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Geology Of The Democratic Republic Of The Congo
The geology of the Democratic Republic of the Congo (DRC or Congo-Kinshasa, formerly Zaire and Belgian Congo) is extremely old, on the order of several billion years for many rocks. The country spans the Congo Craton: a stable section of ancient continental crust, deformed and influenced by several different mountain building orogeny events, sedimentation, volcanism and the geologically recent effects of the East Africa Rift System in the east. The country's complicated tectonic past have yielded large deposits of gold, diamonds, coltan and other valuable minerals. Stratigraphy, tectonics & geologic History Archean terranes in the Congo Craton are exposed as part of the Angolan Shield in Kasai Province, the foreland of the West Congolian mobile belt in the northwest and as granite and greenstone belts spanning into neighboring Central African Republic, Uganda and South Sudan. Angolan Shield In Kasai, the metamorphic basement rocks of the Angolan Shield are bounded by a f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Congo Kinshasa Topography
Congo or The Congo may refer to either of two countries that border the Congo River in central Africa: * Democratic Republic of the Congo, the larger country to the southeast, capital Kinshasa, formerly known as Zaire, sometimes referred to as "Congo-Kinshasa" * Republic of the Congo, the smaller country to the northwest, capital Brazzaville, sometimes referred to as "Congo-Brazzaville" Congo or Kongo may also refer to: Places Africa * Congo Basin, or the Congo, the sedimentary basin of the Congo River * Congo Canyon, a submarine canyon * Kingdom of Kongo (1390–1914) * Kingdom of Kakongo (15th century–1885) * Congo Free State (1885–1908) * Republic of the Congo (Léopoldville) or Congo-Léopoldville (1960–1971) * People's Republic of the Congo (1969–1992) * Kongo, Ghana, town in Ghana * Kongo, Liberia, small town in Liberia Former colonies * Belgian Congo * French Congo * Portuguese Congo United States * Congo, Alabama * Congo, Missouri * Congo, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Migmatite
Migmatite is a composite rock found in medium and high-grade metamorphic environments, commonly within Precambrian cratonic blocks. It consists of two or more constituents often layered repetitively: one layer is an older metamorphic rock that was reconstituted subsequently by partial melting ("paleosome"), while the alternate layer has a pegmatitic, aplitic, granitic or generally plutonic appearance ("neosome"). Commonly, migmatites occur below deformed metamorphic rocks that represent the base of eroded mountain chains. Migmatites form under extreme temperature and pressure conditions during prograde metamorphism, when partial melting occurs in metamorphic paleosome. Components exsolved by partial melting are called neosome (meaning ‘new body’), which may or may not be heterogeneous at the microscopic to macroscopic scale. Migmatites often appear as tightly, incoherently folded veins ( ptygmatic folds).Recommendations by the IUGS Subcommission on the Systematics of M ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pan-African Orogeny
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. The Pan-African orogeny and the Grenville orogeny are the largest known systems of orogenies on Earth. The sum of the continental crust formed in the Pan-African orogeny and the Grenville orogeny makes the Neoproterozoic the period of Earth's history that has produced most continental crust. History and terminology The term ''Pan-African'' was coined by for a tectono-thermal event at about 500 Ma when a series of mobile belts in Africa formed between much older African cratons. At the time, other terms were used for similar orogenic events on other continents, i.e. '' Brasiliano'' in South America; ''Adelaidean'' in Australia; and ''Beardmore'' in Antarctica. Later, when plate tectonics became generally accepted, the term ''Pan-A ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anorthosite
Anorthosite () is a phaneritic, intrusive igneous rock characterized by its composition: mostly plagioclase feldspar (90–100%), with a minimal mafic component (0–10%). Pyroxene, ilmenite, magnetite, and olivine are the mafic minerals most commonly present. Anorthosites are of enormous geologic interest, because it is still not fully understood how they form. Most models involve separating plagioclase crystals based on their density. Plagioclase crystals are usually less dense than magma; so, as plagioclase crystallizes in a magma chamber, the plagioclase crystals float to the top, concentrating there. Anorthosite on Earth can be divided into five types: # Archean-age anorthosites # Proterozoic anorthosite (also known as massif or massif-type anorthosite) – the most abundant type of anorthosite on Earth # Layers within Layered Intrusions (e.g., Bushveld and Stillwater intrusions) # Mid-ocean ridge and transform fault anorthosites # Anorthosite xenoliths in other rocks ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mafic
A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include basalt, diabase and gabbro. Mafic rocks often also contain calcium-rich varieties of plagioclase feldspar. Mafic materials can also be described as ferromagnesian. History The term ''mafic'' is a portmanteau of "magnesium" and "ferric" and was coined by Charles Whitman Cross, Joseph P. Iddings, Louis Valentine Pirsson, and Henry Stephens Washington in 1912. Cross' group had previously divided the major rock-forming minerals found in igneous rocks into ''salic'' minerals, such as quartz, feldspars, or feldspathoids, and ''femic'' minerals, such as olivine and pyroxene. However, micas and aluminium-rich amphiboles were excluded, while some calcium minerals containing little iron or magnesium, such as wollastonite or apatite, were included ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Norite
