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Instantaneous dynamics of the cratonic Congo basin

Downey, Nathan J. and Gurnis, Michael (2009) Instantaneous dynamics of the cratonic Congo basin. Journal of Geophysical Research B, 114 (B6). B06401. ISSN 0148-0227. doi:10.1029/2008JB006066.

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Understanding the formation mechanisms of cratonic basins provides an examination of the rheological, compositional and thermal properties of continental cratons. However, these mechanisms are poorly understood because there are few currently active cratonic basins. One cratonic basin thought to be active is the Congo basin located in equatorial Africa. The Congo basin is coincident with a large negative free-air gravity anomaly, an anomalous topographic depression, and a large positive upper mantle shear wave velocity anomaly. Localized admittance models show that the gravity anomaly cannot be explained by a flexural support of the topographic depression at the Congo. We analyze these data and show that they can be explained by the depression of the Congo basin by the action of a downward dynamic force on the lithosphere resulting from a high-density object within the lithosphere. We formulate instantaneous dynamic models describing the action of this force on the lithosphere. These models show that the gravity and topography of the Congo basin are explained by viscous support of an anomalously dense region located at 100 km depth within the lithosphere. The density anomaly has a magnitude within the range of 27–60 kg m^−3 and is most likely compositional in origin. Our models do not provide a constraint on the lithospheric viscosity of the Congo craton because the shallow location of the anomaly ensures strong coupling of the anomaly to the surface regardless of viscosity structure.

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Gurnis, Michael0000-0003-1704-597X
Additional Information:© 2009 American Geophysical Union. Received 2 September 2008; accepted 26 February 2009; published 3 June 2009. This is contribution 10019 of the Division of Geological and Planetary Sciences and 107 of the Tectonics Observatory, Caltech. All calculations carried out on the Caltech Geosciences Supercomputer Facility partially supported by NSF EAR-0521699. Additional support provided through the Tectonics Observatory by the Gordon and Betty Moore Foundation. Much of the analysis presented in this paper was carried out while N. J. D. was a visiting student in the Department of Earth and Planetary Sciences, Harvard University. We thank Dan Schrag, Rick O’Connell, and John Shaw for their generous support. We also thank Jeroen Ritsema for help with analysis of the tomographic data. We thank Nicky White and Mike Daly for their insightful reviews of this paper.
Group:Caltech Tectonics Observatory, Seismological Laboratory
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Gordon and Betty Moore FoundationUNSPECIFIED
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Other Numbering System NameOther Numbering System ID
Caltech Division of Geological and Planetary Sciences 10019
Caltech Tectonics Observatory107
Issue or Number:B6
Record Number:CaltechAUTHORS:20090630-113107733
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Official Citation:Downey, N. J., and M. Gurnis (2009), Instantaneous dynamics of the cratonic Congo basin, J. Geophys. Res., 114, B06401, doi:10.1029/2008JB006066
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14463
Deposited By: Tony Diaz
Deposited On:12 Aug 2009 22:43
Last Modified:08 Nov 2021 23:12

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