Mafic magmatic enclaves as tracer of protracted mixing and hybridization

Volcanic eruptions are a major natural hazard. Understanding the processes leading up to volcanic eruption help greatly to improve hazard forecasting and the long-term assessment of individual magmatic systems. Hot magma rising from depth that recharges and mixes within a shallow magma storage region is considered an important mechanism to start volcanic unrest.

In some cases, such recharge may be the direct triggering mechanism for an eruption. Evidence for recharge exists in the form of mafic enclaves–compositionally distinct pieces of magma dispersed at the centimeter to decimeter scale. The hot magma provides thermal energy that mobilizes the magma and drives stirring and mingling.

Using chemical signatures in crystals from the recharge magmas, this project will explore over which spatial and temporal scales the thermal disruption operates. Such information provides unique constraints for chamber-scale dynamic models of magma mixing and whether these thermal transient episodes are short-lived or disrupt a magmatic system for years to decades.

This research will be conducted on the Holocene eruptions of the Chaos Crags in Lassen Volcanic National Park that lasted for several decades. A second component of this project uses a novel numerical modeling technique to constrain the mechanical integrity of the crystal-rich mafic enclaves, which provide independent information on how long these enclaves can survive during mixing and mingling and therefore represent faithful records of that thermal history.

This team will study the dynamics of magma mixing recorded in mafic magmatic enclaves using a dual approach of plagioclase zoning and numerical modeling of multiphase flow. Mafic enclaves are unique recorders of the mixing dynamics as they are both the archive and the agent that drives mixing. The objective is to track the emerging thermal transients of mixing and the potential return to a new uniform storage condition.

This thermal evolution can be captured because the study site, the Chaos Crags domes, CA, erupted in six separate events and the entire unrest period lasted years to decades. The thermal transients will be documented using mineral-mineral based equilibria and elemental diffusion methods. In order to assess the survival times and mechanical integrity of such enclaves, we will employ a novel numerical approach for investigating mechanical erosion of mafic enclaves in a host dacitic magma.

Researchers will use coupled Discrete Element Method and Lattice Boltzmann Method (DEM-LBM) numerical simulations to directly simulate the fluid-solid interaction during mechanical erosion of the enclaves by the host melt to constrain the survival time of mafic enclaves experiencing plucking/erosion in response to chaotic mixing. With their coupled approach, they will be able to assess how the temperature, captured through the viscosity, of the host magma as well as the shape and relative packing of crystals influences the mechanical erosion of the crystal-rich aggregate.

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.