Reconstructing the morphotectonic evolution of passive margins: a morphogenetic study of the northern Brazilian “Nordeste”
Résumé
Rich in paleolandforms, the northern Brazilian “Nordeste” offers unique opportunities to reconstruct its history by morphostratigraphic methods, to obtain reliable timings and rates of morphotectonic evolution as well as depths of denudation, and to constrain available models of passive margins. Its relief reflects a complex geological history in which the most significant events are the Early Cretaceous rifting, followed by unequal post-rift subsidence, transform oceanic opening (Aptian-Albian), and formation of the margin, with differentiated evolution of compartments inherited from rifting and break-up patterns. On the basis of morphostructural data and of published stratigraphic and thermochronometric results, we propose a reconstruction of its evolution, illustrated by a series of sketch block-diagrammes, and an evaluation of the uplift and erosion values and rates. Through an analysis of the roles of tectono-eustatic controls and morphotectonic-climatic couplings, it offers new insights on the influence of superposed structural legacies in the geomorphic development and lateral variations of marginal escarpments. From our observations, northeastern Brazil appears as an ideal place for calibrating results of low temperature thermochronometry and for developing new conceptual models of morphotectonic evolution of passive margins and marginal scarps.