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Constraining mantle density structure using geological evidence of surface uplift rates: The case of the African Superplume

Gurnis, Michael and Mitrovica, Jerry X. and Ritsema, Jeroen and van Heijst, Hendrik-Jan (2000) Constraining mantle density structure using geological evidence of surface uplift rates: The case of the African Superplume. Geochemistry, Geophysics, Geosystems, 1 (7). 1999GC000035. ISSN 1525-2027. http://resolver.caltech.edu/CaltechAUTHORS:GURggg00

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Abstract

We explore the hypothesis that southern Africa is actively being uplifted by a large-scale, positively buoyant structure within the mid-lower mantle. Using a new formulation in which dynamic topography and uplift rate are jointly used, we place constraints on mantle density and viscosity. The solution of the momentum equation is coupled with the advection of the density field to solve for the surface uplift rate in both an axisymmetric and fully spherical geometry. We demonstrate how dynamic topography and its rate of change depend on density and lateral and radial variations in viscosity. In the full spherical models the geometry of mantle density is derived by scaling a tomographic shear velocity model. Using a variety of geologic observations, we estimate residual topography (i.e., the topography remaining after shallow sources of density are removed) and an average Cenozoic uplift rate to be 300–600 m and 5–30 m/Myr, respectively, for southern Africa. We are able to satisfy these constraints with a mantle model in which the mid-lower mantle beneath southern Africa is 0.2% less dense and has a viscosity of ∼ 10^22 Pa s. In addition, if the continental lithosphere is thick beneath southern Africa, as suspected from seismic inversions, and has a high effective viscosity, then we find that southern Africa can be further elevated owing to increased coupling between the deep mantle and surface. We show that recent estimates of mantle density, suggesting that the lowest parts of the African anomaly may be anomalously dense are compatible with geologic constraints. We conclude that uplift rate, when combined with estimates of present-day dynamic topography, provides a powerful tool to constrain the properties of the deep mantle.


Item Type:Article
Additional Information:Copyright 2000 by the American Geophysical Union Received December 9, 1999; Revised June 19, 2000; Accepted June 20, 2000; Published July 19, 2000. This work has been supported by NSF grants EAR-9809771 and EAR-9814908. J.X.M. acknowledges support from NSERC, Lithoprobe, and the Canadian Institute for Advanced Research. We thank C. Conrad, C. Lithgow-Bertelloni, A. Nyblade, and M. Summerfield for helpful comments on the manuscript and A. M. Forte for assistance in the geoid calculations. This represents contribution 8693, Division of Geological and Planetary Sciences, California Institute of Technology.
Group:Seismological Laboratory
Subject Keywords:Mantle convection; Africa; lower mantle; mantle rheology; continental uplift; seismic tomography
Issue or Number:7
Record Number:CaltechAUTHORS:GURggg00
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:GURggg00
Alternative URL:http://dx.doi.org/10.1029/1999GC000035
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:3133
Collection:CaltechAUTHORS
Deposited By: Archive Administrator
Deposited On:16 May 2006
Last Modified:11 Jun 2015 12:58

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