On the Hydrodynamics of Crystal Clustering

The formation of crystal clusters may influence the mechanical behaviour of magmas. However whether clusters form largely from physical contact in a mobile state during sedimentation and stirring, or require residence in a crystal mush is not well understood. We use discrete-element fluid dynamics numerical experiments to illuminate the potential for clustering from both sedimentation and open-system mixing in a model olivine basalt reservoir for three different initial solid volume fractions. Crystal clustering is quantified using both bulk measures of clustering such as the R index and Ripley's L(r) and g(r) functions and with a variable scale technique called Voronoi tessellations, which also provide orientation data. Probability density functions for the likelihood of crystal clustering under freely circulating conditions indicates that there is nearly an equal likelihood for clustering and non-clustered textures in natural examples. A crystal cargo in igneous rock suites exhibiting a dominance of crystal clusters may be largely sampling magmatic materials formed in a crystal mush.