Norite is a mafic intrusive igneous rock composed largely of the calcium-rich plagioclase labradorite, orthopyroxene, and olivine. The name ''norite'' is derived from ''Norge'', the Norwegian name for Norway. Norite also known as orthopyroxene gabbro. Norite may be essentially indistinguishable from gabbro without thin section study under the petrographic microscope. The principal difference between norite and gabbro is the type of pyroxene of which it is composed. Norite is predominantly composed of orthopyroxenes, largely high magnesian enstatite or an iron bearing intermediate hypersthene. The principal pyroxenes in gabbro are clinopyroxenes, generally medially iron-rich augites. Norite occurs with gabbro and other mafic to ultramafic rocks in layered intrusions which are often associated with platinum orebodies such as in the Bushveld Igneous Complex in South Africa, the Skaergaard igneous complex of Greenland, and the Stillwater igneous complex in Montana. Norite is als ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gabbro
Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is chemically equivalent to rapid-cooling, fine-grained basalt. Much of the Earth's oceanic crust is made of gabbro, formed at mid-ocean ridges. Gabbro is also found as plutons associated with continental volcanism. Due to its variant nature, the term ''gabbro'' may be applied loosely to a wide range of intrusive rocks, many of which are merely "gabbroic". By rough analogy, gabbro is to basalt as granite is to rhyolite. Etymology The term "gabbro" was used in the 1760s to name a set of rock types that were found in the ophiolites of the Apennine Mountains in Italy. It was named after Gabbro, a hamlet near Rosignano Marittimo in Tuscany. Then, in 1809, the German geologist Christian Leopold von Buch used the term more restrictively in his descri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Charnockite
Charnockite () is any orthopyroxene-bearing quartz-feldspar rock formed at high temperature and pressure, commonly found in granulite facies metamorphic regions, ''sensu stricto'' as an endmember of the charnockite series. Charnockite series The ''charnockite suite'' or ''series'' is a particularly widespread form of granofels. Granofels are one of the few non-foliated rocks to form under relatively high temperatures and pressures. This combination is generated only deep in the crust by tectonic forces that operate on a grand scale, so granofels is a product of regional, rather than contact, metamorphism. It is formed mostly from the granite clan of rocks, or occasionally from thoroughly reconstituted clays and shales. It is of wide distribution and great importance in India, Sri Lanka, Madagascar and Africa. It was named by geologist T. H. Holland in 1893 after the tombstone of Job Charnock, in St John's Church in Kolkata, India, which is made of this rock. Composition The c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 with quartz and anhydrous ferromagnesian minerals, with granoblastic texture and gneissose to massive structure.D.R. Bowes (1989), ''The Encyclopedia of Igneous and Metamorphic Petrology''; Van Nostrand Reinhold They are of particular interest to geologists because many granulites represent samples of the deep continental crust. Some granulites experienced decompression from deep in the Earth to shallower crustal levels at high temperature; others cooled while remaining at depth in the Earth. The minerals present in a granulite will vary depending on the parent rock of the granulite and the temperature and pressure conditions experienced during metamorphism. A common type of granulite found in high-grade metamorphic rocks of the continent ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alaskite
Leucogranite is a light-colored, granitic, igneous rock containing almost no dark minerals. Alaskite is a synonym. Leucogranites have been reported from a variety of orogenies involving continental collisions. Examples include the ( of Proterozoic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metamorphic Facies
A metamorphic facies is a set of mineral assemblages in metamorphic rocks formed under similar pressures and temperatures.Essentials of Geology, 3rd Edition, Stephen Marshak The assemblage is typical of what is formed in conditions corresponding to an area on the two dimensional graph of temperature vs. pressure (See diagram in Figure 1). Rocks which contain certain minerals can therefore be linked to certain tectonics, tectonic settings, times and places in the geological history of the area. The boundaries between facies (and corresponding areas on the temperature v. pressure graph) are wide because they are gradational and approximate. The area on the graph corresponding to rock formation at the lowest values of temperature and pressure is the range of formation of sedimentary rocks, as opposed to metamorphic rocks, in a process called diagenesis. Historic definition The name ''facies'' was first used for specific Sedimentary depositional environment, sedimentary environments i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amphibolite
Amphibolite () is a metamorphic rock that contains amphibole, especially hornblende and actinolite, as well as plagioclase feldspar, but with little or no quartz. It is typically dark-colored and dense, with a weakly foliated or schistose (flaky) structure. The small flakes of black and white in the rock often give it a salt-and-pepper appearance. Amphibolite frequently forms by metamorphism of mafic igneous rocks, such as basalt. However, because metamorphism creates minerals entirely based upon the chemistry of the protolith, certain 'dirty marls' and volcanic sediments may also metamorphose to an amphibolite assemblage. Deposits containing dolomite and siderite also readily yield amphibolite (tremolite-schist, grunerite-schist, and others) especially where there has been a certain amount of contact metamorphism by adjacent granitic masses. Metamorphosed basalt (metabasalt) creates ''ortho-amphibolite'' and other chemically appropriate lithologies create ''para-amphibolite''. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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