The Araçuaí Belt

Abstract

The Araçuaí belts extends along the curved southeastern margin of the São Francisco craton between the Brazilian coast and Lat 21°S, where it merges with the Ribeira belt. It represents the external, basement-involved fold-thrust belt of the Araçuaí-West Congo confined orogen (AWCO), which formed due to the closure of the terminal branch of the Adamastor ocean during the amalgamation of West Gondwana in the Ediacaran and beginning of the Cambrian. Bounded to the east and southeast by the high grade and granitic core of the AWCO, the Araçuaí belt involves a basement assemblage older than 1.8 Ga, the 1.7–0.9 Ga rift to rift-sag successions of the Espinhaço Supergroup, the Tonian-Edicaran rift-passive margin Macaúbas Group, as well as the syn-orogenic Salinas Formation and crustal derived granitic intrusions. The Macaúbas Group, the type unit of the belt, contains a glaciomarine sequence made up of thick diamictites, sandstones and Rapitan-type banded iron formations. The units exposed along the belt were metamorphosed under greenschist to amphibolite facies conditions and affected by thrusts, reverse faults and cratonward verging folds, developed between 575 and 530 Ma. The Araçuaí orogenic front propagates into the craton interior and interacts with preexistent rift structures. This chapter describes the stratigraphic framework and overall structure of the Araçuaí belt, emphasizing the paleogeographic and tectonic significance of its sedimentary and volcanic assemblages.