HR: 0800h
AN: GP11A-0814    [Abstracts]
TI: New Magnetotelluric Measurements across the Magnetic Beattie Anomaly and the Southern Cape Conductive Belt in South Africa.
AU: * Weckmann, U
EM: ute@cp.dias.ie
AF: GeoForschungsZentrum, Telegrafenberg, Potsdam, 14473 Germany
AU: * Weckmann, U
EM: ute@cp.dias.ie
AF: Dublin Institute for Advanced Studies, School of Cosmic Physics 5 Merrion Square, Dublin, 2 Ireland
AU: Ritter, O
EM: oritter@gfz-potsdam.de
AF: GeoForschungsZentrum, Telegrafenberg, Potsdam, 14473 Germany
AU: de Wit, M
EM: maarten@cigces.uct.ac.za
AF: University of Cape Town, Department of Geological Sciences, Rondebosch, 7700 South Africa
AU: Jung, A
EM: ajung@gfz-potsdam.de
AF: GeoForschungsZentrum, Telegrafenberg, Potsdam, 14473 Germany
AU: H\"ubert, J
EM: jhuebert@gfz-potsdam.de
AF: GeoForschungsZentrum, Telegrafenberg, Potsdam, 14473 Germany
AU: Branch, T
EM: tbranch@geology.uct.ac.za
AF: University of Cape Town, Department of Geological Sciences, Rondebosch, 7700 South Africa
AU: Stankiewicz, J
EM: jacek@cigces.uct.ac.za
AF: University of Cape Town, Department of Geological Sciences, Rondebosch, 7700 South Africa
AU: Mabidi, T
EM: tshifi@cigces.uct.ac.za
AF: University of Cape Town, Department of Geological Sciences, Rondebosch, 7700 South Africa
AB: South Africa hosts two of the Earth's largest known geophysical anomalies, the Beattie Magnetic Anomaly (BMA) and the Southern Cape Conductive Belt (SCCB), that extend in South Africa for almost 1000 km in east-west direction, and possibly continue also into Antarctica and southern South America. In South Africa, the surface expressions of these anomalies appear to coincide approximately with the mapped boundary of the Cape Fold Belt and the Namaqua-Natal Mobile Belt. The nature of both anomalies remains enigmatic. However, they have been interpreted as a slice of paleao-oceanic lithosphere or alternatively as thrust zones, but the existence of a common source, their extent and internal structures are all unknown. We report on the first results of a high resolution magnetotelluric (MT) study conducted in March, 2004 along a profile between Prince Albert and Fraserburg crossing the BMA and the SCCB in their entirety. Within the framework of the multi-disciplinary integrated German-South African project "Inkaba yeAfrica", MT data were collected at 82 sites in the frequency range from 1000 Hz to 0.001 Hz with an average site spacing of 2 km. With the new data we are able to resolve conductivity structures associated with both geophysical anomalies, and an initial 2D inversion model resolves the conductivity distribution of the entire crust. A zone of very high electrical conductivity (~$1 \Omega m$), at a depth of approximately 5-10 km, seems to be associated with the BMA. Another conductivity anomaly is located beneath the northern boundary of the SCCB, extending from the shallow crust down to approx. 15 km depth. Both conductors are inclined towards the south, which coincides with a general southward dipping trend of mapped faults of the Cape Fold Belt. We therefore interpret these high conductivity anomalies as images of tectonic structures which may have evolved during the formation of the Karoo basin. The conductivity image furthermore reveals several sub-horizontal regions of high conductivity ($2 \Omega m$) in the upper 5 km of the crust, which may reflect sedimentary sequences of the Namaqua-Natal Mobile Belt.
DE: 8010 Fractures and faults
DE: 8100 TECTONOPHYSICS
DE: 5109 Magnetic and electrical properties
DE: 1645 Solid Earth
DE: 0600 ELECTROMAGNETICS
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting