The transition of a silicate melt (complex silicate systems) to a solidified material (rock) is one of the major phase transformations in Earth Sciences and in glass/ceramic manufacturing. However, the kinetics of these physical-chemical processes and the deviations from the thermodynamic equilibrium are surprisingly poorly known. The aim of the present proposal is to experimentally study the transformation kinetics of natural magmas. The main goals are to reconstruct the temperature-pressure-time paths of solidification of natural volcanic systems; to provide new data for industrial glass applications. Two main processes characterize the crystallisation of a melt: i) nucleation (homogeneous vs. heterogeneous), which is the formation of atomic clusters with structural features similar to the corresponding crystal phases; ii) crystal growth (single vs. coarsening), which consists in a size increase from a molecular up to a millimeter/centimeter scale. Because the above processes are dependent on chemical composition of the melt, different dry and hydrous compositions representative of the majority of solidified magmas will be investigated. Two main types of kinetic solidification experiments will be performed: a) static experiments (fixed T and/or P with variable time t) aimed to investigate the role of undercooling and incubation time on the formed crystal phases; b) dynamic experiments (variable T, P or both as a function of t) aimed to study the glass forming ability and the role of cooling rate, decompression or both and their effects on the final crystal/glass assemblages. Both experimental approaches are required to well depict the solidification paths of complex silicate melts as a function of intensive (T, P, fO2) and extensive (liquid and volatile components) parameters. These experimental investigations represent the only way to obtain a reliable and quantitatively constrained models of crystallisation and/or vitrification.
In summary, the advancements and ground-breaking features of this proposal concern aspects that, up to now, are fully unknown for natural magmatic suspensions and melts or poorly known for restricted compositions. The main ground-breaking features may be summarized as follows:
1) Constraining and characterising the complex processes responsible for the transformation of magmatic melt(s) (± crystals ± volatiles) in solid(s) (glass, glass + crystals, crystals) as a function of (i) intensive physical parameters, (ii) melt composition, and (iii) absolute-relative time variations of both parameters and compositions following an experimental approach. This analysis will focus on selected magmatic compositions representative of about 90 vol.% of magmas erupted on the Earth.
2) Quantitatively analyse the crystallisation parameters of natural magmas (silicate liquid ± crystals ± volatiles) as a function of fixed T, P, fO2 and time (static experiments) and at varying T, P, time (dynamic experiments).
3) Measuring the parameters relevant for the processes of homogeneous and heterogeneous nucleation and crystal growth in natural magmatic systems and ceramic-glass composites (e.g., critical cooling rate, glass forming ability).
4) Understanding the crystallisation kinetics and its dependence on melt composition by crystallisation parameters.
5) Investigating the role of water, pre-existing textural heterogeneities (e.g. bubbles, pre-existing crystals), thermally cracking, decompression rate, cooling rate and redox conditions on nucleation/crystallisation processes.
6) Elucidating the effect of chemical composition of the melts on the amount and chemistry of crystals in disequilibrium conditions.
7) Shedding light on the relevance and role of crystal coarsening and/or Ostwald ripening processes on melt plus crystals mixtures, as the relative balance between these two processes is poorly known.
8) Conducting the "in situ", real-time analysis of nucleation and crystal growth at micrometric scale.
9) Providing a relevant dataset of experimental results open to the Earth Sciences, chemistry, physics, and material science communities useful to fully constrain theoretical kinetic models of nucleation and crystallisation, and models of magma ascent in conduits and flow of lavas on the Earth surface.
10) Improving methods for the formation of glasses and glass ceramics in technical applications. The knowledge of the relation between the chemistry of natural starting compounds and kinetic of solidification is directly applicable to commercial glass and glass/ceramics manufacturing. The possibility to control the chemical variables as a function of T and t is extremely important to reduce the material and energetic costs and has direct application of this project to industry.
11) Calculating the time dependence of liquid-to-solid threshold of magmatic suspensions due to crystal amounts as a function of intensive parameters and compositions.
12) Developing a quantitative model of nucleation, crystal growth and solidification of the most important dry or nearly-dry natural silicate compositions by coupling ex- and in-situ experiments.