Electromagnetic constraints for subduction zones beneath the northwest Borborema province: Evidence for Neoproterozoic island arc-continent collision in northeast Brazil

The Borborema province in northeast Brazil occupies a crucial position in the complex Neoproterozoic West Gondwana reconstruction puzzle. However, correlation attempts between northeast Brazil and West Africa have been hampered because key links in the internal structure of the Borborema province have yet to be identified. To aid such an correlation, a magnetotelluric study was undertaken along two subparallel profiles to image the deep electrical structure in the northwestern part of the province. Despite the occurrence of recurrent tectonothermal episodes that affected the region in the past, two-dimensional models show that a large-scale signature of the assembled terrane during the Neoproterozoic accretion and collision is plausibly preserved in the area. Two resistive features dipping from the upper crust into the upper mantle in downward convergence (opposite directions) are defined beneath one of the profiles that are interpreted to be related to remnants of former subduction slabs, since the observed high-resistivity zone is consistent with a dehydrated oceanic lithosphere depleted of sediments. On the basis of geological and geochemical information, a model of collision of an intraoceanic magmatic arc coalesced into an earlier passive margin is proposed for the Neoproterozoic tectonic evolution of the province, involving processes of reversal of subduction polarity and oceanic slab breakoff.