Mylonite

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mylonite

[′mī·lə‚nīt]
(petrology)
A hard, coherent, often glassy-looking rock that has suffered extreme mechanical deformation and granulation but has remained chemically unaltered; appearance is flinty, banded, or streaked, but the nature of the parent rock is easily recognized.

Mylonite

 

finely ground, crushed rock formed by the movement of rock masses along the surface of tectonic faults. As a result of great pressure, the rocks (granite, gneiss, schists, quartzite) are crushed and ground into a compact state. Microscopic analysis makes possible the identification of finely ground mica flakes and minute quartz and feldspar fragments in the finely pulverized mass, which is made up of the softer minerals of the primary rock and sometimes such new formations as sericite and zoisite. Unlike cataclasis, mylonitization represents the final stage in the crushing of rock into microscopic form. Mylonite zones are located along the major regional thrust faults in the Urals, Tien-Shan, the Caucasus, and the Altai. These zones are several hundred meters wide and extend several dozen kilometers.

REFERENCE

Polovinkina, Iu. I. Struktury i tekstury izverzhennykh i metamorficheskikh porod, vol. 2, part 2. Moscow, 1966.
References in periodicals archive ?
In some cases, crenulations, kink bands in chlorite, and weak to intense deformation superimposed to the main foliation of the rock, developing a mylonitic texture characterized by the presence of thin strips of actinolite and elongated quartz, intercalated with thicker bands quartz and plagioclase.
During intra-oceanic subduction various parts of the subducted plate were accreted to the base of the overriding slab and subjected to a temperature between about 9001000 C forming mylonitic peridotite and then continued downwards to form the sub-ophiolitic metamorphic rocks.
El Picacho Metagabbros show greenschist-- to lower-amphibolite-facies parageneses, conspicuous mylonitic structure, no relation to metasediments, and spatial association to the Medellin Dunite.
Local bands of mylonitic recrystallization are common, particularly near boundaries between units of differing competencies.
Typical fabrics include a weak to strong foliation trending ENE, gradational contacts and metasomatic changes to pegmatoid and mylonitic rock types.
The Province of Sevilla is bounded on the east by the Seville lineament and on the west by the Guachaca fault; it is composed of mylonitic granitoids and amphibole and micaschists of Paleozoic age (Tschanz et al, 1969, 1974; Cardona et al, 2006).
The intermediate belt (Seville province) represents a polymetamorphic complex that includes gneisses and schists of Paleozoic age with Permian mylonitic granitoids (Tschanz et al.
The foliated peridotite grades downward into basal peridotite displaying mylonitic to porphyroclastic textures.
The provenance of sedimentary and volcanic clasts in the central part of the conglomeratic sequence is not clearly related to local basement sources, which are variably mylonitic metamorphic and plutonic rocks (Force and Barr 2006).
These aquifers are constituted by alluvial formations with thicknesses of up to several hundreds of meters, delimited in their base by mylonitic rocks of the Sierra Juarez from the Mesozoic and metamorphic rocks from the Precambrian.
1960, Mylonitic rocks of the Moine Thrust Zone in the Assynt district, north-west Scotland.