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An obstacle to developing a general mechanical framework for magma mush is the emergence and complexity of a crystal fabric. To illuminate the conditions that produce a crystal fabric we performed time-dependent numerical simulations using a Computational-Fluid-Dynamics and Discrete-Element-Method (CFD-DEM) model in three dimensions. The specific focus was on the role of shear strain in the creation of a preferential orientation of crystals in mush. CFD-DEM method allows for the simultaneous coupling and frictional interactions of melt and crystals undergoing shear strain. The crystal shapes are represented using spheroids (either oblate or prolate). Simulations consist in imposing a compression stress (pressure) and a simple shear to a dense suspension of crystals in a viscous liquid, and monitoring the evolution of the orientation and strength of the shape fabrics. We ran a series of simulations by varying the size and aspect ratio of the particles. We considered samples in which all the solids have the same volume and shape, and cases including size and aspect ratio distributions. Results show that the strength of the shape fabric and the angle between the crystal preferential orientation and the compression plane both increase with the shear strain up to steady state values, which are primarily controlled by the aspect ratio of the particles. The stronger the aspect ratio, the greater the magnitude of the preferential orientation and the lower its angle relative to the compression plane. When introducing a distribution in the size of the crystals, we observed a decrease in the strength of the shape fabric and an increase in the angle between the preferential orientation of the crystals and the compression plane compared with samples composed of crystals having the same shape and size. Similarly, the distribution in the aspect ratio further decreases the strength of the shape fabric and increases the angle between the preferential orientation of the solids and the compression plane. Finally, we employed an alternative approach to quantify the amount of foliation and lineation and show that the samples always display a stronger foliation than lineation, although the shear strain increases both the foliation and the lineation. 

The mechanical behavior of crystal-rich mush controls the dynamics and evolution of magma bodies but is poorly understood, . The presence of a semi-rigid contact network in the crystal phase greatly affects the rheology of mush but the contributions of crystal shape to the force, contact and shape fabric remains poorly characterized. This in turn influences the transmission of stress in the mush, the packing stiffness, and the volume fraction at jamming. It is also unclear whether the total amount of deformation of a mush can be quantitatively determined from the shape preferred orientation of the crystals. We performed 3D numerical simulations using a coupled computational fluid dynamics and discrete element method to illuminate the dynamic states of non-spherical crystals in a viscous melt. Simulations consisted of the simple shear of a mush under a constant pressure upper boundary. Crystals are represented by elongated cuboids having an aspect ratio of four. Our results differ from those obtained with smooth spheres and shed light on the influence of the crystal shape and orientation fabric on the mechanical properties of a mush. We found two distinct behaviors associated with the transient and steady-state, however at all times strain is nonaffine. During the transient, the strain is accommodated by the emergence of multiple shear bands and tends to concentrate on a single one. The shear bands emerge because of steric blocking and space limitations preventing the rotation of elongated particles, generating the local and temporary jamming of the crystal network. On the contrary, in the residual and steady-state, the strain is accommodated by one main shear band. The analysis of the orientation of the crystals shows that the deformation of the mush tends to increase the foliation of the crystals more than their alignment.