Title

Absence of Thermal Influence from the African Superswell and Cratonic Keels on the Mantle Transition Zone Beneath Southern Africa: Evidence from Receiver Function Imaging

Abstract

The depths of the 410 km (d410) and 660 km (d660) discontinuities beneath southern Africa, which is presumably underlain by the lower-mantle African Superswell, are imaged in 1 radius consecutive circular bins using over 6400 P-to-S receiver functions (RFs) recorded by 130 seismic stations over a 27 yr period. When the IASP91 standard Earth model is utilized for moveout correction and time-depth conversion, a normal mantle transition zone (MTZ) thickness of 246 ± 7 km is observed, suggesting that the Superswell has no discernible effect on mantle transition zone temperature. Based on the negligible disparity of the mean MTZ thicknesses between on (246 ± 6 km) and off (246 ± 8 km) cratonic regions, we conclude that the deep Archean cratonic keels possess limited influence on MTZ thermal structure. The apparently shallower-than-normal MTZ discontinuities and the parallelism between the d410 and d660 are mostly the results of upper mantle high wave speed anomalies probably corresponding to a thick lithosphere with a mean thickness of about 245 km beneath the Kaapvaal and 215 km beneath the Zimbabwe cratons. In contradiction to conclusions from some of the previous studies, the resulting spatial distribution of the stacking amplitudes of the P-to-S converted phases at the discontinuities is inconsistent with the presence of an excessive amount of water in the MTZ and atop the d410.

Department(s)

Geosciences and Geological and Petroleum Engineering

Comments

The study was partially supported by the Continental Dynamics Program of the U.S. National Science Foundation under grants No. 1009946 and 1321656 to S.G. and K.L.

Keywords and Phrases

Mantle transition zone; Southern Africa; African Superswell; Receiver function; Lithosphere

International Standard Serial Number (ISSN)

0012-821X

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2018 Elsevier, All rights reserved.

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