Magmatic processes recorded in plagioclase crystals of the Rio Jacaré Batholith, Sergipano Orogenic System, Northeast Brazil

Abstract

Plagioclase crystallization is common in magmatic systems and are textures can provide valuable information about the physicochemical conditions present during magmatic evolution. This work presents a systematic study of textures and compositional variation in plagioclase crystals in the granites and microgranular enclaves of the Rio Jacaré Batholith (RJB) aiming to infer the magmatic processes that were recorded in these crystals. Plagioclase of the inequigranular facies has composition ranging from albite to andesine (An7-33), while in the porphyritic facies it is albite and oligoclase (An5-23). In microgranular enclaves plagioclase composition ranges from albite to labradorite (An6-51). In addition to the presence of chemical zoning in plagioclase of the RJB rocks, patchy zoning, boxy cellular texture, crystal cores showing embayed or homogeneous composition as well as inclusion zones of mafic and synneusis minerals also occur. The textures identified in the RJB rocks allowed us to infer that during the evolution of the RJB magma, there was a period of stable conditions followed by a period with injections of mafic magmas, which modified the conditions (temperature, pressure, and H2O activity) of this magmatic system and stimulated mixing between magmas. The mafic magma injections are most likely to have generated convection currents in the magmatic chamber of the RJB. In addition to this process, it is also necessary to consider the decompression of magma, caused by its rapid rise. This complex evolution of the Rio Jacaré magmatic system was registered in the textures and compositions of the plagioclase crystals and suggests at least five successive moments of resorption in these crystals.