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Akia Terrane
The Akia terrane is a tectonostratigraphic terrane located in the North Atlantic Craton in southern West Greenland. The Akia terrane is bounded to the Southeast by the Eo- to Neo-archaean tectonostratigraphic terranes of the Nuuk region, and to the North by the recently recognised Alanngua Complex, which separates the Akia terrane from the Neoarchaean Tuno terrane. The crust in the Akia terrane formed in two major pulses. The first at ~3.2 Ga, predominantly comprises dioritic gneisses, whereas the second, at ~3.0 Ga comprises a more diverse mix of TTG and dioritic gneisses with enclaves of supracrustal rocks and mafic-ultramafic intrusions. Supracrustal rocks are largely tholeiitic and calc-alkaline amphibolites formed at ~3.07 Ga. The mafic-ultramafic intrusions include peridotite cumulates and a belt of noritic intrusions formed at the same time as the TTG gneisses, the Maniitsoq Norite Belt. Various tectonic settings have been proposed for the 3.0 Ga crust forming event, incl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tectonostratigraphic 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 distinctive geologic history, which is different from that of the surrounding areas—hence the term "exotic" terrane. The suture zone between a terrane and the crust it attaches to is usually identifiable as a fault. A sedimentary deposit that buries the contact of the terrane with adjacent rock is called an overlap formation. An igneous intrusion that has intruded and obscured the contact of a terrane with adjacent rock is called a stitching pluton. Older usage of ''terrane'' simply described a series of related rock formations or an area having a preponderance of a particular rock or rock groups. Overview A tectonostratigraphic terrane is not necessarily an independent microplate in origin, since it may not contain the full thickness ... [...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] |
Granite
Granite () is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies underground. It is common in the continental crust of Earth, where it is found in igneous intrusions. These range in size from dikes only a few centimeters across to batholiths exposed over hundreds of square kilometers. Granite is typical of a larger family of ''granitic rocks'', or ''granitoids'', that are composed mostly of coarse-grained quartz and feldspars in varying proportions. These rocks are classified by the relative percentages of quartz, alkali feldspar, and plagioclase (the QAPF classification), with true granite representing granitic rocks rich in quartz and alkali feldspar. Most granitic rocks also contain mica or amphibole minerals, though a few (known as leucogranites) contain almost no dark minerals. Granite is nearly alway ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pegmatite
A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic composition to granite. However, rarer intermediate composition and mafic pegmatites are known. Many of the world's largest crystals are found within pegmatites. These include crystals of microcline, quartz, mica, spodumene, beryl, and tourmaline. Some individual crystals are over long. Most pegmatites are thought to form from the last fluid fraction of a large crystallizing magma body. This residual fluid is highly enriched in volatiles and trace elements, and its very low viscosity allows molecules to migrate rapidly to join an existing crystal rather than coming together to form new crystals. This allows a few very large crystals to form. While most pegmatites have a simple composition of minerals common in ordinary igneous rock, a few ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 chemically active fluids, but the rock remains mostly solid during the transformation. Metamorphism is distinct from weathering or diagenesis, which are changes that take place at or just beneath Earth's surface. Various forms of metamorphism exist, including regional, contact, hydrothermal, shock, and dynamic metamorphism. These differ in the characteristic temperatures, pressures, and rate at which they take place and in the extent to which reactive fluids are involved. Metamorphism occurring at increasing pressure and temperature conditions is known as ''prograde metamorphism'', while decreasing temperature and pressure characterize ''retrograde metamorphism''. Metamorphic petrology is the study of metamorphism. Metamorphic petrologists re ... [...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] |
Orogeny
Orogeny is a mountain building process. An orogeny is an event that takes place at a convergent plate margin when plate motion compresses the margin. An ''orogenic belt'' or ''orogen'' develops as the compressed plate crumples and is uplifted to form one or more mountain ranges. This involves a series of geological processes collectively called orogenesis. These include both structural deformation of existing continental crust and the creation of new continental crust through volcanism. Magma rising in the orogen carries less dense material upwards while leaving more dense material behind, resulting in compositional differentiation of Earth's lithosphere ( crust and uppermost mantle). A synorogenic process or event is one that occurs during an orogeny. The word "orogeny" () comes from Ancient Greek (, , + , , ). Although it was used before him, the term was employed by the American geologist G. K. Gilbert in 1890 to describe the process of mountain-building as distinguished f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stagnant Lid
