Magmatismo pós-breakup nas Bacias de Santos e Campos

Abstract

Rifted margins are formed by crustal extension and thinning until the rupture of the continental lithosphere, often accompanied by magmatic events. Magmatism may influence the location of deformation, facilitating extension, and altering stress fields. After rifting, tectonic reactivations of pre-existing faults can transport magma to the surface and thermally impact sedimentary basins. Post-breakup magmatism in the Campos and Santos basins, located on the passive southeastern Brazilian margin, played a crucial role in the region's geological evolution and in the presalt hydrocarbon reservoirs. Between the Upper Cretaceous and the Paleogene, this magmatic activity was particularly intense, manifesting as volcanic cones, sills, dikes, and lava flows. Understanding the duration and mechanisms of magmatic intrusion is essential not only for the understanding of the tectonic evolution of the margin and the South Atlantic Ocean but also for the exploration of marine mineral resources, as intrusions can thermally impact hydrocarbon reservoirs and reduce their economic potential. Numerous studies have addressed the topic since the 1970s, but few detail and characterize the spatial distribution and the magmatic feeder system. A total of 96 sills and inclined sheets, 33 volcanoes, 8 laccoliths, 20 hydrothermal vents, a possible magma chamber, and numerous dikes were mapped. The volcanoes, possibly cinder cones with or without craters, occupy a total volume of approximately 44 km³ and are distributed in clusters or isolated, following N-S, NE-SW, and E-W trends, aligned with magnetic anomalies and crustal discontinuities of the basins. In the Cabo Frio High, the volcanoes are located beyond the Eocene shelf edge, suggesting predominantly submarine volcanism, although some volcanoes exceeding 500 meters in height may indicate episodes of subaerial volcanism. Radial intrusive complexes of sills were identified beneath some volcanoes, especially in saucer-shaped forms, suggesting their fundamental role as part of their feeding system. Furthermore, in the northern Santos basin, a possible shallow intracrustal magma chamber was identified, which may have fed various igneous features mapped in the drift section. For the first time, vents from Upper Cretaceous and Paleogene were mapped in the Santos basin, associated with sill emplacement and, in some cases, located above the volcanoes. The spatial distribution of these igneous features reveals a significant correlation with magnetic lineaments and crustal discontinuities, suggesting a possible tectonic control over post-breakup magmatism. This study provides a detailed three-dimensional view of volcanism and its feeding system in the Santos and Campos basins, contributing to a better understanding of its morphology, interconnection, and spatial relationship with magnetic lineaments and geological structures of the sedimentary basins, enabling safer future exploration of marine resources. The methodologies and results presented can also be applied to similar studies in other sedimentary basins worldwide, especially in contexts related to hydrocarbon exploration.