Metamorphic and structural evolution of the Várzea do Capivarita Complex, Dom Feliciano Belt, Encruzilhada do Sul, RS

Abstract

The Várzea do Capivarita Complex is represented by paragneisses disposed as megaxenoliths in the granites of the Encruzilhada do Sul Suite and as smaller fragments in the Quitéria and Cordilheira granites. These granitic units crop out in the northernmost part of the Pelotas Batholith, eastern portion of the Dom Feliciano Belt, near Encruzilhada do Sul. The complex is constituted by pelitic gneisses with subordinate calc-silicate gneisses, marble, quartz-feldspathic gneisses and rare quartzites. The pelitic gneisses have injections of centimetric to metric wide tabular bodies of muscovite bearing peraluminous leucogranites. In this work, petrographical and microestructural analysis of representative thin sections of the lithologies and the structural characterization of the area were made. The integration of these data allowed evaluating the migmatization of the paragneisses and the generation of the leucogranitic injections. The metamorphic conditions established based on the identified paragenesis indicate temperatures of the order of 850 to 1000 °C and pressures between 6 and 10 kbar, characterizing a granulite facies orogenic metamorphism belonging to the intermediate pressure and ultra-high temperature (UHT) series. The structural concordance between the paragneiss (S₂ ) metamorphic foliation and the leucogranite magmatic foliation (S₀ ) indicates that both were formed in the same event, implying that the migmatization of the paragneisses of the Várzea do Capivarita Complex generated the peraluminous leucogranites during the apex of the collisional orogenic metamorphism.