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 Eastern Highlands Shear Zone has been recognized to display a protracted period of motion (Lin 1995), although the dominant phase of mylonite development ended in the Late Devonian.
SAMPLE DESCRIPTION The selected sample (TV-336) is an augen granitoid mylonite from the Tverecius-336 drill core, located in the eastern part of the DPDZ close to the Belarus border (Fig.
zoned, helicitic, calcium-rich almandine garnets from the Hyde School Marginal Mylonite of the Adirondack Lowlands and to date (U-Pb) monazite inclusions in the cores and rims to verify the hypothesis that there were two episodes of garnet growth, currently based upon textural observations, chemical zoning, and geothermometry.
The above geological and analytical results continue to be consistent with those previously encountered for the B-14 Zone with the zone persisting as a moderately dipping shear zone marked by increased sericite and carbonate alteration, quartz veining, and pyrite hosted by mylonite.
In the Hosenbein pluton, modal layering is most abundant in the Marginal Zone, where it shows mostly gneissic texture that locally grades into mylonite.
It is possible that these high grade shoots are oriented such that the drill density to-date, designed to define the mylonite zone, is insufficient in delineating the smaller, but much higher grade shoots.
The SZD has been traced over a 1 km strike length and remains open under the glacial-fluvial deposits of the Todd Creek Valley towards the Knob Zone, 4 km to the north; and, towards the Mylonite Zone, 3 km to the south.
The Company continues to find that the B-14 Zone persists as a moderately dipping shear zone marked by increased sericite and carbonate alteration, quartz veining, and pyrite hosted by mylonite.
We've got one high grade, quartz-rich shoot within a very broad lower grade mylonite zone.
Also anomalous on Isle Madame are three long narrow belts of "basement" rocks, together with voluminous chloritic microbreccia and minor semi-ductile mylonite, which are separated from the conglomerate-dominated successions by faults.
Old pits and trenches were mapped along a 300 m length and a series of vein grab samples were taken that often contained chalcopyrite (copper), galena(lead) within a reddish-brown mylonite (shear) and gave the following distribution of values.
Project site geology is characterized by a gentle dipping, Miocene-age detachment fault juxtaposing upper plate Tertiary andesite with lower plate, Precambrian, granitic mylonite.