Magma dominantly exists in a slowly cooling crystal-rich or mushy state1, 2, 3. Yet, observations of complexly zoned crystals4, some formed in just one to ten years5, 6, 7, 8, 9, as well as time-transgressive crystal fabrics10 imply that magmas mix and transition rapidly from a locked crystal mush to a mobile and eruptable fluid5, 6. Here we use a discrete-element numerical model that resolves crystal-scale granular interactions and fluid flow, to simulate the open-system dynamics of a magma mush. We find that when new magma is injected into a reservoir from below, the existing magma responds as a viscoplastic material: fault-like surfaces form around the edges of the new injection creating a central mixing bowl of magma that can be unlocked and become fluidized, allowing for complex mixing. We identify three distinct dynamic regimes that depend on the rate of magma injection. If the magma injection rate is slow, the intruded magma penetrates and spreads by porous media flow through the crystal mush. With increasing velocity, the intruded magma creates a stable cavity of fluidized magma that is isolated from the rest of the reservoir. At higher velocities still, the entire mixing bowl becomes fluidized. Circulation within the mixing bowl entrains crystals from the walls, bringing together crystals from different parts of the reservoir that may have experienced different physiochemical environments and leaving little melt unmixed. We conclude that both granular and fluid dynamics, when considered simultaneously, can explain observations of complex crystal fabrics and zoning observed in many magmatic systems.
At a glance
- Olivine slurry replenishment and the development of igneous layering in a Franklin Sill, Victoria Island, Arctic Canada. J. Petrol. 56, 83–112 (2015). , &
- Origin of basalts by hybridization in andesite-dominated arcs. J. Petrol. 56, 325–346 (2015). , , , &
- Seismic imaging of the magmatic underpinnings beneath the Altiplano-Puna volcanic complex from the joint inversion of surface wave dispersion and receiver functions. Earth Planet. Sci. Lett. 404, 43–53 (2014). , , , &
- Dynamic plumbing system beneath volcanoes revealed by kinetic modeling, and the connection to monitoring data: An example from Mt. Etna. Earth Planet. Sci. Lett. 308, 11–22 (2011). , , &
- Rapid remobilization of magmatic crystals kept in cold storage. Nature 506, 480–483 (2014). &
- Localized rejuvenation of a crystal mush recorded in zircon temporal and compositional variation at the Lassen volcanic center, northern California. PLoS ONE 9, e113157 (2014). &
- Short eruption window revealed by absolute crystal growth rates in a granitic magma. Nature Geosci. 7, 524–528 (2014). &
- Mush disaggregation in basaltic magma chambers: Evidence from the AD 1783 Laki eruption. J. Petrol. 53, 2593–2623 (2012). , , &
- The time scales of magma mixing and mingling involving primitive melts and melt–mush interaction at mid-ocean ridges. Contrib. Mineral. Petrol. 159, 371–387 (2010). , &
- Magmatic tubes, pipes, troughs, diapirs, and plumes: Late-stage convective instabilities resulting in compositional diversity and permeable networks in crystal-rich magmas of the Tuolumne batholith, Sierra Nevada, California. Geosphere 5, 496–527 (2009).
- A rapid mechanism to remobilize and homogenize highly crystalline magma bodies. Nature 471, 212–215 (2011). &
- Thermo-mechanical reactivation of locked crystal mushes: Melting-induced internal fracturing and assimilation processes in magmas. Earth Planet. Sci. Lett. 304, 443–454 (2011). , &
- Multiple reinjections and crystal-mush compaction in the beacon sill, McMurdo Dry Valleys, Antarctica. J. Petrol. 53, 2567–2591 (2012). &
- Crystal-melt relationships and the record of deep mixing and crystallization in the AD 1783 Laki eruption, Iceland. J. Petrol. 54, 1661–1690 (2013). , , , &
- Mineralogy of the Martian surface. Annu. Rev. Earth Planet. Sci. 42, 291–315 (2014). &
- Plagioclase preferred orientation in layered mylonites: Evaluation of flow laws for the lower crust. J. Geophys. Res. 113, B05202 (2008). &
- Growth of complex sheeted zones during recycling of older magmatic units into younger: Sawmill Canyon area, Tuolumne batholith, Sierra Nevada, California. J. Volcanol. Geotherm. Res. 177, 457–484 (2008). , &
- Fingering versus stability in the limit of zero interfacial tension. Nature Commun. 5, 5265 (2014). , &
- Replenishment of magma chambers by light inputs. J. Geophys. Res. 91, 6113–6122 (1986). , , &
- Coiling, entrainment, and hydrodynamic coupling of decelerated fluid jets. Phys. Rev. Lett. 95, 184501 (2005). et al.
- Hydrodynamic characteristics of fluidization in liquid-solid tapered beds. Chem. Eng. Sci. 52, 2277–2290 (1997). &
- Localized fluidization in a granular medium. Phys. Rev. E 87, 042206 (2013). &
- The distribution of olivine compositions in Icelandic basalts and picrites. J. Petrol. 54, 745–768 (2013). &
- Mineral disequilibrium in lavas explained by convective self-mixing in open magma chambers. Nature 411, 1037–1039 (2001). , &
- Developments in the theory of particle mixing. J. Appl. Chem. 4, 257–268 (1954).
- Reconciling heterogeneity in crystal zoning data: An application of shared characteristic diagrams at Chaos Crags, Lassen volcanic center, California. Contrib. Mineral. Petrol. 149, 98–112 (2005). &
- Modeling of gas-driven magmatic overturn: Tracking of phenocryst dispersal and gathering during magma mixing. Geochem. Geophys. Geosyst. 9, Q07017 (2008). , &
- On the conditions of magma mixing and its bearing on andesite production in the crust. Nature Commun. 5, 5607 (2014). et al.
- A discrete numerical model for granular assemblies. Géotechnique 29, 47–65 (1979). &
- 2012); https://mfix.netl.doe.gov/download/mfix/mfix_current_documentation/dem_doc_2012-1.pdf , , & Documentation of Open-Source MFIX-DEM Software for Gas-Solids Flows (Department of Energy, National Energy Technology Laboratory,