Thermochemical Models of Earth's Mantle Convection: New Insight from Fractionation and Outgassing Processes

University Of California-Davis, Davis CA

Investigators

Abstract

Basalt geochemistry records information about mantle dynamics, indicating that there are at least five reservoirs in the mantle. However, the dynamical meaning of such reservoirs is ill-constrained. Efforts to reconcile the full range of types of observational data have recently given rise to several new geodynamic models that include layers of different composition in the mantle. The investigators will evaluate these and related models, by using numerical models of thermo-chemical convection in the mantle to determine the geochemical signatures predicted by different dynamical models. Simulations will include tracers to represent various chemical species. Partial melting processes at ridges are taken into account, yielding fractionation between oceanic crust and lithosphere, and outgassing into the atmosphere. These processes have not been included in previous large-scale, fully dynamic, convective models. The simulations keep track of ancient oceanic crust, and include intrinsic density variations between eclogite and peridotite, as well as inhomogeneous heat production rates. The investigators will address the ability of their different models to reproduce some of the features of basalt, and to be in agreement with geodynamical observations such as the heat flow. They will also test the sensitivity of the results to petrologic and geodynamic parameters.