Noble gases in tracking volcanic processess

    Risultato della ricerca: Other

    Abstract

    The expressions able to evaluate the contributions of the three natural sources of helium (e.g., atmosphere,in magma, following the solubility model proposed byNuccio and Paonita (2001). In particular, variations of He/Ne and He/CO2 ratios have been used to compute the initial and final pressure of an ascending magma (Fig. 2) (Caracausi et alii 2003b, Rizzo et alii 2006). This model was subsequently implemented with S, Cl and F (Aiuppa et alii 2004), providing an useful geochemical tool aimed at giving an early warning for forecasting volcanic eruptions.The high helium flux measured at Mefite d’Ansanto in the Irpinian Apennines, displaying a He isotope composition analogous to that of Mt. Vesuvius (which is located only 40 km away), together with the extremely high heat flow, up to 215 mW m-2 (Fig. 3) and the low rock magneto-telluric resistivity values (down to 10 hom m) at depth of 25 km below the axial zone of Apennines,strongly suggests the presence of a crustal magma intrusion, possibly connected to the mantle wedge formed by the sub-ducting Adria slab below the Apennines(Italiano et alii 2000).The heat source of thermal aquifers in western-Sicily were investigated by means of noble gases (Caracausi et alii 2005).In particular it was possible to recognize:- A mantle source, capable to transfer a heat flow of about 36 mW m-2 by conduction through the crust;- a crustal source, where heat is generated by 238U,235U, 232Th and 40K decay, supporting a heat flow of only6 mW m-2, because the thick sedimentary carbonates containing an average of 1.9 p.p.m. of uranium, 1.2 p.p.m. of thorium and almost no potassium.The measured heat flows in the region give values up to 38 mW m-2 in excess to the computed contributions of these two sources, implying that an additional source most be involved in the generation of the measuredheat flow.On the basis of the helium isotope ratios measured in gas dissolved in the thermal waters, we observed a significant mantle helium component, able to shift the typicalcrustal isotope helium signature from 0.02 Ra (being 1 Ra the in the atmosphere, where the 3He/4He ratio = 1.39×10-6) up to 2.8 Ra. That He isotope ratio crust and mantle) are described, taking into account both the He isotope compositions and abundances of helium, neon and argon.These evaluations are relevant in many geochemical applications, as in volcano monitoring, tectonics and geodynamics.Data acquired during geochemical monitoring of Mt.Etna clearly show synchronous variations of helium isotope composition (Fig. 1) measured in various peripheralgas manifestations (mofettes, mud volcanoesand bubbling gases), located several kilometers apart to each other, indicating an almost pure magmatic helium source and an Etnean plumbing system much more extensivethan previously reported. Furthermore, thosevariations cannot be related to any change of mixing process between magmatic and crustal helium, while they are related to pre-eruptive pulses of magma ascent towards the surface (Caracausi et alii 2003a).Changes of abundance ratios in magmatic gases are interpreted in terms of different solubility of volatiles causi et alii 2005). In particular it was possible to recognize:- A mantle source, capable to transfer a heat flow of about 36 mW m-2 by conduction through the crust;- a crustal source, where heat is generated by 238U,235U, 232Th and 40K decay, supporting a heat flow of only 6 mW m-2, because the thick sedimentary carbonatescontaining an average of 1.9 p.p.m. of uranium, 1.2 p.p.m. of thorium and almost no potassium.The measured heat flows in
    Lingua originaleEnglish
    Pagine131-133
    Numero di pagine3
    Stato di pubblicazionePublished - 2007

    Fingerprint Entra nei temi di ricerca di 'Noble gases in tracking volcanic processess'. Insieme formano una fingerprint unica.

    Cita questo