Genesis and evolution of the South Atlantic volcanic islands offshore Brazil

Abstract

The Brazilian continental margin includes several volcanic islands, submerged volcanic seamounts, and a unique non-volcanic archipelago located in a transform segment of the Equatorial South Atlantic. The mechanism of formation of these islands is related to post-breakup magmatic episodes dated as Late Cretaceous to Pleistocene. Diverse Late Cretaceous to Paleogene alkaline magmatic episodes are registered in southeast Brazil, resulting in igneous plugs onshore and volcanic structures offshore. The Abrolhos Volcanic Complex in eastern Brazil is characterized by several volcanic features on the continental shelf, including small islands that expose Paleogene sedimentary layers interbedded with volcanic sequences. The adjacent Vitoria-Trindade Chain extends to oceanic crust forming basaltic to alkaline seamounts that outcrop at the Trindade Archipelago, the easternmost islands in Brazil with the youngest volcanic eruptions. The Fernando de Noronha lineament in northeast Brazil is characterized by Neogene alkaline igneous plugs. The small islets in the Sao Pedro—Sao Paulo archipelago, located near the mid-Atlantic ridge, are formed by exhumed mantle rocks related to compressional episodes a transform fault zone. The Rio Grande Rise in southern Brazil is characterized by shallow Paleogene seamounts and a large oceanic plateau probably related to subaerial spreading centers formed in the Late Cretaceous. Multiple mechanisms are responsible for the origin and evolution of the volcanic islands offshore Brazil in continental, transitional, and oceanic crust settings, including volcanic build-ups, leaking fracture zones, and hotspots. Some of the islands might be related to mantle plume activity, as indicated by comparisons with modern mantle plume analogues in the South Atlantic.