Geophysical characteristics of the Namaqua-Natal Belt and its boundaries, South Africa

Beer, J. H. de; Meyer, Rudi

doi:10.1016/0264-3707(84)90020-6

Cited by 40 publications

(25 citation statements)

References 29 publications

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“…The NamaquaNatal Belt is distinguished by characteristic elongate, high-amplitude and craton-parallel anomalies that continue into western Dronning Maud Land (Corner and Groenewald 1991;Golynsky and Jacobs 2001). An especially large feature is the Beattie anomaly, interpreted to represent a large body of mafic rocks (De Beer and Meyer 1983), although drilling has not yet revealed any mafic rocks (Moyes, personal communication). Possibly, this anomaly points to the remnants of the ocean that closed during the collision of Kalahari with Laurentia and could thus represent the suture.…”

Section: Discussionmentioning

confidence: 98%

New age constraints for Grenville-age metamorphism in western central Dronning Maud Land (East Antarctica), and implications for the palaeogeography of Kalahari in Rodinia

Jacobs

Bauer

Fanning

2003

International Journal of Earth Sciences

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Section: Discussionmentioning

confidence: 98%

New age constraints for Grenville-age metamorphism in western central Dronning Maud Land (East Antarctica), and implications for the palaeogeography of Kalahari in Rodinia

Jacobs

Bauer

Fanning

2003

International Journal of Earth Sciences

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“…In previous models, the southernmost boundary of the NNMB was defined by a deep BMA (serpentinised ophiolite wedge in Figure 10a) and the Southern Cape Conductive Belt, possibly abutting a Pan African (Neoproterozoic) suture zone beneath the Cape Supergroup (e.g. de Beer et al, 1982;de Beer and Meyer, 1983;1984;Pitts et al, 1992;Eglington et al, 1993;Cornell et al, 2006;Eglington, 2006). The seismic data do not support these models: In our model, the top of the NNMB reflections ( Figure 9) are truncated by a major angular unconformity at 5 km depth in the north, dipping to 12 km depth in the south and traceable along the full profile length.…”

Section: Extent Of the Nnmb Mid-crustmentioning

confidence: 97%

“…de Beer et al, 1982;de Beer and Meyer, 1983;Hälbich, 1993; Figure 10a). In contrast, the new data show that the BMA appears to be confined to the gneisses of the NNMB mid-crust and can therefore not be a Neoproterozoic suture zone.…”

Section: Deep Crustal Profile Southern Karoo Basin and Beattie Magnementioning

confidence: 99%

Deep Crustal Profile Across the Southern Karoo Basin and Beattie Magnetic Anomaly, South Africa: An Integrated Interpretation With Tectonic Implications

Lindeque

Wit

Ryberg

et al. 2011

South African Journal of Geology

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Two geophysical onshore-offshore lines on the southern margin of Africa form the Agulhas-Karoo Geophysical Transect (AKGT) and cross prominent geological features such as the Karoo Basin, Cape Fold Belt (CFB) and the Beattie Magnetic Anomaly (BMA). Geophysical data acquired along this AKGTransect between 2004 and 2007 within the Inkaba yeAfrica (lyA) framework, provide the platform for constructing a deep crustal section (IyA-200501) for the centre 100 km of the western AKGT-transect in order to resolve these features at depth. We present a detailed deep crustal model constructed from the joint interpretation of: i. archive data comprising surface geology, aeromagnetic data, nearby deep boreholes, teleseismic receiver functions and regional seismic reflection profiles, and ii. line coincident newly acquired high-resolution geophysical data consisting of near vertical seismic reflection data, shallow P-and S-wave velocity data, wide-angle refraction data, high resolution magnetotelluric data and impedance spectroscopy measurements on borehole samples. Our model differentiates four components in the up to 45 km thick crust: 1. a ~2 to 5 km thick folded Karoo Supergroup, disrupted by low-angle thrust faults rooted in a zone of local décollements in the lower Ecca Group and resting paraconformably on 2. a continuous undeformed sub-horizontal ~1.5 to 10 km thick wedge of the Cape Supergroup (CSG). This CSG wedge stretches from the Escarpment in the north to the tectonic front of the CFB in the south, and rests on an unconformity that dips about three degrees to the south. The angular unconformity is interpreted as an erosional peneplain that separates the CSG wedge from component 3. the ~13 to 21 km mid-crust basement below. The mid-crust contains a distinct north-dipping seismic fabric, here interpreted as 1.4 to 1.0 Ga Mesoproterozoic Namaqua-Natal Metamorphic Belt (NNMB) crust. A south-dipping mid-crustal detachment, interpreted as a ductile thrust zone, separates the mid-crust from component 4. a highly reflective ~10 to 24 km thick lower crust. The latter is interpreted as an older Palaeoproterozoic section of the NNMB (or even Archean cratonic basement), and bounded by a ~2 to 5 km thick, highly reflective bottom layer below that lies subparallel to a clear Moho. This bottom layer is interpreted as a mafic underplate, metasomatic reaction zone, or lower-crust to mantle transition zone. Collectively the seismic reflection and wide-angle refraction data support an interpretation that the NNMB mid-crustal layer contains the BMA source, possibly connected to two zones of strong reflectivity: a ~10 to 12 km wide northern zone and a ~5 to 7 km wide southern zone, both about 5 km thick and 7 to 8 km below surface. We interpret the BMA source to be at least in part, a Namaqua-like massive to disseminated, deformed/metamorphosed stratiform sulphide-magnetite ore body with metasomatic overprint.

