CSEDI Collaborative Research: Geochemical Structure and Dynamics of the Mantle Below the East African Rift System

点击翻译按钮获取中文摘要

The East African Rift System (EARS) is the only place on the planet where the geochemical and isotopic compositions of continental mafic lavas spanning 40 million years of volcanism can be studied. This geochemical information must be used in conjunction with modern geophysical and seismic information to address fundamental geodynamic questions about the relationship between features of the deep Earth and those at the surface. We focus on the evolution of upper mantle temperature and composition by using numerical models of limited mantle depth extent. Geological and geochemical observations in the EARS provide strong constraints on the timing and location of melt formation in the mantle. The dynamical modeling provides the ability to predict the formation of melt in a self-consistent manner and make quantitative estimates of the temperature, depth and rate of melting. We will also pursue a comprehensive geochemical study of select MgO-rich EARS basalts. New geochemical and isotopic (Sr-Nd-Pb-Hf-He) data, coupled with existing data from the literature, will be used to define the distribution of chemically distinct reservoirs that sustain EARS magmatism. Trace element and isotope geochemical data enable refinement of the compositional structure of the upper mantle and will help constrain reasonable dynamical models. Our main hypothesis is that one or more plumes bring hot material from the Earths interior to melt below the EARS lithosphere, since we find it difficult to understand how long-lived and voluminous volcanism can be generated without such deep transport. A sensitivity study will allow us to estimate whether and how non-plume models can predict the timing and location of melt generation observed in the EARS. For plume models, we will assess a variety of dynamical scenarios by incorporating tracer techniques to test whether the observed distribution of geochemical signatures and volumes of magmatic products along the EARS can be satisfied with a single compositionally heterogeneous plume. The resulting dynamical models will enhance our understanding of the origin of the EARS, the African superswell and eventually the African superplume. The collaboration between geochemists with mutually supporting areas of expertise (Furman trace element geochemistry, Bryce lithophile radiogenic isotope geochemistry, Graham helium isotope geochemistry) and a geophysicist / numerical modeler (van Keken) will provide a much-needed interaction between observational and theoretical efforts. The results of the work will be incorporated into residential and electronic delivery courses at the participating universities, including several Historically Black Colleges and Universities. We will support graduate students at Penn State, Michigan and New Hampshire, introducing this next generation of scientists to interdisciplinary research and collaboration.