Análisis volcano-físicos y petrográficos de los productos de las erupciones riolíticas del volcán Alcedo, archipiélago de Galápagos : Caracterización petrológica de los productos de las erupciones riolíticas del volcán Alcedo, archipiélago de Galápagos.

Abstract

Alcedo volcano, located in Galapagos Islands, stands out among western shield volcanoes for its record of both basaltic and rhyolitic eruptions, an unusual phenomenon in oceanic islands. Its recent activity, evidenced by internal magmatic movement between 2007 and 2011, classifies it as an active volcano. During a field expedition in 2023, samples of pyroclastic deposits and obsidian lava flows were collected. These samples were the basis of this study, which include petrographic and microscopic thin section descriptions, as well as geochemical analyses of total rock and plagioclases crystals. The pyroclastic deposits feature the presence of mingled pumice and scoria, indicating a clear interaction between reservoirs of diverse composition. In contrast, crystal geochemical analyses of plagioclases showed a homogeneity in their composition, suggesting an absence of magma mixing or any evidence of interaction between the two compositions. Whole rock geochemical analysis evidence a plagioclase-rich tholeiitic trend and compositional sequence varying from trachybasalts to rhyolites. The hypovolcanic model of Alcedo volcano still presents challenges due to the lack of concordant evidence between hand samples and geochemical data. However, an interaction among three magma reservoirs: basaltic, icelanditic and rhyolitic is postulated, with the latter being smaller than represented in other conceptual models. The eruption likely commenced with the expulsion of icelandite, followed by the rhyolitic eruption, wich, upon contact with basaltic magma, results in the presence of mixed material on the surface.