Can the Kilauea Iki glomerocrysts offer insights into the magmatic processes leading up to the 1959 eruption?

The 1959 eruption at Kilauea Iki, Hawaii, was unusually violent for a near-summit extrusion and the sequence of processes leading up to it remain debated. The eruption might have resulted from the progressive emptying of a stratified magma chamber or from a new magma batch bypassing the base of the magma storage region and mixing with the differentiated magma at shallow depth. In this study, we test if the picritic scoria erupted during the 1959 eruption can shed light on the conditions in the magmatic plumbing system prior to eruption. Scoria from the 1959 eruption contain glomeroporphyritic aggregates of olivine crystals, primarily composed of 2-4 crystals but comprising as many as 16, which vary in composition and three-dimensional texture. The clustering of crystals from different environments and their preferential alignment along crystallographic axes suggest that the glomerocrysts may be the result of synneusis - the drifting together of crystals (Schwindinger and Anderson, 1989). Analogue laboratory experiments of clay crystals in Karo syrup (Schwindinger, 1999), however, show that two crystals settling in a still liquid will not reorient themselves into alignment. Here, we test the hypothesis that a shear-dominated flow field might have facilitated the synneusis of the Kilauea olivines. We investigate the fluid-dynamical conditions under which the glomerocrysts might have formed using direct numerical simulations at the scale of individual crystals. We have implemented an iterative numerical method for simulating the hydrodynamic interactions between olivine crystals and their feedback on the flow field in a magmatic liquid. We solve the Stokes equation in the fluid phase and include rigid, rectangular bodies representing the olivine crystals through distributed Lagrange multipliers. To allow crystals to stick together after collision, the numerical method includes a multibody collision scheme. Additionally, it uses an analytical quadrature scheme instead of discretizing the solid body into material volumes, increasing accuracy and reducing computational expense. Our simulations show that the Kilauea Iki glomerocrysts formed in a magmatic liquid with very low crystallinity (likely less than about 10%) and that shear might have facilitated preferential alignment.