Adamastor - an ocean that never existed?

Existing models of tectonic evolution of the Neoproterozoic orogenic system rimming the shores of the South Atlantic Ocean (the Aracual-Ribeira-Congo and Dom Feliciano-Kaoko-Gariep belts) interpret the belts as subduction-related orogens and emphasize the role of the Adamastor Ocean in their pre-collisional evolution. A critical problem in such an interpretation is the confined nature of the northern termination of the orogenic system, as well as a very short time span between the end of rifting and onset of convergence recognized in its southern part. In this contribution, we review the data for the pre- and synorogenic evolution of this system of orogens (here collectively called the South Atlantic Neoproterozoic Orogenic System) and show that the data speak against the presence of a large oceanic domain before the onset of its orogenic evolution. We propose a new and simple intracontinental model, suggesting that Neoproterozoic oceanic crust played only a minor role in the development of the South Atlantic Neoproterozoic Orogenic System and that its overall architecture and thermal evolution is the result of inversion of large-scale rift structures with a protracted, and probably episodic, extensional history. True oceanic crust probably developed only in the southern part of the rift system, but it must have been narrow, akin to the Red Sea-Gulf of Aden stage of the Adamastor Rift evolution just before the onset of convergent thickening.