Magmatismo E Tectônica Do Orógeno Araçuaí No Extremo Leste De Minas E Norte Do Espirito Santo (18°-19°s, 41°-40°30’w)1

Abstract

This paper focuses on magmatic episodes and their relations to the main regional deformation in thebackarc region of the Araçuaí Orogen (southeastern Brazil). The main tectonic event took placeduring the syncollisional stage (ca. 585-560 Ma) and imprinted the regional, solid-state foliation (Sn)in most rocks of this orogen. In the mapped region (18°-19°S, 41°-40°30’W), the older unit (NovaVenécia Complex) occurs in small areas and consists of migmatitic, sillimanite-garnet-cordieritebiotiteparagneisses with minor calcsilicate intercalations. The widespread garnet-biotite granites(Carlos Chagas, Montanha and Ataléia suites) are correlated to the syncollisional, S-type, G2 supersuite(ca. 585-560 Ma) of the Araçuaí Orogen, because they persistently record Sn, usually associated tostriking mylonitic features. However, we also correlate some massifs of undeformed garnet-biotitegranite to the Carlos Chagas Suite. Outwards from such undeformed pods, this Sn-free, garnet-biotitegranite progressively shows solid-state deformation features superimposed on its igneous fabric, andgives place to the mylonitized granite typical of the Carlos Chagas Suite. In fact, both the undeformedand mylonitized granites of the Carlos Chagas Suite yielded similar magmatic crystallization ages (ca.585-575 Ma; zircon, U-Pb SHRIMP). These G2 suites often show restites and xenoliths of paragneissand calcsilicate rock, and gradational contacts with migmatitic inliers, suggesting a genesis related toanatexis of the Nova Venécia Complex. The usually small, irregular-shaped bodies and veins composedof garnet-cordierite leucogranites, free of Sn, belong to the post-collisional, S-type, G3 suite (ca.540-530 Ma, in the focused region). Most G3 bodies are enveloped by and contain restites of foliatedG2 granites, representing autochthonous to parautochthonous partial melts from the Carlos Chagas,Montanha and Ataléia suites. Sn-free granites and pegmatites, representing post-Sn partial meltsfrom the Nova Venécia paragneisses, also can be correlated to the G3 suite. Very large to relativelysmall intrusions composed of biotite granite, charnockite and/or norite, free of Sn, represent the lastmagmatic episode of the Araçuaí Orogen, in the focused region. These intrusions (Aimorés Suite)belong to the post-collisional, I-type, G5 supersuite (ca. 520-490 Ma). Such a succession of magmaticepisodes suggests that this middle crust sector of the Araçuaí Orogen remained hot (T > 650 °C) fora long time interval (ca. 100 Ma), from ca. 585 Ma to the Cambrian-Ordovician boundary. Thisrequires a long-lasting release of orogenic heat that could be explained by a combination of threesources: i) heat input by convective asthenosphe under the backarc region from the precollisional tothe syncollisional stages; ii) release of radiogenic heat from the crustal pile thickened by thrusts; andiii) ascent of mantle magmas and partial melting of the deep crust during the extensional collapse ofthe Araçuaí Orogen.

Applications and limitations of thermobarometry in migmatites and granulites using as an example rocks of the Araçuaí Orogen in southern Bahia, including a discussion on the tectonic meaning of the current results

“…The calculated P-T conditions are compatible with tectonic settings of the middle crust with high geothermal gradient, which matches either a magmatic arc setting or portions of back-arc basin, as proposed before for these rocks (Noce et al 2004;Pedrosa-Soares et al 2006;Silva et al 2008;Roncato 2009;Gradim 2013;Gradim et al 2014). The tectonic switching model enhances the Araçuaí Orogen evolution in comparison with previous proposals, as it can explain the time gap between main metamorphism and associated G2 suite with later and hot G4 and G5 suites.…”

The Brasiliano collage in South America: a review

“…The accretionary systems are not continuous along the strike of the province, but are supported by a wealth of geological, geochemical and geochronological data. These include: ■ Rio Doce, in Minas Gerais, Espírito Santo and Rio de Janeiro (Heilbron et al 2004;Pedrosa Soares et al 2006, possibly extending to the coastal Serra Mar in São Paulo (Campos Neto 2000): 630 -590 Ma < 580 -570 Ma (main accretionary phases). ■ Serra da Bolívia, from southern Espírito Santo to the south of Rio de Janeiro : 620 -595 Ma.…”

Popularização E Difusão Da Geologia: Uma Proposta De Inclusão Social E Desenvolvimento Econômico Aplicado À Região Do Monumento Natural Dos Pontões Capixabas

“…A região de Pancas e Águia Branca engloba um domínio geomorfológico caracterizado pela grande freqüência de pontões (pães-de-açúcar) e morros rochosos de encostas íngremes e topo plano, que atingem 800 metros de altitude, esculpidos em rochas graníticas e charnockíticas (Gradim et al 2006, Pedrosa-Soares et al 2006a) (Figura 2). Extensos lineamentos estruturais de direção NW (Lineamento Vitória-Colatina-Ecoporanga) e NE cortam a região, onde controlam vales de drenagens que entalham o relevo em altitudes de até 550 metros abaixo dos pães-de-açúcar vizinhos.…”

“…As unidades litoestratigráficas que ocorrem na área do Monumento Natural, bem como nas adjacências, são resumidamente descritas a seguir (Figura 3). A unidade mais antiga engloba granadabiotita granito e cordierita-granada-biotita granito, com sillimanita freqüente, e granito a duas micas, representantes da granitogênese G2, do tipo S e idade ediacariana (585-560 Ma; Pedrosa-Soares et al 2006b). Estruturalmente são heterogêneos, afetados total ou parcialmente pela deformação dúctil regional do estágio sincolisional do Orógeno Araçuaí (registram a foliação Sn), mas homogêneos em termos composicionais (Pedrosa Soares et al 2006b).…”

“…520-490 Ma) do Orógeno Araçuaí. As intrusões G5 são livres da foliação regional Sn, e têm composições granítica (G5bg) e charnockítica (G5ck), predominantes, com termos noríticos (G5n) subordinados (Pedrosa-Soares & Wiedemann-Leonardos 2000, Gradim et al 2006, Pedrosa-Soares et al 2006b). …”