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

Abstract

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.

New plate kinematic model and tectono‐stratigraphic history of the East African and West Madagascan Margins

“…Both interpretations agree broadly with our plate kinematic model, in which EA-ANT breakup occurs around 160 Ma, later than at the other margin segments. Interpretations of the MCPs as underlain by stretched continental crust or transitional crust (e.g., Leinweber & Jokat, 2011) are consistent with the notion of a longer lasting period of continental stretching before breakup.…”

Evidence of Middle Jurassic magmatism within the Seychelles microcontinent: Implications for the breakup of Gondwana

“…By ~130 Ma, east Gondwana drifted from western Gondwana and sea floor spreading ceased in the north Somali and Owen basins and slowed in the west Somali basin due to convergence between western India and Somalia/Arabia [ Gaina et al ., ]. South of Madagascar, the Weddell Sea, and Mozambique proto‐Ocean opened via two stages, the first beginning during the Early Jurassic (i.e., ~180 Ma) until Late Jurassic (i.e., ~160 Ma), as Antarctica rotated anticlockwise with respect to Africa, followed by the second stage during the Late Jurassic (i.e., ~150 Ma) in which Antarctica moved southward and formed the Mozambique basin and Riiser‐Larsen Sea (Figure b) [ Jokat et al ., ; Konig and Jokat , , ; Leinweber and Jokat , , ].…”

Reassembling Gondwana: A new high quality constraint from vibroseis exploration of the sub‐ice shelf geology of the East Antarctic continental margin

“…This supports the concept of the magnetic anomaly representing the edge effect of a vanishing magnetization contrast between the weakly magnetized continental crust and an overlying basalt wedge of with higher magnetization. Similar coinciding transitions from low to high amplitude magnetic anomalies and volcanic wedge onsets are observed along the Lebombo monocline [ Leinweber and Jokat , ], continental margin segments off Argentina [ Hinz et al ., ], Namibia [ Bauer et al ., ], and Norway [ Olesen et al ., ]. The refraction results of Hübscher et al .…”

“…Thinning of the crust at the Lebombo and Mwenetzi‐Save monoclines toward the east and south is indicated by the gravity data [ Darracott , ; Gwavava et al ., ; Watts , ]. A more comprehensive study by Leinweber and Jokat [] suggests the Mozambique Coastal plain and the northern Natal Valley are most likely floored by thickened oceanic crust. The Mozambique Ridge has geophysical characteristics [ König and Jokat , ] of a volcanic feature and oceanic basalts have been recovered at DSDP Site 249 and in dredges at four locations over a distance of about 500 km along the southern part [ Thompson et al ., ].…”