Dynamics of volcanic systems. Physical and chemical models applied to equilibrium versus disequilibrium solidification of magmas

The solidification of magmas can occur by cooling (ΔT/Δt) and/or degassing-induced decompression (ΔP/Δt), as a function of solidus, glass transition, and melting temperatures, respectively Ts, Tg, and Tm . These three parameters strongly depend on the bulk composition (X) of the system and vary with T, P, fO2, and H2 O. In recent decades, physical and chemical models of magmas have been profoundly refined, such as thermal, rheological and density behaviors, the formation conditions of mineral/melt phases, and volatile solubility. However, variations of physical and chemical features of magmas through time are still poorly constrained. This means that mechanisms binding the formation of different phases under equilibrium and disequilibrium conditions are still poorly quantified, although they are of paramount importance for reconstructing magmatic dynamics encrypted in volcanic rocks. Here, the most relevant solidification conditions of magmas leading to possible crystallization paths are tested in physical models. The textural and, especially, chemical attributes of minerals are reviewed in order to summarize the salient features able to discriminate between formation of equilibrium and disequilibrium phases. Finally, the reconstruction of magmatic intensive variables deduced from composition of minerals is discussed.