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 ?
The main structures propagated in this phase are mylonitic and S-C fabric, Minerals fish and lensoid structures, and shear folds.
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.
The calibre of grades returned in TGA089 may be an indication that the drilling may have encountered another high grade sub-body within the broader mylonitic mineralisation, similar to Terrace Creek.
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 axial zone of the Pyreeneees provides outcrops of Hercynian basement and faults, such as the CMNC "Chevauchement Mylonitic Nord Canigou" (Mylonitic North Canigou Thrust).