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“…Applying the different spreading directions and velocities of AFR and SAM, this breakup model implies no strike slip along the EE during the drift period. For the initial position of AFR relative to ANT we considered two pronounced magnetic anomalies along the Cape Fold Belt (Figure 7a, Beattie-A) and in DML (Figure 7a, western part of SKA) to be a continuous prebreakup feature [De Beer and Meyer, 1983;Corner and Groenewald, 1991;Golynsky and Aleshkova, 2000]. The Beattie Anomaly in southern Africa has a strike length of approximately 900 km.…”

Section: Antarctica-africamentioning

confidence: 99%

“…Its counter piece in Antarctica has a similar signature in terms of amplitude (100 -900 nT), wavelength, and strike length (>600 km). The age of the Beattie Anomaly is unknown, and speculations range from 500 Ma (Cape orogeny ) to a Grenville age [De Beer and Meyer, 1983;Corner and Groenewald, 1991]. Both features may belong to the Namaqua-Natal-Maud Belt, which can be partly mapped in southern Africa and Dronning Maud Land.…”

Section: Antarctica-africamentioning

confidence: 99%

Timing and geometry of early Gondwana breakup

et al. 2003

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[1] The Mesozoic opening history of the Southern Ocean between South America, Africa, and Antarctica is one of the largest gaps in knowledge on the evolution of this region. Competing geodynamic models were published during the last two decades to explain the geophysical and geological observations. Here we report on aeromagnetic data collected along the East Antarctic coast during five seasons. These data provide new constraints on the timing and geometry of the early Gondwana breakup. In the Riiser-Larsen Sea/ Mozambique Basin, the first oceanic crust between Africa and Antarctica formed around 155 Ma. In the west the Weddell Rift propagated from west to east with a velocity of 63 km/Myr between chrons M19N and M17N. At chron M14N, South America and Africa finally were split off the Antarctic continent. Stretching in the area of the South Atlantic started at the latest from 155 Myr onward. The different spreading velocities and directions of South America and Africa created at chron M9N the first oceanic crust in the South Atlantic. A new model indicates that the Karoo and Dronning Maud Land magmatism occurred well before any new ocean floor was created and therefore the first formation of new oceanic crust cannot directly be related to a plume interaction.

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Geophysical characteristics of the Namaqua-Natal Belt and its boundaries, South Africa

Cited by 40 publications

References 29 publications

New age constraints for Grenville-age metamorphism in western central Dronning Maud Land (East Antarctica), and implications for the palaeogeography of Kalahari in Rodinia

New age constraints for Grenville-age metamorphism in western central Dronning Maud Land (East Antarctica), and implications for the palaeogeography of Kalahari in Rodinia

Deep Crustal Profile Across the Southern Karoo Basin and Beattie Magnetic Anomaly, South Africa: An Integrated Interpretation With Tectonic Implications

Timing and geometry of early Gondwana breakup

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