Asthenospheric Melting and Melt-induced Evolution of the Lithosphere Beneath the Colorado Plateau and the Basin and Range from a Seismic Characterization of Mantle Layering

DESCRIPTION: Partial melting in the Earth's upper mantle plays a key role in controlling surface volcanism. It also impacts the evolution of tectonic plates and the deformation of the hot mantle underneath, called the asthenosphere. In recent years, the continental United States has been blanketed by EarthScope's Transportable Array, a program that deployed thousands of seismic instruments. The collected data provide unprecedented new constraints on the structure of the uppermost mantle, informing its dynamics and history of formation and alteration. Here, the researchers analyze the data from the Colorado Plateau, an area with ancient Proterozoic crust. This area has remained relatively undeformed through multiple compression episodes and subsequent extension of the surrounding Basin and Range. The rise of the Plateau from near sea level to its current elevation is not well understood. The volcanism of the Basin and Range is now actively encroaching on the ancient Plateau. By combining seismology and thermodynamic modeling, the team maps out the partial melt and alteration of the uppermost mantle. This project brings new light on the past evolution and present state of an important region of the southwestern United States. It also supports an early-career female scientist, the principal investigator, and provides training to an undergraduate student in the field of seismology.

The team investigates the Colorado Plateau region, where disparate tectonic settings are juxtaposed within a small geographical area. The researchers use surface-wave dispersion data and information derived from S-to-P receiver functions about sharp velocity gradients in the upper mantle. They calculate accurate seismic-velocity models which employ a geologically reasonable layered framework. The models build on the Principal Investigator's previous work with receiver functions, which provides the layered lithosphere-asthenosphere framework in which to invert the dispersion data. The team combine seismic analysis with thermodynamic modeling in a self-consistent way to estimate regional velocity structures. The modeling accounts for the composition, pressure and temperature, as well as melt fraction at depth. These estimates are constrained by compositional and temperature data from the abundant volcanism and xenoliths in the area.

OUTCOMES: We will develop a new methodology for inverting surface wave data with layering constrained from coincident receiver function data. We will analyse seismic data from the Colorado Plateau region to trial our new methodology. The Colorado Plateau is of particular interest, as there is ongoing debate as to the role of melt and alteration of the upper mantle in the still evolving tectonism of this area. The generated seismic velocity model will be modelled, with the help of Ben Holtzman and Chris Havlin, to better understand how these velocities reflect uppermost mantle conditions. The work will be written up for publication.