Combining chemical and X-ray microtomography investigations on crustal xenoliths at Mount Etna: evidence of volcanic gas fluxing

Crustal xenoliths embedded in lavas offer chances to provide information on the lithology of the volcano basement and the process occurring during magma ascent. In this work we studied seven xenoliths found among the scoriae ejected during several paroxysms occurred between 2011 and 2016 at the South East Crater (SEC) of Mount Etna volcano. These samples are characterized by massive presence of glass and vesicles resulting in a foam-like appearance of their texture. A detailed study of their textural and chemical features was carried out combining XRF, SEM-EDS, two-dimensional observation and Synchrotron X-ray microtomography (3D imaging). This multidisciplinary approach allowed us to identify and quantify the components of the samples, individuate the likely provenance rock, ascribable to the Numidian Flysch outcropping west of the Etnean edifice. 2D and 3D imaging were successfully applied to estimate the amount of the phases constituting the samples (grains + glass + vesicles) and the degree of partial melting that occurred during the interaction with the basaltic melt and gaseous phase. The sedimentary xenoliths underwent profound textural and geochemical changes led by partial melting, vesiculation and selective alkali enrichment. These processes could not be driven exclusively by the prolonged contact with the molten phase, but could be considered as resulting of a significant gas fluxing of the volatiles rising through the plumbing system and the sedimentary basement.