In the Vila Tancredo Neves region, northeast of the São Félix do Xingu city, Amazonian Craton, Carajás Mineral Province (Brazil), the Archean basement is regionally deformed in greenschist to upper amphibolite facies, as well as affected by ductile shear zones. These rocks are orthogneisses, migmatites, and foliated granitoids (compositionally biotite monzogranites, biotite granodiorites, potassic leucogranites, hornblende-biotite monzogranites and biotite trondhjemites). Regional metamorphism is related to deformational microtectonics evolving from ruptile behavior of resistant phases, associated with greenschist facies, to mafic minerals segregation and gneissic banding formation and ductile behavior related to reaching the elastic force peak of minerals at medium to upper amphibolite facies. Locally these rocks are protomylonites to mylonites.Geochemical data revealed: (G1) trondhjemite, peraluminous, tholeiitic affinity, magnesian, weakly fractionated and enriched in HREE, and U-Pb dating yielded 2841 ± 19 [±20] Ma (MSWD = 0.6). (G2) granites, metaluminous, alkaline to slightly tholeiitic affinity, ferric, high Zr, Y, Nd, and HREE, intermediate fractionation and A-type granites affinity, with U-Pb age of de 2745 ± 8 Ma (MSWD=0,62), TDM 3.25 Ga and negative εNd(t) -4,11. (G3) high La/Yb(N) index; (G4) low La/Yb (N) index. G3 and G4: granites, peraluminous, calk-alkaline to alkali-calcic affinity, ferric, more fractionated (varying La/Yb and Sr/Y) and mixed tectonic signature, between anorogenic and fractionated, zircon U-Pb of these groups yielded the age of 2854 ± 32 Ma (MSWD=0,074), TDM 3.10-3.37 Ga and negative εNd(t) between -0,75 and -5,69. These data suggests great conformity to the Canaã dos Carajás subdomain granites signature, indicating mantle extraction of at least 3.2 Ga, with Nd isotopes suggesting old crust contribution, and intense granitoid formation at 2.96–2.83 Ga and reworking at 2.75–2.70 Ga. However, the model age data show older mantle extraction and more negative εNd(t) parameter, suggesting this region is related to the first stages of evolution of this domain.
|
