Scales of transient convective support beneath Africa

Beneath sub-equatorial Africa, there is convincing evidence for a gigantic, slow, velocity anomaly within the lower mantle that is inferred to be a thermochemical superplume. Here, we define the spatial and temporal pattern of uplift across the northern edge of this putative superplume by analyzing...

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Bibliographic Details
Published in:Geology (Boulder) 2009-10, Vol.37 (10), p.883-886
Main Authors: Al-Hajri, Yasir, White, Nicky, Fishwick, Stewart
Format: Article
Language:English
Subjects:
Africa
African Plate
applied (geophysical surveys & methods)
Atlantic Ocean
Cenozoic
continental shelf
convection
epeirogeny
geophysical methods
geophysical profiles
geophysical surveys
Geophysics
inverse problem
lower mantle
mantle
mantle plumes
Neogene
plate tectonics
reflection methods
Rocks
Sedimentary geology
sedimentary rocks
Sediments
seismic methods
seismic profiles
solid Earth (tectonophysics)
South Atlantic
Southeast Atlantic
Studies
superplumes
surveys
Tertiary
theoretical models
thermochemical properties
transient phenomena
uplifts
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Summary:Beneath sub-equatorial Africa, there is convincing evidence for a gigantic, slow, velocity anomaly within the lower mantle that is inferred to be a thermochemical superplume. Here, we define the spatial and temporal pattern of uplift across the northern edge of this putative superplume by analyzing stratal geometries and stacking velocities of Neogene sedimentary rocks. These marine deposits are imaged on a dense grid of seismic reflection profiles that straddle the southwest African coastal shelf. Inverse modeling of stacking velocity profiles demonstrates that there have been at least two significant phases of uplift. A post-Pliocene uplift event increases from 0 to approximately 500 m elevation over a distance of approximately 1000 km, in close agreement with geophysical estimates of the present-day variation of dynamic topography. An earlier phase of uplift occurred in middle Oligocene time (ca. 30-35 Ma ago). We propose a two-stage development of epeirogeny in which a Middle Oligocene phase of uplift may be related to initiation and growth of the African superplume. Post-Pliocene denudation records rapid (100-250 m/Ma) vertical motions generated by upper mantle convection, which vary on length scales of 500-1000 km. Our results support the existence of a convective circulation system that has operated on different temporal and spatial scales beneath the African Plate.
ISSN:0091-7613
1943-2682
DOI:10.1130/G25703A.1