HR: 1340h
AN: T13A-0426    [Abstracts]
TI: Electrical Anisotropy Across the Kaapvaal Craton Derived From SAMTEX MT Studies Compared With SASE SKS Seismic Anisotropy Results
AU: * Hamilton, M
EM: mh@cp.dias.ie
AF: Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin, 2 Ireland
AU: * Hamilton, M
EM: mh@cp.dias.ie
AF: The University of the Witwatersrand, School of Geosciences, Private Bag 3, Johannesburg, 2050 South Africa
AU: Jones, A G
EM: alan@cp.dias.ie
AF: Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin, 2 Ireland
AU: Evans, R L
EM: revans@whoi.edu
AF: Woods Hole Oceanographic Institution, Department of Geology and Geophysics, Clark South 172, 360 Woods Hole Road, Woods Hole, MA 02543-1542 United States
AU: Evans, S
T13A-0426 AF: De Beers, De Beers Group Services, Private Bag X01, Southdale, 2135 South Africa
AU: Fourie, S
EM: stoffel@geoscience.org.za
AF: Council for Geoscience, 280 Pretoria Street, Silverton, Pretoria, 12 South Africa
AU: Mountford, A
EM: Andy.Mountford@riotinto.com
AF: Rio Tinto, Rio Tinto Mineral Exploration Inc., PO Box 695, 7th Floor Castlemead, Lower Castle Street, Bristol, BS99 1FS United Kingdom
AU: Garcia, X
EM: xavi@cp.dias.ie
AF: Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin, 2 Ireland
AU: Spratt, J
EM: jsp@cp.dias.ie
AF: Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin, 2 Ireland
AB: Data from part of the Southern African Magnetotelluric Experiment (SAMTEX) have been analysed using an impedance tensor decomposition method in order to gain a better understanding of the geoelectric directionality and dimensionality and electrical anisotropy properties of the region. The SW-NE transect from Sutherland to Messina, in South Africa is coincident with part of the Southern Africa Seismic Experiment (SASE) deployment. Shear-wave splitting observations, from SKS analyses, have been conducted on the SASE data, where it was observed that splitting delay times appear to exhibit geological control, with the Neoarchean regions showing greater anisotropy and the older Mesoarchean core in the SE exhibiting no detectable anisotropy. In contrast however to the inherent depth ambiguity with the SKS method, MT has the ability to place relatively accurate bounds on the depth at which the anisotropy is most significant, making for a very complementary study. The electrical anisotropy is derived in terms of approximate depth, rather than frequency. Our results for upper lithospheric mantle depths (40-100 km) indicate very similar northeast-southwest strike directions to those inferred from the SKS shear-wave splitting analyses. However our results for crustal depths (5-40 km) have a distinctly different orientation, thereby further validating the interpretation that the causative region for seismic anisotropy is in the upper lithospheric mantle, i.e., it is a fossil anisotropy, and not at the base of the lithosphere nor in the crust. Not surprisingly, the crustal electrical anisotropy directions appear to be strongly controlled by surface geological structure. As with seismic anisotropy, the electrical lithospheric mantle anisotropy likely indicates Archean deformation that occurred during the formation of the Kaapvaal and Zimbabwe cratons, and has been preserved in the lithospheric roots typical of Archean cratons.
DE: 0925 Magnetic and electrical methods (5109)
DE: 8031 Rheology: crust and lithosphere (8159)
DE: 8103 Continental cratons
DE: 8125 Evolution of the Earth (0325)
DE: 9623 Archean
SC: Tectonophysics [T]
MN: Fall Meeting 2005