Mylonites

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Mylonites are crushed rocks, typically in shear zones. When formed at higher grades, they will be re-crystallized and are known formally as blastomylonites. The distinction between blastomylonites and metamorphic foliation is sometimes difficult to make. This author errs on the side of inclusion of many metamorphic foliation as mylonitic foliation, because in many cases shear zones can be many kilometers wide.


69_048. Mylonitic granite. Brodill Lake, Sudbury, ONT. [46.367145,-80.951142]

Wyangalla dam, New South Wales, Australia.


62_003. Mylonite in granite.  Wyangalla dam, New South Wales, Australia. [-33.970328,148.95155]


62_004.  Fold in mylonite. Wyangalla dam, New South Wales, Australia. [-33.970328,148.95155]


62_007. Passively folded pegmatite in mylonitic granite. Tim Hopwood. Wyangalla dam, New South Wales, Australia. [-33.970328,148.95155]

Terrapinna, Mt. Painter region, South Australia.

This area shows a magnificent transition from porphyritic granite to mylonite. The section is overlain by Precambrian Sturt tillite. A study published in ?1954 in the Quarterly Journal of the Geological Society of London (now simply Journal of the Geological Society) concluded the transition from tillite to granite was a classic case of granitization.
The sequence of photos is from the least deformed to most deformed rocks.


66_017. Terrapinna, Mt. Painter region, South Australia. [-29.91532,139.646673]


66_025. Terrapinna, Mt. Painter region, South Australia. [-29.91532,139.646673]


66_024. Terrapinna, Mt. Painter region, South Australia. [-29.91532,139.646673]


66_018. Terrapinna, Mt. Painter region, South Australia. [-29.91532,139.646673]


66_019. Terrapinna, Mt. Painter region, South Australia. [-29.91532,139.646673]

Lincoln sill, Boothbay Harbor, Maine

The Lincoln sill shows on the map as a giant tadpole, a bulbous center and a long tail. It can be regarded as a giant boudin, the tail showing the most deformation.
The sequence of photos is from the least deformed to most deformed rocks.


69_079. Massive part of the Lincoln sill with irregular orientation of blue feldspar phenocrysts. Boothbay Harbor, Maine. [43.847731,-69.644237]


69_075. Deformed sill with the feldspars now aligned. Boothbay Harbor, Maine. [43.847731,-69.644237]


69_088. Schistose sill. Boothbay Harbor, Maine. [43.847731,-69.644237]


69_090. A highly schistose zone within the less deformed part of the sill. Boothbay Harbor, Maine. [43.847731,-69.644237]

Rainy Lake, Ontario, Canada

Superior Province schist, gneiss, amphibolite, and granite are cut by a large east-west shear. These are all blastomylonites.


70_006. Well layered mylonitic granitoid. Rainy Lake, Ontario, Canada. [48.698246,-92.999468]


70_005. Folded mylonitic layering in gneiss. Rainy Lake, Ontario, Canada. [48.698246,-92.999468]


70_008. A foliated pegmatite (pencil) cut by pegmatite (hammer) and aplite (notebook). Rainy Lake, Ontario, Canada. [48.698246,-92.999468]


70_011. Sheared amphibolite cut by pegmatites. Rainy Lake, Ontario, Canada. [48.698246,-92.999468]


70_015. Mylonite layer bordering augen structure in monzonite. Rainy Lake, Ontario, Canada. [48.698246,-92.999468]


70_017. Mylonite in amphibolite. Rainy Lake, Ontario, Canada. [48.698246,-92.999468]

Yellow Aster Butte, WA.


84_110. Mylonite with pod showing right lateral movement. Yellow Aster Butte, WA. [48.955771,-121.678698]


84_111. Mylonite cutting gneiss. Yellow Aster Butte, WA. [48.955771,-121.678698]

Moine Thrust area, Scotland


85_108. Brittle zone in mylonite. Stack of Glencoul, NW Highlands. [NC272303; 58.219611,-4.928112]


85_109. Looking down on mylonitic foliation to show a stretching lineation. [NC272303; 58.219611,-4.928112]


85_113.  The Moine thrust. Moine schist, above scale, over Cambrian quartzite. Stack of Glencoul. [NC272303; 58.219611,-4.928112]


85_140. Asymmetric Hornblendite ball in Lewisian gneiss. Achmelvic, NW Highlands. [NC059248. 58.169259, -5.301737].


85_246. Cambrian quartzite. Blue quartz in breccia shear zone. Ben Uidhe, Assynt, NW Highlands. [NC283242. 58.173156, -4.921061].


85_247. Shear zone (through middle of photo) in Cambrian quartzite.  Ben Uidhe, Assynt, NW Highlands. [NC283242. 58.173156, -4.921061].

North coast of Spain


86_045. Folds in cataclasites.  Lake Luna.


86_086. Shear in brecciated quartzite. Reidel shears.   El Portizuela beach, Luarca. [43.550994,-6.541761]


86_087. Same as 86. R Y & P shears. El Portizuela beach, Luarca. [43.550994,-6.541761]


86_099. Extensional crenulation cleavage. Basal shear of the Mondon nappe, west of Foz.


86_105. Augen gneiss of doubtful origin, with lineation.  Ollo de Sapo. [43.559645,-8.035927]


86_110. Melange below the Cedeira nappe, with Reidel shears.  Punta Candelaria lighthouse, Cedeira.

Cascade Ranges, WA


87_058. S-C mylonite.  Cascade River.


87_059.  S-C mylonite.  Cascade River.


87_060. Extensional crenulation cleavage.  Marblemount.


88_014. Mylonite in syenite.  Similkameen, west of the Okanogan valley. [48.984645,-119.398584]


88_015. Mylonite in syenite with large feldspars. Similkameen, west of the Okanogan valley. [48.984645,-119.398584]


88_016. Aligned feldspar in pyroxene syenite. As a caution against interpreting all alignments as tectonic. [48.984645,-119.398584]


88_017. Ditto 16. [48.984645,-119.398584]

Harrison Lake, BC


87_076. C-S structures in pelites in the Harrison Lake fault zone.
Hammer lies along an S surface, the C surface is at a lower angle.


88_053. S/C fabric in schist.  C is nearly horizontal. Cogburn Creek. [49.55357,-121.732006]


88_070. Mylonite with folds parallel to lineation.  Hornet Creek. BC. [49.644802,-121.784191]


89_048. S/C structures in boudins. Bridge at Fir Creek.

Holden, Lake Chelan, WA


88_083. Longitudinal profile of lineated hornblende gneiss showing right lateral movement. Holden, Lake Chelan, WA. [48.224175,-120.831857]


88_084. Longitudinal profile of sheared hornblende gneiss. Holden, Lake Chelan, WA. [48.224175,-120.831857]

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