Rheological evolution of a trachybasalt from Mt. Etna under slow cooling

Understanding the rheological evolution of solidifying magma during its migration through the crust and the subsequent emplacement as lava is critical for assessing volcanic hazards. Crystallization plays a primary role in governing the rheology of low-viscosity basaltic magmas, thereby controlling lava inundation potential. While several studies have addressed this behavior under faster cooling conditions, experimental data bridging the gap toward the quasi-equilibrium regime remain scarce due to the technical challenges of long-duration high-temperature rheometry experiments. This highlights the critical need for new datasets designed to quantify the rheological evolution pertinent to lava flow emplacement conditions. Here, we present a rheological dataset carried out on an Etnean trachybasalt, focusing on low cooling rates (0.1 and 0.5 °C/min) under variable shear strain rates (1-10 s^-1). Within the range of cooling and shear rates applied, results indicate that the cooling rate exerts a first-order control on crystallization kinetics, whereas the shear rate plays a secondary role, consistent with previous literature data. The technical validation is provided through instrument calibration and the verification of the chemical integrity of the pre- and post-run sample. Interestingly, the dataset captures the non-linear dependence of the crystallization onset temperature, which asymptotically approaches the thermodynamic liquidus (~1210 °C) as the cooling rate decreases. Beyond improving our understanding of magma crystallization kinetics, this dataset provides critical constraints for parameterizing the rheological evolution of lava flows during their emplacement in numerical models under varying thermal and dynamic regimes.