Publication Date:
2022-05-25
Description:
Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 14 (2013): 806–827, doi:10.1002/ggge.20075.
Description:
Seismic velocity is a function of bulk vibrational properties of the media, whereas electrical resistivity is most often a function of transport properties of an interconnected minor phase. In the absence of a minor conducting phase then the two should be inter-relatable primarily due to their sensitivity to temperature variation. We develop expressions between shear wave velocity and resistivity for varying temperature, composition, and water content based on knowledge from two kimberlite fields: Jagersfontein (Kaapvaal Craton) and Gibeon (Rehoboth Terrane). We test the expressions through comparison between a new high-resolution regional seismic model, derived from surface wave inversion of earthquake data from Africa and the surrounding regions, and a new electrical image from magnetotelluric (MT) data recorded in SAMTEX (Southern African Magnetotelluric Experiment). The data-defined robust linear regression between the two is found to be statistically identical to the laboratory-defined expression for 40 wt ppm water in olivine. Cluster analysis defines five clusters that are all geographically distinct and tectonically relate to (i) fast, cold, and variably wet Kaapvaal Craton, (ii) fast and wet central Botswana, (iii) slow, warm, and wet Rehoboth Terrane, (iv) moderately fast, cold, and very dry southernmost Angola Craton, and (v) slow, warm, and somewhat dry Damara Belt. From the linear regression expression and the MT image we obtain predicted seismic velocity at 100 km and compare it with that from seismic observations. The differences between the two demonstrate that the linear relationship between Vs and resistivity is appropriate for over 80% of Southern Africa. Finally, using the regressions for varying water content, we infer water content in olivine across Southern Africa.
Description:
We wish to again acknowledge the three
main funding agencies, the U.S. National Science Foundation’s
Continental Dynamics Program (grant EAR0455242 to RLE),
the South African Department of Science and Technology (grant
to South African Council for Geoscience), and Science Foundation
Ireland (grant 05/RGP/GEO001 to AGJ), for their support.
Industry support for SAMTEX from De Beers Group Services,
BHP Billiton and Rio Tinto Mining and Exploration resulted
in a program far more extensive than originally conceived.
S.F. has been supported by the NERC New Investigator grant
NE/G000859/1. M.M. wishes to thank Science Foundation
Ireland (grant 08/RFP/GEO1693 SAMTEX to AGJ) for support.
J.F. wishes to thank Enterprise Ireland (grant Topo-Med to AGJ),
Science Foundation Ireland (grant 10/IN.1/I3022 IRETHERMto
AGJ), and the JAE-DOC Programme from Spanish CSIC,
cofunded by FSE for support.
Description:
2013-10-05
Keywords:
Continental lithosphere
;
Cratons
;
Velocity
;
Resistivity
Repository Name:
Woods Hole Open Access Server
Type:
Article
Format:
application/pdf
Permalink
