Shear-induced crystallization as a trigger for rapid solidification of basalts: implications for magma dynamics

The eruptive style of mafic volcanoes is critically influenced by magma rheology, which is dynamically modulated by crystallization during cooling and decompression of ascending magma. Although the role of undercooling is well established, the influence of deformation on crystallization kinetics in magmas remains poorly constrained. Here, we experimentally investigate the rheological and textural evolution of Mt. Etna trachybasalt under isothermal conditions (1170°C) using concentric cylinder rheometry at varying shear rates (up to 10 s⁻¹). Real-time viscosity monitoring reveals that stirring exerts a fundamental influence in enhancing magma solidification due to crystallization, shortening the incubation time of nucleation and the time needed to reach thermomechanical equilibrium. Crystal textures confirm that stirring shifts crystallization from growth-dominated to nucleation-dominated regimes, with nucleation rates increasing by up to two orders of magnitude at the highest shear rate. Electron back-scatter diffraction analysis of the experimental samples indicates a non-linear structural response to deformation. Low-to-intermediate shear rates (0.1–1 s⁻¹) induce a moderate degree of crystals preferred orientation, while higher shear rate (10 s⁻¹) produces chaotic, isotropic textures due to rapid and spatially dispersed nucleation. These findings outline that deformation actively drives crystallization, dramatically accelerating magma solidification. We discuss how shear-enhanced crystallization is a key mechanism in volcanic systems, facilitating the attainment of rheological thresholds that trigger transitions in eruptive style. These deformation-driven effects offer new constraints for the understanding of basaltic Plinian eruption trigger mechanisms, identifying a threshold above which microlite production and magma strengthening can be significantly accelerated during ascent.