Abstract
AbstractGlobal tomography models show a large low‐velocity anomaly extending from the core‐mantle boundary (CMB) beneath South Africa to the upper mantle in East Africa. Although it is believed that this anomaly is linked to mantle upwellings that control key surface features of the African continent, its origin and evolution are still debated. Here we assemble geochemical and seismological constraints along with information from new seismic analyses and geodynamic laboratory experiments to propose that presently there are at least two different plume heads beneath Afar and Kenya that originated at the CMB. A third plume between Kenya and Afar may have caused the Ethiopia‐Yemen traps 30 Ma, now merging with the Afar plume. We infer that the Afar plume is presently detached from the CMB probably because of an interaction with the subducted Tethyan slab and that it is likely a dying plume. This may imply that rifts along the Main Ethiopian Rift would fail by the loss of thermal sources, which consequently hampers continental breakup.
Highlights
Global tomography models consistently show two large low shear‐velocity provinces (LLSVPs) in the lowermost mantle beneath the South Pacific and Africa (e.g., Chang et al, 2014; Lekic et al, 2012), which may have been stable over 200 Myr (Burke et al, 2008) due to their thermochemical nature (e.g., Garnero & McNamara, 2008)
Global tomography models show a large low‐velocity anomaly extending from the core‐mantle boundary (CMB) beneath South Africa to the upper mantle in East Africa
A large low‐velocity anomaly rooted in the African LLSVP extends from the core‐mantle boundary (CMB) beneath South Africa to the upper mantle beneath East Africa (e.g., Hansen et al, 2012; Ritsema et al, 1999)
Summary
Global tomography models consistently show two large low shear‐velocity provinces (LLSVPs) in the lowermost mantle beneath the South Pacific and Africa (e.g., Chang et al, 2014; Lekic et al, 2012), which may have been stable over 200 Myr (Burke et al, 2008) due to their thermochemical nature (e.g., Garnero & McNamara, 2008). Many geophysical studies including regional and global tomography models (e.g., Benoit, Nyblade, Owens, et al 2006; Benoit, Nyblade, & VanDecar, 2006; Hansen & Nyblade, 2013; Hansen et al, 2012; Ritsema et al, 1999) and geodynamical simulations using buoyancy forces inferred from tomography models (e.g., Daradich et al, 2003; Moucha & Forte, 2011) have supported the idea of one single large, tilted upwelling from beneath South Africa to Afar In order to satisfy all the observations, we propose that the low‐velocity anomaly beneath East Africa observed in global tomography models currently consists of at least two separate plumes, the Afar plume and the Kenya plume, which originated from the African LLSVP at the CMB. We propose that the Afar plume is detached from the CMB, likely a dying plume, hampering continental breakup of the African plate
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