1. The Seismic Signature of Upper‐Mantle Plumes: Application to the Northern East African Rift
- Author
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Saskia Goes, Chiara Civiero, John J. Armitage, James Hammond, Dublin Inst Adv Studies DIAS, Dublin, Ireland, Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), Department of Earth Science and Technology [Imperial College London], Imperial College London, Department of Earth and Planetary Sciences [UCL/Birkbeck], Birkbeck College [University of London], Department of Earth Science and Engineering at Imperial College London Project SPIDER from the Fundacao para a Ciencia e a Tecnologia PTDC/GEO-FIQ/2590/2014French National Research Agency (ANR) NERC Natural Environment Research CouncilNE/I020342/1, and Natural Environment Research Council (NERC)
- Subjects
Geochemistry & Geophysics ,ATLANTIC ,010504 meteorology & atmospheric sciences ,04 Earth Sciences ,Inversion (geology) ,WESTERN MAGHREB REGION ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,tomography ,010502 geochemistry & geophysics ,01 natural sciences ,Mantle plume ,Physics::Geophysics ,Mantle convection ,dynamic modeling ,Geochemistry and Petrology ,UPWELLINGS ,East African Rift ,Transition zone ,thermal boundary layer ,TEMPERATURE ,Rayleigh Taylor ,0105 earth and related environmental sciences ,Science & Technology ,02 Physical Sciences ,Rift ,Geophysics ,thermal anomaly ,mantle plumes ,AFAR ,Plume ,Boundary layer ,CONVECTION ,[SDU]Sciences of the Universe [physics] ,Physical Sciences ,STRUCTURE BENEATH ,TRANSITION ,Geology ,GENERATION - Abstract
International audience; Several seismic and numerical studies proposed that below, some hotspots upper-mantle plumelets rise from a thermal boundary layer below 660 km depth, fed by a deeper plume source. We recently found tomographic evidence of multiple upper-mantle upwellings, spaced by several 100 km, rising through the transition zone below the northern East African Rift. To better test this interpretation, we run 3-D numerical simulations of mantle convection for Newtonian and non-Newtonian rheologies, for both thermal instabilities rising from a lower boundary layer, and the destabilization of a thermal anomaly placed at the base of the box (700-800 km depth). The thermal structures are converted to seismic velocities using a thermodynamic approach. Resolution tests are then conducted for the same P and S data distribution and inversion parameters as our traveltime tomography. The Rayleigh Taylor models predict simultaneous plumelets in different stages of evolution rising from a hot layer located below the transition zone, resulting in seismic structure that looks more complex than the simple vertical cylinders that are often anticipated. From the wide selection of models tested, we find that the destabilization of a 200 degrees C, 100 km thick thermal anomaly with a non-Newtonian rheology, most closely matches the magnitude and the spatial and temporal distribution of the anomalies below the rift. Finally, we find that for reasonable upper-mantle viscosities, the synthetic plume structures are similar in scale and shape to the actual low-velocity anomalies, providing further support for the existence of upper-mantle plumelets below the northern East African Rift.
- Published
- 2019