Seismic refraction measurements in the southwestern Indian Ocean

Green, R. W. E.; Hales, A. L.

doi:10.1029/jz071i006p01637

Cited by 34 publications

(6 citation statements)

References 9 publications

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“…Seismic refraction data acquired prior to this SETARAP project include a number of irregularly spaced profiles over the northeast, northwest and central Agulhas Plateau (Green & Hales 1966; Ludwig et al . 1968; Hales & Nation 1973; Barrett 1977; Tucholke et al .…”

Section: Discussion Of Geophysical Evidencementioning

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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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: Discussion Of Geophysical Evidencementioning

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 Natal Valley is usually divided into a southern and a northern part, whereby the transition between both parts is located around 29°S. As result of seismic and gravimetric studies in the 1970s–80s [ Green and Hales , 1966; Ludwig et al , 1968; Hales and Nation , 1973; Dingle and Scrutton , 1974; Scrutton , 1976; Chetty and Green , 1977], there is no debate about the oceanic nature of the Transkei Basin and the adjacent Southern Natal Valley (SNV). There, Goodlad et al [1982] and Martin et al [1982] identified the Mesozoic spreading anomaly sequence from M0 to M10 with indications for even older anomalies M11 and M12.…”

Section: Introductionmentioning

confidence: 99%

Is there continental crust underneath the northern Natal Valley and the Mozambique Coastal Plains?

Leinweber

Jokat

2011

Geophys. Res. Lett.

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To draw conclusions about the crustal nature and history of the Natal Valley and the Mozambique Ridge, systematic potential field data were obtained during the AISTEK III cruise with R/V Pelagia in 2009. This paper presents and interprets the results of that expedition. The new magnetic data reveal a pattern of linear magnetic spreading anomalies, NW‐SE trending in the southwestern part of the Mozambique Ridge and E‐W trending on its central part. The Ariel Graben, which separates the Mozambique Ridge from the Northern Natal Valley, is represented by a pronounced negative anomaly in the magnetic‐ as well as the free‐air gravity field. The Northern Natal Valley bears a complicated pattern of anomalies with mainly SW‐NE trends. In the Northern Natal Valley, no indications for a continent‐ocean‐boundary between continental crust in the north and oceanic crust in the south exist, either in the free‐air gravity or in the magnetic field. The magnetic wavelengths of the Mozambique Coastal Plains are similar to those of the Northern Natal Valley and the Mozambique Ridge. Particularly in the gravity data, the Mozambique coastal plains, the Northern Natal Valley and the Mozambique Ridge appear as one continuous geological province. We interpret the region from the Mateke‐Sabi monocline in the north to the southwestern tip of the Mozambique Ridge as mainly being floored by thickened oceanic crust.

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“…2 km s-') and the main lower crustal layer ( Vp N 7-2kmsd'). The mean velocity of the sedimentary layer has been calculated by averaging all the observed velocities in the constituent layers (Green & Hales 1966;Ludwig et al 1968;Spence 1970;Leyden, Ewing and Simpson 1971) weighted in proportion to the thicknesses of these layers. 2.72 km s-l was obtained as the mean.…”

Section: Seismic Refractionmentioning

confidence: 99%

Crustal Structure at the Continental Margin South of South Africa

Scrutton

1976

Geophys J Int

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Summary Four gravity profiles over the continental margin south of South Africa are interpreted in the light of existing seismic, gravity and magnetic results. There is a marked difference in shallow and deep crustal structure between the rifted segment of margin facing the Atlantic Ocean and the margin offset facing the Indian Ocean. Both margin segments have a mass excess beneath the continental rise and a mass deficit beneath the outer continental shelf and continental slope, but this distribution is much more pronounced at the margin offset. It can be explained by a rapid transition from continental to oceanic crust which, in the Indian Ocean, probably results from the mode of formation of the margin (strike slip faulting). In the Atlantic Ocean the cause of the rapid transition is less obvious. The shallow structure at the continent‐ocean boundary changes around the margin. At the rifted segment, the sedimentary sequence of the continental rise north of 36° S gives way southwards to a basement high thought to be of volcanic origin. At the margin offset the Agulhas fracture zone appears to contain slivers of both oceanic and continental crust. The latter is in the form of a marginal fracture ridge. Beneath the continental shelf a high density lower crust may compensate for the low density sedimentary rocks in the Outeniqua Basin.

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Seismic refraction measurements in the southwestern Indian Ocean

Cited by 34 publications

References 9 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

Is there continental crust underneath the northern Natal Valley and the Mozambique Coastal Plains?

Crustal Structure at the Continental Margin South of South Africa

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