Collaborative Research: Geochemistry and Whole Mantle Convection

Carnegie Institution Of Washington, Washington DC

Investigators

Abstract

Van Keken, Hauri EAR-0229962, 0229755 The investigators are interested in the role that the generation and recycling of oceanic crust plays in the formation of geochemical heterogeneity. The formation of oceanic crust is a fundamental differentiation process that causes distinct variations in trace element and bulk composition. The related variations in density and rheology have important consequences for mantle dynamics and mantle mixing. Our main hypothesis is that the formation and recycling of oceanic crust can explain a vast proportion of the geochemical observations. The central goal of this project is to study the role that compositional density plays in preserving geochemical heterogeneity. As part of the investigators' hypothesis testing approach they will address following questions: 1) How does the recycling of oceanic crust affect mantle chemistry? 2) What are the relationships between noble gas and lithophile isotope ratios? 3) Is it possible that the large-scale differentiation during Earth's formation accounts for the presently observed heterogeneity? The team will use a combination of geodynamical and geochemical modeling to answer these questions. This provides an excellent tool to test conceptual ideas by quantifying the effects of mantle mixing, fractionation, differentiation, and degassing. The approach is based on previously established collaboration between Van Keken, Ballentine and Hauri. Previous models will be improved by the modeling of oceanic crust formation, incorporation of lithophile isotopes, and significantly higher spatial and temporal resolution. Van Keken and a graduate student will be responsible for the model improvements and dynamical computations, while Hauri and Ballentine will guide the hypothesis testing approach and aid the geochemical modeling. The collaborative aspects are an essential component of this proposal. This project will lead to a better understanding of the processes that are responsible for the thermal and chemical evolution of our planet. It will aid in the development of essential dynamical modeling tools and provide cross-disciplinary integration, international collaboration, and education of students in quantitative geophysics and geochemistry.