GNGTS 2013 - Atti del 32° Convegno Nazionale

During field surveys in the Pisciarelli made during the year 2006 were observed, compared to similar surveys conducted in the past (the year 2005), changes emission style of gases and fluids. Particularly the first are characterised by several point sources of emission while, along the eastern side of the small hill to the east, it is a mud boiling characterised by a diffuse and active degassing zone. A on-line gas monitoring station was localised close the fumaroles field (100 m) during the period May 16-30 th 2012, June 1 st -5 th , 2012. The main relationships of good tracer of magmatic fluids injection such us CO 2 /CH 4 and H 2 S/CO 2 was reconstructed due to this continuous monitoring (Fedele, 2013). In particular, the CO 2 /CH 4 is a good tracer of magmatic fluids injection because CO 2 concentration increased, due to its the higher content of the magmatic component, and CH 4 , a gas species formed within the hydrothermal system, is lowered both by dilution and by the more oxidizing, transient conditions caused by the arrival of SO 2 into the hydrothermal system (Chiodini, 2009, 2012). This opposite behaviour causes rapid increases of the CO 2 /CH 4 ratio in fumarolic fluids like it showed by the Fig. 2. This trend seems to be confirmed by the data of GPS ground deformation that show a general tendency to uplift with an acceleration of the phenomenon in the period spanning from June to August 2012 (25 mm/month in average) and increasing during the last month beginning on December 2012 (10 mm/month), as also shown in Fig. 2. Discussion and conclusion. In effect, periodic injections of hot CO 2 -rich fluids at the base of a relatively shallow hydrothermal system has been correlated to ground uplift in a wide range of numerical modelling of the CFc unrests, that highlight a strong correlation between chemical composition of the Solftara and Pisciarelli fumaroles, seismicity and ground movements (D’Auria et al. , 2011, Todesco et al ., 2004; Todesco and Berrino, 2005, Troiano et al ., 2011). In particular, a new simulation has been realised via the coupling of TOUGH2® and Comsol Multiphysics®, (Troiano et al. , 2011). Recent uplift episodes in the in the centre of Pozzuoli Bay have been reconstructed imposing fluid flows in the system as experimentally recorded. The comparison between numerical simulation, geochemical data and EM survey highlight the main features of the shallower part of the hydrothermal system of the Pisciarelli area. The high CO 2 /CH 4 ratio indicate a plausible magmatic component. For such magmatic origin, the plume identified in the MT imaging below the Solfatara crater seems to contribute also to fluid flow uplift below Piasciarelli. The low resistivity values under Pisciarelli, that indicate a strong local fluid circulation, support this kind of hypothesis. The fluid flow patterns reconstructed by our numerical simulations enforce this interpretation (Fig. 3). Fluids migrate, in the upper part of our model, from its central part, ideally placed below the Solfatara crater, toward an area localised some hundreds of meters away, fitting the Pisciarelli zone. The clear evidence that the thermodynamic condition of the system in the shallower part results compatible with the presence of convective cells enforce the idea that the degassing of the magma batch localised under the Solfatara crater contribute also to fluid circulation under Pisciarelli. References AGIP, 1987: Geologia e geofisica del sistema geotermico dei Campi Flegrei . Unpublished Internal Report, 1-17. Battaglia, J., Zollo, A., Virieux, J., and Dello Jacono, D., 2008: Merging active and passive data sets in travel-time tomography: The case study of Campi Flegrei caldera (Southern Italy), Geophys. Prospect., 56, 555-573. Caliro, S., Chiodini, G., Moretti, R., Avino, R., Granieri, D., Russo, M., and Fiebig, J., 2007: The origin of the fumaroles of La Solfatara (Campi Flegrei, South Italy) , Geochim. Cosmochim. Acta, 71, 3040-3055, doi: 10.1016/j.gca.2007.04.007. Chelini, W., and Sbrana, A., 1987: Phlegrean Fields. Subsurface geology , Quad. Ric. Sci., CNR, 114, 94-103. Chiodini G., Frondini, F., C. Cardellini, C., D. Granieri, D., Marini, D., and G. Ventura, G., 2001: CO2 degassing and energy release at Solfatara volcano, Campi Flegre i, Italy, J. Geophys. Res., 106, B8, 16213-16221. Chiodini, G., Todesco, M., Caliro, S., Del Gaudio, C., Macedonio, G., and Russo, M., 2003: Magma degassing as a trigger of bradyseismic events: The case of Phlegrean Fields (Italy), Geophys. Res. Let., 30 (8), doi: 10.1029/2002GL016790. Chiodini G.; 2009: CO2/CH4 ratio in fumaroles a powerful tool to detect magma degassing episodes at quiescent volcanoes . Geophysical Research Letters, v. 36, L02302, doi:10.1029/2008GL036347. 292 GNGTS 2013 S essione 1.3