Density structure of the cratonic mantle in southern Africa: 1. Implications for dynamic topography Irina M. Artemieva a , Lev P. Vinnik a,b a Geology Section, IGN, University of Copenhagen, Denmark b Institute of Physics of the Earth, Moscow, Russia abstract article info Article history: Received 26 July 2015 Received in revised form 21 February 2016 Accepted 3 March 2016 Available online 11 March 2016 Handling Editor: M. Santosh The origin of high topography in southern Africa is enigmatic. By comparing topography in different cratons, we demonstrate that in southern Africa both the Archean and Proterozoic blocks have surface elevation 500–700 m higher than in any other craton worldwide, except for the Tanzanian Craton. An unusually high topography may be caused by a low density (high depletion) of the cratonic lithospheric mantle and/or by the dynamic support of the mantle with origin below the depth of isostatic compensation (assumed here to be at the lithosphere base). We use free-board constraints to examine the relative contributions of the both factors to surface topography in the cratons of southern Africa. Our analysis takes advantage of the SASE seismic experiment which provided high resolution regional models of the crustal thickness. We calculate the model of density structure of the lithospheric mantle in southern Africa and show that it has an overall agreement with xenolith-based data for lithospheric terranes of different ages. Density of lithospheric mantle has significant short-wavelength variations in all tectonic blocks of southern Africa and has typical SPT values of ca. 3.37–3.41 g/cm 3 in the Cape Fold and Namaqua–Natal fold belts, ca. 3.34–3.35 g/cm 3 in the Proterozoic Okwa block and the Bushveld Intrusion Complex, ca. 3.34–3.37 g/cm 3 in the Limpopo Belt, and ca. 3.32–3.33 g/cm 3 in the Kaapvaal and southern Zimbabwe cratons. The results indicate that 0.5–1.0 km of surface topography, with the most likely value of ca. 0.5 km, cannot be explained by the lithosphere structure within the petrologically permitted range of mantle densities and requires the dynamic (or static) contribution from the sublithospheric mantle. Given a low amplitude of regional free air gravity anomalies (ca. +20 mGal on average), we propose that mantle residual (dynamic) topography may be associated with the low-density region below the depth of isostatic compensation. A possible candidate is the low velocity layer between the lithospheric base and the mantle transition zone, where a temperature anomaly of 100–200 °C in a ca. 100–150 km thick layer may explain the observed reduction in Vs velocity and may produce ca. 0.5–1.0 km to the regional topographic uplift. © 2016 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. Keywords: Cratonic lithosphere Mantle density Dynamic topography Upper mantle temperature Kaapvaal and Zimbabwe cratons 1. Introduction The cratons of the southern Africa have an unusually high topography, 1.0–1.5 km on average, with an increase to 1.5–2.0 km in the eastern Kaapvaal and up to 2.5 km in Lesotho, and a depression down to 0.6– 0.9 km in the Limpopo Belt (Fig. 1a). The topography of other cratons, including even the Archean parts of the Sino-Korean Craton which has been significantly affected by the India–Eurasia collision, is significantly lower, only 0.2–0.6 km (Fig. 2a, b). The only other high standing craton is the Tanzanian Craton, where the high topography may be caused by active mantle dynamics related to the Cenozoic rifting in East Africa. In southern Africa and the Tanzanian region, the high topography is a regional phenomenon that is observed both in the Archean and Proterozoic blocks, which have topography 500–700 m higher than any other craton worldwide (Table 1). High surface elevation may result either from low density lithosphere or from the contribution (e.g. dynamic support) of the mantle below the LAB, or from the combination of both. The first factor is expected to play an important role in all Precambrian cratons, where the lithospheric mantle is depleted and has low-density (e.g. Gaul et al., 2000). In particular, petrological studies demonstrate that the lithospheric mantle beneath the Archean Kalahari Craton (which includes the Archean Kaapvaal and Zimbabwe cratons, melded along the Archean collisional Limpopo Belt) is depleted and has low-density (Boyd and Mertzman, 1987; O'Reilly and Griffin, 2006). Negative Bouguer anomalies (Fig. 3c) also indicate that low density material in the cratonic lithosphere contributes to high regional topography in southern Africa. Nonetheless, given a large number of craton-scale magmatic events in southern Africa (Fig. 1b), one may expect that the composition of the lithospheric mantle in the region could have been significantly modified through melt-metasomatism (Simon et al., 2007; Pearson and Wittig, 2008; Artemieva, 2009) with the Gondwana Research 39 (2016) 204–216 E-mail addresses: irina@ign.ku.dk (I.M. Artemieva), vinnik@ifz.ru (L.P. Vinnik). http://dx.doi.org/10.1016/j.gr.2016.03.002 1342-937X/© 2016 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Gondwana Research journal homepage: www.elsevier.com/locate/gr