On The Kinematic And Dynamic Evolution Of A Magma Mush PDF Download

Magmas are dynamic hydrogranular systems where the interactions between the melt and the residing crystals influences the eruptive behavior of volcanoes, the concentration of economic metals, and the stratification of the Earth's crust. Despite the importance of the interaction between these phases, little is known about the mechanics of these systems. The purpose of this dissertation is to investigate the interactions of the melt and crystals of magma from the formation of the crystal-rich mush to the expulsion of the melt from its interstitial spaces. I first examine the dilute case where suspended crystals are coupled to the fluid. I employed a combination of discrete element computational fluid dynamic (DEM-CFD) numerical simulations, field observations, and electron backscatter diffraction (EBSD) analyses to explore the mechanics of the interactions between the crystals and the melt of magmas. The formation of crystal clusters was explored using Voronoi tessellations in both a settling only model at a solid volume percent of 9 and an open system models (where a magma like fluid is injected into the accumulating mush) with solid volume percents of 1, 9, and 20. I find that there is statistically no difference in the distribution of clustering between the two systems and that clusters are just as likely as a random distribution. Indicating that abundant crystal clusters found in sampled magmatic systems are likely from a disaggregated magma mush. Next, I examined the crystal-rich state where the formation of granular flows transfer momentum to the resident fluid. I employed a DEM-CFD numerical dam break model of a polydisperse particle column to explore the kinematics of the collapse and runout of the particle column. The column develops two collapse regimes a toppling collapse, and a sliding collapse, which transition into three kinematic runout regimes, gravity current, heap flow, and a quasi-static region. Both a force and contact fabric develop in the heap flow where the particles have enduring contacts. The difference in anisotropy between the normal force and contact fabrics illustrates the non-affine nature of granular material and the issue with applying the concepts of continuum modelling to hydrogranular systems. The first two chapters were based on numerical models analyses to create an idealized framework of knowledge on hydrogranular systems. The final chapter builds on geological observations and fieldwork with a goal of determining the mechanisms of pore space reduction in a crystal-rich magma mush. I collected 12 samples from the mafic complex of Sierra Valle Fértil from which I conducted EBSD analyses to quantify the crystallographic preferred orientation (CPO) and the internal lattice distortions. I considered the evidence for tectonic filter pressing, mechanical compaction, and viscous compaction. The internal lattice distortions have a similar distribution across plagioclase, hornblende, and quartz. This suggests the crystal deformation happened subsolidus and was not caused by either viscous compaction or tectonic filter pressing, and that a mechanical compaction process was responsible for pore space reduction. Future work should focus on the physics of hydrogranular systems with non-spherical particles employing analogue and numerical models to better capture natural systems.