Ricerc@Sapienza

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.