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U-Pb geochronology of gneisses and granitoids in the quadrilátero Ferrífero (southern São Francisco Craton): age constraints for Archean and Paleoproterozoic magmatism and metamorphism

1998; Sociedade Brasileira de Geologia; Volume: 28; Issue: 1 Linguagem: Inglês

10.5327/rbg.v28i1.614

2317-4889

Carlos Maurício Noce, Nuno Machado, Wilson Teixeira,

Geochemistry and Geologic Mapping

U-Pb analyses were carried out on gneisses and granitoids from the Quadrilatero Ferrifero area, in the southern Sao Francisco craton. The Belo Horizonte complex represents a segment of Archaean crust principally composed of migmatized banded TTG-type gneisses. Migmatization event took place at 2860+14/-10 Ma. Granitic plutons intruded in the complex are crust-derived and one of them yielded a zircon age of 2712+5/-4 Ma. The emplacement of a small granitic pluton at 2612+37-2 Ma defines the youngest Archaean magmatic event in the Quadrilatero Ferrifero. This set of geochronological determinations together with published data allows the establishment of a fairly accurate framework for the evolution of the Archaean crust in the Quadrilatero Ferrifero. The main period of crust generation at 3.0 to 2.9 Ga is indicated by Nd isotopic signature of TTG gneisses. The evolutionary trend followed the progressive amalgamation of continental blocks, associated with intensive reworking of the primitive crust, renewed events of granitoid emplacement and greenstone belt deposition. An extensive cratonic area consolidated at ca. 2.6 Ga and was subsequently covered by stable-shelf sediments. The Alto Maranhao pluton was emplaced at 2124±1 Ma. This tonalitic intrusion represents an isotopically juvenile body related to the Transamazonian Orogeny. Titanite of the TTG-gneiss and leucosome align in a discordia with a lower intercept at 2041 ±5 Ma defining the metamorphic peak of this event.