The Upper Mantle Seismic Velocity Structure of South-Central Africa and the Seismic Architecture of Precambrian Lithosphere Beneath the Congo Basin - Geology and Resource Potential of the Congo Basin - page 2

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The Upper Mantle Seismic Velocity Structure
of South-Central Africa and the Seismic Architecture
of Precambrian Lithosphere Beneath the Congo Basin

Andriamiranto Raveloson, Andrew Nyblade, Stewart Fishwick,
Azangi Mangongolo, and Sharad Master

1.1 Introduction 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.

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

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 Topic).
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

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