O papel das cadeias vulcânicas na compartimentação, magmatismo e sedimentação da margem Equatorial Brasileira

Abstract

The North Brazilian Ridge (NBR) and the Fernando de Noronha Ridge (FNR) are volcanic features that extend between the Barreirinhas and Potiguar basins, mainly along its deepest portion. Even though they constitute significant features and impose a notable control factor in the compartmentalization and sedimentary architecture of the Brazilian Equatorial Margin, several factors remain unknown, such as the origin of the volcanism and its interaction with marine sedimentation. For this, through the analysis of seismic and bathymetric data from the LEPLAC project (Plano de Levantamento da Plataforma Continental Brasileira), this current study aims to analyze evidence about the origin of these submarine ridges and how they affected the margin throughout its geological history. The morphology of the margin indicates how the ridges segment the margin, imposing distinct bathymetric patterns, which indicates, together with the maps of basement top and sedimentary isopachs, that the ridges, even though presenting morphological expression of isolated seamounts, are constituted by, at least relatively, a continuous pedestal/barrier in subsurface. In addition, volcanic bodies, associated laterally with the ridges have been identified and dated based on chronostratigraphic horizons, indicate that both ridges show a common and gradual evolution, with decreasing ages from west of NBR to east of FNR, at an average rate and a offset compatible with the estimated by the South American plate. Such characteristics, in addition to the spatial correlation with basement structures and probable pre-existing structures associated with the ridges, lead us to propose that the most accepted hypothesis for the origin and evolution of NBR and FNR is the presence of a mantle plume, which generated the magmatism, that then used of pre-existing structures: the fracture zone of São Paulo and Romanche (northern and southern segments of the NBR), the Chain Fracture Zone (FNR), and a ridge-jump (central segment of the CNB), deep listospheric structures.