Migmatite is a rock at the frontier between igneous and metamorphic rocks. In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere Igneous rocks (etymology from Latin ignis, fire are rocks formed by solidification of cooled Magma (molten rock Metamorphic rock is the result of the transformation of an existing rock type the protolith, in a process called Metamorphism, which means "change They can also be known as diatexite.
Migmatites form under extreme temperature conditions during prograde metamorphism, where partial melting occurs in pre-existing rocks. Migmatites are not crystallized from a totally molten material, and are not generally the result of solid-state reactions. Migmatites are composed of a leucosome, new material crystallized from incipient melting, and a mesosome, old material that resisted melting. Commonly, migmatites occur within extremely deformed rocks that represent the base of eroded, mountain chains, typically within Precambrian cratonic blocks. The Precambrian ( Pre-Cambrian) is an informal name for the supereon comprising the eons of the Geologic timescale that came before the current
Migmatites often appear as tightly, incoherently folded (ptygmatic folds) dikelets, veins and segregations of light colored granitic composition called leucosome, within dark colored amphibole and biotite rich material called the melanosome. A dike or dyke in Geology is a type of Sheet intrusion referring to any geologic body that cuts Discordantly ' across planar Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. Amphibole (pronounced amfi-bowl defines an important group of generally dark-colored rock-forming inosilicate Minerals composed of double chain SiO4 Biotite is a common phyllosilicate Mineral within the Mica group with the approximate chemical formula K(Mg Fe3AlSi3O10(F The light colored material has the appearance of having been mobilized or molten. Once enough leucosomes join up to form a network and granite is produced, the residual material is known as restite. Restite is the residual material left at the site of melting during the in place production of Granite through intense Metamorphism.
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Textures
Migmatite textures are the product of thermal softening of the metamorphic rocks. Schlieren textures are a particularly common example of granite formation in migmatites, and are often seen in restite xenoliths and around the margins of 'S-type granites. Schlieren (from German; singular "schliere" are optical inhomogeneities in transparent material not visible to the human eye Restite is the residual material left at the site of melting during the in place production of Granite through intense Metamorphism. This article concerns the geologic term for other uses see Xenolith (disambiguation A xenolith ( Greek: 'foreign rock' is a rock
Ptygmatic folds are formed by highly plastic ductile deformation of the gneissic banding, and thus have little to no relationship to a defined foliation unlike most regular folds. Foliation is any penetrative planar fabric present in rocks. Foliation is common to rocks affected by regional metamorphic compression typical of orogenic Ptygmatic folds can occur restricted to compositional zones of the migmatite, for instance in fine-grained shale protoliths versus in coarse granoblastic sandy protolith. Granoblastic is an Anhedral Phaneritic equi-granular Metamorphic rock texture
Migmatite and the origin of Granites
For migmatised argillaceous rocks, the partial or fractional melting would first produce a volatile and incompatible-element enriched rich partial melt of granitic composition. "Argillite" may also refer to Argillite Kentucky. An argillite (ˈɑrdʒɨlaɪt is a fine-grained Sedimentary rock composed Within the field of Geology, Bowen's reaction series is the work of the Petrologist, Norman L Volatility in the context of Chemistry, Physics and Thermodynamics is a measure of the tendency of a substance to Vaporize. Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. Such granites derived from sedimentary rock protoliths would be termed S-type granite, are typically potassic, sometimes containing leucite, and would be termed adamellite, granite sensu stricto and syenite. Sedimentary rock is one of the three main rock types (the others being igneous and Metamorphic rock) Leucite is a rock -forming Mineral composed of Potassium and Aluminium tectosilicate K Quartz monzonite (or adamellite) is an intrusive Igneous rock that has an approximately equal proportion of Orthoclase and Plagioclase Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. Syenite is a coarse-grained intrusive Igneous rock of the same general composition as Granite but with the Quartz either absent or present in relatively Volcanic equivalents would be rhyolite and rhyodacite. This page is about a volcanic rock For the ghost town see Rhyolite Nevada, and for the satellite system see Rhyolite/Aquacade. Rhyodacite is an extrusive Volcanic rock intermediate in composition between Dacite and Rhyolite.
Migmatised igneous or lower-crustal rocks which melt do so to form a similar granitic I-type granite melt, but with distinct geochemical signatures and typically plagioclase dominant mineralogy forming monzonite, tonalite and granodiorite compositions. Igneous rocks (etymology from Latin ignis, fire are rocks formed by solidification of cooled Magma (molten rock The continental crust is the layer of granitic, Sedimentary, and Metamorphic rocks which form the Continents and the areas of shallow seabed The field of geochemistry involves study of the chemical composition of the Earth and other Planets chemical processes and reactions that govern the composition Plagioclase is a very important series of tectosilicate Minerals within the Feldspar family Monzonite is an intermediate Igneous Intrusive rock composed of approximately equal amounts of sodic to intermediate Plagioclase and Orthoclase Tonalite is an igneous, Plutonic ( Intrusive) rock, of Felsic composition with Phaneritic texture Granodiorite (ˌgrænəˈdaɪəraɪt/ /ˌgreɪn- is an intrusive Igneous rock similar to Granite, but contains more Plagioclase than Potassium feldspar Volcanic equivalents would be dacite, trachyte and trachydacite. Dacite ( deɪsaɪt) is an igneous, volcanic rock with a high iron content Trachyte is an Igneous, Volcanic rock with an Aphanitic to Porphyritic texture
It is difficult to melt mafic metamorphic rocks except in the lower mantle, so it is rare to see migmatitic textures in such rocks. Mafic is an adjective describing a Silicate mineral or rock that is rich in magnesium and iron the term was derived by contracting "magnesium" and "ferric" However, eclogite and granulite sensu stricto are roughly equivalent mafic rocks. Eclogite (ˈɛklədʒaɪt is a coarse-grained Mafic ( Basaltic in composition Metamorphic rock. Granulites are fine to medium–grained Metamorphic rocks that have experienced high Temperatures of metamorphism composed mainly of Feldspars sometimes associated
Etymology
The Finnish petrologist Jakob Sederholm first used the term in 1907 for rocks within the Scandinavian craton in southern Finland. Finland, officially the Republic of Finland ( is a Nordic country situated in the Fennoscandian region of northern Europe. In Geology, petrology (from Greek πέτρα petra, rock and λόγος logos, knowledge is the study of rocks and the conditions on which Jakob Johannes Sederholm (1863-1934 was a Finnish petrologist most associated with his studies of Migmatites ref> The Baltic Shield (sometimes referred to as the Fennoscandian Shield) is located in Fennoscandia ( Norway, Sweden and Finland) northwest Finland, officially the Republic of Finland ( is a Nordic country situated in the Fennoscandian region of northern Europe. The term was derived from the Greek word μιγμα: migma meaning a mixture. Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly
See also
References
- Blatt, Harvey and Tracy, Robert J. Igneous rocks (etymology from Latin ignis, fire are rocks formed by solidification of cooled Magma (molten rock Metamorphic rock is the result of the transformation of an existing rock type the protolith, in a process called Metamorphism, which means "change Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. This page is intended to be a list of rock textural and morphological terms Rock microstructure includes the texture of a rock and the small scale rock structures ; 1996, Petrology: Igneous, Sedimentary, and Metamorphic, 2nd ed. , p. 463-466, W. H. Freeman, ISBN 0-7167-2438-3
- R. V. Dietrich - Migmatites
- North Cascades National Park: Orthogneisses and Migmatites
- Cooma Complex, SE Australia
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