The Tanzania Craton is an old and stable part of the continental
lithosphere
A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust (geology), crust and the portion of the upper mantle (geology), mantle that behaves elastically on time sca ...
in central
Tanzania
Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands and ...
.
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
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 ...
is surrounded by
Proterozoic
The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...
mobile belts of various ages and grades of metamorphism.
These include the Ubendian, Usagaran, Karagwe-Ankolean and Bukoban systems. 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 Mozambiq ...
lies to the east.
The craton divides the east and west branches of the
East African Rift
The East African Rift (EAR) or East African Rift System (EARS) is an active continental rift zone in East Africa. The EAR began developing around the onset of the Miocene, 22–25 million years ago. In the past it was considered to be part of a ...
.
The southern end of the
Gregory Rift Valley
The Gregory Rift is the eastern branch of the East African Rift fracture system. The rift is being caused by the separation of the Somali plate from the Nubian plate, driven by a thermal plume. Although the term is sometimes used in the narrow s ...
terminates against the craton. The volcanic area of this rift covers the surface interface between the Mozambique
orogenic fold belt and the Tanzania Craton. A
superplume
Large low-shear-velocity provinces, LLSVPs, also called LLVPs or superplumes, are characteristic structures of parts of the lowermost mantle (the region surrounding the outer core) of Earth. These provinces are characterized by slow shear wave vel ...
exists beneath the craton. An indirect effect of rift and plume associated volcanism in the Tanzania Craton is the high levels of soil nutrients in
Serengeti
The Serengeti ( ) ecosystem is a geographical region in Africa, spanning northern Tanzania. The protected area within the region includes approximately of land, including the Serengeti National Park and several game reserves. The Serengeti ...
provided by
volcanic ash
Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcano, volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used t ...
from
Ol Doinyo Lengai
Ol Doinyo Lengai (Oldoinyo Lengai), "Mountain of God" in the Maasai language, is an active volcano located in the Gregory Rift, south of Lake Natron within the Arusha Region of Tanzania, Africa. Part of the volcanic system of the East African Ri ...
.
Composition
The craton is a composite of several different terranes of Archaean metasediments. The Dodoman is the oldest, and others include the Nyanzian and Kavirondian. Some of the greenstone belts are more than 3 billion years old. They were intruded by granites and
migmatized in different events that date back to 2.9, 2.7, 2.4 and 1.85 billion years ago.
The
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 ...
mainly consists of
Archaean granitic
A granitoid is a generic term for a diverse category of coarse-grained igneous rocks that consist predominantly of quartz, plagioclase, and alkali feldspar. Granitoids range from plagioclase-rich tonalites to alkali-rich syenites and from quart ...
complexes, but also includes rocks from the Dodoma System in the central area, and belts of greenstone to the south and east of
Lake Victoria
Lake Victoria is one of the African Great Lakes. With a surface area of approximately , Lake Victoria is Africa's largest lake by area, the world's largest tropical lake, and the world's second-largest fresh water lake by surface area after ...
.
Gneisses, schists, quartzites, migmatites, amphibolites and granulite are also found.
There was widespread intrusion of
kimberlite
Kimberlite is an igneous rock and a rare variant of peridotite. It is most commonly known to be the main host matrix for diamonds. It is named after the town of Kimberley in South Africa, where the discovery of an diamond called the Star of ...
s in the
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
Period, mostly in the part of the craton that lies south of Lake Victoria.
This includes the
Mwadui
The Williamson Diamond Mine (also known as the Mwadui mine) is a diamond mine northeast of Shinyanga in Tanzania; it became well known as the first significant diamond mine outside of South Africa. The mine was established in 1940 by Dr. John Wi ...
kimberlite pipe in the center of Tanzania.
References
Sources
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{{Major African geological formations
Cratons
Geology of Tanzania
Plate tectonics