MULTIPLE MAGMAS: A TEXTURAL ANALYSIS OF FIAMME FROM THE ORA SUPERERUPTION (PERMIAN, ITALY)
We studied these samples with a petrographic microscope and backscatter electron images to document general textural features and to identify areas of interest for further study. We obtained glass and phenocryst major element compositions using quantitative EDS analysis on an SEM.
Our results show that there are at least three varieties of fiamme present: coarse-grained crystal rich (CGR), fine-grained crystal rich (FGR), and fine-grained crystal poor (FGP). The CGR samples from the Southern intracaldera deposit have high silica rhyolite (HSR) (76-77% SiO2) glass encompassing large crystals (1-3 mm) which are resorbed. The Northern extracaldera outflow CGR samples have fragmented clusters of feldspars (1-2 mm) and resorption textures as well. The FGR samples from that unit are heterogeneous with ribbons of lower silica (67-70% SiO2) throughout the sample. The FGP fiamma from the outflow has small (<0.5 mm) crystals and the fiamma is rimmed with HSR.
Detailed textural analyses of phenocrysts within the fiamme help illuminate the magmatic history of Ora. As a crystal rich high silica rhyolite, the individual crystal histories may help us to understand how the magmatic system transitioned from a state of potential rheological lock-up to a stage capable of eruption. For example, the resorption textures suggest that Ora underwent re-melting prior to eruption. Also, the presence of multiple glass populations within a single fiamma strongly suggests that the eruption occurred shortly after magma mingling. Further geochemical analyses and rhyolite MELTs modeling will be done to constrain P-T conditions of the magma bodies prior to eruption.