Thermal Regime and Evolution of the Congo Basin as an Intracratonic Basin - Geology and Resource Potential of the Congo Basin - page 221

12

Thermal Regime and Evolution of the Congo
Basin as an Intracratonic Basin

Francis Lucazeau, John Armitage, and ´ tienne Kadima Kabongo

12.1 Introduction the subsidence during two episodes, the first one in the late

Paleozoic (350-300 Ma) and the second one in the late
Jurassic (155-145 Ma) (Fig. 12.2 ).
The subsidence of the Congo basin is to a large extent
poorly constrained, as the sedimentation is not continuous
and the stratigraphy is not always well established. As the
deepest parts of the basin have not been drilled, there is a
large uncertainty about the thickness and the age of the
oldest (non metamorphic) sedimentary sequences, which
can reach to depths of 5-6 km in the central part and locally
8-9 km in the Dekese and Gilson areas (Kadima Kabongo
et al. 2011b ). These sediments cover an Archean and Late-
to-Meso-proterozoic crystalline basement, and are probably
late Neo-Proterozoic in age (Kadima Kabongo et al. 2011a ).
Here, we discuss the past and the present-day thermal regime
of the CB, from published data mainly and unpublished oil
exploration reports. The stratigraphic record, the

The interior of the continents is generally considered as the
most stable part of the Earth surface that survive through a
succession of tectonic episodes. The heat-flow and the litho-
spheric thickness of these stable pieces of continents

( ) are usually much lower and thicker

than the younger neighbouring lithosphere (Artemieva
2006 ). Within these stable continents, cratonic basins can
subside progressively over longer periods of time than other
rifted continental basins, because the thicker lithosphere has
a longer thermal relaxation (Xie and Heller 2009 ) and exten-
sion proceeds at lower strain rates (Armitage and Allen
2010 ). The Congo Basin (CB) located in the central part of
central Africa is a classical example of an intracratonic basin
(Fig. 12.1 ). It is a sub-circular basin filled in its upper part by
Mesozoic and Cenozoic sediments, and surrounded by dif-
ferent Archean and Paleo-Proterozoic units. The origin of
this basin can be related to a late Proterozoic rift (Daly et al.
1992 ; Crosby et al. 2010 ; Kadima Kabongo et al. 2011b ) that
has been inferred from a lower crustal gravity anomaly when
the effect of sediment is removed (Fig. 12.1 ). From Early to
Late Proterozoic, several extensional basins (such as the
West Congolese Supergroup, Sembe-Ouesso basin, Sangha
Aulacogen, Mbuji-Mayi Supergroup, Lufilian Copperbelt
in Katanga and Northern Zambia basin) were formed on
the Congo Craton basement during the Rodinia breakup
(see Chap. 6 , this Topic). A recent stratigraphic study
(Linol et al. 2013c , d ) suggests a possible reactivation of

“ cratons ” or “ shields ”

”
subsidence and the maturation of the organic matter are used
to reconstruct the paleo-geotherms, but the Cretaceous and
Neogene kimberlites also provide constraints on the P-T
conditions at the time they took place. As some of the
subsidence variations are difficult to explain by the litho-
spheric thermal regime, we also introduce the possibility that
instabilities may have developed at the base of the continen-
tal lithosphere with subsequent dynamic subsidence or uplift
contributions to the topography.

“ tectonic

12.2 The Present Thermal Structure of the

Congo Basin

The thermal regime of continents is determined by the dis-
tribution of radiogenic heat sources (mostly concentrated in
the upper crust) and by the mantle heat-flow at the base of
the lithosphere. In stable continents, variations of heat-
production in the specific geological units can explain most
of the variations of the surface heat-flow: in the North
American Craton for instance, the mantle heat-flow is
uniformly between 11 and 15 mW m 2 , while larger