Nd and Sr Isotopic, Geochemical and Petrographic Characteristics of the Morro de São João Alkaline Intrusion: Geodynamic Implications and the Composition of the Sub-lithosperical Mantle

Authors

  • Carlos Eduardo Miranda Mota Universidade Estadual do Rio de Janeiro; Faculdade de Geologia; Programa de Pós-graduação em Análise de Bacias e Faixas Móveis
  • Mauro Cesar Geraldes Universidade Estadual do Rio de Janeiro; Faculdade de Geologia
  • Julio Cesar Horta de Almeida Universidade Estadual do Rio de Janeiro; Faculdade de Geologia
  • Thaís Vargas Universidade Estadual do Rio de Janeiro; Faculdade de Geologia
  • Débora Marinho de Souza Universidade Estadual do Rio de Janeiro; Faculdade de Geologia; Graduação
  • Renata de Oliveira Loureiro Universidade Estadual do Rio de Janeiro; Faculdade de Geologia; Graduação
  • Aline Pimentel da Silva Universidade Estadual do Rio de Janeiro; Faculdade de Geologia; Graduação

DOI:

https://doi.org/10.5327/Z1519-874X2009000100006

Keywords:

Morro de São João, Alkaline rocks, Isotopic chemistry

Abstract

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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Published

2009-01-01

Issue

Vol. 9 No. 1 (2009)

Section

Articles

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How to Cite

Mota, C. E. M., Geraldes, M. C., Almeida, J. C. H. de, Vargas, T., Souza, D. M. de, Loureiro, R. de O., & Silva, A. P. da. (2009). Nd and Sr Isotopic, Geochemical and Petrographic Characteristics of the Morro de São João Alkaline Intrusion: Geodynamic Implications and the Composition of the Sub-lithosperical Mantle . Geologia USP. Série Científica, 9(1), 85-100. https://doi.org/10.5327/Z1519-874X2009000100006