Regional Geology of Africa
(Lecture Note)
2 Units
Prerequisite: GEM 204
Lecturer: Mr. Adeyemi M.O
Course Outline
• Precambrian Setting of Africa
• Geological history and mineral deposits in Africa
• Proterozoic cratonic basins and mobile belts
• Geology of Niger Delta
• Phanerozoic magmatism
• Quaternary in Africa
Definitions
• Orogeny also called tectogenesis refers to the process of creation of
a mountain belt by TECTONIC activity generally by the collision of
Plates orMicroplates . It is characterized by regional
continental
metamorphism, igneous activity and vertical movements.
• Anorogenic : refers to a feature, forming during tectonic quiescence
between orogenic periods that is, lacking in tectonic disturbance.
• Archean [GEOL] A term, meaning ancient, which has been applied to
the oldest rocks
Definitions
•Craton refers to the stable interior of a continental Plate, unaffected by Plate
margin activity since Precambrian.
• Shield refers to a large area of exposed Precambrian crystalline igneous and
high-grade metamorphic rocks that form tectonically stable areas.
• In all cases, the age of these rocks is greater than 570 million years and
sometimes dates back 2 to 3.5 billion years.
• Shields have been slightly affected by tectonic events following the end of
the Precambrian, and are relatively flat regions where mountain building,
faulting, and other tectonic processes are greatly diminished compared with
the activity that occurs at the margins of the shields and the boundaries
between tectonic plates.
Physical Setting of Africa
• Africa has the third largest tectonic plate (~60 million km2)
• with approximately half of it covered by land with an area of
30.3 million km², occupying about one-fifth of the land surface
of the Earth.
Physical Setting of Africa
• This plate comprises several old cratonic units and accreted
younger crust, representing a period of more than 2.5 billion
years of continental and oceanic crust growth.
• The African continent preserves evidence for major crust-
forming events dating back to 3.8 Ga.
• These events represent cycles of continental break-up and
growth, which have been recognized worldwide and can be
largely explained in a plate-tectonic context, within the confines
of partly overlapping Wilson cycles.
• Africa was initially part of Gondwana (550 Ma) and Pangea (320 Ma)
• It is now surrounded almost entirely by spreading centers, the African plate
moved relatively slowly for the last 150 Ma.
• However, its continental interior experienced many changes throughout this
time including rifting and variations in sedimentary basin subsidence, most
of them in regions situated thousands of kilometers away from plate
boundaries.
• The African plate was also partly underlain by mantle with above the
average temperature either induced by a series of hotspots or a superswell,
or both that contributed to episodic volcanism (including several Large
Igneous Provinces—LIPS), basin-swell topography, and consequent sediment
deposition, erosion, and structural deformation (e.g., Bumby and Guiraud,
2005).
Main orogenic events in Africa
Orogeny Age (GA) Main Outcome (Events)
Paleoarchean 3.55-3.15 Formation of early Archean cratonic cores (Kaapvaal, Tokwe)
Mesoarchean 3.15-2.75 Accretionary growth of Kaapval, Zimbabwe, Congo, Tanzania cratons and
the Man and Reguibat shields; merging Kaapvaal and Zimbabwe cratons as
South African Cratons
Eburnian 2.2-1.8 Growth of West African Craton along active accretionary margin (Birrimian).
Merging of Congo and Tanzanian cratons in the Central Africa Craton.
Passive margin development and orogenesis along the W margin of Central
and Southern Africa craton
Kibarian 1.4-0.85 Merging of Southern and Central African cratons as part of Rodinia
supercontinent
Pan-African 0.85-0.5 Merging of all cratonic fragments to form the Gondwana supercontinent to
which Africa is central
Hercynian 0.45-0.25 Limited collision and tectonic activity along NW and S margins of the African
plate
Alpine 0.12-0 Subduction of the African plate under Eurasia and formation of the Atlas
mountains
