The regional magnetic data set of Namibia: Compilation, contributions to crustal studies and support to natural resource management

Eberle, D.

doi:10.2113/1050361

Cited by 7 publications

(5 citation statements)

References 4 publications

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“…Superimposed on the coastparallel Mehlberg dikes south of Luderitz are small bodies of alkaline felsic rocks (granite, syenite, foyaite) at Pomona, Granitberg and Drachenberg (Figure 3), which Marsh (1975; interpreted as isolated parts of a larger Cretaceous igneous center that he termed the Luderitz Province. The Luderitz centers are not directly associated with positive magnetic anomalies that would indicate mafic magmas in depth (compare Bauer et al, 2003) but there is a major belt of positive magnetic anomalies just north of the Luderitz Province and intersecting the coast at Luderitz Bay (Corner, 2000;Eberle et al, 2002).…”

Section: Distribution Of Dolerite Dikesmentioning

confidence: 99%

Magmatism and continental breakup at the west margin of southern Africa: A geochemical comparison of dolerite dikes from northwestern Namibia and the Western Cape

Trumbull

Reid

Beer

et al. 2007

South African Journal of Geology

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This paper presents a comparative geochemical study of Early Cretaceous mafic dike swarms along the rifted volcanic margin of southern Africa from northwestern Namibia to the Cape Peninsula. These dikes are under study to provide a record of magma compositions and conditions of mantle melting at margin segments with high and low magma flux. Our focus is on localities representing the two ends of the spectrum: the Henties Bay-Outjo dike swarm (HOD) in the high magma-flux Etendeka Province of Namibia, and the False Bay dike swarm from the low-flux margin segment in the Western Cape Province, RSA. At False Bay and other localities examined in the south, dikes are low-Ti, tholeiitic dolerites representing a single magma type. Whole-rock MgO contents and olivine compositions in these dikes reach a maximum of 8 weight % and Fo 70 , respectively. Differentiated dikes (MgO = 6 to 2 weight %) show correlations of trace element and isotopic ratios indicating crustal assimilation, but the least-evolved dikes have uniform incompatible trace element ratios and initial Sr-Nd-Pb isotope compositions (87 Sr/ 86 Sr= 0.7056 to 0.7064, εNd =-1.9 to-2.3 and 206 Pb/ 204 Pb = 18.53 to 18.59) suggesting a lithospheric mantle source or a mixture of enriched lithosphere and asthenospheric sources. The dolerites from the HOD swarm in Namibia are mainly low-Ti tholeiites like their counterparts in the south but with much higher Mg-contents (up to 16 weight % MgO in whole rock and Fo 86-90 in olivine). The compositional diversity is also greater in the HOD dikes and at least three magma types are recognized: (1) qz-or ol-normative Tafelberg type, with "spiky" mantle-normalized trace element patterns and initial isotope ratios consistent with a lithospheric mantle source and minor crustal input (87 Sr/ 86 Sr= 0.7101 to 0.7122, εNd =-2 to-7, and 206 Pb/ 204 Pb = 18.74 to 19.10); (2) ol-normative Horingbaai-type with trace element patterns and initial isotope ratios similar to E-MORB (87 Sr/ 86 Sr= 0.7037 to 0.7050, εNd = +2 to +6, and 206 Pb/ 204 Pb = 18.00 to 18.83); and (3) ne-normative magmas, with moderate to high incompatible trace element abundances and intermediate initial isotope ratios (87 Sr/ 86 Sr= 0.7055 to 0.7059, εNd = 0 to-2, and 206 Pb/ 204 Pb = 18.30 to 18.61). The contrast in magmatic intensity between the low-and high-flux margin segments corresponds with systematic compositional differences in contemporary dike swarms. This is supported by geophysical evidence for a change in both the thickness and the average seismic velocity of intruded lower crust at the continent-ocean boundary in the two regions. The greater diversity of magma types and the sharp rise in MgO contents of dikes in northwestern Namibia (maximum 8 weight % MgO for False Bay versus 16 weight % MgO for HOD) suggest that elevated temperatures and active upwelling of a mantle plume caused the enhanced melt production in the north. Dolerite compositions from the False Bay swarm and other localities south of the Orange River are consistent with a passive upwell...

