The Magmatic Rifting of Santos Basin: Aeromagnetic Mapping of Dykes, Terranes and Marginal Structures and the Interplay Between Tectonism and Volcanism

Abstract

AbstractWe present a new magnetic map integrating continental and oceanic features at the Santos Basin, in order to investigate the connection between onshore and offshore tectonics and magmatism at the early stages of rifting. The magnetic and seismic data evidence the offshore continuity of the Florianópolis and Serra do Mar dyke swarms, while the Ponta Grossa Dyke Swarm is interrupted by the marginal structures. This structural relationship brings to evidence a different timing of formation of the Ponta Grossa Dyke Swarm relative to the early opening of the margin. A very high amplitude magnetic lineament ‐ the Santos Marginal Anomaly (SAMA) reaches up to 1,500 nT and trends NE‐SW, with local E‐W inflections forming the Cananéia and Guaratiba Arcuate anomalies. Our modeling suggests that the SAMA can be associated with dykes and syn‐rift extrusive rocks linked at depth to larger magmatic bodies at the proximal and necking domains. Based on the increasing width and amplitude of the magnetic anomalies oceanwards, we propose a mechanism whereby the igneous accretion (i.e., the amount of magmatism) augmented as rifting evolved from continent to ocean, creating a volcanic rift axis. This rift was segmented by crustal discontinuities that probably nucleated on preexisting rheological contrasts, forming tectonomagmatic segments during the early extensional stages. The onshore‐offshore relationships highlight that where there was an agreement between basement fabric and dyke orientation, inheritance may have influenced their emplacement, although it was not a limiting factor for their formation. The regional geodynamics of the Gondwana opening was the first order control on the emplacements of the dyke swarms, with deviations of the magmatically influenced rift by tectonic inheritance.