Emplacement and deformation of the Cachoeirinha pluton (Borborema province, NE Brazil) inferred through petrostructural studies: Constraints on regional strain fields

Abstract

The East Pernambuco shear zone system (EPSZ) conventionally has been taken as the limit between the central and southern domains of the oriental sector of the Neoproterozoic Borborema province (NE Brazil). To constrain the tectonic evolution of the southern domain during the Brasiliano orogeny, the authors undertake a structural and anisotropy of magnetic susceptibility study of the 580 Ma Cachoeirinha pluton, located 10 km south of the EPSZ. The results suggest a model for its emplacement and deformation in which (1) successive magma batches accumulated at the gently dipping interface between orthogneisses and overlying schists and paragneisses and (2) homogeneous NNE–SSW stretching of the pluton was followed by strain localization along conjugate subvertical corridors of noncoaxial shear during the last stages of crystallization. Outcrop-scale, magmatic to solid-state dextral and sinistral shear zones that affect the pluton have similar orientations to the large transcurrent mylonitic belts that characterize the central domain of the Borborema province. Thus, at the time of intrusion of the Cachoeirinha pluton, the central and southern domains of the Borborema province were undergoing deformation related to the same far-field stresses, and the EPSZ is not a major suture zone between domains with distinct geological histories. Instead, the present-day separation of the eastern Borborema province into central and southern domains resulted from progressive deformation that led to the development of the EPSZ. The absence of large shear zones in the southern domain can be explained by the faster regional cooling than in the central domain, where the longer magmatism duration resulted in persistent elevated crustal temperatures, which in turn allowed a greater amount of finite strain to accumulate.