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(Referência obtida automaticamente do Web of Science, por meio da informação sobre o financiamento pela FAPESP e o número do processo correspondente, incluída na publicação pelos autores.)

Geochemical signatures of metasedimentary rocks of high-pressure granulite facies and their relation with partial melting: Carvalhos Klippe, Southern Brasilia Belt, Brazil

Texto completo
Autor(es):
Cioffi, Caue Rodrigues [1] ; Campos Neto, Mario da Costa [1] ; da Rocha, Brenda Chung [1] ; Moraes, Renato [1] ; Henrique-Pinto, Renato [1]
Número total de Autores: 5
Afiliação do(s) autor(es):
[1] Univ Sao Paulo, Inst Geociencias, Dept Mineral & Geotecton, BR-05508080 Sao Paulo - Brazil
Número total de Afiliações: 1
Tipo de documento: Artigo Científico
Fonte: Journal of South American Earth Sciences; v. 40, p. 63-76, DEC 2012.
Citações Web of Science: 8
Resumo

High-grade metasedimentary rocks can preserve geochemical signatures of their sedimentary protolith if significant melt extraction did not occur. Retrograde reaction textures provide the main evidence for trapped melt in the rock fabrics. Carvalhos Klippe rocks in Southern Brasilia Orogen, Brazil, present a typical high-pressure granulite assemblage with evidence of mica breakdown partial melting (Ky + Grt + Kfs +/- Bt +/- Rt). The metamorphic peak temperatures obtained by Zr-in-Rt and ternary feldspar geothermometers are between 850 degrees C and 900 degrees C. The GASP bane peak pressure obtained using grossular rich garnet core is 16 kbar. Retrograde reaction textures in which the garnet crystals are partially to totally replaced by Bt + Qtz +/- Fsp intergrowths are very common in the Carvalhos Klippe rocks. These reactions are interpreted as a result of interactions between residual phases and trapped melt during the retrograde path. In the present study the geochemical signatures of three groups of Carvalhos Klippe metasedimentary rocks are analysed. Despite the high metamorphic grade these three groups show well-defined geochemical features and their REE patterns are similar to average compositions of post-Archean sedimentary rocks (PAAS, NASC). The high-pressure granulite facies Grt-Bt-Pl gneisses with immature arenite (wacke, arkose or lithic-arenite) geochemical signatures present in the Carvalhos Klippe are compared to similar rocks in amphibolite facies from the same tectonic framework (Andrelandia Nappe System). The similar geochemical signatures between Grt-Bt-Pl gneisses metamorphosed in high-pressure granulite facies and Grt-Bt-Pl-Qtz schists from the Andrelandia and Liberdade Nappes, with minimal to absent melting conditions, are suggestive of low rates of melt extraction in these high-grade rocks. The rocks with pelitic compositions most likely had higher melt extraction and even under such circumstances nevertheless tend to show REE patterns similar to average compositions of post-Archean sedimentary rocks (PAAS, NASC). (C) 2012 Elsevier Ltd. All rights reserved. (AU)

Processo FAPESP: 04/09682-8 - O papel dos líquidos silicáticos na evolução de rochas de alto grau da Faixa Brasília
Beneficiário:Renato de Moraes
Linha de fomento: Auxílio à Pesquisa - Regular
Processo FAPESP: 10/11152-8 - Tectônica do orógeno Brasília na Margem Sul do Cráton São Francisco: perspectiva paleogeográfica, metamórfica e estrutural
Beneficiário:Mario da Costa Campos Neto
Linha de fomento: Auxílio à Pesquisa - Regular
Processo FAPESP: 05/58688-1 - A América do Sul no contexto dos supercontinentes: fusão e fissão
Beneficiário:Miguel Angelo Stipp Basei
Linha de fomento: Auxílio à Pesquisa - Temático