Constraining the recent plumbing system of Vulcano (Aeolian Arc, Italy) by textural, petrological and fractal analysis: The 1739 AD Pietre Cotte Lava Flow

Abstract

The 1739 A.D. Pietre Cotte lava flow is part of a sequence of low-explosive to weak effusion events occurred at La Fossa Cone, the active vent on Vulcano Island (Aeolian Arc, Italy). This lava is rhyolitic, texturally heterogeneous, and contains lati-trachytic enclaves. These compositions are recurrent in the La Fossa volcanic products and are representative of the recent Vulcano plumbing system. The host lava is vesicular, relatively phenocryst-free, and locally contains microlites and millimeter-sized spherulites. The enclaves are up to 10 cm in size, display angular to spherical shapes, and can form the core of spherulites. Enclaves mostly consist of plagioclase and augitic phenocrysts set in a weakly vesicular groundmass characterized by variable abundance of glass and feldspar microlites. Field, textural, and fractal data allow us to constrain the rheological features of the rhyolitic and lati-trachytic magmas. In situ major, trace, and volatile element analyses provide evidence for heterogeneities in the glassy matrix and zoning of phenocrysts. Processes of magma evolution have been quantitatively constrained by using the apparent distribution ratios of trace elements measured between mineral phases and glassy matrices. The collected data in combination with petrological and fluid inclusion data from the literature provides evidence for (1) a genetic relationship between the two magmas through assimilation fractional crystallization process; (2) a mingling mechanism between an uprising rhyolitic magma and a shallower partly crystallized lati-trachytic magma plug; (3) the desegregation (enclaves) at variable scales of the lati-trachyte within the rhyolite; and (4) the possible eruptive scenarios consequent to a future magmatic unrest.