The Upper Mantle Seismic Velocity Structure of South-Central Africa and the Seismic Architecture of Precambrian Lithosphere Beneath the Congo Basin 1 Andriamiranto Raveloson, Andrew Nyblade, Stewart Fishwick, Azangi Mangongolo, and Sharad Master 1.1 Introduction The Congo Basin, covering approximately 10 % of the African continent, is one of the largest intracratonic basins on any continent, and its origin remains poorly understood (e.g. Daly et al. 1992; Downey and Gurnis 2009; Crosby et al. 2010; Kadima et al. 2011a,b). It contains up to 9 km of sedimentary rocks, which may date back to the Neoprotero- zoic, and its tectonic history is punctuated with major periods of compression during the late Neoproterozoic for- mation of Gondwana and Late Paleozoic subduction along the southern margin of Pangea. Stratigraphic information from drill holes and outcrops, seismic reflection profiles, and gravity and magnetic observations have led to a number of models for the formation of the basin, many of which begin with Neoproterozoic rifting (e.g. Daly et al. 1992; Kadima et al. 2011b) and call upon anomalous density either within or below the lithospheric mantle to sustain the long- lived (e.g. ca. 700 Ma), basin-wide subsidence (e.g. Crosby et al. 2010; Downey and Gurnis 2009). Seismic images of mantle structure beneath the basin from continental-scale tomography place first order constraints on explanations for how the basin may have formed (e.g. Fishwick 2010; Pasyanos 2010; Priestley et al. 2008; Pasyanos and Nyblade 2007; Ritsema and van Heijst 2000), and all but one show fast, thick (i.e. > 200 km) lithosphere beneath the interior of the basin. The thick shield lithosphere imaged by most of the tomography studies underpins many of the geodynamic models explaining how the basin formed. At lithospheric mantle depths (i.e. >~40 km) the model by Pasyanos and Nyblade (2007) shows slower velocities beneath the central and eastern portions of the basin, which they suggested could indicate the presence of thinner (mobile belt) lithosphere that may have formed during the Proterozoic amalgamation of the three major cratonic blocks of the greater Congo Shield that surround the basin, the Kasai Craton to the south, the Ntem Craton to the west and the Bomu Craton to the north- east (Fig. 1.1). The suggestion that Proterozoic mobile belt lithosphere lies beneath the northern part of the basin has also been made by Master (2004), De Wit et al. (2008), and Gubanov and Mooney (2009) using geological evidence. Daly et al. (1992) and De Wit et al. (2008) showed a NW–SE trending Neoproterozoic belt running through the centre of the Congo Basin. To the NW of the basin, this belt extends into in a region with poorly dated metasedimentary rocks of Paleoproterozoic (>2080 Ma) and Mesoproterozoic (1167 Ma –ca. 1.0 Ga) age (Vicat et al. 1997), which in turn are overthrust by the south-verging nappes of the Oubanguide Belt, dated at c. 571–620 Ma (Moloto-A- Kanguemba et al. 2008; Toteu et al. 1994; De Wit et al. 2008; see also de Wit and Linol, Chap. 2, this Book). Here we briefly review the basin’s geological setting and some of the geophysical studies relevant to understanding how the basin formed, and then present a new model of upper mantle structure for central and southern Africa A. Raveloson Department of Geosciences, Pennsylvania State University, University Park, PA 16802, USA e-mail: ahr12@psu.edu A. Nyblade (*) Department of Geosciences, Pennsylvania State University, University Park, PA 16802, USA School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa e-mail: andy@geosc.psu.edu S. Fishwick Department of Geology, University of Leicester, Leicester, LE1 7RH, UK e-mail: sf130@leicester.ac.uk A. Mangongolo Council for Geosciences, Private Bag x112, Pretoria, 0001, South Africa e-mail: amangongolo@geoscience.org.za S. Master School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa e-mail: Sharad.Master@wits.ac.za M.J. de Wit et al. (eds.), Geology and Resource Potential of the Congo Basin, Regional Geology Reviews, DOI 10.1007/978-3-642-29482-2_1, # Springer-Verlag Berlin Heidelberg 2015 3