Mineral chemistry and crystallization conditions (P-T-fO2 ) of Plúton Maravilha, PEAL Domain (Borborema Province)

Abstract

Plúton Maravilha, located in the Pernambuco-Alagoas Domain, crops out with approximately 200 km², and WSW-ENE major axis. It shows tonalitic modal composition, an unigranular, sometimes porphyritic phaneritic texture, with varying amounts of plagioclase, biotite, amphibole and quartz, sometimes microcline. Magmatic epidote, titanite, apatite, zircon and allanite occur as the main accessory phases in the Maravilha Pluton. In this work, we analyzed the main mineral phases present in the pluton, aiming to understand their petrogenetic evolution and crystallization conditions. In more deformed portions, the pluton is very strongly leafy, marked by the presence of primary biotites, mostly chloritized at the edges, and may be a product of hydrothermalism or early stages of metamorphic reactions, being classified among the astonitesiderophyllite
solid solution. Amphiboles are predominantly magmatic, largely classified as pargasite and ferro-pargasite. Geobarometric calculations show values from 6 to 7.18 kbar, while geothermometry was estimated at 706 to 785ºC using Al^IV content in plagioclases and amphiboles in equilibrium. The presence of the magnetite+titanite+quartz assemblage in equilibrium, the values of Fe # in biotites and amphiboles, as well as euhedral and subhedral crystals of magnetite associated with rhombic euhedral titanite as early phases, indicate that the parent magma was relatively oxidized.