The East African Orogeny (EAO) is the main stage in the
Neoproterozoic
The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago.
It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is ...
assembly
Assembly may refer to:
Organisations and meetings
* Deliberative assembly, a gathering of members who use parliamentary procedure for making decisions
* General assembly, an official meeting of the members of an organization or of their representa ...
of East and West
Gondwana
Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...
(Australia–India–Antarctica and Africa–South America) along the
Mozambique Belt
The Mozambique Belt is a band in the earth's crust that extends from East Antarctica through East Africa up to the Arabian-Nubian Shield. It formed as a suture between plates during the Pan-African orogeny, when Gondwana was formed.
The Mozambi ...
.
Gondwana assembly
The notion that Gondwana was assembled during the Late Precambrian from two older fragments along the Pan-African Mozambique Belt was first proposed in the early 1980s. A decade later this continental collision was named the East African Orogeny, but it was also realised that this was not the simple bringing together of two halves. Rather, it was the piecemeal assembly of several much smaller
craton
A craton (, , or ; from grc-gre, κράτος "strength") is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging and ...
ic elements that once formed an earlier supercontinent (today known as
Rodinia
Rodinia (from the Russian родина, ''rodina'', meaning "motherland, birthplace") was a Mesoproterozoic and Neoproterozoic supercontinent that assembled 1.26–0.90 billion years ago and broke up 750–633 million years ago.
were probably ...
), a process that eventually culminated in the relatively short-lived Gondwanan supercontinent.
Two partly incomparable scenarios have been proposed for this assembly. In one model, the EAO evolved from an
accretionary orogeny involving the amalgamation of arcs and evolved into a collisional orogeny when the Neoproterozoic continent
Azania
Azania ( grc, Ἀζανία) is a name that has been applied to various parts of southeastern tropical Africa. In the Roman period and perhaps earlier, the toponym referred to a portion of the Southeast Africa coast extending from northern Kenya ...
collided with the Congo-Tanzania-Bangweulu Block at . In another model, the assembly of East Gondwana was a multiphase process which included two main periods of orogenesis: the older EAO ( ) and the younger
Kuunga Orogeny
The Kuunga orogeny (from Swahili, "to unite") was an orogeny that occurred in South-east Africa during the Ediacaran and Cambrian. Composed of three separate orogenic belts (Damara, Zambesi, and Lurio) that are slightly younger than the East Afr ...
( ). In the former scenario the Kuunga Orogeny of the latter scenario are two coeval events: the collisions between India and Australia-East Antarctica and Azania and India. Furthermore, the two orogens of the latter scenario intersect in Madagascar, the proposed location of the Azania-India collision, and this part of the Kuunga Orogeny should be renamed the
Malagasy Orogeny.
Erosion and Cambrian explosion
The East African orogeny resulted in the formation of an enormous mountain chain, known as the Transgondwanan Supermountain, which was more than -long and -wide. The sedimentary deposition from this mountain chain, known as the Gondwana Super-fan, exceeded or the equivalent to covering the United States with of sediment, lasted for 260 million years and coincided with the
Cambrian explosion
The Cambrian explosion, Cambrian radiation, Cambrian diversification, or the Biological Big Bang refers to an interval of time approximately in the Cambrian Period when practically all major animal phyla started appearing in the fossil recor ...
, the sudden radiation of animal (
Metazoan
Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motility, able to move, ca ...
) life . These unprecedented sedimentary depositions probably made the diversification of early animal life possible.
The orogen was eroded to such extent that by the
Ordovician
The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...
epoch it had been leveled to a
planation surface
In geology and geomorphology a planation surface is a large-scale surface that is almost flat with the possible exception of some residual hills. The processes that form planation surfaces are labelled collectively planation and are exogenic (chi ...
in Ethiopia.
Cenozoic reopening
The Cenozoic
East African Rift System
East or Orient is one of the four cardinal directions or points of the compass. It is the opposite direction from west and is the direction from which the Sun rises on the Earth.
Etymology
As in other languages, the word is formed from the f ...
mostly evolved along the complex pattern of Proterozoic prerift systems in eastern Africa. It passes through the Mozambique Belt east of the
Tanzania Craton
The Tanzania Craton is an old and stable part of the continental lithosphere in central Tanzania.
Some of the rocks are over 3 billion years old.
Setting
The Tanzania Craton forms the highest part of the East African Plateau.
The craton is surr ...
.
References
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{{Major African geological formations
Orogenies of Africa
Neoproterozoic Africa
Neoproterozoic orogenies