The Borborema shear zone system, NE Brazil

Abstract

The Neoproterozoic evolution of the Borborema Province is characterized by the development of a continental-scale network of transcurrent shear zones. These shear zones form a kinematically consistent system over more than 200,000 km 2. This shear zone system is coeval with a high-temperature, medium- to low-pressure metamorphism, partial melting of the crust, and synkinematic magmatism involving both crustal- and mantle-derived magmas. Preliminary geochronological data suggests that the deformation in the shear zones probably began around 570–600 Ma and continued under decreasing temperature to around 500 Ma. The Borborema shear zone system is subdivided in two domains, a western domain in which rectilinear NE-trending dextral strike-slip shear zones dominate, and an eastern domain characterized by sinuous, discontinuous EW-trending shear zones that terminate in NE-trending metasedimentary belts. The sinuous pattern of the EW-trending shear zones may be due to pre-existing lithospheric heterogeneities: basins or domains where crustal accretion occurred at different ages. Finally, it is suggested that the Borborema shear zone system developed within a heterogeneous continental plate to accommodate the deformation imposed by plate tectonic processes (oblique collision?) active at the margin.