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

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.