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Cashan Mountains
The Magaliesberg (historically also known as ''Macalisberg'' or ''Cashan Mountains'') of northern South Africa, is a modest but well-defined mountain range composed mainly of quartzites. It rises at a point south of the Pilanesberg (and the Pilanesberg National Park) to form a curved prominence that intersects suburban Pretoria before it peters out some to the east, just south of Bronkhorstspruit. The highest point of the Magaliesberg is reached at Nooitgedacht, about above sea level. A cableway reaching to the top of the mountain range is located at Hartbeespoort Dam, providing sweeping views of the Magaliesberg and surrounding area. Geology The Magaliesberg has ancient origins. Its composition is ascribed to successive geological processes over a very protracted history. Its quartzites, shales, chert and dolomite were deposited as sediments in an inland basin on top of a 3 billion year old Archaean Basement Complex, known as the Kaapvaal Craton. This process of sedimentatio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hartebeespoort Dam
Hartbeespoort Dam (also known as ''Harties'') is an arch type dam situated in the North West Province of South Africa. It lies in a valley to the south of the Magaliesberg mountain range and north of the Witwatersberg mountain range, about 35 kilometres north west of Johannesburg and 20 kilometres west of Pretoria. The name of the dam means "dam at the gorge of the hartebeest" (a species of antelope) in Afrikaans. This "poort" in the Magaliesberg was a popular spot for hunters, where they cornered and shot the hartebeest. The dam was originally designed for irrigation, which is currently its primary use, as well as for domestic and industrial use. The dam has suffered from a hypertrophic state since the early 1970s. Mismanagement of waste water treatment from urban zones within the Hartbeespoort Dam catchment area is largely to blame, having distorted the food web with over 280 tons of phosphate and nitrate deposits. The town of Hartbeespoort is situated close to the dam wall an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quartzite
Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to grey, though quartzites often occur in various shades of pink and red due to varying amounts of hematite. Other colors, such as yellow, green, blue and orange, are due to other minerals. The term ''quartzite'' is also sometimes used for very hard but unmetamorphosed sandstones that are composed of quartz grains thoroughly cemented with additional quartz. Such sedimentary rock has come to be described as orthoquartzite to distinguish it from metamorphic quartzite, which is sometimes called metaquartzite to emphasize its metamorphic origins. Quartzite is very resistant to chemical weathering and often forms ridges and resistant hilltops. The nearly pure silica co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Drakensberg
The Drakensberg (Afrikaans: Drakensberge, Zulu: uKhahlambha, Sotho: Maluti) is the eastern portion of the Great Escarpment, which encloses the central Southern African plateau. The Great Escarpment reaches its greatest elevation – within the border region of South Africa and Lesotho. The Drakensberg escarpment stretches for more than from the Eastern Cape Province in the South, then successively forms, in order from south to north, the border between Lesotho and the Eastern Cape and the border between Lesotho and KwaZulu-Natal Province. Thereafter it forms the border between KwaZulu-Natal and the Free State, and next as the border between KwaZulu-Natal and Mpumalanga Province. The escarpment winds north from there, through Mpumalanga, where it includes features such as the Blyde River Canyon, Three Rondavels, and God's Window. It then extends farther north to Hoedspruit in southeastern Limpopo where it is known as 'Klein Drakensberg' by the Afrikaner. From Hoedsp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transvaal Basin
The Transvaal Basin is one of three basins of the Transvaal Supergroup on the Kaapvaal craton. The evolution of this 2.65–2.05 Ga Neoarchaean– Palaeoproterozoic basin is thought to have been derived largely from magmatism, palaeoclimate and eustasy, while plate tectonics played an intermittent role. The supergroup is made up of basal ‘ protobasinal’ rocks, upon which followed the Black Reef Formation, Chuniespoort Group and the uppermost Pretoria Group. The Transvaal Supergroup displays three unconformity-bounded sequences that surface in two geographically distinct areas – the Transvaal Basin, which circumscribes the Bushveld Igneous Complex, and the Griqualand West basin, lying between Kimberley and Sishen at the western Kaapvaal craton rim, extending into southern Botswana beneath the Kalahari Sands as the Kanye Basin. The two basins are separated by the broad Vryburg Arch. Between approximately 2.640 and 2.516 Ga, two successive stromatolitic c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ravine
A ravine is a landform that is narrower than a canyon and is often the product of streambank erosion.Definition of "ravine" at Ravines are typically classified as larger in scale than gullies, although smaller than s. Ravines may also be called a cleuch, dell, ghout (), [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dolerite
Diabase (), also called dolerite () or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-grained to aphanitic chilled margins which may contain tachylite (dark mafic glass). ''Diabase'' is the preferred name in North America, while ''dolerite'' is the preferred name in the rest of the English-speaking world, where sometimes the name ''diabase'' refers to altered dolerites and basalts. Some geologists prefer to avoid confusion by using the name ''microgabbro''. The name ''diabase'' comes from the French ', and ultimately from the Greek - meaning "act of crossing over, transition". Petrography Diabase normally has a fine but visible texture of euhedral lath-shaped plagioclase crystals (62%) set in a finer matrix of clinopyroxene, typically augite (20–29%), with minor olivine (3% up to 12% in olivine diabase), magnetite (2%), and i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Intrusive Rock
Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form '' intrusions'', such as batholiths, dikes, sills, laccoliths, and volcanic necks.Intrusive RocksIntrusive rocks accessdate: March 27, 2017.Igneous intrusive rocks, accessdate: March 27, 2017.Britannica.comintrusive rock , geology , Britannica.com accessdate: March 27, 2017. Intrusion is one of the two ways igneous rock can form. The other is extrusion, such as a volcanic eruption or similar event. An intrusion is any body of intrusive igneous rock, formed from magma that cools and solidifies within the crust of the planet. In contrast, an ''extrusion'' consists of extrusive rock, formed above the surface of the crust. Some geologists use the term plutonic rock synonymously with intrusive rock, but other geologists subdivide intrusive rock, by crystal size, into coarse-grained plutonic rock (typically formed deeper in the Earth's crust in batholiths or stocks) a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dip Slope
A dip slope is a topographic (geomorphic) surface which slopes in the same direction, and often by the same amount, as the true dip or apparent dip of the underlying strata.Jackson, JA, J Mehl and K Neuendorf (2005) ''Glossary of Geology.'' American Geological Institute, Alexandria, Virginia. 800 pp. Allaby, M (2008) ''A Dictionary of Earth Science.'' Oxford University Press, New York, New York. 654 pp. A dip slope consists of the upper surface of a resistant layer of rock, often called ''caprock'', that is commonly only slightly lowered and reduced in steepness by erosion. Dip slopes form the backslopes of cuestas, homoclinal ridges, hogbacks, and flatirons. The frontslopes of such ridges consist of either an escarpment, a steep slope, or perhaps even a line of cliffs. Generally, cuestas and homoclinal ridges are asymmetrical in that their dip slopes are less steep than their escarpments. In the case of hogbacks and flatirons, the dip of the rocks is so steep that their dip s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Escarpment
An escarpment is a steep slope or long cliff that forms as a result of faulting or erosion and separates two relatively level areas having different elevations. The terms ''scarp'' and ''scarp face'' are often used interchangeably with ''escarpment''. Some sources differentiate the two terms, with ''escarpment'' referring to the margin between two landforms, and ''scarp'' referring to a cliff or a steep slope. In this usage an escarpment is a ridge which has a gentle slope on one side and a steep scarp on the other side. More loosely, the term ''scarp'' also describes a zone between a coastal lowland and a continental plateau which shows a marked, abrupt change in elevation caused by coastal erosion at the base of the plateau. Formation and description Scarps are generally formed by one of two processes: either by differential erosion of sedimentary rocks, or by movement of the Earth's crust at a geologic fault. The first process is the more common type: the escarpment is a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bushveld Igneous Complex
The Bushveld Igneous Complex (BIC) is the largest layered igneous intrusion within the Earth's crust. It has been tilted and eroded forming the outcrops around what appears to be the edge of a great geological basin: the Transvaal Basin. It is approximately 2 billion years old and is divided into four different limbs: the northern, southern, eastern, and western limbs. The Bushveld Complex comprises the Rustenburg Layered suite, the Lebowa Granites and the Rooiberg Felsics, that are overlain by the Karoo sediments. The site was first discovered around 1897 by Gustaaf Molengraaff. Located in South Africa, the BIC contains some of the richest ore deposits on Earth. The complex contains the world's largest reserves of platinum-group metals (PGMs) or platinum group elements (PGEs)—platinum, palladium, osmium, iridium, rhodium, and ruthenium along with vast quantities of iron, tin, chromium, titanium and vanadium. These are used in, but not limited to, jewellery, automobiles and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kaapvaal Craton
The Kaapvaal Craton (centred on Limpopo Province in South Africa), 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 cratons, especially of the overlying late Archean 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 to the north by the Limpopo Belt. To the south and west, the Kaapvaal Craton is flanked by Proterozoic orogens, and to the east by the Lebombo monocline that contains Jurassic igneous rocks associated with the break-up of Gondwana. The Kaapvaal Craton formed and stabilised between 3.7 and 2.6 Ga by the emplacement of major granitoid batholiths that thickened and stabilised the continental crust during the early stages of an arc-related magmatism and sedimentation cycle. The craton is a mixtur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Basement (geology)
In geology, basement and crystalline basement are crystalline rocks lying above the mantle and beneath all other rocks and sediments. They are sometimes exposed at the surface, but often they are buried under miles of rock and sediment. The basement rocks lie below a sedimentary platform or cover, or more generally any rock below sedimentary rocks or sedimentary basins that are metamorphic or igneous in origin. In the same way, the sediments or sedimentary rocks on top of the basement can be called a "cover" or "sedimentary cover". Crustal rocks are modified several times before they become basement, and these transitions alter their composition. Continental crust Basement rock is the thick foundation of ancient, and oldest, metamorphic and igneous rock that forms the crust of continents, often in the form of granite. Basement rock is contrasted to overlying sedimentary rocks which are laid down on top of the basement rocks after the continent was formed, such as sandstone and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
