The Tectonic History of the Southern Adamastor Ocean Based on a Correlation of the Kaoko and Dom Feliciano Belts

Abstract

Closure of the southern Adamastor Ocean led to the development of the Neoproterozoic-Early Cambrian orogens on both margins of the present South Atlantic Ocean, which preserve a rich record of West Gondwana assembly and large-scale crustal evolution. Here we describe the distinct stages and tectonic regimes related to the evolution of the southern Adamastor Ocean as reconstructed from the geological record in southeastern Brazil, Uruguay and southwestern Africa. The welding of the Rio de la Plata/Paranapanema and African cratons was the result of a long history that generated the Dom Feliciano Belt in southeastern Brasil and Uruguay and its African counterparts, the Kaoko, Gariep and Saldania belts. Recent ideas and previous hypotheses are discussed and integrated into a tectonic model for the evolution of the southern Adamastor Ocean, largely based on comparison of the Neoproterozoic Kaoko and Dom Feliciano belts. The history of the southern Adamastor Ocean spans between 900 and 590 Ma, from the earliest records of magmatism related to Rodinia break-up (980–780 Ma), through the climax of the extensional phase that led to the opening of a vast ocean (780–640 Ma). Tectonic inversion led to subduction towards the east (in today’s coordinates), which generated an extensive magmatic arc on the western margin of the Congo and Kalahari cratons (640–600 Ma) and eventually the collision between the Congo and Rio de La Plata Cratons (600–590 Ma) juxtaposing the magmatic arc and the western South American schist belts. At around 530 Ma, still under the influence of plate convergence, a positive flower structure was generated causing the extrusion of the Granite Belt, the eroded remnant of the magmatic arc, and reactivation of the doubly verging thrusts that affected the supracrustal units of the Kaoko and Dom Feliciano belts. Only at that time did deformation reach the Itajai and Nama foreland basins.