Occurrence and geochemistry of metamafic rocks from the Forquilha Eclogite Zone, central Ceara (NE Brazil): geodynamic implications

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Exhumation of high-pressure granulites of the Guaxupe Complex, southeastern Brazil

This paper describes tectonic and metamorphic features of Precambrian rocks from the Guaxupe Complex and Varginha Shear Zone (VSZ) near the city of Guaxupe in the southern part of the Sao Francisco Craton, southeastern Brazil. The VSZ separates the metasediments of Araxa Group to the north from the granulites of Guaxupe Complex to the south. The sinistral transcurrent VSZ crosses the entire area striking approximately E-W, bending towards SE in the eastern part. Because of this bend, transpressional movement occurred, facilitating the exhumation of the garnet-rich rocks of the deepest exposed part of the granulite-facies terrane.In the garnet granulites the highest pressure-temperature conditions recorded are approximately 1040 degreesC and 14.4 kbar. The rocks underwent decompression from 14.0 kbar to 8.0 kbar, cooling from 980 degreesC to 710 degreesC, the retrograde path following the boundary between the kyanite and sillimanite stability fields. This interval is interpreted to record the uplift of the lower crustal granulite-facies terrane and re-equilibration during magmatic intrusions. For the felsic granulites an interval of 700-810 degreesC and 8.0-11.5 kbar was attained, also pointing to regional decompression.The granulites of the Guaxupe Complex comprise a medium- to high-pressure lower-crustal terrane, with local occurrences of higher-pressure garnet-rich gneisses, which were uplifted along a transpressional segment of the VSZ. Copyright (C) 2000 John Wiley & Sons, Ltd.

Vertical displacement during late-collisional escape tectonics (Brasiliano Orogeny) in the Ribeira Belt, São Paulo State, Brazil

During the Brasiliano-Pan-African Orogeny, West Gondwana formed by collisional processes around the Sao Francisco-Congo Craton. The Ribeira belt, in southeastern Brazil, resulted from northwestward collision (650-600 Ma), followed by large-scale northeast-southwest dextral strike-slip shear movements related to late-collisional escape tectonics (ca 600 Ma).In São Paulo State, three groups, also interpreted as terranes, are recognised in the Ribeira Belt, the Embu, Itapira and Sao Rogue Groups. The Embu and Itapira Groups are formed of sillimanite-gneisses, schists and migmatites intruded by Neoproterozoic calc-alkaline granitoids, all thrusted northwestward. The Sao Rogue Group is composed of metasediments and metavolcanics in greenschist-facies. Its deformation indicates a transpressional regime associated with tectonic escape. Sub-alkaline granites were emplaced in shallow levels during this regime. Microstructural studies along the Itu, Moreiras and Taxaquara Shear Zones demonstrate the coexistence of horizontal and Vertical displacement components during the transpressional regime. The vertical component is regarded as responsible for the lateral juxtaposition of different crustal levels. (C) 1999 Elsevier B.V. Limited. All rights reserved.

Correlação entre propriedades petrográficas e comportamento tecnológico e de alterabilidade das rochas ornamentais silicáticas Diamante Negro (BA), Ocre Itabira e Banco Galaxy (ES)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Avaliação dos granitos Giallo São Francisco Real, Branco Dallas e Branco Marfim, do muncípio de Barra de São Francisco/ES para aplicação como rocha ornamental e de revestimento

Pós-graduação em Geologia Regional - IGCE