Landforms and neotectonics in the equatorial passive margin of Brazil
Résumé
Neotectonic movements have been proposed in the literature in order to explain some landforms of the equatorial, passive margin of northeastern Brazil. Its seismo-tectonic activity is concentrated in a few sectors located on or near the coast. Active or recently active structures are mainly identified in Neogene deposits. Identifying a contribution of neotectonics to the morphogeny is difficult in a context where most major morphostructural patterns are explained by Cretaceous tectonics related to oceanic opening and by differential erosion induced by Tertiary epeirogenic uplift. We aim to assess the nature of features considered as possibly neotectonic in origin. Seismogenic faults are not related to significant topographic breaks, except on the coast, where they usually reach only a few meters in height. A study of landforms located near zones of seismo-tectonic activity indicates a possible, probably weak, contribution of neotectonics to the formation of a few high scarps. These scarps occur along or near fault zones reactivated in Cretaceous times. We conclude that neotectonic movements are the result of ongoing deformation along predominantly strike-slip fault zones, with long term deformation rates similar to those recorded by dated landmarks (0.01 mm.yr-1). Despite reported deformation rates that can amount in places to 0.4 mm.yr-1, neotectonic rates are lower than erosion rates. The consequence is that major structural landforms in the region mainly originated in Cretaceous to early Tertiary events.