The Kaapvaal Craton (centred on

Limpopo Limpopo is the northernmost province of South Africa. It is named after the Limpopo River, which forms the province's western and northern borders. The capital and largest city in the province is Polokwane, while the provincial legislature is ...

Province in

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...

), along with the

Pilbara Craton The Pilbara Craton is an old and stable part of the continental lithosphere located in the Pilbara region of Western Australia. The Pilbara Craton is one of only two pristine Archaean 3.6–2.7 Ga (billion years ago) crusts identified on the ...

of Western Australia, are the only remaining areas of pristine 3.6–2.5 Ga (billion years ago) crust on Earth. Similarities of rock records from both these

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 ...

s, especially of the overlying late

Archean The Archean Eon ( , also spelled Archaean or Archæan) is the second of four geologic eons of Earth's history, representing the time from . The Archean was preceded by the Hadean Eon and followed by the Proterozoic. The Earth Earth ...

sequences, suggest that they were once part of the

Vaalbara Vaalbara was an Archean supercontinent consisting of the Kaapvaal Craton (now in eastern South Africa) and the Pilbara Craton (now in north-western Western Australia). E. S. Cheney derived the name from the last four letters of each craton's name ...

supercontinent In geology, a supercontinent is the assembly of most or all of Earth's continent, continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", ...

Description

The Kaapvaal Craton covers an area of approximately and is joined to the

Zimbabwe Craton The Zimbabwe Craton is an area in Southern Africa of ancient continental crust, being a part of the ancient continent of Western Gondwana, with rocks dating back to the early Archean Eon, possibly as early as 3.46 billion years ago ( Ga.). The cra ...

to the north by the

Limpopo Belt The Limpopo Belt is located in South Africa and Zimbabwe, runs E-NE, and joins the Kaapvaal Craton to the south with the Zimbabwe Craton to the north. The belt is of high-grade metamorphic rocks that have undergone a long cycle of metamorphism and ...

. To the south and west, the Kaapvaal Craton is flanked 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 ...

orogen An orogenic belt, or orogen, is a zone of Earth's crust affected by orogeny. An orogenic belt develops when a continental plate crumples and is Tectonic uplift, uplifted to form one or more mountain ranges; this involves a series of geological pr ...

s, and to the east by the Lebombo

monocline A monocline (or, rarely, a monoform) is a step-like fold in rock strata consisting of a zone of steeper dip within an otherwise horizontal or gently-dipping sequence. Formation Monoclines may be formed in several different ways (see diagram) * ...

that contains

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main The three types of rocks, rock types, the others being Sedimentary rock, sedimentary and metamorphic rock, metamorphic. Igneous rock ...

s associated with the break-up of

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 ...

. The Kaapvaal Craton formed and stabilised between 3.7 and 2.6 Ga by the emplacement of major

granitoid 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 quartz ...

batholith A batholith () is a large mass of intrusive igneous rock (also called plutonic rock), larger than in area, that forms from cooled magma deep in Earth's crust. Batholiths are almost always made mostly of felsic or intermediate rock types, such ...

s that thickened and stabilised the continental crust during the early stages of an arc-related

magmatism Magmatism is the emplacement of magma within and at the surface of the outer layers of a terrestrial planet, which solidifies as igneous rocks. It does so through magmatic activity or igneous activity, the production, intrusion and extrusion of ...

and

sedimentation Sedimentation is the deposition of sediments. It takes place when particles in suspension settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to the ...

cycle. The craton is a mixture of early Archean (3.0–3.5 Ga) granite greenstone

terrane In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust fragment formed on a tectonic plate (or broken off from it) and accreted or " sutured" to crust lying on another plate. The crustal block or fragment preserves its own ...

s and older tonalitic

gneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures an ...

es (ca. 3.6–3.7 Ga), intruded by a variety of granitic

pluton In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

s (3.3–3.0 Ga). Subsequent evolution of the Kaapvaal Craton (3.0–2.7 Ga) is thought to be associated with continent–arc collision that caused an overlaying succession of basins filled with thick sequences of both

volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates a ...

