Structural control of the southeastern border of the Parnaíba Basin, Northeastern Brazil: relationships with geodynamic events in Gondwana

Abstract

Along the frontier between Piauí, Bahia and Pernambuco States (Northeast Brazil), the southeastern border of the Parnaíba Basin (BPar) is been mapped as a nonconformity between the Serra Grande Group (GSG) and the Precambrian basement. However, this border is characterized by an expressive NE trend parallel to the one of the Transbrasiliano Lineament, as well as a narrowing of the outcropping belt of the Silurian-devonian formations, as compared to the situation further north, in the east basin border. A swarm of NE-trending photolineaments was interpreted from remote sensing images. They occur very close (or coinciding) to the basin/basement limit or superimposed on the paleozoic units (especially the GSG and the Pimenteiras Formation). Supported by field data, three structural patterns were recognized and correlated to distinct deformation events. D_n deformation, of ediacaran-cambrian age and observed just in the Precambrian basement rocks, is related to a retrometamorphic, plastic-brittle late stage of Brasiliano mylonite zones. It is characterized by NE-trending dextral transcurrent shear zones, as well as quartz veins filling E-W extension joints. D_n+1 Deformation corresponds to a new stage of transcurrent dextral movement along the NE-trending structures, accompanied by normal faults and extension joints oriented WNW to E-W, in this case overprinting the Silurian-Devonian formations. D_n+2 Deformation is characterized by normal faults, basic dykes (correlated to the Eocretaceous Sardinha Suite), siliceous veins and ridges of silicified sandstones, all of them along the NE-SW trend. This last phase results from a NW-SE extension, analogous to the one recognized further east in the Interior Basins of Northeast Brazil, associated to the South Atlantic rifting.