Craton, the stable interior portion of a continent characteristically composed of ancient crystalline basement rock. The term craton is used to distinguish such regions from mobile geosynclinal troughs, which are linear belts of sediment accumulations subject to subsidence (i.e., downwarping).
Which two cratons combined is know as the Kalahari Craton?
The Kalahari Craton is a craton, an old and stable part of the continental lithosphere, that occupies large portions of South Africa, Botswana, Namibia and Zimbabwe. It consists of two cratons separated by the Limpopo Belt: the larger Kaapvaal Craton to the south and the smaller Zimbabwe Craton to the north.
Which rocks constitute the oldest rocks of the Kaapvaal Craton?
The oldest rocks consist of gneisses, granites, metasediments, and metavolcanic rocks 3.6 to 2.5 billion years old; all are variably deformed and metamorphosed to some degree. The best-preserved assemblages occur in the Kaapvaal and Zimbabwe cratons and contain large deposits of gold and sulfide minerals.
What type of rock is chalk?
Chalk is a soft white limestone made from the microscopic skeletons of marine plankton.
How old is the Acasta gneiss and why is it significant?
The Acasta Gneiss, a rock that formed from magma that cooled and solidified deep within Earth’s crust is the oldest rock yet dated at just over 4,000 million years old. The Jack Hills Conglomerate contains the oldest mineral yet dated at almost 4,200 million years old.
How is Greenstone formed?
Nature and formation
Greenstone belts have been interpreted as having formed at ancient oceanic spreading centers and island arc terranes. Greenstone belts are primarily formed of volcanic rocks, dominated by basalt, with minor sedimentary rocks inter-leaving the volcanic formations.
What is Pan African in geology?
From Wikipedia, the free encyclopedia. The Pan-African orogeny was a series of major Neoproterozoic orogenic events which related to the formation of the supercontinents Gondwana and Pannotia about 600 million years ago. This orogeny is also known as the Pan-Gondwanan or Saldanian Orogeny.
What is a craton and why is it important?
The term craton is used to distinguish the stable portion of the continental crust from regions that are more geologically active and unstable. Cratons can be described as shields, in which the basement rock crops out at the surface, and platforms, in which the basement is overlaid by sediments and sedimentary rock.
What is a craton divided into?
A craton is the oldest part of a continental plate. … Cratons are subdivided geographically into geologic provinces. A geologic province is an area with common geologic properties.
What is the difference between a craton and a mobile belt?
The cratons are relatively rigid blocks, but have a history of ductile and brittle deformations. The surrounding mobile belts are either high-strain, high-grade metamorphic belts or folded basins. Thus, the relatively rigid cratons are surrounded by more ductile zones of mobility.
Where is the Yilgarn Craton?
The Archaean Yilgarn Craton in the southern half of Western Australia covers an area of ~650 000 km2. It is bounded to the south and SE by the Mesoproterozoic Albany-Fraser Orogen, to the north by the Palaeoproterozoic Capricorn Orogen, and to the west by the Mesozoic Perth Basin.
Which other rock types are found underneath the Karoo Supergroup?
(A) Horizontally bedded conglomerate, red sandstone and siltstone are attributed to the Karoo Supergroup.
How did the Transvaal sediments form?
Transvaal sedimentation began with predominantly clastic sedimentary rocks (Black Reef-Vryburg Formations) followed by carbonate rocks and banded iron formations (Chuniespoort-Ghaap-Taupone Groups). … A final stage of predominantly volcanic succession (Rooiberg Group-Loskop Formation) is limited to the Transvaal Basin.
What is orogenic cycle?
Orogeny is the process of forming mountain belts by folding and thrust faulting. … Holmes (1926 and 1965) proposed that orogenic zones are affected by a cyclic repetition of events that is part of what he called an orogenic cycle (also called an orogenetic cycle).
What are the types of Orogenesis?
(2009) categorized orogenic belts into three types: accretionary, collisional, and intracratonic. Notice that both accretionary and collisional orogens developed in converging plate margins.
What is the Eburnean event?
The Eburnean orogeny, or Eburnean cycle, was a series of tectonic, metamorphic and plutonic events in what is now West Africa during the Paleoproterozoic era about 2200–2000 million years ago. During this period the Birimian domain in West Africa was established and structured.
Is it bad luck to buy your own greenstone?
Certain pieces of greenstone were actually recognized as having their own spirits, which chose their wearer, so carving or taking one for yourself was extremely bad luck as it would anger the spirit or guardian of the jade.” Today however, it is increasingly common to purchase a piece for yourself.
Is greenstone valuable?
Imbued with spiritual significance to New Zealand’s Indigenous tribes, pounamu – otherwise known as greenstone or New Zealand jade – is highly prized. For centuries Māori have fashioned it into jewellery, tools and even weapons, which could denote status or be used as ceremonial objects or symbols of peace agreements.
Why are greenstone belts important?
Greenstone belts host important ore deposits of metals such as gold, Cu–Zn, Ni, and Fe. Well-known examples include the Abitibi and Flin Flon belts in Canada, the Norseman-Wiluna belt in Australia and the Barberton belt in South Africa.
Which is the oldest rock in the world?
Bedrock along the northeast coast of Hudson Bay, Canada, has the oldest rock on Earth. Canadian bedrock more than 4 billion years old may be the oldest known section of the Earth’s early crust.
How old are the oldest rocks on Earth How do you know?
Scientists have found the oldest known rocks on Earth. They are 4.28 billion years old, making them 250 million years more ancient than any previously discovered rocks. Earth formed about 4.6 billion years ago from a disk of gas and dust circling the sun.
Who found the Acasta Gneiss?
Geological Survey of Canada geologist Janet King discovered the Acasta Gneiss during fieldwork in 1983. The composition and texture of the Acasta Gneiss suggest that, before metamorphism, the gneiss was an igneous rock that formed about 4.03 billion years ago.
How is chalk made naturally?
Chalk forms from a fine-grained marine sediment known as ooze. When foraminifera, marine algae, or other organisms living on the bottom or in the waters above die, their remains sink to the bottom and accumulate as ooze. … Extensive deposits of chalk are found in many parts of the world.