- © The Mineralogical Society Of America
A quantitative understanding of crystallization and solidification is central to appreciating a variety of phenomena at the interface between volcanology and petrology. Interpretation of magmatic processes from the textures of erupted lavas and pyroclasts in turn depends upon understanding how textures evolve during cooling, decompression, and devolatilization. Crystal size, shape, and compositional distribution depend upon the underlying phase equilibria, mass transport processes, and kinetics of reactions at interfaces. Applications of kinetics in physical volcanology include estimating intra-eruptive magma residence times using crystal growth rates (e.g., Mangan 1990); interpreting perturbations in the melt composition or thermal state from microtextures (e.g., Sharp et al. 1996); assessing degassing as a driver of crystal growth (e.g., Blundy and Cashman 2001) and microlite nucleation (e.g., Hammer et al. 1999) during volcanic eruptions; and interpreting magmatic conditions as they change through time using crystal population trends (e.g., Zieg and Marsh 2002).
This contribution is chiefly concerned with magmas out of chemical and textural equilibrium evolving due to changes in temperature, pressure, or composition. However, studies concerned with dynamic aspects of syn-eruptive magma evolution are predicated on an understanding of the equilibrium steady-state, with experiments typically incorporating an initial stage of equilibration, imposing magma reservoir conditions as a prelude to controlled cooling or decompression. This review likewise includes a brief overview of the phase equilibria approach for determining the “initial conditions” for volcanic eruptions. The remainder of the chapter considers kinetic aspects of crystallization, which are essential for interpreting the information encoded in the compositions and textures of volcanic materials. A section each is allotted to (1) presenting concepts and controversies in the theoretical understanding of kinetics of crystallization since the last RIMG review on this topic (Kirkpatrick 1981), (2) summarizing generic aspects of experimental methods and experiment design in geological studies, (2) reviewing established trends …