Contribuição à petrologia de stocks graníticos dos municípios de Canhoba e Aquidabã, NE sergipano

Abstract

The granitic stocks of Canhoba (≈6,0 km2), Gravatá (≈3,5 km2) and Lagoa do Mato (≈5,0 km2) occur intrusive in the metasediments of the northeastern part of the Macururé Domain in the Sergipano Orogenic System. These stocks exhibit rounded shapes include angular xenoliths of metasediments and in the contacts regions have abundant dykes and granitic pegmatites. The granites have well-developed tectonic foliation marked by the alignment of muscovite and quartz crystals. Leucocratic granitic compositions are dominate and exist granodioritic types, with muscovite and biotite. The petrographic and mineraloquímicos studies revealed that the dominant mafic mineral is biotite, the plagioclase is albite and oligoclase, has muscovite and titanite, opaque minerals, epidote, zircon and F-apatite are accessory minerals. The biotite crystals have 0.4 <Fe / (Fe + Mg) <0.7, the most ferrous being those of the Canhoba and Gravatá stocks. Based on the FeO content, MgO, Al2O3 the biotite crystals indicate that these granites have peraluminous affinities (Canhoba and Gravatá) and calc-alkaline (Lagoa do Mato). Temperatures obtained with biotite are too low to reflect igneous conditions and should indicate metamorphic conditions. The geochemical data confirm that rhese granites have subalkaline affinity, and are peraluminous and metaluminous and calc-alkaline high potassium. The Stock Lagoa do Mato belongs to the group of magnesia granites while the others (Canhoba and Gravatá) are ferrous. The early crystallization of zircon in the magma was calculated as between 772 and 811 oC which is reasonable for rhyolite magmas. In multielement diagrams it is clear that there valleys pronounced in Nb, Ta and Ti associated with the strong fractionation of LREE reflect orogenic affinity of the rocks of the studied stocks. In these diagrams tectonic granites position in volcanic arc environment. These data support the current hypothesis that granites occurring in Macururé Domain are orogenic.