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ESTUDO ISOTÓPICO Sm-Nd REGIONAL DA PORÇÃO CENTRAL DA FAIXA BRASÍLIA, GOIÁS: IMPLICAÇÕES PARA IDADE E ORIGEM DOS GRANULITOS DO COMPLEXO ANÁPOLIS-ITAUÇU E ROCHAS METASSEDIMENTARES DO GRUPO ARAXÁ

1999; Sociedade Brasileira de Geologia; Linguagem: Inglês

10.25249/0375-7536.199929271276

2177-4382

Márcio Martins Pimentel, Reinhardt A. Fuck, Danielle Piuzanna Fischel,

Paleontology and Stratigraphy of Fossils

In the central part of the Brasilia Belt, central Brazil, a high grade terrain, the Anápolis-Itauçu Complex, is exposed within the metasedimentary rocks of the Araxá Group. The Anápolis-Itauçu Complex in Goiás represents a complex association of high-grade rocks including mafic-ultramafic bodies, charnockites, enderbites, as well as aluminous granulites of sedimentary origin, associated with marbles and quartzites. Narrow volcano-sedimentary belts formed mainly by amphibolites and micaschists are also recognized within the complex. This high-grade terrain has been traditionally interpreted as part of the old (Archaean/Paleoproterozoic) sialic basement to the Neo- or Mesoproterozoic sediments of the Araxá Group, Brasilia Belt. The granulites and metasediments of the Araxá Group are intruded by a large number of granite intrusions, many of which show peraluminous character. Sm-Nd isotopic analyses for the garnet- and sillimanite-bearing aluminous granulites indicate T DM model ages between ca. 1.3 and 1.6 Ga. These values represent the upper limit for the age of the protoliths of the granulites, demonstrating that they are (at least in part) younger than suggested in previous models. The intrusive granites have a Sm-Nd isotopic pattern which is not much different from that observed for the felsic granulites, with T DM model ages ranging in the interval between ca. 1.37 and 1.85 Ga. The isotopic compositions of the granitic and granulitic rocks investigated are also similar to those determined for metasediments of the internal zone of the Brasilia Belt (Araxá Group) in central-southern Goiás. These metasediments show Nd model ages between ca. l .2 and 2.2 Ga. The preliminary isotopic data presented are consistent with a model in which the voluminous granitic magmatism identified in the Anápolis-Itauçu Complex and adjacent areas is Neoproterozoic in age, being the result of re-melting of the older sialic crust. The peraluminous nature of many of these granites/rhyolites (e.g. the Maratá Sequence and associated granites in the Ipameri area) indicates that the original magmas were mostly extracted from a metasedimentary source which is isotopically similar to the metasedimentary rocks of the Araxá Group. We suggest a model in which at least part of the aluminous granulites of the Anápolis-Itauçu Complex represents high-grade equivalents of the metasedimentary sequences of the internal part of the Brasilia Belt.