Ilhas oceânicas brasileiras e suas relações com a tectônica atlântica

Abstract

The Brazilian oceanic islands and relationships with the Atlantic tectonics. A synthesis of modern knowledge on the Brazilian oceanic islands and archipelagoes shows that the oceanic lithosphere have influenced their origin and geographic situation. Distribution, allignment and age of the volcanic chains evidence a relationship between the origin of islands and archipelagoes and the activity of hotspots along fracture zones. At the Ceará coast, in the extension to the continent of a reactivated zone of oceanic breaking, typical structures, alkaline magmatism, high thermal flow and sismicity result from the influence of a hotspot, presumed to be astenospheric. A volcanic chain is formed as the plate is displaced and the reactivated breakings penetrate the ocean. The Fernando de Noronha Archipelago is at the end of the fracture zone. A similar evolution would have originated the Island of Trindade and the Archipelago Martin Vaz, that constitute the eastern emerged top of two chains of great volcanic mountains. The strange Archipelago of São Pedro and São Paulo is of a quite different origin, because it emerges on an active transforming segment of a fracture zone chain where it cuts the axial rift-valley of the Meso-Atlantic Ridge, exposing a protrusion of volcanic mantle rocks without exposed volcanic rocks, but they exist submerged.