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Section: Distribution Of Dolerite Dikesmentioning

confidence: 99%

Magmatism and continental breakup at the west margin of southern Africa: A geochemical comparison of dolerite dikes from northwestern Namibia and the Western Cape

Trumbull

Reid

Beer

et al. 2007

South African Journal of Geology

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“…Regional aeromagnetic anomaly maps, available from the Geological Survey of Namibia website (see Eberle et al, 2002), were used to extrapolate the results of mapping to east and west under the Nama Group cover. The result of the mapping and reinterpretation is presented as Figure 1.…”

Section: New Mapping and Reinterpretation Of Previous Mapping Backgromentioning

confidence: 99%

“…Study of the regional aeromagnetic anomaly maps (published by the Geological Survey of Namibia at http://www.gsn.gov.na/magnetics.htm -see Eberle et al, 2002 for details) suggests that a prominent geophysical boundary coincides with the transition from metavolcanic to metasedimentary rocks. This geophysical boundary is not necessarily linear on a detailed scale.…”

Section: Lord Hill Boundary Zonementioning

confidence: 99%

Age of Metavolcanic rocks at the northern margin of the Namaqua-Natal Metamorphic Province in the Karas Mountains, Namibia, defined by SHRIMP U-Pb dating of zircons

Evans¹,

Windrim²,

Armstrong

2007

South African Journal of Geology

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Mapping in the Karas Mountains area of southern Namibia has shown the presence of a major lithotectonic boundary at the northern margin of the Namaqua-Natal Metamorphic Province. The area is subdivided into the Northern Volcanic Zone largely comprising mafic, intermediate and felsic volcanic and intrusive rocks metamorphosed to greenschist to amphibolite facies, and the Southern Sedimentary Zone, dominated by pelitic rocks, metamorphosed at amphibolite to granulite facies, and intruded by syntectonic granites. The intervening Lord Hill Boundary Zone is characterized by anastomosing mylonite belts with dips and lineations plunging steeply to the south, within less-deformed metalavas and intrusions similar in character to those of the Northern Volcanic Zone. The intrusive and metavolcanic rocks of the Northern Volcanic and Lord Hill Boundary Zones have geological characteristics of present-day volcanic arcs. Texturally well-preserved felsic metavolcanic rocks of the Lord Hill Boundary Zone have been dated by SHRIMP U-Pb isotope analysis of zircons, and gave an age of 1286.0 ± 7.3 Ma. The age and tectonic setting are very similar to those of the Jannelsepan and Copperton Formations in South Africa, and point to an extensive Mesoproterozoic volcanic arc at the southern edge of the Kalahari Craton.

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“…High-resolution airborne geophysical surveys in Namibia defined the distribution of Mesoproterozoic belts in that country. The Namibian Geological Survey used the geophysical information to highlight new mineral targets (Eberle et al, 2002). Field and geochronological studies in northwest Zambia indicated that the type Kibaran belt of central Africa may not continue southwest into Angola [but see Rainaud et al (2005) for a different interpretation].…”

Section: Detailed Fieldwork By National Geological Surveymentioning

confidence: 99%

Mesoproterozoic orogenic belts in southern and central Africa

McCourt

Hanson

2006

Journal of African Earth Sciences

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The regional magnetic data set of Namibia: Compilation, contributions to crustal studies and support to natural resource management

Cited by 7 publications

References 4 publications

Magmatism and continental breakup at the west margin of southern Africa: A geochemical comparison of dolerite dikes from northwestern Namibia and the Western Cape

Magmatism and continental breakup at the west margin of southern Africa: A geochemical comparison of dolerite dikes from northwestern Namibia and the Western Cape

Age of Metavolcanic rocks at the northern margin of the Namaqua-Natal Metamorphic Province in the Karas Mountains, Namibia, defined by SHRIMP U-Pb dating of zircons

Mesoproterozoic orogenic belts in southern and central Africa

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