Petrografia, química mineral e geoquímica das rochas calciossilicáticas do Domínio Macururé, Sistema Orogênico Sergipano

Abstract

The Macururé Domain is a metasedimentary package that reaches up to 13 km thick, is located in the central region of the Sergipano Orogenic System and makes contacts with the other geological domains of this orogen by shear zones. In the outcrops of the metasediments (slates, phyllites and quartzites) and in the shales of this domain, the presence of calc-silicate rocks forming centimetric layers is in agreement with the primary sedimentary bedding. In the central and eastern portions of the Macururé Domain in the State of Sergipe, the petrographic study identified the presence of three distinct groups of chalky silicate rocks. In the first group, the rocks preserve the sedimentary mineralogy and structure, being formed by angular rock fragments, quartz and muscovite phenoblasts immersed in fine-grained matrix. The second group consists of samples that show the features of regional metamorphism, and apparently is the most abundant type, and the minerals present are diopside, hornblende, quartz, muscovite, opaque minerals and zircon. The third group is formed by samples that have static metamorphic textures and the rocks are formed by quartz, hornblende, garnet, muscovite, biotite, plagioclase, carbonate, muscovite, zoisite, having as accessory minerals apatite, ilmenite, zircon. The plagioclase of these rocks presents compositions ranging from albite to oligoclase, amphibole (Mg-hornblenda, edenite, tschermakita); brown mica corresponds to biotite and phlogopite; epidotes (Al-epidote and zoisite) and garnets have equilibrium indicative compositions in the green schist and amphibolite facies. The geochemistry showed that the studied rocks do not correspond to typical calc-silicate rocks, since they have higher Al2O3 contents, comparable to those of graywacke and arcose. The ambience of the source of these sediments according to geochemical data is multiple and suggests important participation of arc lands (volcanic and island).