Unraveling the physics of the Yellowstone magmatic system using
geodynamic simulations
Abstract
The Yellowstone magmatic system is one of the largest magmatic systems
on Earth, and thus an ideal location to study magmatic processes.
Whereas previous seismic tomography results could only image a shallow
magma chamber, a recent study using more seismometers showed that a
second and massive partially molten mush chamber exists above the Moho
(Huang et al., 2015). To understand the mechanics of this system, it is
thus important to take the whole system from the mantle plume up to the
shallow magma chambers into account. Here, we employ lithospheric-scale
3D visco-elasto-plastic geodynamic models to test the influence of
parameters such as the connectivity of the chambers and rheology of the
lithosphere on the dynamics of the system. A gravity inversion is used
to constrain the effective density of the magma chambers, and an adjoint
modelling approach reveals the key model parameters affecting the
surface velocity. Model results show that a combination of connected
chambers with plastic rheology can explain the recorded slow vertical
surface uplift rates of around 1.2 cm/a, as representing a long term
background signal. A geodynamic inversion to fit the model to observed
GPS surface velocities, reveals that the magnitude of surface uplift
varies strongly with the viscosity difference between the chambers and
the crust. Even though stress directions have not been used as inversion
parameter, modelled stress orientations are consistent with
observations. However, phases of larger uplift velocities can also
result from magma inflation which is a short term effect. We consider
two approaches: 1) overpressure in the magma chamber in the
asthenosphere and 2) inflation of the uppermost chamber prescribed by an
internal kinematic boundary condition. We demonstrate that the
asthenosphere inflation has a smaller effect on the surface velocoties
in comparison with the uppermost chamber inflation. We show that the
pure buoyant uplift of magma bodies in combination with magma inflation
can explain (varying) observed uplift rates at the example of the
Yellowstone volcanic system.