Geochronological and isotopic constraints on the Mesoproterozoic Namaqua–Natal Belt: evidence from deep borehole intersections in South Africa

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

“…Their data indicate that the mid-and lower crust beneath the Cape-/Karoo Basin have similar seismic properties up to the continental boundary, thereby implying the nature of the crystalline basement beneath the CFB, and beyond, is likely Mesoproterozoic NNMB. In addition, magnetic crustal anomalies south of the BMA (Du Plessis and Thomas, 1991), borehole data (Eglington and Armstrong, 2003) and inherited ~2 Ga zircons from the ~550 Ma Cape Granite Suite plutons within the Cape Fold Belt (unpublished data, Eglington, 2006), are all consistent with an NNMB that extends much farther south, well beyond the BMA. Backeberg et al (this volume) suggest that Mesoproterozoic crust, interpreted by them to be Bushmanland gneiss equivalents, is required to explain the crustal contamination of dolerite dykes intruding the Cape Peninsula.…”

“…In order to determine what the mid-crust imaged in IyA-200501 may represent, we combined our observations in the seismic reflection data with an earlier interpretation , using far-field boreholes QU-1/65 and KC-1/70 (Figure 1, Eglington and Armstrong, 2003;Eglington, 2006), regional field observations from geological mapping (e.g. Joubert, 1971;1986a, b;Albat, 1984;Macey 2000;2001;Macey et al, 2011), the high resolution magnetotelluric model (Weckmann et al, 2007) and the tomography model derived from the wide-angle refraction data 2008), partly illustrated in Figures 7b-d.…”

“…Hartnady et al, 1985;Joubert, 1986a, b;Cornell et al, 1992;2006;Gibson et al, 1996;Thomas et al, 1994;1996;Basson and Watkeys, 2003;Colliston and Schoch, 2002;Eglington and Armstrong, 2003;Raith et al, 2003;Eglington, 2006;Bailie et al, 2007;Cornell and Pettersson, 2007 and references therein).…”

Comparison of electrical conductivity structures and 2D magnetic modelling along two profiles crossing the Beattie Magnetic Anomaly, South Africa

“…Both regions were affected by high-grade metamorphism and deformation between 1.0 to 1.1 Ga (Jacobs et al, 1993). However, there are distinct geological and isotopic differences (crustal model ages and geochronology) between the Natal and the Namaqualand, and a number of separate terranes have now been identified (Jacobs et al, 1993;Thomas et al, 1994;Eglington and Armstrong, 2003). The Namaqualand metamorphic rocks were derived from older basement (1.3 to 1.8 Ga), whereas the Natal rocks comprise of a mosaic of eastwest elongated volcanic/plutonic arc terranes dating around 1.1 to 1.4 Ga (Thomas et al, 1994;Eglington and Armstrong, 2003).…”

“…Both lines cross the Phanerozoic Karoo Basin that in turn overlies the Mesoproterozoic granitoid basement of the Natal Namaqua Mobile Belt. The Prince Albert line (MT1) is located above the Namaqua sector of the NNMB and the Jansenville profile (MT4) runs across the Natal sector [Eglington and Armstrong, 2003;Thomas et al, 1992]. The 2D magnetotelluric inversion results of profile MT1 reveal an electrical image of the NNMB crust with some previously unknown structures.…”