Ptygmatic folding in migmatite

Migmatite on the coast of Saaremaa.

Migmatite is a rock at the frontier between igneous and metamorphic rocks. They can also be known as diatextite. Image File history File linksMetadata Ptigmatite. ... Image File history File linksMetadata Ptigmatite. ... Image File history File links Download high resolution version (800x742, 365 KB) Siim Sepp, 2005 Migmatite on the coast of Saaremaa (Estonian island). ... Image File history File links Download high resolution version (800x742, 365 KB) Siim Sepp, 2005 Migmatite on the coast of Saaremaa (Estonian island). ... Rugged coastline of the West Coast of New Zealand The coast is defined as the part of the land adjoining or near the ocean. ... This article is about the island. ... The rocky side of a mountain creek near Orosí, Costa Rica. ... Volcanic rock on North America Plutonic rock on North America Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... Quartzite, a form of metamorphic rock, from the Museum of Geology at University of Tartu collection. ...

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 is an informal name for the eons of the geologic timescale that came before the current Phanerozoic eon. ...

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. 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. A dike in geology refers to a tabular intrusive igneous body. ... Quarrying granite for the Mormon Temple, Utah Territory. ... For the logical fallacy, see Amphibology. ... A Biotite slice Biotite is a common phyllosilicate mineral that contains potassium, magnesium, iron and aluminium. ... Restite is the residual material left at the site of melting during the in place production of granite through intense metamorphism. ...

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 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. ... The xenolith (Greek: foreign rock) is a rock which becomes enveloped in a larger rock during the latters development and hardening. ...

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. Ptygmatic folds can occur restricted to compositional zones of the migmatite, for instance in fine-grained shale protoliths versus in coarse granoblastic sandy protolith. Foliation is any penetrative planar fabric present in rocks. ... 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. 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. Volcanic equivalents would be rhyolite and rhyodacite. An argillite is a fine-grained sedimentary rock composed predominately of indurated clay particles. ... Within the field of geology, Bowens reaction series is the work of the petrologist, Norman L. Bowen who was able to explain why certain types of minerals tend to be found together while others are almost never associated with one another. ... Volatile is the name of more than one concept: A financial instrument with high volatility is considered volatile in economics. ... Quarrying granite for the Mormon Temple, Utah Territory. ... Two types of sedimentary rock: limey shale overlaid by limestone. ... Leucite or amphigene is a rock-forming mineral composed of potassium and aluminium metasilicate KAl(SiO3)2. ... Quarrying granite for the Mormon Temple, Utah Territory. ... Syenite 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 small amounts. ... Rhyolite This page is about a volcanic rock. ... BOOOOOOOOYAAAAAAAA!!!!!!!!!!! ...

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. Volcanic equivalents would be dacite, trachtye and trachydacite. Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... The continental crust is the layer of granitic, sedimentary and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. ... The field of geochemistry involves study of the chemical composition of the Earth and other planets, chemical processes and reactions that govern the composition of rocks and soils, and the cycles of matter and energy that transport the Earths chemical components in time and space, and their interaction with... Lunar Ferroan Anorthosite #60025 (Plagioclase Feldspar). ... Monzonite is a felsic to intermediate igneous intrusive rock composed of approximately equal amounts of sodic to intermediate plagioclase and orthoclase feldspars with minor amounts of hornblende, biotite and other minerals. ... Tonalite is an igneous, plutonic (intrusive) rock, of felsic composition, with phaneritic texture. ... Granodiorite is an intrusive igneous rock similar to granite, but contains more plagioclase than potassium feldspar. ... Gray, red, black, altered white/tan, flow-banded pumice dacite Dacite is a high-silica igneous, volcanic rock. ...

It is difficult to melt mafic metamorphic rocks except in the lower mantle, so it is rare to see migmatitic textures in such rocks. However, eclogite and granulite sensu stricto are roughly equivalent mafic rocks. In geology, mafic minerals and rocks are silicate minerals, magmas, and volcanic and intrusive igneous rocks that have relatively high concentrations of the heavier elements. ... Eclogite is a coarse-grained, mafic-to-ultramafic grouping of metamorphic rocks of special interest on account of the variety of minerals they contain and their microscopic structures and geological relationships. ... Modern petrology defnes a granulite sensuo stricto as a coarse grained, high-grade metamorphic rock composed primarily of pyroxene, plagioclase feldspar and accessory garnet, oxide and amphibole. ...

Etymology

The Finnish petrologist Jakob Sederholm first used the term in 1907 for rocks within the Scandinavian craton in southern Finland. The term was derived from the Greek word μιγμα: migma meaning a mixture. Petrology is a field of geology which focuses on the study of rocks and the conditions by which they form. ... Jakob Johannes Sederholm (1863-1934) was a Finnish petrologist most associated with his studies of migmatites. ... The Baltic Shield (or Fennoscandian Shield) is a segment of the Earths crust belonging to the East European Craton, representing a large part of Scandinavia, northwestern Russia and the northern Baltic Sea. ...

See also

• Igneous rocks
• Metamorphic rocks
• Granite
• List of rock textures
• Rock microstructure

Volcanic rock on North America Plutonic rock on North America Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... Quartzite, a form of metamorphic rock, from the Museum of Geology at University of Tartu collection. ... Quarrying granite for the Mormon Temple, Utah Territory. ... 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. ...

References

• Blatt, Harvey and Tracy, Robert J.; 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