Precambrian Basement of the Congo Basin and Its Flanking Terrains - Geology and Resource Potential of the Congo Basin - page 18

2

Precambrian Basement of the Congo Basin
and Its Flanking Terrains

Maarten J. de Wit and Bastien Linol

2.1 Introduction 2013 , 2014 ); in Tanzania (e.g. Boniface et al. 2012 ; Kabette

et al. 2012a , b ;Kasanzu 2014 ); Mozambique (e.g. Bingen
et al. 2009 ); in northern Zambia (e.g. Master et al. 2005 ;de
Waele et al. 2006 ;Lawleyetal. 2013 , 2014 ) and in central-
northeast Angola (e.g. Carvalho et al. 2000 ; Delor et al. 2006 ;
Jelsma et al. 2011 , 2012 ), amongst others.
Here we briefly review and summarize some of these
results to provide a framework of the Precambrian basement
underlying and flanking the Congo Basin (CB), in particular
because this constitutes the upper lithosphere foundation to
this very large (ca. 1.8 million km 2 ) and poorly understood
Phanerozoic sedimentary basin that is the focus of this topic.

Africa is the world s second largest continent, with just over

30 million km 2 , almost entirely underlain by Precambrian
crystalline basement. The geology of this basement, parti-
cularly in central Africa, however, is generally not well-
described and is poorly constrained by geochronology
because of an extensive cover of Phanerozoic rocks, recent
sediments, laterites and vegetation; and because of an
extended period of socio-political instabilities that continues
to make it difficult to explore and study this region.
Until 30 years ago, the Precambrian history and geochrono-
logy of central Africa

'

s basement was based primarily on geo-
logic and low resolution Rb/Sr analyses essentially carried out
and synthesized by Louis Cahen and Norman Snelling, and
their collaborators, in their iconoclastic topic

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2.2 Cratons and Shields in Africa

' The Geochro-

nology and Evolution of Africa (Cahen et al. 1984 ). Since

then there has been a slow exponential increase in more
precise U-Pb dates on zircons and hence improved under-
standing of Africa

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The African continent can be subdivided into four major
Precambrian Shields that amalgamated along Neoprotero-
zoic orogens (Fig 2.1 , inset B), and each of which in turn
comprises assemblages of Archean cratons further embed-
ded within Meso- and Paleo-Proterozoic mobile belts. How-
ever, in the literature, the terms Craton and Shield are not
always clearly defined. For example, geologic terrains in
central Africa are often used indiscriminately and sometimes
interchangeable: Congo Craton, Congo Shield and Central
African Shield or Craton; Kasai Craton or Shield and
Lunda Shield; Angola-Kasai Craton, Angola Craton or
Shield, and NE Angolan Shield, or Cuango Shield or Craton,
and southern Congo Craton; Greater Congo Shield, etc.
To clarify our nomenclature here, we follow the definitions
of Stankiewicz and de Wit ( 2013 ), and specifically refer to
'

s crustal evolution, particularly in the
regions of central Africa: in Gabon, Cameroon, Central Afri-
can Republic (CAR) and Chad (e.g. Feybesse et al. 1998 ;
Toteu et al. 2006 , 2014 ; Nkoumbou et al. 2013 ; de Wit et al.
2014 , under review); in Uganda, Democratic Republic of
Congo (DRC), Rwanda and Burundi (e.g. Link et al. 2010 ;
Tack et al. 2010 ; Fernandez-Alonso et al. 2012 ; Lawley et al.

'

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cratons as Archean blocks (e.g., stabilized > 2.5 Ga), and

to as stabilized, post-Archean continental domains

that formed and/or amalgamated at specified times during
the Proterozoic-Phanerozoic, and within which Archean
cratons (or deformed Archean blocks) are embedded.
We refer collectively then to a number of relatively small
Archean cratons that underlie, or in part underlie, the CB

' shields '