Lid tectonics, commonly thought of as stagnant lid tectonics, is the type of tectonics that is believed to exist on several planets and moons in the Solar System, and possibly existed on Earth during the early part of its history. The lid is the equivalent of the lithosphere in plate tectonics, formed of solid silicate minerals (or solid ice in the case of icy planets and moons). The relative stability and immobility of the strong cooler lids leads to stagnant lid tectonics, which has greatly reduced amounts of horizontal tectonics compared with plate tectonics (which can also be described as mobile lid tectonics). The presence of a stagnant lid above a convecting mantle was recognised as a possible stable regime for convection on Earth, in contrast to the well-attested mobile plate tectonics of the current eon. Formation A lid tectonic regime arises when the cold upper lithosphere is too viscous to participate in the underlying flow of the mantle. The lid's yield strength is hig ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 magma or lava. Volcanism is the surface expression of magmatism. Magmatism is one of the main processes responsible for mountain formation. The nature of magmatism depends on the tectonic setting. For example, andesitic magmatism is associated with the formation of island arcs at convergent plate boundaries while basaltic magmatism is found at mid-ocean ridges during sea-floor spreading at divergent plate boundaries. On Earth, magma forms by partial melting of silicate rocks either in the mantle, continental or oceanic crust. Evidence for magmatic activity is usually found in the form of igneous rocks formed from magma. Convergent boundaries Magmatism is associated with all stages of the development of convergent plate boundaries, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Subduction
Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the heavier plate dives beneath the second plate and sinks into the mantle. A region where this process occurs is known as a subduction zone, and its surface expression is known as an arc-trench complex. The process of subduction has created most of the Earth's continental crust. Rates of subduction are typically measured in centimeters per year, with the average rate of convergence being approximately two to eight centimeters per year along most plate boundaries. Subduction is possible because the cold oceanic lithosphere is slightly denser than the underlying asthenosphere, the hot, ductile layer in the upper mantle underlying the cold, rigid lithosphere. Once initiated, stable subduction is driven mostly by the negative buoyancy of the de ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Frontiers In Earth Science
Frontiers Media SA is a publisher of peer-reviewed, open access, scientific journals currently active in science, technology, and medicine. It was founded in 2007 by Kamila and Henry Markram, and has since expanded to other academic fields. Frontiers is based in Lausanne, Switzerland, with other offices in London, Madrid, Seattle and Brussels. In 2022, Frontiers employed more than 1,400 people, across 14 countries. All Frontiers journals are published under a Creative Commons Attribution License. As of 2022, Frontiers publishes over 185 academic journals, including 48 journals indexed within the Science Citation Index Expanded, and 4 journals indexed within the Social Sciences Citation Index, with a total of 51 journals ranked with an impact factor. Frontiers journals are included in the Directory of Open Access Journals (DOAJ). Frontiers is also a member of the Open Access Scholarly Publishers Association (OASPA), a participating publisher and supporter of the Initiative for Op ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Maniitsoq Norite Belt
The Maniitsoq Norite Belt is a ~75 km x 15 km J-shaped belt of igneous norite intrusions, located in the Akia Terrane of the North Atlantic Craton, Greenland, near the town of Maniitsoq.Ravenelle, J. F., Weiershauser, L., and Cole, G. (2017). Report No.: 3CN024.004. Updated Independent Technical Report for the Maniitsoq Nickel-Copper-Cobalt-PGM Project, Greenland. Available at: https://s1.q4cdn.com/725069486/files/doc_downloads/technical_reports/Technical_Report_2017.pdf The belt is found as enclaves ranging from meter-scale pods to 8 km2 large intrusive bodies within the ~3050 to 2990 Ma TTG and dioritic gneisses of the Akia terrane. and formed contemporaneously with the host gneisses between ~3013 and 3001 Ma The norites underwent high grade granulite facies metamorphism at temperatures of ~800 °C and pressures of ~9 kbar (approximately 30 km depth) from ~3010 to 2980 Ma, soon after they were intruded. The norites were metamorphosed twice more at ~2.7 Ga and ~2.5 Ga. A wide ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
