Interpretação de lineamentos estruturais na borda sudeste da Bacia do Parnaíba

Abstract

The southeast border of the Parnaíba Basin (BPar), which follows the borders between the Piauí, Bahia and Pernambuco states, 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 in the east basin border. The evidence of a structural control in this basin border was analysed interpreting hillshade images obtained from radar imagery. NE-trending photolineaments were highlighted in the crystalline basement and in the sedimentary cover, as well as in the contact zone between these domains. An integrated analysis of macroscale (radar and multispectral images) and mesoscale (outcrop data) structures, lead to the characterization of three deformation events on the basis of their orientation, kinematics and chronology. Dn structures were recognized in the crystalline basement and molassic sequences of Araçá and São Julião basins, being correlated to same context of the Jaibaras Group, in NW Ceará, of Ediacaran-Cambrian age. This deformation event is related to a retrometamorphic, plasticbrittle late stage of Brasiliano mylonite zones. Its signature includes NE-trending dextral transcurrent shear zones, as well as acid veins filling dilational C bands and E-W extension joints. Dn+1 deformation corresponds to a new stage of 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. Dn+2 deformation is characterized by normal faults, basic dykes (correlated to the Eocretaceous Sardinha Suite) and siliceous veins (filling anisotropy in rocks), all of them following a NE-SW trend. The NE-trending faults may occur in the contact between basement and the sedimentary cover, or inside the basin. This event resulted from a NWSE extension, analogous to the one recognized further east in the Northeast Brazil Interior Basins, associated to the South Atlantic rifting.