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A structure in which beds set in a softer matrix are divided by cross fractures into segments resembling pillows.



division of rock strata or veins into separate blocks or lenses extending in the direction of the stratum or vein. It is formed during the crushing of a relatively more competent, flat geological body (stratum or vein) between two relatively more fluid layers under the influence of forces perpendicular to the layers. Such conditions arise, for example, on the limbs of strongly compressed folds, where the more plastic layers, being crushed and spreading in the direction of the axes of the folds, stretch the harder layers locked between them. The harder layers, being unable to flow with the same speed, at first divide into pinches—necks and swellings—lenses (lensing stage of boudinage), and then separate into pieces—boudins (boudinage proper). In the process of further deformation these pieces move farther and farther apart and the spaces between them fill up with material from adjacent plastic layers or with new mineral material (quartz, pegmatite). Boudinage is observed predominantly in metamorphic rocks.


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These features include conspicuous variations in the orientation of the intersection lineation, rootless folds that are cross-cut by cleavage, and boudinage and fragmentation of siltstone layers, all absent in the overlying and underlying members.
However, bedding surfaces that have previously been rotated fall in either the shortening or the extension field of the strain ellipsoid, and are therefore more susceptible to folding and/or boudinage.
Pilot Gold reports that the Western Flank area hosts numerous features that are similar to the geology at the Long Canyon deposit located approximately 75 kilometres (47 miles) to the north, including evidence of potential boudinage of a 100 metre-thick dolomite horizon and focusing of gold mineralization in and around this boudin neck area, which strikes north-northeast.
A mineralized shear zone has also been uncovered some 100 m long and 5-7 m wide on the northern part of an island: it is ankeritized with folded quartz and tourmaline veins which underwent some boudinage and the first results available gave 5.
1] folds and likely caused the folding and boudinage of quartz veins.
This boudinage likely formed synchronously with the ENE-striking dip-slip fault motion (Farrens 1982; Mosher 1983; Mosher and Berryhill 1991).
Locally, the dyke displays pinch and swell type boudinage over 3-4 m.
Boudinage is more prevalent on Aquidneck Island where decametre-scale foliation boudinage is observed.
Deformation also occurs in thin limestone beds immediately above the crystal-laminated layer, where it takes the form of boudinage and small-scale normal faults.
The gold is contained in quartz veins associated with a Birrimian (Proterozoic) age transgressive left lateral shear zone, which boudinages and juxtaposes basement gneisses and supracrustal lithologies.