To the north of the Carajás range granitoid rocks occur in an elliptical domain oriented in toWNE-ESE direction. These rocks are limited to the south and to the north by metabasalts and banded iron formations belonging to the Itacaiúnas Supergroup. The granitoids show a penetrative foliation in the body scale, striking in the WNW-ESE and E-W directions, concordant with the regional structures. Steep dipping foliations predominate but flat lying ones are locally present. Foliations are continuous, smooth, and marked by the weak to strong preferred
orientation of mafic minerals and feldspars and by the flattened quartz aggregates. Stronger degrees of deformation were reached on decimeter-wide E-W mylonite zones. Discrete centimeter-wide conjugate shear bands are locally described. The structural evolution of the studied granitoids indicates emplacement synchronously to N-S compressive stress, similarly to other 2.7 Ga granitoids present in the region. Granodiorites and monzogranites predominate largely over tonalites, leucomonzogranites and syenogranites. Quartz-feldspathic pegmatites occur locally filling decimeter-wide veins. In less deformed rocks, oriented granular textures are common. Sometimes, these rocks show graphic texture accompanied of corroded amphibole crystals (honeycomb or sieve textures). Both textural evidences suggest fast crystallization controlled by undercooling conditions and emplacement at shallow levels. In moderate to strongly deformed rocks corrosion of amphibole
and biotite produce symplectite textures along the surfaces parallel to foliation. In this case the corrosion is stress-controlled and it suggests deformation history of unconsolidated rocks. Two groups of granitoids can be discriminated on the basis of whole-rock chemical data: alkaline (ALK-3) and calc-alkaline (CA-2) granitoids. The rocks of both groups have moderate to high Y, Nb and Zr contents so that the calc-alkaline granitoids in some diagrams plot on the Atype field. The alkaline and the calk-alkaline rocks from the Igarapé Gelado region were most probably originated by partial melting of continental crust. The high Zr contents seem to indicate that both group of rocks were generated by high-temperature partial melting of crustal rocks. Differences of rare-earth elements patterns of the studied ALK-3 and CA-2 granitoids could reflect different depths of the source rocks. The calc-alkaline magmas, are depleted in heavy rareearth elements, compared to alkaline ones and would be produced at deeper levels. Pb-Pb (evaporation) zircon dating yielded 2.5 Ga on the low temperatures steps and 2.73 Ga on the steps of higher temperatures. The later value is considered as the minimum age to the
granitoids crystallization and it is close to the ages obtained by other authors on quartz-fedspathic veins that crosscut rocks from the Igarapé-Pojuca Group. The age of 2.5 Ga could reflect some degree of perturbation on the U-Pb system. The studied granitoids belong to the syntectonic magmatism (e.g. Estrela, Planalto, Serra do Rabo, Plaquê granites) that took place in the Carajás region 2.7 Ga ago.
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