Fig. 5: Rheological transition of a trachybasaltic magma during crystallisation.
a, b Evolution of clinopyroxene aspect ratio (rp) through time as a function of ∆T (undercooling) during the experiments Exp-A (a) and Exp-B (b). c, d Evolution of clinopyroxene crystal fraction (ϕ) through time as a function of ∆T during the experiments Exp-A (c) and Exp-B (d). Diffusion-limited growth, promoted at ∆T = 30 °C (Exp-A) and ∆T = 50 °C (Exp-B), favours dendritic crystal shapes which entrap melt within crystal branches. The entrapped melt within the original dendritic crystals (blue) is considered an additional solid part, which contributes to further increase the crystal volume of the dendritic crystals (red), increasing consequently the crystal volume fraction (a, b). c–h Evolution of the maximum packing fraction (ϕm), ratio ϕ/ϕm and flow index (\(n\)) which are indicators of the rheological behaviour of a crystal-bearing magma (Mader et al.). e, f Newtonian rheology is promoted at relatively low ϕ/ϕm (<0.5), whereas non-Newtonian rheology, characterised for example by shear thinning, is more pronounced as ϕ/ϕm increases. Shear thinning behaviour is promoted when \(n\) <1. a, c, e, g Light grey shading represents ∆T = 10 °C, dark grey shading represents ∆T = 30 °C. b, d, f, h Light grey shading represents ∆T = 20 °C, dark grey shading represents ∆T = 50 °C.
