The Agulhas Magsat anomaly: Implications for continental break-up of Gondwana

Antoine, L.A.G.; Moyes, A.B.

doi:10.1016/0040-1951(92)90138-v

Cited by 6 publications

(7 citation statements)

References 35 publications

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“…(1995) argued for a thinned continental crust beneath the southern plateau. In comparison, large magnetic anomalies mapped from profiles across the plateau (Le Pichon & Heirtzler 1968; Barrett 1977) as well as the dominant MAGSAT anomaly over the region (Antoine & Moyes 1992) have been used as an argument for an oceanic origin.…”

Section: Introductionmentioning

confidence: 99%

“… Overview of present geodynamic features of the southeast Atlantic and southwest Indian Ocean region. The positive Agulhas MAGSAT anomaly (short‐dashed line) covers most of the region over the Agulhas and Mozambique plateaus (Antoine & Moyes 1992). The Bouvet hotspot track is shown according to the coordinate/time reconstructions (Ma) of Hartnady & le Roex (1985) (dotted line and black dots) and Martin (1987) (long‐dashed line and white dots).…”

Section: Introductionmentioning

confidence: 99%

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The crustal role of the Agulhas Plateau, southwest Indian Ocean: evidence from seismic profiling

Gohl¹,

Uenzelmann-Neben²

2001

Geophys J Int

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SUMMAR YIts key geographical position near the reconstructed centre of the Gondwana break-up between Antarctica, South America and Africa has brought attention to the Agulhas Plateau, an oceanic plateau in the southwest Indian Ocean, with regard to its crustal nature and origin. The majority of previous studies have suggested a dominantly continental origin. As part of the project SETARAP (Sedimentation and Tectonics of the Agulhas Ridge and Agulhas Plateau), we conducted an extensive seismic survey over the plateau with the aim of solving the questions about its crustal structure, origin and role in a plate tectonic reconstruction context. In addition to 1550 km of high-resolution seismic re¯ection pro®les, we recorded deep-crustal large-offset and wide-angle re¯ection/ refraction data from an ocean-bottom hydrophone (OBH) pro®le across the southern plateau. The re¯ection data show clear indications of numerous volcanic extrusion centres with a random distribution. We are able to date this phase of voluminous volcanism to Late Cretaceous time, a period when numerous other large igneous provinces formed. Traveltime inversion of the deep-crustal OBH records reveals an up to 25 km thick crust with velocities between 7.0 and 7.6 km s x1 for the lower 50±70 per cent of its crustal column. We do not ®nd indications for continental af®nity but rather a predominantly oceanic origin of the Agulhas Plateau, similar to that inferred for the Northern Kerguelen and Ontong±Java plateaus. In Late Cretaceous time, its main crustal growth was controlled by the proximity of spreading centres and by passage over the Bouvet hotspot at 80±100 Ma.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The crustal role of the Agulhas Plateau, southwest Indian Ocean: evidence from seismic profiling

Gohl¹,

Uenzelmann-Neben²

2001

Geophys J Int

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“…The Agulhas anomaly on the other hand, is the largest and most intense anomaly within the southern African region, and appears to have internal structure, delineated by several oceanic floor features: the eastern spur of the Agulhas anomaly is truncated by the Davie Ridge, while the northwestern boundary coincides with the Agulhas Fracture Zone which follows the continental shelf as far as the Maputo embayment. It was argued [ Antoine and Moyes , 1992] that the Agulhas anomaly underlies a large portion of Gondwana, encompassing part of the Falklands Plateau and the microplates of West Antarctica. The Agulhas anomaly is therefore the remanant of an extensive region of the lithosphere which initiated the break‐up of Gondwana in this region, underlying a fragmented region at the junction of the South America, Africa and Antarctica plates.…”

Section: Resultsmentioning

confidence: 99%

“…This paper discusses the modelling of near‐earth Ørsted total intensity magnetometer data over southern Africa by means of Spherical Cap Harmonic Analysis (SCHA) to identify the external field and the subsequent identification of long‐wavelength crustal anomalies. Previous analysis of Polar Orbiting Geomagnetic Survey (POGS) satellite measurements over the southern African region [ Kotzé and Barraclough , 1997] revealed strong correlations between both continental and oceanic magnetic anomalies and major tectonic features as identified using Magsat data [ Antoine and Moyes , 1992].…”

Section: Introductionmentioning

confidence: 99%

Modelling and analysis of Ørsted total field data over Southern Africa

Kotzé¹

2002

Geophysical Research Letters

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Ørsted total intensity data were analysed over the southern African region between 10° South and 45° South in latitude and between 10° East and 45° East in longitude, measured between May 1999 and October 1999. The satellite magnetic field measurements were selected corresponding to magnetic quiet conditions during local day and night times before carrying out an analysis of external fields by subdividing the data into Dst bins 5 nT wide, centred at multiples of 5 nT. The technique of Spherical Cap Harmonic Analysis (SCHA) was then applied to each of these Dst data bins to obtain external field coefficients, after removing the core field by means of the IGRF model. Combining all data sets after removing main ‐ and external fields, enabled the compilation of a total intensity crustal anomaly map over southern Africa at an average satellite altitude of 800 km. The Walvis Ridge and Agulhas anomalies are understood to represent thickened remanently magnetised ocean crust. The Agulhas anomaly however, represents the remnant scar of the process that led to the Gondwana fragmentation.

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“…Analyses of the sea floor magnetic anomalies suggest that the Maud Rise and Agulhas Plateau were conjugate features during the Cretaceous as rifting separated southern Africa from East Antarctica (e.g., Martin and Hartnady, 1986;Schandl et al, 1990;Antoine and Moyes, 1992;Fullerton et al, 1994). Initially, the Agulhas Plateau was considered foundered continental crust based on seafloor dredging results (Tucholke et al, 1981).…”

Section: Tectonic Implicationsmentioning

confidence: 99%

Crustal analysis of maud rise from combined satellite and near-surface magnetic survey data

et al. 2005

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We produced a crustal magnetization model for the Maud Rise in the southwest Indian Ocean off the coast of East Antarctica using magnetic observations from the Ørsted satellite and near-surface surveys complied by the Antarctic Digital Magnetic Anomaly Project (ADMAP). Joint inversion of the two anomaly fields suggests that the magnetic effects due to crustal thickness variations and remanence involving the normal polarity Cretaceous Quiet Zone (KQZ) dominate at satellite altitude (∼700 km). The crustal thickness effects were modeled in the Ørsted data using crustal thickness variations derived from satellite altitude gravity data. Modeling of the residual Ørsted and near-surface magnetic anomalies supports extending the KQZ eastwards to the Astrid Ridge. The remaining near-surface anomalies involve crustal features with relatively high frequency effects that are strongly attenuated at satellite altitudes. The crustal modeling can be extended by the satellite magnetic anomalies across the Indian Ocean Ridge for insight on the crustal properties of the conjugate Agulhas Plateau. The modeling supports the Jurassic reconstruction of Gondwana when the African Limpopo-Zambezi and East Antarctic Princess Astrid coasts were connected as part of a relatively demagnetized crustal block.

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The Agulhas Magsat anomaly: Implications for continental break-up of Gondwana

Cited by 6 publications

References 35 publications

The crustal role of the Agulhas Plateau, southwest Indian Ocean: evidence from seismic profiling

The crustal role of the Agulhas Plateau, southwest Indian Ocean: evidence from seismic profiling

Modelling and analysis of Ørsted total field data over Southern Africa

Crustal analysis of maud rise from combined satellite and near-surface magnetic survey data

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