Corresponding author: Darien Florez (dflorez1@mit.edu)
Key Points:
- Continuum model fits repacking experiments data of Hoyos et al.(2022) despite their stochastic nature.
- At intermediate melt fractions, mechanical repacking of particles may
contribute significantly to the resistance of mushes to compaction.
- Particle-particle friction, rather than
hydrodynamic effects, dominates viscous resistance associated with
mechanical repacking.
Abstract
Before large volumes of crystal poor rhyolites are mobilized as melt,
they are extracted through the reduction of pore space within their
corresponding crystal matrix (compaction). Petrological and mechanical
models suggest that a significant fraction of this process occurs at
intermediate melt fractions (ca. 0.3 – 0.6). The timescales associated
with such extraction processes have important ramifications for volcanic
hazards. However, it remains unclear how melt is redistributed at the
grain-scale and whether using continuum scale models for compaction is
suitable to estimate extraction timescales at these melt fractions. To
explore these issues, we develop and apply a two-phase continuum model
of compaction to two suites of analog phase separation experiments –
one conducted at low and the other at high temperatures, T, and
pressures, P. We characterize the ability of the crystal matrix to
resist porosity change using parameterizations of granular phenomena and
find that repacking explains both datasets well. Furthermore, repacking
may explain the difference in compaction rates inferred from high T + P
experiments and measured in previous deformation experiments. When
upscaling results to magmatic systems at intermediate melt fractions,
repacking may provide an efficient mechanism to redistribute melt.
Finally, outside nearly instantaneous force chain disruption events
occasionally recorded in the low T + P experiments, melt loss is
continuous, and two-phase dynamics can be solved at the continuum
scale with an effective matrix viscosity. Further work, however, must be
done to develop a framework to parameterize the effect of particle size
and shape distributions on compaction.