|
Migmatites
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 Met ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Migmatite 2005
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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 and pressures than schist. Gneiss nearly always shows a banded texture characterized by alternating darker and lighter colored bands and without a distinct cleavage. Gneisses are common in the ancient crust of continental shields. Some of the oldest rocks on Earth are gneisses, such as the Acasta Gneiss. Description Orthogneiss from the Czech Republic In traditional English and North American usage, a gneiss is a coarse-grained metamorphic rock showing compositional banding ( gneissic banding) but poorly developed schistosity and indistinct cleavage. In other words, it is a metamorphic rock composed of mineral grains easily seen with the unaided eye, which form obvious compositional layers, but which has only a weak tendency to fra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Melanosome (geology)
In geology, a melanosome is a dark,Recommendations by the IUGS Subcommission on the Systematics of Metamorphic Rocks, Part 6. Migmatites and related rocks, p2/ref> mafic mineral band formed in migmatite which is melting into a eutaxitic texture ; often, this leads to the formation of granite. The melanosomes form bands with leucosomes, and in that context may be described as ''schlieren Schlieren ( ; , ) are optical inhomogeneities in transparent media that are not necessarily visible to the human eye. Schlieren physics developed out of the need to produce high-quality lenses devoid of such inhomogeneities. These inhomogeneit ...'' or '' migmatitic''. See also * Metamorphism References External linksmetamorphic rock classification Petrology {{geology-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anatexis
Anatexis (via Latin from Greek roots meaning "to melt down") is the partial melting of rocks. Traditionally, anatexis is used specifically to discuss the partial melting of crustal rocks, while the generic term " partial melting" refers to the partial melting of all rocks, in both the crust and mantle. Anatexis can occur in a variety of different settings, from zones of continental collision to mid-ocean ridges. It is believed that anatexis is the process largely responsible for the formation of migmatites. Furthermore, scientists have recently discovered that partial melting plays an increasingly important role in active crustal processes, including the advancement of active deformation and the emplacement of crustal granites. As a result, active feedback between crustal shearing, melting, and granite emplacement has become largely accepted in the place of large scale, unreasonable models involving fractional melting of the mantle into granitic batholiths and plutons. Evidence ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 compositions, illustrated by examples like the Palisades Sill of New York and New Jersey; the Henry Mountains of Utah; the Bushveld Igneous Complex of South Africa; Shiprock in New Mexico; the Ardnamurchan intrusion in Scotland; and the Sierra Nevada Batholith of California. Because the solid country rock into which magma intrudes is an excellent insulator, cooling of the magma is extremely slow, and intrusive igneous rock is coarse-grained ( phaneritic). Intrusive igneous rocks are classified separately from extrusive igneous rocks, generally on the basis of their mineral content. The relative amounts of quartz, alkali feldspar, plagioclase, and feldspathoid is particularly important in classifying intrusive igneous rocks. Intrusio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diagenesis
Diagenesis () is the process that describes physical and chemical changes in sediments first caused by water-rock interactions, microbial activity, and compaction after their deposition. Increased pressure and temperature only start to play a role as sediments become buried much deeper in the Earth's crust. In the early stages, the transformation of poorly consolidated sediments into sedimentary rock (lithification) is simply accompanied by a reduction in porosity and water expulsion (clay sediments), while their main mineralogical assemblages remain unaltered. As the rock is carried deeper by further deposition above, its organic content is progressively transformed into kerogens and bitumens. The process of diagenesis excludes surface alteration (weathering) and deep metamorphism. There is no sharp boundary between diagenesis and metamorphism, but the latter occurs at higher temperatures and pressures. Hydrothermal solutions, meteoric groundwater, rock porosity, permea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Protolith
A protolith () is the original, unmetamorphosed rock from which a given metamorphic rock is formed. For example, the protolith of a slate is a shale or mudstone. Metamorphic rocks can be derived from any other kind of non-metamorphic rock and thus there is a wide variety of protoliths. Identifying a protolith is a major aim of metamorphic geology. Protoliths are non-metamorphic rocks and have no protoliths themselves. The non-metamorphic rocks fall into two classes: sedimentary rocks, formed from sediment, and igneous rocks, formed from magma. The source of the sediment of a sedimentary rock is termed its provenance. Magmatic protoliths can be further divided into three categories: ultramafic rock, 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 includ ... rock, and quartzo-feld ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phyllite
Phyllite ( ) is a type of foliated metamorphic rock created from slate that is further metamorphosed so that very fine grained white mica achieves a preferred orientation.Stephen Marshak ''Essentials of Geology'', 3rd ed. It is primarily composed of quartz, sericite mica, and chlorite. Phyllite has fine-grained mica flakes, whereas slate has extremely fine mica flakes, and schist has large mica flakes, all mica flakes of which have achieved a preferred orientation. Among foliated metamorphic rocks, it represents a gradation in the degree of metamorphism between slate and schist. The minute crystals of graphite, sericite, or chlorite, or the translucent fine-grained white mica, impart a silky, sometimes golden sheen to the surfaces of cleavage, called "phyllitic luster". The word comes from the Greek ''phyllon'', meaning "leaf". The protolith (or parent rock) for phyllite is shale or pelite, or slate, which in turn came from a shale protolith. Its constituent platy mine ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Schist
Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes or plates. This texture reflects a high content of platy minerals, such as micas, talc, chlorite, or graphite. These are often interleaved with more granular minerals, such as feldspar or quartz. Schist typically forms during regional metamorphism accompanying the process of mountain building (orogeny) and usually reflects a medium grade of metamorphism. Schist can form from many different kinds of rocks, including sedimentary rocks such as mudstones and igneous rocks such as tuffs. Schist metamorphosed from mudstone is particularly common and is often very rich in mica (a ''mica schist''). Where the type of the original rock (the protolith) is discernible, the schist is usually given a name reflecting its protolith, such as ''schis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lyell Frontispiece 1837
Lyell is a surname of Scotland traced to Radulphus de Insula, 11th-century Lord of Duchal Castle. "De insula" was subsequently translated into the Old French "de l'isle" and developed into a number of variants ( eLyell; eLisle; eLyle; see below). John Lyell in 1706 emigrated to Virginia and is the progenitor of the American Lyells. Lyell may refer to: People * Henry Lyell (1665-1731), Swedish-born English businessman * Charles Lyell (botanist) (1767–1849), Scottish botanist :* Charles Lyell (1797–1875), British geologist; son of the botanist; 1st Baronet Lyell of Kinnordy :* Mary Horner Lyell (1808–1873), conchologist; wife of the geologist :* Katharine Murray Lyell (1817–1915), British botanist and author; sister-in-law of the geologist :::* Leonard Lyell, 1st Baron Lyell (1850–1926), Scottish Liberal politician; son of Katharine Murray Lyell ::::* Charles Henry Lyell (1875–1918), Liberal MP; son of Leonard Lyell :::::* Charles Anthony Lyell, 2nd Baron Lyell (1913 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
