GNGTS 2019 - Atti del 38° Convegno Nazionale

178 GNGTS 2019 S essione 1.3 and integrated together with GPS observations collected from the permanent monitoring network of Mt. Etna during the December 2015 – December 2018 period of activity. Olivine crystals were selected and grouped in populations based on their core compositions and zoning types in order to detect the presence of magmas with distinct differentiation degrees. Olivine cores spanning from more basic (Fo 84 ) to slightly evolved compositions (Fo 70 ) reflect crystal residence and growth in five magmatic environments, which are variably distributed beneath Mt. Etna. The physical parameters, such as P, T, and ƒO 2 , associated to each environment were constrained through thermodynamic modeling. Thus, high-Fo core compositions at Fo 84 designate a deep environment of crystallization at ca. 650 MPa, here indicated as M 00 ; olivines with Fo 80-81 cores are representative of the M 0 environment located at pressure of 420-380 MPa; Fo 78 cores refer to the M 1a environment at 290-230 MPa; olivines with Fo 76 core compositions belong to the M 1b environment at 160-120 MPa, whereas the Fo 70-74 cores cover a compositional range which is between 30 and 40 MPa (i.e., the environment M 2 ). A detailed investigation of the diversity of the olivine chemical zoning from core to rim allowed the identification of some dominant paths of ascent and mechanisms of interactions between different magmas. This finally led us to detect those environments that were reactivated before each eruptive episode since December 2015. The timescales associated to these magmatic interactions were obtained by modeling the diffusional relaxation of the Fe-Mg zoning in olivine crystals (Costa et al. , 2018; Costa and Morgan, 2010). The petrological evidence of multiple magmatic environments beneath the volcano is strongly connected with the evidence of active magmatic sources inferred through geodetic data inversions and associated to main ground deformation stages. For instance, in the case of the 2015-2016 eruptions at VOR, ground deformation data indicate the presence of a magmatic source at depth of 4.9–5.7 km bsl, which is rather consistent with the depth of storage of the M1b reservoir defined by petrological investigations. Moreover, the olivine chemistry indicates as trigger of the 2015-2016 eruptions the injection of high-Mg magmas (Fo 86-89 ) that rose up from the deepest regions of the Mt. Etna plumbing system (>650 MPa), moving to shallow crustal levels in very short time scales (ca. 1 month). Evidence of this mafic end-member is given by the reverse zoning patterns observed in most of the crystals erupted during the episodes of the 2015-2016. At the end of the activity at VOR on May 2016, ground deformation data recorded a new inflation of the volcano edifice which lasted about 10 months. The inflation resulted by magma injection that caused the pressurization of the shallow portion of the plumbing system within the pressure range of M1b. Associated to this main deformation stage, we inferred a source of deformation that well overlaps the environment M1b, as for the events of VOR. All over the 2017 eruptive period, olivine chemistry highlights processes of continuous replenishment of the volcano plumbing system with basic M1a and M1b magmas that rapidly moved throughout the crust, reaching the surface in 1-3 weeks. The recharging magmas had more evolved compositions than those feeding the volcanic activity at VOR. Noteworthy, the continuous magma injections from depth was completely balanced by lava effusion at the surface, resulting in a nearly flat deformative pattern during the episodes of February and March 2017. Similarly, a new inflationary deformative pattern was recorded since April 1, 2017 albeit conspicuous magma discharges occurred during the eruptions of April 11, 19 and 27. In spite of the end of the activity at the NSEC, the inflation of the volcano edifice continued steadily until December 24, 2018, when a new effusive lateral eruption took place from a fracture system extending from the base of the NSEC down into the western wall of the Valle del Bove. Through geodetic data modeling we inferred a magmatic source of deformation at 7025±352 m bsl, which is therefore located at depth slightly higher than magmatic sources feeding the 2015-2016 activity at VOR (5661±471 m; Cannata et al. , 2018) and at the NSEC during 2017 (6298 ± 350 m; Viccaro et al. , 2019). Conclusion. The integrated analysis of geodetic and petrological data applied to a complex volcanic system like Mt. Etna has proved to be a powerful tool to gain insights into the spatial and temporal history of magma transfer and recharge beneath the volcano. We explored the