Regional Metamorphism


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Related to Regional Metamorphism: dynamic metamorphism, burial metamorphism

regional metamorphism

[′rēj·ən·əl ‚med·ə′mȯr‚fiz·əm]
(geology)
Geological metamorphism affecting an extensive area.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Regional Metamorphism

 

the changes that occur in rock acted upon by abyssal transmagmatic solutions (fluids), oriented (unilateral) and hydrostatic (all-encompassing) pressure, and temperature.

Regional metamorphism, involving profound transformations in the structure and mineral composition of rocks over vast areas, is related to the development of folding and orogeny. Unilateral pressure produces slaty and gneiss textures in meta-morphic rocks. Hydrostatic pressure is determined by depth, and as the pressure increases it causes metamorphic reactions among minerals that reduce the rock volume. Depth facies of metamorphic rocks are identified with respect to hydrostatic pressure. These facies make it possible to judge the depth of erosion of regionally metamorphosed structures (folded belts, blocks, and shields). Depending on the temperature, three levels of regional metamorphism may be distinguished: high, medium, and low.

The products of regional metamorphism (amphibolites, phyllites, gneisses, and migmatites) crop out at the earth’s surface within ancient shields and crystalline blocks. At great depths, regional metamorphism is usually uniform (the same degree of metamorphism is maintained over large areas). At shallower depths, where different degrees of metamorphism are observed, regional metamorphism is not uniform. A consecutive decrease in the degree of metamorphism can be traced in anticlinoria, granite-gneiss domes, and other geological structures where there is a zonal distribution of regional metamorphic products that differ mineralogically and structurally (zonal metamorphism). As the scope of metamorphic manifestations diminishes, regional metamorphism gives way to local metamorphism, which is controlled by such local structures as contacts with intrusive masses (contact metamorphism) and fractures (fracture metamorphism).

REFERENCE

Marakushev, A. A. Petrologiia metamorficheskikh gornykh porod. Moscow, 1973.

A. A. MARAKUSHEV

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Multi-stage emerald formation during Pan- African regional metamorphism: The Zabara, Sikait, Umm Kabo deposits, South Eastern desert of Egypt.
Brown, M.: 1993, P-T-t evolution of organic belts and the causes of regional metamorphism, J.
It displays a moderate preferred orientation of elongate crystals (contain quartz and ilmenite inclusions parallel to [S.sub.e]) parallel to [S.sub.e], indicating that it formed during the late regional metamorphism. On the other hand, in the direction of shear, staurolite porphyroblasts with high aspect ratios tend to lie with their long axis parallel to [S.sub.e].
Early somewhat random muscovite and biotite growth (with garnet and andalusite in rocks of suitable composition) followed by peak regional metamorphism produced cordierite porphyroblasts up to 10 cm in suitable (though rare) compositions.
Particularly puzzling is the origin of Eocene igneous complexes which outcrop within the Tethyan Himalaya, as the heat source needed to generate Eohimalayan peraluminous magmatism (and regional metamorphism) in the eastern Tethyan Himalaya is not predicted by existing models.
The importance of the role of late Variscan low-pressure high-temperature regional metamorphism in crustal melting and granite magma generation of extensive granite batholiths in the Moldanubian Zone of the Bohemian Massif is widely accepted (Buttner and Kruhl 1997, Kalt et al.
Fe and Mn skam bodies enveloping the oxide-dominated carbonate-rich ores have formed during Svecocarelian regional metamorphism and presumably also associated magmatism.
Orville, "Volatile production and transport in regional metamorphism," Contributions to Mineralogy and Petrology, vol.
However, they may also form in rocks affected by metasomatic processes linked to the regional metamorphism or hydrothermal alteration.

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