GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 1.3 255 April 11 and April 19. Petrological evidence of multiple magmatic environments beneath the volcano appears strongly connected with geodetic data, through which we inferred the presence of two active magmatic sources associated to two main ground deformation stages, T2 (from June 16, 2016 to March 15, 2017) and T3 (from March 16 to April 1, 2017; Fig. 2). For the deformation stage T2, the magmatic source is located at depth of ~6.3 km bsl and covers the same pressure range of the M 1a environment. For the T3 stage, the modeled source is at depth of ~4.6 km bsl, corresponding to that of the M 1b environment. Such inferred magmatic sources are connected and they strictly interacted before and during the eruptive events of 2017. We were able to recover the timescales associated to these magmatic interactions by modeling the diffusional smoothing of the Fe-Mg zoning in olivine crystals (Costa et al., 2018; Costa and Morgan, 2010). Final results show a reasonable fit between the observed deformation patterns and inferred transfer dynamics from olivine normal and reverse zoning, allowing to follow the evolution through time of the volcanic activity between February and April 2017. Specifically, at the end of the May 2016 activity at VOR, ground deformation data recorded a new inflation of the volcano edifice (T2) which lasted about 10 months, but had a different deformation rate, which was very high from June 2016 to early February 2017 (T2a) and then changed to low rate from February to mid-March 2017 (T2b; Fig. 2). During T2a, the normal zoning of the Fo 78 and Fo 80-81 olivines indicates the ascent of fresh magma that occurred as a consequence of the pressure imbalance between the magmatic reservoir M 1b and a deeper one (M1 a or M 0 ). The diffusive relaxation of such zoning patterns produces, indeed, timescales of about 181- 256 days, in accordance with processes of magma movement that started 8-10 months before the beginning of the 2017 eruptive activity. After T2a, the plumbing system pressurized at constant rate, up to the beginning of the vigorous explosive activity in late February. During this period, low-Fo olivine crystals record a new injection of basic magma that occurred 23- 44 days before March 25 (i.e., end of February), causing the pressurization of the shallow portion of the plumbing system within the pressure range of M 1b and M 2 environments. From the reverse zoning of Fo 76 to Fo 78 olivines erupted between April 11 and April 19, 2017 we recovered longer diffusion timescales of 34-54 days associated to episodes of mafic recharge. Such timescales suggest that during T2b (from February 28 to March 15, 2017) the M 1b and M 1a environments underwent continuous recharge which balanced eruptive phenomena occurring at the surface. After a brief period of volcano flank deflation between mid-March and April 1, due to the intensification of the effusive activity, we have new evidence of ascent of basic magmas (M 0 ) from depth which rapidly moved throughout the crust during the period T3, reaching the surface in about 1 week. Fig. 2 . The upper panel shows the temporal evolution of the volcanic activity at summit area: 1) fire fountain activity, 2) Strombolian activity, 3) ash emission/weak explosive activity, 4) effusive activity. The lower panel displays daily baseline changes of EDAM and EINT stations. The visual inspection of such a baseline allows the detection of main ground deformation stages T1, T2 and T3. Detection of sub-period T2a, T2b, T3a and T3b accounts for changes in the deformation rates within a main deformative stage.