Adamastor – an ocean that never existed?

Abstract

Existing models of tectonic evolution of the Neoproterozoic orogenic system rimming the shores of the South Atlantic Ocean (the Araçuaí–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.