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Solubility of volatiles in magmas

Final Report Summary - SOLVOM (Solubility of volatiles in magmas)

The goal of the SolVoM project was the determination of the role of compositional parameters on the distribution of volatiles, H2O and CO2, between silicate melts and coexisting gas phase at high pressure and high temperature. In accord to this goal, experiments were performed at magmatic conditions and results are already submitted to international journal for publication and some are already published and available to the scientific community (see below). In agreement with the previous submitted report, an empirical equation is now available to predict the maximum CO2 solubility at 500 MPa and 1100-1300 °C in various silicate melts as a function of the parameters NBO/T, (Na + K)/∑cation and Na/(Na+K). The equation has now the following form:
-0.246+0.014exp(6.995*NBO/T)+3.150*(Na+K)(sum of cations)+0.222*Na/(Na+K) (1)
NBO/T can be calculated according to Mysen et al. (1985) and (Mysen, 1988).
This model allows estimation of CO2 solubility in most of the natural magmatic systems and is valid for melt compositions with NBO/T between 0.0 to 0.6 (Na + K)/∑cation between 0.08 to 0.36 and Na/(Na+K) ratio from 0.25 to 0.95 at oxygen fugacities around the quartz-fayalite-magnetite (QFM) buffer and above.
Moreover, cooperation with Prof. Webster on the Cl solubility in aluminosilicate melt results in 121 experiments performed between Hannover and New York with the aim to construct a model able to predict the solubility of water and Cl for most magma. The model determines the exsolution of hydrosaline liquid, with or without a coexisting vapor, as magmas ascend from depth, cool, crystallize, and differentiate from mafic to felsic compositions. In combination with H2O solubility models, this new model supports determination of H2O-Cl solubility relations for most magmas and is useful for barometric estimations based on silicate melt inclusions containing low CO2 and moderate to high Cl concentrations. The model is applied to the phase relations of fluids in volatile-enriched magmas of Augustine volcano, Alaska.
The investigation of volatile rich mafic magmas (doped with desired amount of volatile such as H2O, CO2, S) flushing into silicic bodies was tested with the aim to provide a new inside into the so called “rejuvenation processes”. Results have shown that volatiles are able, via porous medium, to be incorporated into the “dormant magma chamber” and that for the performed pilot experiments, the viscosity of the magma mush could be dropped down by about four orders of magnitude just incorporating about 2 wt% water. The evolution of the viscosity could result in a movable melt layer that, via Rayleigh Taylor instability could re-activate the magma chamber and proceed for a possible eruption. This scenario has been proved by using mathematical model only and the experimental approach is going to be developed with the aim to fully demonstrate the ability of the “Rejunenation process”.
Last but not least, a series of decompression experiments were performed with the aim to investigate natural volcanic scenarios: continuous, isothermal decompression experiments were conducted using trachybasaltic magma from Etna volcano to investigate the dynamics of volatile release and possible influences on crystallinity in basaltic magmas. The experiments were performed at 1030 °C, log(fO2) = QFM (quartz-magnetite-fayalite buffer) and are right now under investigation for phases proportion and chemical analyses as well as for image analyses. Preliminary results show that the sulfur-bearing systems may crystallize faster than sulfur-free systems.Thus the presence of sulfur within magma chamber can lead to a strong increase of the magma viscosity during magma ascent resulting in a much explosive behavior of the volcanic systems. This scenario is actually been tested with duplicated experiments and a publication is in preparation and should be submitted during the fall of this year.

Complementary to my main project on solubility of water and CO2 in magmas (one paper already published and others submitted and under review), F. Vetere has been involved in an experimental study on the viscosity change during crystallization of shoshonitic magmas and its influence on lava flow emplacement. A paper has been published on this subject:

F. Vetere, H. Sato , H. Ishibashi, R. De Rosa, P. Donato. (2013) Viscosity changes during crystallization in shoshonitic magma: new insight on the lava flow emplacement. Journal of Mineralogical and Petrological Sciences Vol. 108 no. 3 144-160.

