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 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 supercontinent.
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. 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 ...
orogens, 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
ARC may refer to:
Business
* Aircraft Radio Corporation, a major avionics manufacturer from the 1920s to the '50s
* Airlines Reporting Corporation, an airline-owned company that provides ticket distribution, reporting, and settlement services
* ...
-related
magmatism and
sedimentation 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
Succession is the act or process of following in order or sequence.
Governance and politics
*Order of succession, in politics, the ascension to power by one ruler, official, or monarch after the death, resignation, or removal from office of ...
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
rifting 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
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 ...
approximately 2.8–2.5 Ga by the wide
orogenic Limpopo Belt. The belt is an east-northeast trending zone of
granulite 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 ...
tectonites 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
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 ...
high-grade metamorphic conditions produced partial melting that formed large amounts of granitic melt.
There is no indication that the
Neoarchean to early
Paleoproterozoic succession on the craton were sourced from the 2.65–2.70 Ga orogenic event preserved in the Limpopo Metamorphic Complex. However, younger late-
Paleoproterozoic red bed
Red beds (or redbeds) are sedimentary rocks, typically consisting of sandstone, siltstone, and shale, that are predominantly red in color due to the presence of ferric oxides. Frequently, these red-colored sedimentary strata locally contain th ...
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 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
Paleoproterozoic red beds of southern Africa. Evidence of the horizontal layering and riverine erosion can be found throughout the
Waterberg Massif 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.
Geogr ...
, 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, .
See also
*
*
*
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