GNGTS 2021 - Atti del 39° Convegno Nazionale

GNGTS 2021 S essione 1.2 124 populations based on their core compositions and zoning types in order to detect the presence of magmas at distinct differentiation degrees. Fo concentration profiles reveal a variety of zoning patterns, from nearly flat core-to-rim profiles (OZ), to simple normal (N) or reverse (R) zoning at the rim, or more complex zonation (N+R; R+N). Olivine cores, spanning from more basic (Fo 83 ) to slightly evolved compositions (Fo 68 ), reflect crystal residence and growth in different magmatic environments, which are variably distributed beneath Mt. Etna. We noted that both abundance and concentrations of the detected plagioclase and olivine types significantly vary throughout the whole period under investigation in a way that volcanic products erupted at NSEC on July 27-28 display crystals with rather evolved concentrations, complex zoning patters and abundant disequilibrium textures, whereas the beginning of the activity at VOR on September 2019 marks a drop in the compositions of crystals, which show lower Fo and An contents, and also display homogeneous chemical profiles from core to rim, with just little or no evidence of disequilibrium textures. The abundance of crystal disequilibrium textures and complex zoning increased again starting from January 2020, in accordance with changes in eruptive dynamics. We interpret characteristics of crystals erupted on July 2019 at the NSEC as reflecting mul- tiple episodes of magma recharge from deep portions of the plumbing system followed by intrusion into the mid-upper section of the plumbing system (within 290-120 MPa). Olivine data indicate that this section of the plumbing system acted as the main zone of magma ac- cumulation and crystallization before the beginning of the eruptive activity. Episodes of reple- nishments were also detected seismically, in consequence of the intensification of volcanic tremor that led the tremor amplitude to higher level since the end of April 2019 ( Fig. 2 ). Such signals were precursory of the eruptive episodes of May and July 2019 at NSEC. We used ele- mental diffusion on zoned olivine erupted at NSEC to calculate the time at which the rechar- ging phases began and led to the July 28, 2019 eruption. Our modeling reproduces timescales of 28-41±8-12 days, therefore indicating that the episodes of deep recharge happened in the second half of June 2020 ( Fig. 2 ). Over this period, there is no significant variation of the seismo-volcanic signals, as magma movements detected from crystals dominantly occurred at deep levels of the plumbing system. Crystals erupted at VOR chiefly indicate a volcanic activity driven by recharge/discharge pha- ses that involved magmas coming from a nearly unperturbed magmatic environment located at Fig. 2 - Timeline of the 2019-2020 volcanic activity at NSEC (in blue), NEC (green) and VOR (red). The temporal variation fromMarch 1, 2019 to February 1, 2020 of the reduced root-mean-square (RMS) tremor amplitude (upper panel) is shown together with the main magmatic intrusive episodes (lower panel) involving compositionally-distinct environments (M i ). Coloured rectangles refer to the time of intrusion in a given environment as determined from olivine diffusion. Horizontal black lines departing from a single rectangle indicate the uncertainties on time calculations. The rectangle size is proportional to the time interval over which magmatic intrusions are recorded.