Produção Nacional
Estudo Sm-Nd do Complexo Mafico-Ultramafico Bacuri, Amapa: idade da intrusao, metamorfismo e natureza do magma original
2002; Sociedade Brasileira de Geologia; Volume: 32; Issue: 3 Linguagem: Inglês
10.5327/rbg.v32i3.992
ISSN2317-4889
AutoresMárcio Martins Pimentel, Carlos Alberto Spier, César Fonseca Ferreira Filho,
Tópico(s)Geochemistry and Elemental Analysis
ResumoThe Bacuri mafic-ultramafic complex is a metamorphosed and deformed intrusion made of amphibolite and etaultramafic rocks (serpentinite and chromitite), exposed in centralsouthern Amapa, within the Paleoproterozoic Maroni-Itacauinas mobile belt, northern Brazil. Its age, nature of original magma and tectonic significance are still poorly constrained. A whole-rock Sm-Nd “errorchron” (MSWD = 5,1) for the mafic and ultramafic rocks indicates the age of 2.22 ± 0.12 Ga and e Nd (T) of –3.8. Despite the large uncertainty, this represents the only estimate available so far for the age of crystallization of the complex. The initial Nd isotopic composition indicates that the original magma is strongly contaminated with older sialic crust. Gneiss country-rocks have T DM model ages between ca. 3.1 and 3.3 Ga and might represent the crustal contaminants. Garnet amphibolites of the Vila Nova Group yielded whole rockgarnet isochron indicating the age of 2.08 ± 0.02 Ga for the regional metamorphic event. This is roughly coeval with the voluminous late-orogenic granitic magmatism in the Maroni-Itacaiunas mobile belt. The isotopic data agrees with previous field and petrological studies which concluded that the intrusion is a layered body intruded into and contaminated with older continental crust. This kind of intrusion in northern Brazil may represent a significant source of metals such as Cr, PGE, Fe- Ti-V, Cu-Ni, enlarging the possibilities for mineral exploration in the Guiana Shield.
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