Geodynamic and Seismic Constraints on the Evolution of the Oceanic Lithosphere and Asthenosphere

Author: Ethan H. Fahy
December 7, 2011
Poster presentation
AGU Fall Meeting 2011

Ethan H. Fahy; Paul S. Hall; Colleen A. Dalton; Ulrich Faul (2011) Geodynamic and Seismic Constraints on the Evolution of the Oceanic Lithosphere and Asthenosphere. AGU Fall Meeting 2011

We report on a series of numerical geodynamic experiments undertaken to investigate the evolution the oceanic lithosphere and the characteristics of the underlying asthenosphere. In particular, we used the CitcomCU finite element package to model mantle flow beneath an oceanic plate. Experiments incorporated deformation by both diffusion creep and dislocation creep mechanisms, with experimentally constrained constants used for the relevant flow laws. We find that the use of flow laws appropriate for wet olivine aggregates leads to the formation of instabilities at the base of the thermal boundary layer corresponding to the lithosphere, which are not found in the experiments employing flow laws for dry olivine. These instabilities effectively thin the older portions of the thermal boundary layer, resulting in an average temperature structure closely resembling the GDH1 plate model [Stein and Stein, 1992] within the model domain. In contrast, the thermal structure of experiments in which instabilities do not form resembles resembles that of a half-space cooling model. Comparison of experimental results to seismic models of variations in shear wave velocity and shear attenuation with both depth and age within the oceanic upper mantle indicates that experiments in which instabilities occur provide a better match to seismic observations than do experiments without such instabilities.