Competition between nucleation and growth processes of plagioclase in basaltic andesite are investigated to bring new constraints on textural evolution (crystal number density, size, and shape) in relation with the super-liquidus history and the cooling path. Our experimental approach investigates the role of super-liquidus initial conditions (e.g., superheating magnitude and duration, plagioclase relic cores) and of the crystallization paths (isothermal vs. cooling) on plagioclase shape. Experiments were conducted at 1 atm under anhydrous conditions with a Ni-NiO oxygen buffer, using natural basaltic andesite from the Osorno volcano (Chile). The starting powder was partially melted at 1190–1450 °C (ΔT = 15–260 °C) to adjust the density of plagioclase relic cores, producing a fully glassy groundmass.

Results reveal a clear textural evolution from euhedral tabular crystals to larger skeletal/dendritic shapes as cooling rate and superheating degree increase. We demonstrate that the magnitude and duration of superheating above the liquidus exert a comparable influence as an increase of the undercooling by cooling/decompression. Higher superheating degrees reduce crystal number density by 1–2 orders of magnitude, indicating that superheating significantly affects nucleation and growth dynamics. Even minimal initial densities of nuclei (~10⁻⁶ µm⁻³) greatly enhance final crystal density, confirming that nucleation is fundamentally heterogeneous, involving relic cores, Pt-wire, and sample edges. This questions the possibility of a real homogeneous nucleation in such systems.

Finally, this study shows that the super-liquidus history also indirectly affects how crystals grow by altering their shape and the balance between nucleation and growth. Faster cooling rates or higher superheating enhance undercooling, promoting crystal growth by delaying nucleation.

These findings highlight the importance of both superheating and cooling paths in controlling the textural evolution of basaltic andesite, offering insights into the interplay of nucleation and growth processes.