and sedimentary rocks. This was then followed by episodic extension and

rift In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-grabe ...

ing when the Gaborone–Kanye and Ventersdorp sequences were developed. Early Archean crust is well exposed only on the east side of the craton and comprises a collage of subdomains and crustal blocks characterised by distinctive igneous rocks and deformations. Late Archean

metamorphism Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of chem ...

joined the Southern Marginal Zone of the Kaapvaal Craton to the Northern Marginal Zone of the

approximately 2.8–2.5 Ga by the wide

orogenic Orogeny is a mountain building process. An orogeny is an event that takes place at a convergent boundary, convergent plate margin when plate motion compresses the margin. An ''orogenic belt'' or ''orogen'' develops as the compressed plate crumpl ...

Limpopo Belt. The belt is an east-northeast trending zone of

granulite Granulites are a class of high-grade metamorphic rocks of the granulite facies that have experienced high-temperature and moderate-pressure metamorphism. They are medium to coarse–grained and mainly composed of feldspars sometimes associated w ...

facies In geology, a facies ( , ; same pronunciation and spelling in the plural) is a body of rock with specified characteristics, which can be any observable attribute of rocks (such as their overall appearance, composition, or condition of formatio ...

tectonite Tectonites are metamorphic or tectonically deformed rocks whose fabric reflects the history of their deformation, or rocks with fabric that clearly displays coordinated geometric features that indicate continuous solid (ductile) flow during fo ...

s that separates the granitoid-greenstone terranes of the Kaapvaal and Zimbabwe cratons.

Limpopo Central Zone

The crustal evolution of the Limpopo Central Zone can be summarised into three main periods: 3.2–2.9 Ga, 2.6 Ga, and 2.0 Ga. The first two periods are characterised by magmatic activity leading to the formation of Archaean Tonalite-Trondhjemite-Granodiorite (TTG) such as the Sand River Gneisses and the Bulai Granite intrusion. Early

high-grade metamorphic conditions produced partial melting that formed large amounts of granitic melt. There is no indication that the

Neoarchean The Neoarchean (; also spelled Neoarchaean) is the last geologic era in the Archean eon that spans from 2800 to 2500 million years ago—the period being defined chronometrically and not referencing a specific level in a rock section on Earth. ...

to early

Paleoproterozoic The Paleoproterozoic Era (;, also spelled Palaeoproterozoic), spanning the time period from (2.5–1.6 Ga), is the first of the three sub-divisions (eras) of the Proterozoic Eon. The Paleoproterozoic is also the longest era of the Earth's ...

succession on the craton were sourced from the 2.65–2.70 Ga orogenic event preserved in the Limpopo Metamorphic Complex. However, younger late-

red bed successions contain

zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of the r ...

s of this time interval as well as many ~2.0 Ga

detrital Detritus (; adj. ''detrital'' ) is particles of rock derived from pre-existing rock through weathering and erosion.Essentials of Geology, 3rd Ed, Stephen Marshak, p G-7 A fragment of detritus is called a clast.Essentials of Geology, 3rd Ed, Stephen ...

zircons. This implies that the Limpopo Complex together with the Zimbabwe Craton only became attached to the Kaapvaal Craton at approximately 2.0 Ga during formation of the Magondi Mobile Belt which in turn sourced the voluminous late

red beds of southern Africa. Evidence of the horizontal layering and riverine erosion can be found throughout the

Waterberg Massif The Waterberg ( nso, Thaba Meetse) is a mountainous massif of approximately in north Limpopo Province, South Africa. The average height of the mountain range is 600 m with a few peaks rising up to 2000 m above sea level. Vaalwater town is l ...

within the Limpopo Central Zone.

