Mantle volatiles and attenuation in the East African Rift

University Of California-Riverside, Riverside CA

Investigators

Abstract

The mantle under the East African Rift features one of the most prominent geophysical anomalies observed in Earth's upper mantle, defined by a broad region of very low seismic wave speeds. Though increased mantle temperatures could slow seismic wave speeds, constraints from erupted lava compositions indicate that the mantle in this region is warm, but not hot enough to account for the observed maximum slowness of seismic waves. Elevated concentrations of volatile elements (e.g., water, carbon) in the mantle can also slow seismic wave speeds, but these are unconstrained for the mantle along the East African Rift. Quantifying the abundance of water and carbon in the mantle in this region is critical to describing the magmatism that has occurred along the length of the rift, and its relationship to the process of rifting itself. Additionally, reconciling geophysical and geochemical models for the mantle in this region is a key test of the current understanding of Earth's mantle more broadly. This work will inform future field and experimental campaigns by presenting a synthesis of information that can be gleaned by existing sample sets and geophysical data sets. In addition to the scientific impacts, this work broadens the participation of underrepresented groups and supports several undergraduate and graduate students. This work will also inform an exhibit for the University of California-Riverside (UCR) Earth Sciences Museum. If the mantle is significantly water- or carbon-rich, this could lead to mantle melting at higher pressures and lower temperatures than for a dry and carbon-free mantle. The presence of melts may also slow seismic wave speeds. This work will constrain the mantle source volatile composition at individual volcanic edifices and assess the importance of elevated volatiles, temperatures, and melts on the extreme nature of the geophysical anomaly under the rift, and to the initiation and evolution of the rift itself. This work will test existing, quantitative relationships between petrological descriptions of the mantle and the properties of seismic waves in this region. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.