Geochemical, geochronological, and isotopic constraints for the Archean metamorphic rocks of the westernmost part of the Carajas Mineral Province, Amazonian Craton, Brazil

摘要

The Archean nucleus of the Amazonian Craton, represented by the Caraj ' as Mineral Province (northern Brazil), crops out as a broad exposition of igneous, sedimentary, and metamorphic rocks showing a complex polyphase geologic history. A succession of orthogneisses (metagranitoids), amphibolites, and metavolcano-sedimentary rocks that show greenstone belt characteristics occur in Tancredo Neves Village district, northeast of Sao Felix do Xingu city (state of Par ' a), is the focus of this study. Detailed field, petrographic, and stratigraphic data reveal that these metamorphic rocks underwent two different tectono-metamorphic events: (i) the regional meta-morphism (2.8 Ga), which occurred under greenschist-to mid-upper amphibolite-facies conditions; and (ii) the dynamic metamorphism (2.6 Ga) which reached amphibolite-facies conditions and overprinted previous metamorphic textures. Associated regional strike-slip NW-SE to EW-trending ductile shear zones generated mylonitic, ultra-mylonitic, and migmatitic zones. Whole-rock geochemistry discriminates four groups of meta-granitoid protoliths. G1 group is composed of peraluminous trondhjemitic rocks samples, calc-alkaline, weakly fractionated, and enriched in HREE. G2 group comprises metaluminous and alkaline monzogranite samples with high Zr, Y, Nd, HREE, and intermediate fractionation. U-Pb (LA-MC-ICP-MS) dating of G2 zircons yields a crystallization age of 2745.6 +/- 5.0 Ma. Groups G3 and G4 encompass peraluminous, calc-alkaline to alkali-calcic, anorogenic, fractionated monzogranitic and granodioritic rocks. G3 and G4 groups are further distinguished by high and low La/Yb-(N) ratios, respectively. The results obtained for Tancredo Neves Village district very much resemble the Canaa dos Caraj ' as (Caraj ' as Mineral Province) area characteristics, comprising intense magmatism (2.7-3.0 Ga) and reworking related to at least two distinct metamorphic events in the Archean. As Canaa dos Carajas, Tancredo Neves Village can be a promising area for mining exploration.