Dave Hutchins

Geological Survey of Namibia

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R. L. Evans

Woods Hole Oceanographic Institution

Xavier García

Institut de Ciències del Mar

Alan G. Jones

Heart of England NHS Foundation Trust

T. Ngwisanyi

Electromagnetic Geoservices (Norway)

Mark Müller

Friedrich-Alexander-Universität Erlangen-Nürnberg

S. J. Webb

University of the Witwatersrand

C.J.S. Fourie

Walter Sisulu University

Mark P. Hamilton

Stanford University

P. Cole

Council for Geoscience

W. Pettit

BHP (Australia)

Cooperative Institutions

Electromagnetic Geoservices (Norway)

Dublin Institute For Advanced Studies

Council for Geoscience

Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences

University of Potsdam

University of the Witwatersrand

Geological Survey of Canada

Lamont-Doherty Earth Observatory

Columbia University

University of Cape Town

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Compilation of the Namibian airborne magnetic surveys: procedures, problems and results

Journal of African Earth Sciences (1996)

D. Eberle Dave Hutchins R.J. Rebbeck I. W. Somerton

Magnetic survey

10.1016/0899-5362(96)00117-0

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Citations (8)

Rapid Mesozoic Thermal and Chemical Modification of the Rehoboth Terrane and Kaapvaal Craton from Broadband Magnetotellurics and Xenolith Geochemistry

11th SAGA Biennial Technical Meeting and Exhibition (2009)

Mark Müller Alan G. Jones R. L. Evans Herman Grütter Chris Hatton

A 1400 km-long, 2-D magnetotelluric (MT) profile across the Archaean Kaapvaal Craton, the Proterozoic Rehoboth Terrane and the Late Proterozoic/Early Phanerozoic Ghanzi-Chobe/Damara Belt reveals significant lateral heterogeneity in the electrical resistivity structure of the southern African lithosphere. The profile indicates the following present-day average lithospheric thicknesses, to a precision of about ± 20 km, for each of the terranes traversed (inferred conductive geotherms in brackets): Eastern Kimberley Block of the Kaapvaal Craton 220 km (41 mWm-2), Western Kimberley Block 190 km (44 mWm-2), Rehoboth Terrane 180 km (45 mWm-2) and Ghanzi-Chobe/Damara Belt 160 km (48 mWm-2). Previously published mantle xenolith pressure-temperature (P-T) arrays from the Gibeon, Gordonia and Kimberley fields, however, suggest that the Rehoboth Terrane had equilibrated to a cooler conductive palaeo-geotherm (40 – 42 mWm-2 ) very similar to that of Eastern Kimberley Block of the Kaapvaal Craton, at some (unconstrained) time prior to the Mesozoic eruption of the kimberlites. A model consisting of the penetration of heat transporting magmas into the lithosphere, with associated chemical refertilisation, at an early stage of Mesozoic thermalism appears to be the most plausible model at present to account for both the present-day lithospheric structure of the Rehoboth Terrane and an earlier, cooler palaeo-geotherm. Some problems, however, remain unresolved in terms of the isostatic response of the model. Based on a compilation of xenocryst Cr/Ca-in-pyrope barometry observations, the extent of depleted mantle in the Rehoboth Terrane is found to be significantly reduced with respect to the Eastern Kimberley Block: 117 km versus 138 – 167 km. It appears most likely that the chemical depletion depth in both terranes, at least in the vicinity of kimberlite eruption, is accounted for by refertilisation of the lower lithospheric mantle.

Xenolith

10.3997/2214-4609-pdb.241.muller_paper1

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Magnetotelluric Imaging Across a Neoproterozoic Collision Zone: Damara Belt and Surrounding Tectonic Blocks

11th SAGA Biennial Technical Meeting and Exhibition (2009)

David Khoza Alan G. Jones Mark Müller R. L. Evans Mark P. Hamilton

The Southern African Magnetotelluric Experiment (SAMTEX) is the largest ever land-based magnetotelluric (MT) project. The main objective of the project is to define the geo-electric structure across the region in order to gain a better understanding of Archean and Proterozoic tectonic processes. Only the MT profiles crossing the Rehoboth Terrane, the Neoproterozoic Ghanzi-Chobe/Damara belts (collectively termed the DMB) and the southern Angola craton are the focus of this study. One of the ways in which geo-electrical structural information is obtained is by detailed analysis of the measured impedance tensor. The Groom and Bailey decomposition technique was applied to the MT data and indicates significant depth and along-profile variations in geo-electric strike and dimensionality on all transects crossing these three tectonic units (i.e. Rehoboth Terrane, Angola craton and the DMB). The geo-electric strikes are generally parallel to the north-east trending tectonic fabric as inferred from the magnetic data, but the significant strike variations with depth are expressions of heterogeneity in the lithospheric structure. The Rehoboth terrane, south of the DMB, exhibits a strongly one dimensional (1D) to moderate two dimensional (2D) structure, with preferred strike directions in the range 200-450 20for the crust-mantle period (i.e. depth) range, indicating little crust-mantle decoupling. The DMB appears to be moderately 2D at lower crustal and upper mantle depths (10-100 s) with no consistent/preferred strike direction and significant phase differences between the conductive and resistive directions. North of the DMB and into the Angola craton there are significant variations in geo-electric strike direction and dimensionality at most sites for lower-crustal and upper mantle lithosphere. Our results further indicate that the profiles have to be divided into smaller areas having similar strike directions to allow for 2D modelling and inversion.

