GNGTS 2017 - 36° Convegno Nazionale

192 GNGTS 2017 S essione 1.3 et al. , 2016 and reference therein for details). We interpreted this reservoir as the main magma chamber feeding both the December 2015 and May 2016 volcanic activity that involved three of the summit craters (VOR, NSEC and NEC). Volcanic tremor sources were located below the summit craters at depth ranging from ~1 to 3 km asl. Most of the shallowest centroid locations (~3 km asl) fall withinVOR/BN and NSEC areas, and are associated with degassing and eruptive activities of these craters, while the deeper locations (down to 1 km asl) are likely to be related to magma migration in this portion of plumbing system. Infrasonic data provided insights into the shallowest portions of the plumbing system, corresponding with the degassing/eruptive vents, and their variations over time (Cannata et al. , 2013). The infrasonic sources active during the investigated period were NSEC, NEC and VOR. The infrasound emission from NSEC accompanied only Strombolian activity and lava fountains, while infrasonic activity of NEC and VOR was associated with both explosive eruptions and simple degassing. The compositional and textural observations for plagioclase crystals of the 2015-2016 activity at Mt. Etna have provided preliminary evidence that crystals experienced complex and variegate histories from nucleation to eruption, as crystals show a combination of growth and resorption features reflecting changing chemical/physical conditions (fast decompression, recharge, etc.) of the magmatic system. Chemical zoning of olivine crystals also gives us the opportunity to constrain timescales of magmatic processes before the eruptions at VOR. Combining geochemical data with thermodynamic modeling, we fixed 5 main magma environments, distributed across a wide pressure range (from >650 to 30 MPa), which were variously reactivated during the eruptive episodes occurred at VOR. Routes of connection between these different environments and processes of intrusion and mixing Etnean magmas underwent during ascent have been also inferred through the chemical zoning observed at the olivine rims, i.e. the reverse zoning which indicate that crystals were involved in hybrid magmas originated by mafic recharge and mixing, and the normal zoning that are expression of magma transfer and subsequent diffusive relaxation of the olivine zoning after intrusion into a more differentiated melt. Time constraints to magma dynamics preceding eruptions of December 2015 and May 2016 at VOR have been also derived modelling the diffusive relaxation through time of these olivine normal and reverse zoning patterns, which are both the expression of changed initial thermodynamic conditions. The spectrum of timescales determined by diffusion modelling covers a time span from a few days up to about 8 months, with the majority of the recorded timescales confined within 3 months before eruption. In conclusion, the integrated analysis of geodetic, seismic, infrasonic and petrological data proved a powerful tool to investigate the volcano structure and dynamics. In particular, a multilayered plumbing system was highlighted, with a complex spatial and temporal history of magma transfer and recharge beneath the volcano (Fig. 2). Acknowledgements We are indebted to the technicians of the INGV, Osservatorio Etneo for enabling the acquisition of seismic, infrasonic and GPS data. References Cannata A., Di Grazia G., Aliotta M., Cassisi C., Montalto P. and Patanè, D.; 2013: Monitoring seismo-volcanic and infrasonic signals at volcanoes: Mt. Etna case study . Pure Appl. Geophys., 170, 1751-1771, DOI:10.1007/ s00024-012-0634-x. Cannata A., Spedalieri G., Behncke B., Cannavò F., Di Grazia G., Gambino S., Gresta S., Liuzzo, M. Gurrieri, S. and Palano M.; 2015: Pressurization and depressurization phases inside the plumbing system of Mt. Etna volcano: evidence from a multiparametric approach . J. Geophys. Res. 120, 5965-5982, doi:10.1002/2015JB012227. Corsaro R.A., Andronico D., Behncke B., Branca S., Caltabiano T., Ciancitto F., Cristaldi A., De Beni E., La Spina A., Lodato L., Miraglia L., Neri M., Salerno G., Scollo S. and Spata, G.; 2017: Monitoring the December 2015 summit eruptions of Mt. Etna (Italy): Implications on eruptive dynamics . J. Volcanol. Geotherm. Res., 341, 53-69, DOI:10.1016/j.jvolgeores.2017.04.018. Giuffrida M. and Viccaro M.; 2017: Three years (2011–2013) of eruptive activity at Mt. Etna: Working modes and timescales of the modern volcano plumbing system from micro-analytical studies of crystals . Earth-Science Reviews, 171, 289-322, DOI:10.1016/j.earscirev.2017.06.003.