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.

The gabbro to amphibolite transition along a hydration front

“…These rocks record crystallization ages from 2,203 to 2,041 Ma (Brueckner et al., 2000; Figueiredo & Teixeira, 1996; Noce et al., 2007; Silva et al., 2002). Despite the fact that there is plenty of data on geochemical and geochronological characteristics of this unit (see review by Alkmin et al, 2017), there is little information on metamorphism, with most authors generically citing amphibolite facies conditions. Cutts et al.…”

Metamorphic record of collision and collapse in the Ediacaran‐Cambrian Araçuaí orogen, SE‐Brazil: Insights from P–T pseudosections and monazite dating

“…Bounded by cratonic domains on three sides (Figure ), the AWCO was originally viewed as an ensialic orogen. The characterization of passive margin successions and the discovery of ophiolites and arc‐related rocks led authors to portray it as a product of a full Wilson cycle (Pedrosa‐Soares, Vidal, Leonardos, & Brito‐Neves, ; Pedrosa‐Soares et al., ), that is, opening and closure of an inland‐sea basin partially floored by oceanic crust (the so‐called Macaúbas basin) between the Tonian and Cambrian periods (Alkmim, Kuchenbecker, Reis, & Pedrosa‐Soares, ; Alkmim et al., ; Gonçalves et al., ; Pedrosa‐Soares et al., , ; Pedrosa‐Soares, De Campo et al., ; Queiroga et al., ; Tedeschi et al., ).…”

“…From a tectonic perspective, the study area corresponds to a segment of the Araçuaí orogen external fold‐thrust belt, which is also currently referred to as the Araçuaí Belt in the Brazilian geological literature (Figures and ). As a typical basement‐involved fold‐thrust belt (Alkmim et al., , ; Almeida et al., ; Pedrosa‐Soares et al., ), this sector of the orogen encompasses three major regional structures, namely the southern Espinhaço fold‐thrust system (SE‐thrust system), the CASZ and the Salinas synclinorium (Figures and ) (Alkmim et al., , ; Marshak, Alkmim, Whittington, & Pedrosa‐Soares, ; Santos et al., ).…”

Comment on “Tectono Metamorphic Evolution of the Central Ribeira Belt, Brazil: A Case of Late Neoproterozoic Intracontinental Orogeny and Flow of Partially Molten Deep Crust During the Assembly of West by Meira et al.

“…The article contributes with new metamorphic petrology and U-Pb geochronology data concerning the sin-collisional stage of two terranes (Embu and Costeiro) belonging to the southern Ribeira orogen (not Central Ribeira belt, as the title suggests), in order to propose an intracontinental evolution for the whole Neoproterozoic Ribeira-Araçuaí orogenic system. Several issues regarding their review of the literature and interpretation of data should be carefully considered in face of the proposition for an intracontinental evolution of such an orogenic system that has long been considered by numerous authors as having developed through a Wilsonian sequence of events, involving continental rifting and opening of oceanic domain, subduction of oceanic lithosphere and magmatic arc development, terrane accretion, and final continental collision in the context of the amalgamation of Gondwana supercontinent (Alkmim et al, 2006(Alkmim et al, , 2017Basei et al, 2009;Campos Neto, 2000;Heilbron et al, 2008Heilbron et al, , 2017Pedrosa-Soares et al, 1998. In order to contribute to a comprehensive discussion of the tectonic evolution of the Ribeira-Araçuaí orogenic system, we bring forward the following points that have not been properly acknowledged by the authors in their proposed tectonic scheme.…”