F. Vetere is also involved in an Italian-German project on the crystallization and glass forming ability of silicate melts. One paper is going to be submitted and one has been published on the subject:
F. Vetere, G. Iezzi, H. Behrens, A. Cavallo, V. Misiti, Marcel Dietrich, Jaayke Knipping, G. Ventura, S. Mollo (2013). Intrinsic solidification behaviour of basaltic to rhyolitic melts: a cooling rate experimental study. Chemical Geology, 354, 233-242.
F. Vetere, G. Iezzi, H. Behrens, F. Holtz, G. Ventura, V. Misiti, A. Cavallo, Marcel Dietrich, S. Mollo (2014). Glass forming ability of subalkaline silicate melts Under preparation to be submitted in an international journal. In this study, the glass forming ability (GFA) of natural sub-alkaline silicate melts is quantified via the experimental determination of their critical cooling rate (Rc), i.e. the cooling rate necessary to produce first crystals (1-2 vol% of crystals). Data on GFA of natural melts are still lacking although it is an important physico-chemical parameter. To experimentally model the GFA, we used six cooling rates of 9000, 1800, 180, 60, 7 and 1 °C/h between 1300 °C (liquidus region) and 800 °C (quenching temperature) and six very common natural silicate melts, with compositions varying systematically from basalt (B) to rhyolite (R) (B100, B80R20, B60R40, B40R60, B20R80 and R100).
The Rc values span 5 order of magnitude being 0.001 0.114 17, 68, 145 and 150 °C/min for R100, B20R80, B40R60, B60R40 and B80R20 and B100, respectively; the variation of Rc can be modelled via the NBO/T (non bridging oxygen per tetrahedron) parameter by the following master sigmoidal equation:

R_c=a/(1+〖exp〗^((-(NBO/T-x_0 ))/b) )
where a, b and xo are fitting parameters equal to 165(5), 0.047(5) and 0.283(6) in the case that Rc is in °C/min or:
R_c=9214.12/(1+〖exp〗^((-(NBO/T-0.297))/0.040) )
Where Rc is given as °C/h.

The cooperation with Italian researchers resulted also in the following paper that has been recently published proving the first evidence of explosive volcanic activity at significant depth (500-800 m bsl) in the Mediterranean Sea in the vicinity of the Marsili volcanoes complex.
Iezzi G., Caso C., Ventura G., Vallefuoco M., Cavallo A., Behrens H., Mollo S., Paltrinieri D., Signanini P, Vetere F. (2014) Historical volcanism at the Marsili Seamount (Tyrrhenian Sea, Italy): first documented deep submarine explosive eruptions in the Mediterranean Sea. Gondwana research 25, 764-774

During the 24 months of the grant, Dr. F Vetere has collaborated with different scientists outside the research group of Hannover:
Dr. Guido Ventura,: Istituto Nazionale di Geofisica e Vulcanologia INGV, Roma;
Dr. Gianluca Iezzi: University of Chieti-Pescara;
Prof. H. Sato University of Kobe Japan;
Dr. H. Ishibashi: Università di Schizuoka, Japan;
Prof. Jim Webster: NY Dept. of Earth & Planetary Sciences AMNH, New York.
Prof. Marco Viccaro: Dipartimento scienze della Terra Universitá di Catania.
Prof.Martin Streck............................................................

The cooperation with Prof. Webster was particularly fruitful and the joint project was also presented at AGU 2013 session:
V31C-05. Sulfur and Chlorine Exsolution from COHSCl-Bearing Melts and the Generation of Mineralizing S- and Cl-bearing Magmatic-Hydrothermal Fluids (Invited)
James D. Webster; Francesco P. Vetere; Roman E. Botcharnikov; Harald Behrens

Cooperation with Profs. Ventura and Iezzi and italian researchers was also fruitful, leading to the publication of two papers (Iezzi et al., 2014, and Vetere et al., 2013, see below):

Futher informations about Dr. Vetere are available at:[alias]=fvetere&cHash=5a2a745dd740b32af3cbaed55bc09d80

Significant results are:
- More than 100 successful H2O-CO2 solubility experiments on different magmas compositions;
- Publications of five manuscripts on silicate magma and melts and other three already submitted and under review right now;
- Two more papers are in progress and hopefully will be submitted at the beginning of the next year.
- Presentation of the work to the AGU 2013 in San Francisco Califonia in December and Convener of one session at the same meeting.