Magnetotellurics

Imbrication

10.3997/2214-4609-pdb.241.khoza_paper1

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Seismic Studies at the Northern Namibian Passive Continental Margin

AGU Fall Meeting Abstracts (2011)

T. Ryberg Christian Haberland Thomas Haberlau M. Weber Jan H. Behrmann

Continental Margin

Passive margin

Margin (machine learning)

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Electrical lithosphere beneath the Kaapvaal craton, southern Africa

Journal of Geophysical Research Atmospheres (2011)

R. L. Evans Alan G. Jones Xavier García Mark Müller Mark Hamilton

[1] A regional-scale magnetotelluric (MT) experiment across the southern African Kaapvaal craton and surrounding terranes, called the Southern African Magnetotelluric Experiment (SAMTEX), has revealed complex structure in the lithospheric mantle. Large variations in maximum resistivity at depths to 200–250 km relate directly to age and tectonic provenance of surface structures. Within the central portions of the Kaapvaal craton are regions of resistive lithosphere about 230 km thick, in agreement with estimates from xenolith thermobarometry and seismic surface wave tomography, but thinner than inferred from seismic body wave tomography. The MT data are unable to discriminate between a completely dry or slightly “damp” (a few hundred parts per million of water) structure within the transitional region at the base of the lithosphere. However, the structure of the uppermost ∼150 km of lithosphere is consistent with enhanced, but still low, conductivities reported for hydrous olivine and orthopyroxene at levels of water reported for Kaapvaal xenoliths. The electrical lithosphere around the Kimberley and Premier diamond mines is thinner than the maximum craton thickness found between Kimberley and Johannesburg/Pretoria. The mantle beneath the Bushveld Complex is highly conducting at depths around 60 km. Possible explanations for these high conductivities include graphite or sulphide and/or iron metals associated with the Bushveld magmatic event. We suggest that one of these conductive phases (most likely melt-related sulphides) could electrically connect iron-rich garnets in a garnet-rich eclogitic composition associated with a relict subduction slab.

Xenolith

Magnetotellurics

Asthenosphere

10.1029/2010jb007883

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Citations (112)

Constraints From Broadband Magnetotellurics on the Lithospheric Evolution of the Rehoboth and Kaapvaal Cratons, Southern Africa.

AGUFM (2006)

M. R. Müller Mark P. Hamilton Alan G. Jones R. L. Evans Xavier García

Magnetotellurics

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Regional geophysical exploration of the Kalahari in Botswana

Tectonophysics (1980)

Dave Hutchins C.V. Reeves

Bedrock

Geophysical survey

Exploration geophysics

Seismic refraction

10.1016/0040-1951(80)90211-5

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Citations (47)

Area selection using magnetotellurics: examples from southern Africa

International Kimberlite Conference Extended Abstracts: 2008 (2019)

Alan G. Jones Mark Müller Mark Hamilton M. P. Miensopust Xavier García

1: Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin, Ireland; 2: Department of Geology and Geo-physics, Woods Hole Oceanographic Institution, Clark South 172, 360 Woods Hole Road, Woods Hole, Massachu-setts, 02543-1542, U.S.A.; 3: Council for Geoscience, 280 Pr etoria Street, Silverton, Pretoria 0001, RSA; 4: Geo-logical Survey of Botswana, Private Bag 14, Lobatse, Botswana; 5: Geological Survey of Namibia, 1 Aviation Road, Windhoek, Namibia; 6: Council for Scientific and Industrial Research, Pretoria, RSA; 7: De Beers Group Services, Private Bag X01, Southdale 2135, South Africa; 8: Rio Tinto Mining and Exploration, London, U.K.; 9: BHP Billi-ton, Johannesburg, RSA; 10: University of the Witwatersrand, 6 Hollard Street, Johannesburg 2001, RSA; 11: ABB AB, HVDC, Ludvika, SE-77180, Sweden; 12: Other members of the SAMTEX team include: Louise Collins, Colin Hogg, Clare Horan, Jessica Spratt, Gerry Wallace (DIAS), Alan D. Chave (WHOI), Janine Cole, Raimund Stettler (CGS), G. Tshoso (GSB), Ed Cunion (RTME), David Khosa (BHPB) and Pieter-Eward Share (CSIR); 13: Now at EMGS, Stiklestadveien 1, N-7041 Trondheim, Norway.

Magnetotellurics

10.29173/ikc3603

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Citations (0)

Crustal structures in central southern Africa

Nature (1975)

C.V. Reeves Dave Hutchins

geodynamics

Basement

10.1038/254408a0

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Citations (39)

Evidence for Incipient Rifting in Southern Africa

Geophysical Journal International (1976)

Christopher H. Scholz T. A. Koczynski Dave Hutchins

A study of microearthquakes in northern Botswana, September to December 1974 indicates that this region is tectonically active. Microearthquakes were found to occur primarily in a zone striking north-east from Lake Ngami through the Okavango delta to the Zambezi River. These events are associated with an en echelon set of north-easterly striking normal faults of Quaternary to Recent age, and appear to be continuous with the activity at Lake Kariba and continuing further north along the Luangwa valley to the main rift zone south-east of Lake Tanganyika. Focal mechanisms indicate normal faulting on NE striking planes. The tectonic setting of the Okavango delta thus appears to be that of a developing graben some 150 km wide. The delta is at the tip of a proposed incipient zone of rifting that follows an old post-Karroo, pre-Cretaceous rift zone. The African rifts are viewed as an incomplete, growing plate margin which is propagating to the south along at least two arms that bifurcate south of Lake Tanganyika.

East African Rift

Rift zone

Rift valley

African Plate

Echelon formation

10.1111/j.1365-246x.1976.tb00278.x

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Citations (156)