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BIBTEX RIS

Características Isotópicas (Nd e Sr), Geoquímicas e Petrográficas da Intrusão Alcalina do Morro de São João: Implicações Geodinâmicas e Sobre a Composição do Manto Sublitosférico

2009; UNIVERSIDADE DE SÃO PAULO; Volume: 9; Issue: 1 Linguagem: Inglês

10.5327/z1519-874x2009000100006

ISSN

2316-9095

Autores

Carlos Eduardo Miranda Mota, Mauro César Geraldes, Júlio Almeida, Thaís Vargas, Débora Marinho de Souza, Renata de Oliveira Loureiro, Aline Pimentel da Silva,

Tópico(s)

Paleontology and Stratigraphy of Fossils

Resumo

The Morro de São João Alkaline Complex (MSJ) is located in the NE part of Rio de Janeiro State and shows pronounced topography, with the following lithology: coarse-grained felsic syenites (K-feldspar, nepheline, hornblende, titanite and pseudoleucite), and mafic syenites (with K-feldspar, hornblende and piroxene). Petrography and lithogeochemistry data suggest a bimodal suite. Felsic and mafic magma mixing and mingling textures are locally observed indicating the presence of coeval magmas. Nd and Sr isotope compositions correspond to EMI (Enriched Mantle I) mantle reservoir signatures, suggesting an asthenospheric enriched mantle source with low 87Sr/86Sr values (from 0.7049 to 0.7061) and low 143Nd/144Nd (from 0.512361 to 0.512428). The εNd values range from -4.03 to -5.54, indicating an anomalous enriched mantle reservoir, confirmed by the high T DM values between 730 - 830 Ma, very different from the 72 - 56 Ma K-Ar cooling ages. The comparison of Sr and Nd signatures with related hotspot traces (Trindade, St. Helena and Tristan da Cunha) indicates that they are similar to those of Tristan da Cunha, but somewhat different from those of Trindade and St. Helena.

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