Kinetics of crystal growth: Implications for understanding magma dynamics

Prof. Silvio Mollo, Sapienza Università di Roma.

Olivine, clinopyroxene, plagioclase and magnetite are the most common mineral constituents of igneous rocks, and both their textures and compositions are highly sensitive to variations in magma crystallization histories. Although most thermometric, barometric, hygrometric, and partitioning models assume archetypal equilibrium-controlled solution energetics, magma solidification beneath active volcanoes typically takes place in chemically and physically perturbed plumbing systems. In such environments, the crystallization of igneous minerals is collectively driven by a range of kinetic processes related to the dynamics of crustal reservoirs and eruptive conduits. Hence variable cooling, decompression, degassing, and convective mass transfer regimes critically influence the textural and compositional evolution of these crystals in the erupted products. Existing petrological models derived from unperturbed mineral-melt exchange reactions hold unquestionable importance and merit, yet they do not fully capture the complexity of natural subvolcanic environments, for which the phenomenological treatment of reaction kinetics plays a pivotal role in the evolution of energetically unstable magmatic systems. The ultimate goal of this scientific communication is to illustrate how the textural attributes of igneous minerals, the mixing properties of solid solution components and, the partitioning energetics of major-trace cations between crystal and melt are axiomatically dominated by the shift from equilibrium to dynamic crystallization regimes. Examining the interplay between kinetics and thermodynamics throughout the composite growth history of olivine, clinopyroxene, plagioclase and magnetite offers a robust framework for a more comprehensive understanding of magmatic processes across multiple interconnected crustal reservoirs and during eruption towards the surface.