Structure & Dynamics of the Oceanic Lithosphere-Asthenosphere System
Oceanic lithosphere covers a majority of the Earth’s surface, but the oceans are still largely unexplored compared to the continents. This work requires us to travel to unexplored regions of the ocean basins, placing seismometers on the seafloor to map temperature, composition, and flow in the mantle to probe plate tectonic processes at a variety of scales.
Rheology and Flow of the Oceanic Mantle
What dynamic processes occur in the upper mantle? To answer this fundamental question, we need to understand how mantle rocks deform and flow. As the mantle flows, the rheological and thermodynamic conditions control what kind of petrologic fabrics form. We can use seismology to infer these fabrics to learn about the dyanmic conditions that produced them. Seismic wave speeds and amplitudes change depending on the temperature, pressure, melt fraction, and volatile content of a mantle rock. Therefore, we can use these observations to constrain the mantle's physical state.
Figure from Russell et al (in prep) showing an interpretation of oceanic upper mantle processes.
Constraining Grain-Scale Mechanisms of Deformation
We combine seismic observations with laboratory and field data to infer grain-scale processing occuring in the upper mantle. This pushes the boundaries of traditional seismology and requires working alongside rock deformation experts. This work has allowed us to ask questions that challenge paradigms such as: Which deformation mechanism(s) are most active in the oceanic upper mantle? Is there melt in the oceanic asthenosphere? If not, what causes the oceanic asthenosphere to be week in some places and not others?
Figure 5 from Russell et al. (2022) showing how in-situ observations of anisotropy at NoMelt compare to laboratory and field samples.
