Caracterização petrográfica e mineralógica dos riolitos dos pequenos Libombos na região de boane, província de Maputo-Moçambique

Abstract

The rhyolites of the Pequenos Libombos region, in southern Mozambique, constitute important records of regional acidic volcanism, whose mineralogical and textural characterization is essential for understanding their geological evolution. This study aimed to characterize these rocks petrographically and mineralogically through the integration of macroscopic observations, thin-section petrographic analyses, and X-ray diffraction (XRD).

The petrographic results indicate that the rhyolites are predominantly composed of quartz and alkali feldspars, accompanied by sodium-rich plagioclase, biotite, and muscovite as accessory minerals. Radial and axiolitic spherulitic textures, cryptocrystalline aggregates, and quartz-feldspar intergrowths suggest that the original volcanic material had a partially vitreous character and was subsequently reorganized by devitrification processes associated with the rapid cooling of the lavas. Secondary minerals, such as sericite, fine muscovite, and iron oxides, record low-temperature post-magmatic alteration processes that primarily affected the feldspars.

X-ray diffraction results confirm the crystalline phases observed petrographically, highlighting the predominance of quartz and feldspars and indicating significant recrystallization of the originally vitreous material. Together, the data obtained allow us to define the mineralogical composition, the main volcanic textures, and the post-magmatic processes responsible for the evolution of the rhyolites in the region, contributing to the improvement of local geological knowledge.