Petrografia, geoquímica e geocronologia de diques máficos a félsicos da região de Água Azul do Norte, Província Carajás, sudeste do Pará

Abstract

In the Água Azul do Norte region, southeast of Pará, mafic to felsic dikes arise in razed area in the form of discontinuous ridges sectioning anorogenic granites and Archean country rocks. Preferentially they occur under NW-SE direction forming tabular subvertical bodies with thicknesses of up to 30m. Four groups were individualized: diabases, andesites, rhyolites and alkali-feldspar rhyolites. Geochemically, are basalts, basaltic andesites, andesites and rhyolites metaluminous to weakly peraluminous of tholeiitic affinity. In Harker diagrams diabase displays the lowest contents of SiO2 and TiO2 and the highest contents of FeOt, MgO and CaO, reflecting the mineralogical composition of these rocks predominantly formed by plagioclase and clinopyroxene. The andesites show intermediate TiO2, FeOt, MgO, CaO, Na2O and K2O values compared to diabases and rhyolites, similar to other andesite dykes already studied in the Rio Maria Domain (RMD). The dikes of alkali-feldspar rhyolite and rhyolite have higher and varied concentrations of SiO2. FeOt, Al2O3, MgO and CaO exhibit negative correlation, while K2O is positively correlated with the silica. Na2O, TiO2 and P2O5 have no clear correlation. The diabase dikes show sub-horizontal pattern of rare earth elements (REE), with light REE fractionation, enrichment of light REE (LREE) relative to heavy REE (HREE) and not too prominent to slightly negative Eu anomalies. Comparatively, the andesite dykes have more accentuated REE fractionation, greater enrichment of LREE compared to the HREE and more pronounced Eu negative anomalies. The rhyolite dyke displays moderate REE fractionation and negative anomaly of Eu, while the alkali-feldspar rhyolites show greater fractionation of REE and enrichment of LREE compared to HREE, besides strongly pronounced Eu negative anomalies. The presence of compositional gaps between groups of Água Azul do Norte dikes rule out the existence of a continuous magmatic series; the mafic magmatism, represented by diabase dikes, has not evolved to form the andesite. On the other hand, the dikes of rhyolite and alkali-feldspar rhyolite would be linked to the anorogenic A-type granite magmatism of approximately 1.88 Ga active in the RMD. The comparative study shows similarities between the Água Azul do Norte dikes and those of other areas of the RMD, suggesting a common origin.