ASPECTOS PETROLÓGICOS DO MAGMATISMO ALCALINO CRETÁCEO DE SANTO ANTONIO DA BARRA, GO

LUCIA CASTANHEIRA DE MORAES

Resumo


Mela-analcimite, olivine mela-analcimite, nepheline analcimite, phonolite, melilite mela-nephelinite, alkali basalt and basanites, both as flows and piroclastic accumulations, make up the alkaline volcanic sequence that occurs near Santo Antônio da Barra, in southwestern Goiás. Volcanism is related to the N40W Rio Verde-Iporá lineament of Cretaceous age. The volcanics show a trend of the fractional crystallization: olivine mela-analcimite -t phonolite, with the mela-analcimites as the most abundant member. The relationship of rocks in this trend with melilite mela- nephelinite and basaltoid are still obscure. Petrographic and petrochemical features demonstrate the sodic/potassic mixed nature of the suite.


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