Morphostructure, emplacement and duration of the Abrolhos Magmatic Province: A geophysical analysis of the largest post-breakup magmatism of the South-Eastern Brazilian margin

Abstract

The Abrolhos Magmatic Province (AMP), located in the Ocean Continent Transition (OCT) of the Brazilian South Atlantic rifted margin, is spatially extensive covering an area larger than 63,000 km2 and was emplaced in the Early Cenozoic, approximately 40 Ma after rifted margin formation in Early Cretaceous. The explanation for the origin of the AMP is that it forms part of a hotspot track that initiated at ~85 Ma in the Poxoréu region, an igneous province located ~1500 km to the west of the AMP, within Brazilian continental lithosphere and is presently located under Trindade and Martin Vaz Islands at the Vitoria-Trindade seamount chain (VTC). The aim of this work is to investigate the morphostructure, duration and spatial distribution of the AMP, exploring its significance for the margin evolution and possible origins. The magnetic, reflexion seismic and well data analysis show that the AMP consists of an assembly of large volcanic edifices formed during the Paleogene, each with individual diameters in excess of 50 km, sizes varying from 280 to 2100 km2, and formed by multiple volcanic events. The igneous bodies are mainly buried at different depths (from ~2 Km to 8 km below seafloor), while some emerge to form the Abrolhos Archipelago. The spatial arrangement of the igneous edifices of the AMP suggest that in its central part are the main feeders for the outer and shallower bodies at the borders which have a radial distribution. Their distribution seems to partially follow preexisting structural trends like Precambrian and Mesozoic weakness zones, represented by the onshore Paramirin Aulacogen, the Araçuaí and Ribeira belts, and the offshore rifting structures. These observations suggest an influence of lithosphere inheritance on the emplacement of the AMP. The tectono-stratigraphic architecture indicate margin uplift at Early Cenozoic related to the emplacement of the AMP, creating an elevated area. Mapped hydrothermal vents indicate AMP magmatic activity continued into the Neogene, and connect Abrolhos volcanism with that in the VTC located 650 km to the east. This and reported low S-wave velocity from tomographic model and anomalous dynamic topography suggest a distinct mantle thermal structure under the AMC and VTC. However, the spatial extent and duration of the AMP are inconsistent with a fixed hotspot mechanism and linear trail.