Emplacement conditions of the mafic magmatism from Macururé Domain, Sergipano Orogenic System: Capela Massif

Abstract

The Capela Massif intrudes the metasedimentary rocks of Macururé Domain, in Sergipano Orogenic System, southern Borborema Province. It is composed of diorites, hornblendites, gabbros and granites, which host tonalitic and hornblenditic enclaves. The shapes and contacts of the tonalite enclaves and presence of inverse and oscillatory zoning in plagioclase crystals and acicular apatite in the enclaves and diorites suggest coexistence of mafic and felsic melts. The pyroxenes identified in the gabbros are consisted of enstatite, augite and diopside. Amphiboles of the mafic rocks are calcic and correspond to pargasite, tschermakite and magnesium-hornblende. Brown mica of the hornblendites, gabbros and diorites is phlogopite-rich, while those of the granites is more enriched in iron. The garnet which occurs in hornblendites and diorites is enriched in the almandina molecule. Plagioclase varies from albite to bytownite and potassic feldspar is the microcline. Magmatic titanite and epidote, coexisting with magnesian mafic silicates indicate crystallization under high fO₂, near the NNO buffer. Pressure estimates provide an average value of 8.5 kbar, matching an approximate emplacement depth of 30 km. Liquidus temperatures obtained with the pyroxene and amphibole compositions vary from 1,261 to 831°C. Solidus temperatures estimated with the amphibole-plagioclase pair are between 775 and 614°C. Mineral chemistry data and thermobarometric estimates suggest that the rocks of the Capela Massif were crystallized from hydrous basaltic magmas in a continental arc environment.