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Structure of the Transkei Basin and Natal Valley, Southwest Indian Ocean, from seismic reflection and potential field data
Authors:Margaret Reznikov  Zvi Ben-Avraham  Chris Hartnady  Tina M Niemi
Institution:aGeophysical Institute of Israel, Holon, Israel;bDepartment of Geological Sciences, University of Cape Town, Rondebosch, South Africa;cDepartment of Geophysics and Planetary Sciences, Tel Aviv University, Tel Aviv, Israel;dHydrotectonics and Hydroseismology Unit (H2U), Umvoto Africa, Muizenberg, South Africa;eDepartment of Geosciences, University of Missouri-Kansas City, Kansas City, MO, USA
Abstract:Marine geophysical data from the southern Natal Valley and northern Transkei Basin, offshore southeast Africa, were used to study the structure of the crust and sedimentary cover in the area. The data includes seismic reflection, gravity and magnetics and provides information on the acoustic basement geometry (where available), features of the sedimentary cover and the basin's development. Previously mapped Mesozoic magnetic anomalies over a part of the basin are now recognized over wider areas of the basin. The ability to extend the correlation to the southeast within the Natal Valley further confirms an oceanic origin for this region and provides an opportunity to amplify the existing plate boundary reconstructions.The stratigraphic structure of the southern Natal Valley and the northern Transkei Basin reflects processes of the ocean crust formation and subsequent evolution. The highly variable relief of the acoustic basement may relate to the crust formation in the immediate vicinity of the continental transform margin. Renewed submarine seismicity and neotectonic activity in the area is probably related to the diffuse boundary between the Nubia and Somalia plates.2.5-D crustal models show that a 1.7–3.2-km-thick sediment sequence overlies a 6.3±1.2-km-thick normal oceanic crust in the deep southern Natal Valley and Transkei Basin. The oceanic crust in the study area is heterogeneous, made up of blocks of laterally varying remanent magnetization (0.5–3.5 A/m) and density (2850–2900 kg/m3). Strong modifications of accretionary processes near ridge/fracture zone intersections may be a reason of such heterogeneity.
Keywords:Oceanic crust  Acoustic basement  Mesozoic magnetic anomalies  Deformations
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