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

The Neoproterozoic-Cambrian (Brasiliano) intracontinental Patos-Pernambuco shear system is developed in Archean to Neoproterozoic crust, reactivating rift margins N of the Sa & SIM;o 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.

Automated summary

This study uses enhanced aeromagnetic images to reveal internal details of the Neoproterozoic-Cambrian intracontinental Patos-Pernambuco shear system and estimate shear strains and displacements. The study confirms the sinistral nature of the shear zones in the Central Domain and suggests different deformation patterns in the Northern Domain.