Series of major mountain-forming events in the Neoproterozoic
The Pan-African orogeny was a series of major
Neoproterozoicorogenic events which related to the formation of the
supercontinentsGondwana and
Pannotia about 600 million years ago.[1] This orogeny is also known as the Pan-Gondwanan or Saldanian Orogeny.[2] The Pan-African orogeny and the
Grenville orogeny are the largest known systems of orogenies on Earth.[3] The sum of the
continental crust formed in the Pan-African orogeny and the Grenville orogeny makes the Neoproterozoic the period of Earth's history that has produced most continental crust.[3]
History and terminology
The term Pan-African was coined by
Kennedy 1964 for a tectono-thermal event at about 500 Ma when a series of mobile belts in Africa formed between much older African
cratons. At the time, other terms were used for similar orogenic events on other continents, i.e. Brasiliano in South America; Adelaidean in Australia; and Beardmore in Antarctica.
Later, when
plate tectonics became generally accepted, the term Pan-African was extended to all of the supercontinent Gondwana. Because the formation of Gondwana encompassed several continents and extended from the Neoproterozoic to the early Palaeozoic, Pan-African could no longer be considered a single orogeny,[4] but rather an orogenic cycle that included the opening and closing of several large oceans and the collisions of several continental blocks. Furthermore, the Pan-African events are contemporaneous with the
Cadomian orogeny in Europe and the
Baikalian orogeny in Asia, and crust from these areas were probably part of Pannotia (i.e. Gondwana when it first formed) during the Precambrian.[5]
Attempts to correlate the African Pan-African belts with the South American
Brasiliano belts on the other side of the Atlantic has in many cases been problematic.[6]
The
Arabian-Nubian Shield, extending from Ethiopia to the southern Levant, it is associated with the opening of the
Red Sea.[7]
The
Mozambique Belt, extending from east
Antarctica through
East Africa up to the
Arabian-Nubian Shield, formed as a suture between plates during the Pan-African orogeny.[8] The Mozambique ocean began closing between Madagascar-India and the
Congo-
Tanzania craton between 700 and 580 million years ago, with closure between 600 and 500 million years ago.[9]
The
Zambezi Belt branches off the Mozambique Belt in northern Zimbabwe and extends into Zambia.[10]
The
Damara Belt is exposed in Namibia between the
Congo and
Kalahari cratons and continues southwards into the coastal Gariep and Saldania Belts and northwards into the Kaoko Belt. It is the result of closure of the
Adamastor and
Damara oceans and includes two horizons associated with a severe equator-ward glaciation explained by the
Snowball Earth hypothesis.[11]
The
Lufilian Arc is most likely a continuation of the Damara Belt in Namibia to which it connects in northern Botswana. It is a broad arc reaching as far north as the southern DRC and Zambia.[10]
The
Gariep and
Saldania belts run along the western and southern edge of the Kalahari Craton. Also the result of the closure of the Adamastor Ocean, the marine deposits, seamounts, and,
ophiolites they contain were accreted onto the Kalahari margin around 540 Ma. They include the granite at
Sea Point, Cape Town visited by
Charles Darwin in 1836.[12]
The
Kaoko Belt branches north-west from the Damara Belt into Angola. Also produced by the closure of the Adamastor Ocean, this belt includes a shear zone known as the 733-550 Ma-old Puros lineament in southern Angola. It contains 2030-1450 Ma-old, strongly deformed
basement rocks, probably derived from the Congo Craton, mixed with Late Archaean granitoid gneisses of unknown origin. No island arcs or ophiolote are known from the Kaoko Belt.[13]
The
West Congo Belt is the product of 999-912 Ma-old rifting along the western margin of the Congo Craton followed by the formation of a
foreland basin onto which the belt was deposited 900-570 Ma. In the western belt
allochthonous Palaeo- and Mesoproterozoic basement rocks override the foreland sequence. It includes glacial deposits similar to those in the Lufilian Arc and is conjugate to the
Araçuaí Belt in Brazil.[13]
The 3000 km-long
Trans–Saharan Belt runs north and east of the more than 2000 Ma-old
West African Craton bordering the
Tuareg and
Nigerian shields. It consists of a strongly deformed pre-Neoproterozoic basement and Neoproterozoic oceanic rocks containing ophiolite,
accretionary prisms, arc-related and high-pressure metamorphic rocks dated to 900-520 Ma.[14]
The Central African belts between the Congo and Nigerian shields consists of Neoproterozoic rocks and deformed granitoids interlayered with wedges of Palaeoproterozoic basement. The southern part is the product of a continental collision during which it was thrusted onto the Congo Craton. The central and northern parts are thrust-and-shear zones correlated with similar structures in Brazil. The belts in Central Africa continue east as the Oubanguide Belt with which they form the
Central African Shear Zone.[15]
The
Rokelide Belt passes along the western margin of the Archaean
Man Shield in the southern West African Craton. It was intensely deformed during the Pan-African orogeny with a peak reached around 560 Ma and can be an accretionary belt.[16]
^
abRino, S.; Kon, Y.; Sato, W.; Maruyama, S.; Santosh, M.; Zhao, D. (2008). "The Grenvillian and Pan-African orogens: World's largest orogenies through geologic time, and their implications on the origin of superplume". Gondwana Research. 14 (1–2): 51–72.
doi:
10.1016/j.gr.2008.01.001.
Kennedy, W. Q. (1964). The structural differentiation of Africa in the Pan-African (±500 my) tectonic episode. Annual Reports of the Institute of African Geology. Vol. 8. Leeds University. pp. 48–49.
Kröner, A.; Stern, R. J. (2004).
"Pan-African Orogeny". In Selley, R. C.; Cocks, R.; Plimer, I. (eds.). Encyclopedia of Geology. Vol. 1. Amsterdam: Elsevier. pp. 1–12.
ISBN9780126363807. Retrieved 31 December 2015.
Meert, J.G. (2003). "A synopsis of events related to the assembly of eastern Gondwana". Tectonophysics. 362 (1–4): 1–40.
doi:
10.1016/S0040-1951(02)00629-7.