lineament with similar expression appears well marked by the 2-D Euler solutions in the Tianguá, Ubajara and Ibiapina region. 2D gravimetric models were generated over the Residual Bouguer Map in order to obtain more reliable results, compatible with geological knowledge. The 2D magnetotelluric inversion shows that the northeast edge of the Parnaíba Basin is marked by low and high resistivity values, and maximum thickness of the sedimentary package reaches approximately 3 km. Subvertical dipping resistive anomalies point features that can represent Brasiliano shear zones which seem to limit the graben features that occur in the region. Such features may indicate areas with greater chances of success in the exploitation of groundwater.