A swarm of dikes crops out on the southwestern of Água Azul do Norte, Carajás Province. The dikes are characterized for diabases, andesite, dacite, rhyolites and alkali-feldspar rhyolites, oriented according a preferential direction NW-SE, and cut tonalite-thondhjemite Archean rocks of Rio Maria Granite-Greenstone Terrane, as well as, locally, Paleoproterozoic anorogenic granites. Petrographically, the diabases show subophitic (intergranular) and porphyritic textures, and consist of plagioclase, pyroxene, and to a lesser extent, amphibole and opaque minerals. The andesite dike is characterized by microcrystalline texture, locally microporphyritic, where rare K-feldspar and quartz are present as phenocrysts, besides laths of amphibole and opaque minerals. The dacite dike has granular texture and is mineralogically composed of plagioclase, quartz, biotite and, in smaller proportions, amphibole. Three petrographic types of rhyolite were identified. The first one is porphyritic with dominant granophyric texture, but spherulitic texture occurs locally. Their mineralogy consists of quartz, alkali feldspar, plagioclase, biotite and amphibole dispersed in a felsitic matrix. The second is a porphyritic alkali-feldspar rhyolite, containing phenocrysts of quartz and alkali-feldspar comparatively smaller than those of previous rock and plagioclase in low modal proportions, and with matrix dominated by spherulitic and granophyric intergrowths. Biotite strongly altered to chlorite is the only mafic phase. The third is aphanitic, pale pink, with dominant spherulitic texture, containing quartz and alkali-feldspar as essential minerals, and chlorite and opaque as secondary phases; quartz phenocrysts occur locally. In order to get the age of the magmatism of this region, one sample of the rhyolite porphyry and dacite were selected for geochronological dating at Laboratory of Isotope Geology of the UFPA using evaporation-ionization in zircon monocrystals method. Five zircons from rhyolite provided an age of 1887 ± 2 Ma, interpreted as the crystallization age of the dike. On the other hand, zircons of the dacite not answered satisfactorily to the analysis, and its zircons were considered inherited from the Archean basement. Pb-Pb geochronological data on single crystals of zircon showed ages of 1879 ± 2 Ma for a rhyolite dike in the region of Bannach, and 1885 ± 4 Ma for a composite dyke, constituted of granite porphyry and a diabase, in the region of Rio Maria.
These ages are slightly younger than those obtained for Seringa (1895 ± 1 Ma) and São João (1890 ± 2 Ma) granites. The data obtained in this study suggest that the felsic dikes of Rio Maria, Bannach and Agua Azul do Norte regions belong to the same Paleoproterozoic magmatic event. As regards the intermediate to mafic dykes could not conclude an age for them, since the zircons presented analytical problems.
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