The Araçuaí orogen extends from the eastern edge of the São Francisco craton to the Atlantic margin, in southeastern Brazil. Orogenic igneous rocks, formed from c. 630 to c. 480 Ma, cover one third of this huge area, building up the Eastern Brazilian Pegmatite Province and the most important dimension stone province of Brazil. G1 supersuite (630-585 Ma) mainly consists of tonalite to granodiorite, with mafic to dioritic facies and enclaves, representing a continental calc-alkaline magmatic arc. G2 supersuite mostly includes S-type granites formed during the syn-collisional stage (585-560 Ma), from relatively shallow two-mica granites and related gem-rich pegmatites to deep garnet-biotite granites that are the site of yellow dimension stone deposits. The typical G3 rocks (545-525 Ma) are non-foliated garnet-cordierite leucogranites, making up autochthonous patches and veins. At the post-collisional stage (530-480 Ma), G4 and G5 supersuites were generated. The S-type G4 supersuite mostly consists of garnet-bearing two-mica leucogranites that are the source of many pegmatites mined for tourmalines and many other gems, lithium (spodumene) ore and industrial feldspar. G5 supersuite, consisting of high-K-Fe calc-alkaline to alkaline granitic and/or charnockitic to dioritic/noritic intrusions, is the source of aquamarine-topaz-rich pegmatites but mainly of a large dimension stone production.

No 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.

The Quadrilátero Ferrífero region, located in the southeast portion of the São Francisco Craton, is one of the main metallogenic provinces in Brazil. Fieldwork, petrography, high-resolution airborne geophysics (magnetic and gamma-ray spectrometry data), and aerial images allowed us to produce a new map at the 1:25,000 scale, with important contributions in the lithotypes detailing, understanding of the geological structures and relationship between the different stratigraphic units. Interpretation of airborne geophysical data integrated with field structural and lithological observations were successfully employed in the creation of the litho-structural framework in a poorly exposed Proterozoic and Archean terrain. Airborne gamma-ray spectrometry data aided in the mapping process in areas with regolith cover including erosional ridges. The magnetic total derivative image revealed regional and local structures. In addition, our work details the units of occurrence of Rio das Velhas and Minas Supergroup. The aerial coverage of the Mindá and Santa Quitéria formations strongly increased, as well as the area of the Cauê Formation was better defined. The new geological map provides many improvements over the pre-existing maps. New lithological facies and structures were identified and others become more visible and lithologicalboundaries are refined or confirmed.

No abstract

No abstract

No abstract

região de Colatina, Estado do Espírito Santo, foi objeto de mapeamento geológico e detalhado estudo petrográfico e geoquímico visando reconhecer e caracterizar paragnaisses migmatíticos do Complexo Nova Venécia e granitóides sincolisionais do tipo S – Granitóide Colatina, que ocorrem no núcleo metamórfico-anatético do Orógeno Araçuaí. O Complexo Nova Venécia, é representado por paragnaisses migmatíticos, cujas relações de campo, dados de mineralogia, petrografia, geoquímica e geocronologia indicam que estas rochas foram, originalmente, sedimentos peraluminosos de composição grauvaquiana, depositados em possível bacia de retroarco. O Granitóide Colatina varia de monzogranitos a tonalitos, representando uma fusão anatética do tipo-S, ocorrida na fase sincolisional do Orógeno Araçuaí, mostrando uma persistente foliação concordante com a foliação regional. As relações do Granitóide Colatina com as rochas do Complexo Nova Venécia evidenciam que se trata de uma fusão autóctone.Palavras chave: Orógeno Araçuaí, núcleo metamórfico, granitóides. ABSTRACTGEOLOGY, PETROLOGY AND GEOTECTONIC CONTEXT OF GNEISSES AND GRANITOIDS OF THE COLATINA REGION, ESPIRITO SANTO, BRAZIL. The Colatina region, Espírito Santo state, Brazil, was the subject of detailed geological mapping and geochemical and petrographic study aiming to recognize and characterize the Nova Venécia Complex: migmatitic paragneisses, and S-type syncolisional granitoids – the Colatina Granitoid – occurring in the metamorphic core of the Araçuaí orogen. The Nova Venécia Complex is represented by migmatitic paragneiss, whose field relations and mineralogical, petrographical, geochemical and geochronological data indicate that these rocks were originally peraluminous sediments with wacke affinities, probably deposited in a retroarc basin. The Colatina Granitoids varies from monzogranites to tonalites, representing a S-type anatetic melt occurred during the syn-collisional event of the Araçuaí orogen, showing a persistent foliation concordant with the regional foliation. An authoctonous melt is interpreted from the relations between the Colatina Granitoids and the rocks from the Nova Venécia Complex.Keywords: Araçuaí orogen, metamorphic core, granitoids.