Crystal Shape Control on the Repacking and Jamming of Crystal‐Rich Mushes

Abstract

The rheology of crustal mushes is a crucial parameter controlling melt segregation and magma flow. However, the relations between mush dynamics and crystal size and shape distribution remain poorly understood because of the complexity of melt‐crystal and crystal‐crystal interactions. We performed analog experiments to characterize the mechanisms that control pore space reduction associated with repacking. Three suspensions of monodisperse particles with different geometries and aspect ratios (1:1, 2:1, 4:1) in a viscous fluid were tested. Our results show that particle aspect ratios strongly control the melt extraction processes. We identify two competing mechanisms that enable melt extraction at grain scale. The first mechanism leads to continuous deformation and melt extraction and is associated with “diffuse” frictional dissipation between neighboring particles. The second is stochastic, localized, and nearly instantaneous and is associated with the development and destruction of force chains percolating through the granular assembly.

Repacking in Compacting Mushes at Intermediate Melt Fractions: Constraints from Numerical Modeling and Phase Separation Experiments on Granular Media

“…To explore the issues outlined above, we develop a numerical model of compaction and apply it first to the phase separation experiments of Hoyos et al (2022). Hoyos et al (2022) performed a series of analog "French Press" experiments on monodisperse (and in some cases, bi-disperse) particles immersed in corn syrup (Fig. 2a ).…”

“…1 ). Because of the limited amount of experimental data published for compaction rates at melt fraction > 0.3, we use both the olivine centrifuge experiments at intermediate melt fractions and the repacking experiments of Hoyos et al (2022) to assess the role of repacking on compaction in this regime. This suite of experiments consists of olivine-MORB melt aggregates that are compacted in a centrifuge apparatus.…”

“…The hypothesis that compaction in the centrifuge experiments may be accommodated by repacking is inspired by a suite of analog experiments on suspensions performed at or near ambient pressures and temperatures (Boyer et al , 2011, Cassar et al , 2005, Costa et al , 2009, Faroughi & Huber, 2015, Hoyos et al , 2022, Jopet al , 2006. For instance, the experiments of Boyer et al (2011) included applied shear stresses to suspensions housed in a shear cell and revealed that at intermediate fractions (ca.…”

“…The second objective is to constrain the rheology associated with repacking by developing a compaction model and applying it to the high T + P centrifuge experiments and to the low T + P experiments of Hoyoset al (2022) (section 3). The experiments of Hoyos et al(2022), unlike those of Boyer et al (2011), were performed under conditions of uniaxial compression with no macroscopic shear component. We demonstrate that a transition between compaction by repacking to grain boundary-controlled diffusion near the maximum packing of the mush can explain the sharp increase in effective resistance to compaction between the centrifuge and partially molten rock experiments and is consistent with petrologic observations in natural magma chamber systems.…”

A unified numerical model for two-phase porous, mush and suspension flow dynamics in magmatic systems

“…As solid grains come into contact, they transmit stresses along force chains and develop a matrix pressure distinct from the melt phase (e.g. Bergantz et al, 2017;Hoyos et al, 2022).…”