The Borborema Strike-Slip Shear Zone System (NE Brazil): Large-Scale Intracontinental Strain Localization in a Heterogeneous Plate

Abstract

Large-scale strike-slip faults are fundamental tectonic elements of the continental lithosphere. They constitute plate boundaries (continental transforms), separate terranes with contrasting geological histories within accretionary orogens, or accommodate heterogeneous deformation in intracontinental settings. In ancient orogens, where deeper levels of the crust are exposed, these faults are expressed as shear zones materialized by up to tens of km-wide mylonitic belts. The Borborema shear zone system in northeastern Brazil is one of the largest and best-exposed intracontinental strike-slip shear zone systems in the world, cropping out over 250,000 km2. Here, we review its main geophysical, structural, petrologic, and geochronologic characteristics and discuss the factors controlling its development. This complex continental scale shear zone system is composed of a set of NE- to NNE-trending dextral shear zones from which there are two major E-trending dextral shear zones with horse-tail terminations into the transpressional belt branch, as well as several smaller E-trending dextral and NE-trending dextral and sinistral shear zones. The major shear zones are marked by extensive linear or curvilinear magnetic gradients, implying their continuation at depth. The major shear zones are materialized by migmatite to amphibolite-facies mylonites, but the entire system shows evidence of late deformation at lower temperatures. The system developed during the late stages of the Neoproterozoic Brasiliano (Pan-African) orogeny (mainly from 590 to 560 Ma), postdating by more than 20 Ma the main stage of contractional deformation. Localization of strike-slip shearing in this intraplate setting was controlled by rheological contrasts between blocks with distinct Paleoproterozoic histories, the presence of preorogenic Neoproterozoic rifts, the craton geometry, and zones of enhanced magmatic activity, highlighting the importance of rheological heterogeneity in controlling shear zone nucleation and evolution.

Estudo integrado de aerogeofísica e geologia estrutural aplicado ao mapeamento geológico do entorno da Serra do Jatobá, Terreno Alto Pajeú, Província Borborema

“…Essas estruturas não foram devidamente caracterizadas pelo mapeamento na escala 1:250.000 realizado por Brasilino e Morais (2020), provavelmente por questão de escala de trabalho, mas refletem tipicamente a tectônica pré-transcorrente da região descrita também em diversos domínios ou terrenos ao longo da Subprovíncia Transversal (e.g., Brito Neves et al, 2000;Rodrigues e Archanjo, 2011;Santos et al, 2012). Já o segundo evento é responsável pela trama estrutural dominante relacionada a milonitos subverticais, com intensa evidência de deformação não coaxial provocada pelo regime transcorrente brasiliano, comum em toda a Província Borborema (e.g., Vauchez et al, 1995;Neves et al, 2021;Santos e Viegas, 2021). Essas estruturas são correlacionáveis regionalmente com fases de tectônica intrusiva gerada em torno de 590 a 580 Ma, resultantes de episódios colisionais entre a litosfera dominante da Província Borborema com o Cráton São Francisco (Ganade de Araújo et al, 2014).…”