The Patos-Pernambuco shear system of NE Brazil: Partitioned intracontinental transcurrent deformation revealed by enhanced aeromagnetic data

Abstract

The Neoproterozoic-Cambrian (Brasiliano) intracontinental Patos-Pernambuco shear system is developed in Archean to Neoproterozoic crust, reactivating rift margins N of the São Francisco Craton. We here use enhanced aeromagnetic images to reveal internal details of the broad E-W dextral Patos and Pernambuco shear zones, the intervening Central (Transversal) Domain and the adjacent Northern Domain. We estimate shear strains up to 50–60 and a total of ca. 350 and 200 km dextral displacement for the Patos and Pernambuco shear zones, respectively. Deflection of foliations, fold axial surfaces and plutons as well as internal S-C fabrics and asymmetric folds within these large shear zones confirm dextral displacement. However, the dominant population of NE-trending shear zones in the Central Domain, by many considered dextral, are here confirmed to be sinistral and thereby elongating this domain. The Northern Domain behaved differently, hence large-scale Ediacaran strain partitioning in the region is suggested, where different blocks experienced different deformation between major simple-shear dominated shear zones. We show how much more structural information can now be obtained from enhanced aeromagnetic data than from field mapping alone; aeromagnetic interpretations, nevertheless, still draw on analysis techniques epitomized by John Ramsay.