The mainly meta-volcano-sedimentary Vila Nova Group and associated granites constitute separate belts, which form part of a large paleoproterozoic (mainly rhyacian) province in the Guyana Shield of which northern Brazil forms a part, and the West African Craton. In Brazil the southwestern Serra do Ipitinga and Serra Tumucumaque-Serra do Navio belts have no obvious geometrical extensions in the Guyanas or Venezuela, and may represent deposits formed at penecontemporaneous passive continental margins and ocean floor spreading centres. To the Northeast the Serra Lombarda-Tartarugalzinho and Oiapoque belts are continuations of Guianese belts. In the former the igneous rocks have geochemical characteristics of suprasubduction environments. Belts in the Guyana Shield and West African Craton have many similar features. The megaprovince evolved in a number of stages, which may have started at about 2.3 Ga, and continued with diminished activity after 2.11 Ga. Both major juvenile additions and (possibly minor) reworking of earlier crust contributed to the growth of the province. The major transcurrent deformation, responsible for the present structure of the belts, probably occurred during the later stages of evolution of the province, but metamorphism and deformation are registered even in the oldest rocks.Palavras-chave: terrenos paleoproterozóicos de greenstones e granitos; Escudo das Guianas; Norte brasileiro; Craton Oeste-Africano. RESUMOO Grupo Vila Nova, predominantemente meta-vulcanossedimentar e os granitos associados constituem cinturões que formam parte de uma grande província paleoproterozóica (predominantemente riaciana) localizada no Escudo Guianense do qual o Norte brasileiro faz parte, e no Craton Oeste-Africano. No Brasil identificam-se ambientes tectônicos diferenciados para os diferentes cinturões. No sudoeste da província os cinturões da Serra de Ipitinga, e da Serra de Tumucumaque ao Serra do Navio não encontram extensões geometricamente claras nas Guianas e Venezuela, e talvez representem depósitos penecontemporâneos formados em margens continentais passivas e bacias oceânicas. Seguindo para nordeste, os cinturões da Serra Lombarda até Tartarugalzinho e Oiapoque são continuações de cinturões presentes nas Guianas. Naquele, as características geoquímicas, tanto das rochas máficas metavulcânicas como das félsicas plutônicas posteriores, apontam para origens em zonas de supra-subducção. Os cinturões guianenses e oeste-africanos apresentam muitas feições e características semelhantes. A evolução da megaprovíncia ocorreu por etapas, desde talvez 2,3 Ga com atividade em diminuição depois de 2,11 Ga. Adições crustais, tanto juvenis quanto por retrabalhamento de crosta antiga, contribuíram para o crescimento da megaprovíncia. É provável que a deformação maior de transcorrência, responsável pela estrutura atual dos cinturões, ocorresse em fase tardia da evolução, embora mesmo as unidades mais antigas sejam deformadas e metamorfizadas.
The Geological and Geodiversity Mapping binational program along the Brazil-Guyana border zone allowed reviewing and integrating the stratigraphy and nomenclature of the Roraima Supergroup along the Pakaraima Sedimentary Block present in northeastern Brazil (Fig. 1). Of unparalleled scenic beauty, it gathers a dozen tepuys, which stand out Mount Roraima, a triple frontier between Brazil, Venezuela and Guyana (Reis 2009). The basin register a historical gold and diamond mining activity in a stratigraphic framework poorly investigated and deserving attention at the application of sequence stratigraphy, tectonic setting and geochronological studies.This paper discusses the correlation of the stratigraphy of the Roraima Supergroup on both sides of the border of Brazil with Guyana, based on the work performed during the Geological and Geodiversity (land-use) Mapping of the Brazil-Guyana Project, carried out by geologists of the CPRM -Geological Survey of Brazil and the GGMCGuyana Geology and Mines Commission. The area of geological mapping includes the three main villages of Uiramutã and Mutum on the Brazilian side and Orinduik on the Guianese side, all of them located within that buffer zone of 25 kilometers on both sides of the frontier (Fig. 2). In spite of the bad weather conditions and the impossibility to drive along the dirt roads between Karasabai Village and Monkey Mountains, it was possible to reach Orinduik by plane. During the flight, it was possible to observe an interesting area of the Roraima Supergroup where the first sedimentary rocks form cliffs overlying the Iwokrama volcanics
The Iriri-Xingu domain, located in the central part of the Amazonian craton, consists of extensive occurrences of Paleoproterozoic volcanic rocks and granites with published ages of ca. 1990 to 1840 Ma, which show a strong crustal contribution for their magmas. Exposures of basement rocks are small and rare. Samples from two areas were dated in this work by U-Pb SHRIMP in zircon. In the northern Maribel area, a high-grade pelitic paragneiss presented an age of 2160 ± 8 Ma and the leucosome of a migmatitic orthogneiss, probably a diatexite, crystallized at 2149 ± 20 Ma. These Rhyacian ages suggest that it is part of the Bacajá domain, related to the Trans-Amazonian cycle. The Morro Grande area occurs in the central part of Iriri-Xingu domain, where a high-grade muscovite gneiss with a protolith of 2120-2180 Ma is dated at 1982 ± 7 Ma, and the leucosome of a migmatitic orthogneiss is crystallized at 1979 ± 8 Ma. These are the first records of high-grade metamorphism at ca. 1980 Ma in the Central Brazil shield and may be related to the generation of this Orosirian felsic magmatism, which is widespread throughout the nearby Ventuari-Tapajós province.
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