RICERCA ITALIANA     

Physical and chemical properties of volatile-bearing silicate melts: experiments, modeling and application to volcanic degassing.

Università degli Studi Roma Tre

Abstract

Magmatic processes are governed by transport and thermodynamic properties of the silicate melts and minerals constituting the magma. The properties that most affect the fluid-dynamic behaviour of magmas are viscosity, density and calorimetric properties and all the first (enthalpy, entropy, V) and second (Cp, adiabatic compressibility, isobaric thermal expansivity) order thermodynamic variables associated with them.
Although the experimental data base for many properties is growing, these data are often from chemically comparatively simple systems. Therefore, direct experimental determination and modelling of such properties for natural magma compositions to understand magmatic processes is of extreme importance.
The project has three main objectives:
1)Modeling of transport and thermodynamic properties of natural magmas and of the associated volatile phases. To do so, the following tasks will be addressed:
a.Modelling of the rheology of magmas as a function of T, volatile and crystal content and deformation regime:
b.Implementation of the current construction of PVT equations of state for silicate melts to include for the effect of volatiles;
c.Implementation of the current parameterization of the Cp and Cpconf of silicate glasses and liquids to include for volatile components.
2)Development of a computational tool able to depict the thermo-chemical features of chemically complex melts in a wide P-T regime. In particular, the >>>

Principal Investigator

Claudia Romano Università degli Studi ROMA TRE

Research Objectives

This research project has three main objectives:

1)Modeling of the transport and thermodynamic properties of natural magmas and of the associated volatile phases, which govern volcanic and magmatic processes. To do so, the following tasks will be addressed:
a.Modelling of the rheology of magmas as a function of T, volatile and crystal content and deformation regime:
b.Implementation of the current contruction of PVT equations of state for silicate melts to include for the effect of volatiles both at 1 atm and at high P, low and high T;
c.Implementation of the current parameterization of the Cp and Cpconf of silicate glasses and liquids to include for the volatile components.

2)Development of a computational tool able to depict the thermo-chemical features of chemical complex silicate melts in a wide thermo-baric regime. In particular, the polymeric model of silicate melt reactivity will be applied to the modelling of:
a.Volumetric properties in a wide thermo-baric regime;
b.Viscosity of silicate liquids in terms of Sconf;
c.Solubility in the multicomponent system CO2-H2O-H2S-Cl-F-silicate melt;
d.Diffusivity of volatiles in silicate liquids.

3)Development of a model of volatile degassing during magma ascent, which includes multicomponent solubility (2a, 2b), volatile diffusivity (2d) and nucleation and growth models. This modelling will be based on the polymeric model HPA, extended >>>

First Results

As described above, the general expected results from this research consist of (1) a parameterization of the thermodynamic and transport properties of magmas, (2) a general model for the chemical reactivity of silicate melts, and (3) on the theoretical basis of this model, a model for the degassing of volatiles during magma ascent along a volcanic conduit. These expected results, in a sense, are the product of the individual results of each research unit. Additionally, the various individual results of each unit and the combined product have potentially strong applications. Attainment of these results will require a strongly concentrated collaboration and cooperation between all of the research units involved in the project.

UR 1 (Romano) will provide, as a result of their study, a general parameterization of transport and thermodynamic properties of silicate melts and of the associated volatile phases. To achieve this task, this unit will execute a careful experimental work aimed at investigating: (1) the viscosity of magmatic liquids and magmatic mixtures (liquid + solid; liquid + bubbles) and (2) the multiphase rheology of volatile-bearing volcanic materials as they undergo viscous (flow) and brittle (fracturing) deformation at different deformation regimes; (3) Heat capacity of volatile-free and volatile-bearing glasses and liquids; (4) thermal expansivity and compressibility of glasses and liquids in a wide thermobaric regime. The experimental work will >>>

Timescale

24 months

National and international background

Magmatic and volcanic processes (e.g., partial melting, formation and ascent of magma, crystallization/degassing kinetics, fragmentation and eruptive style) are governed by transport properties (e.g., density, viscosity) and properties defining the energy exchanges among the phases of magmatic silicate mixtures. In particular, the density and the rheological properties (e.g., viscosity) control the buoyancy forces, fluid-dynamics of transport, eruptive style and rates of physicochemical processes (degassing, crystallization) in natural magmas [1-3]. On the other hand, the calorimetric properties of first (H, S, V) and second order (Cp, adiabatic compressibility, thermal expansivity) give us information about the energy budget and their variation with thermodynamic conditions associated to the magmatic mixtures.
As a consequence, understanding the mechanisms that control the above mentioned processes, and their impact on the environment, depends, first, on our ability to describe the physico-chemical properties by the proper computational tools and secondly, on our capability to use our model to evaluate and forecast the process evolution.
The investigation of the chemical, physical and structural properties for natural systems is extremely complex and frequently such kinds of analyses are limited to the characterization of simplified systems in a narrow range of P-T-composition (X)-volatile content and type (G) conditions.
Composition, T, solid and gas >>>