Collaborative Research: Modes of melt extraction in silicic mushes: processes, efficiency and timescales

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

The most dangerous eruptions captured in the geologic record are related to magmatic systems that erupt large volume of silica-rich magmas explosively into the atmosphere. The deposits of such eruptions are generally well-characterized both chemically and in terms of their physical attributes, however petrologists have yet to fully understand the mechanisms by which these large volume of magma with low crystal content emplace at shallow level in the crust and evolve prior to an eruption. This project aims at combining laboratory experiments on analogs as well as natural samples and developing physical models to constrain the physics that allows for these systems to evolve as they do and the rates (or timescales) required for a system to be susceptible for a large volcanic eruption. The separation of melt from a crystalline residue has implications for long-term volcanic hazards. The research of a graduate student will be funded and collaboration with an experimental laboratory at MIT established. The challenge to understand how viscous silicic melts separate from their crystal cargo comes from (1) the small discrepancy in density between these phases, (2) the large crystal fraction at which melt extraction is occurring (1 and 2 imply that melt extraction should be sluggish and likely inefficient process) and (3) the presence in many cases of an exsolved volatile phase impacting melt-crystal separation. Understanding and quantifying the efficiency of phase separation in crystal mushes is contingent upon understanding the rheology of multiphase magmas specifically over conditions where information is very limited (experimental or unambiguous clues from the rock record). Novel syringe-type compaction experiments will be executed, where interstitial fluid extraction can be measured over time and correlated with changes in packing for the residual solid fraction. These experiments will span various size and shape distributions for particles and will be coupled to numerical simulations of 2 and 3 phase compaction to understand how repacking (mush reorganization rather than deformation of particles) impacts melt extraction. Samples from exhumed plutons will be used to constrain how melt extraction processes studied in the lab and theoretically extrapolate to nature. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.