Barberton greenstone belt

The Barberton greenstone belt, also known as the

Makhonjwa Mountains The Makhonjwa Mountains are a range of small mountains and hills that covers an area of , about 80% in Mpumalanga, a province of South Africa, and the remainder in neighbouring Eswatini. It constitutes 40% of the Barberton Greenstone Belt. Geo ...

, is situated on the eastern edge of Kaapvaal Craton. It is well known for its gold mineralisation and for its

Komatiites Komatiite () is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava of at least 18 wt% MgO. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Komatiite wa ...

, an unusual type of ultramafic volcanic rock named after the Komati River that flows through the belt. Some of the oldest exposed rocks on Earth (greater than 3.6 Ga) are located in the Barberton greenstone belt of the Swaziland–Barberton areas and these contain some of the oldest traces of life on earth. Only the rocks found in the Isua Greenstone Belt of Western

Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland is t ...

are older.

Johannesburg Dome

The Archaean Johannesburg Dome is located in the central part of the Kaapvaal Craton and consists of trondhjemitic and tonalitic granitic rocks intruded into mafic-ultramafic greenstone.Nguuri, T.K. et al. (2001
“Crustal structure beneath southern Africa and its implications for the formation and evolution of the Kaapvaal and Zimbabwe cratons”
"Geophysical Research Letters", 28, 2501–2504. Studies using U-Pb single zircon dating for granitoid samples yield an age of 3340 +/- 3 Ma and represents the oldest granitoid phase recognised so far. "Following the trondhjemite-tonalite gneiss emplacement a further period of magmatism took place on the dome, which resulted in the intrusion of mafic dykes that are manifest as hornblende amphibolites. The age of these dykes has yet to be determined quantitatively, but they fall within the time constraints imposed by the age of the trondhjemitic gneisses (3340–3200 Ma) and later, crosscutting, potassic granitoids. These rocks consisting mainly of granodiorites constitute the third magmatic event and occupy an area of batholithic dimensions extending across most of the southern portion of the dome. The southern and southeastern parts of the batholith consist mainly of medium-grained, homogeneous, grey granodiorites dated at 3121 +/- 5 Ma....The data, combined with that from other parts of the Kaapvaal craton, further supports the view that the evolution of the craton was long-lived and episodic, and that it grew by accretionary processes, becoming generally younger to the north and west of the ca. 3.5 Ga Barberton- Eswatini granite-greenstone terrane situated in the southeastern part of the craton."Poujol, M. and Anhaeusser, C.R. (2001
"The Johannesburg Dome, South Africa: new single zircon U-Pb isotopic evidence for early Archaean granite-greenstone development within the central Kaapvaal Craton"
''Precambrian Research'', 108 (1–2), 139–157, .

References

Bibliography

* Glikson, A. and Vickers, J. (2006
"The 3.26–3.24 Ga Barberton asteroid impact cluster: Tests of tectonic and magmatic consequences, Pilbara Craton, Western Australia"
''Earth and Planetary Science Letters'', 241 (1–2), 11–20, * Louzda, K.L. (2003

Utrecht University : unpubl. MSc project abstr. * Poujol, M., Robb, L.J., Anhaeusser, C.R. and Gericke, B. (2003) "A review of the geochronological constraints on the evolution of the Kaapvaal Craton, South Africa", ''Precambrian Research'', 127 (1–3), 181–213, . * Westraat, J.D, Kisters, A.F.M., Poujo, M. and Stevens, G. (2005
"Transcurrent shearing, granite sheeting and the incremental construction of the tabular 3.1 Ga Mpuluzi batholith, Barberton granite–greenstone terrane, South Africa"
''Journal of the Geological Society'', 162 (2), 373–388, * Yearron, L.M., Clemens, J.D., Stevens, G. and Anhaeusser, C.R.(2003
"Geochemistry and Petrogenesis of the Granitoids of the Barberton Mountainlan, South Africa"
''Geophysical Research Abstracts'', 5, 02639 {{Major African geological formations Archean Africa Cratons Geology of South Africa