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The optical photomicrographs below illustrate the classic cataclasite fault rock evolution in Cambrian Pipe Rock Quartzite (Skiag Bridge back thrust fault) via grain size reduction due to fracturing to produce a fine grain size fault rock. The photomicrographs are viewed towards NE and were cut normal to fault plane and parallel to movement direction; field of view 2mm.
For other examples see: cathodoluminescence, SEM, EBSD, TEM, indentation.
For further details, see the original micrographs and descriptions in: Lloyd and Knipe. 1991, Journal of Structural Geology, and Knipe and Lloyd, 1994, Pure and Applied Geophysics.
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1. Parental rock with inherited subgrain microstructures. | |
2. Initial intragranular microfractures, usually propagating from inter-grain contacts. |
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3. Through-going microcracks. | |
4. The first indications of localised grain size reduction via cataclasis. |
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5. Through-going cataclastic seams. | |
6. Well-developed through-going cataclastic seam. |
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7. Incipient pervasive gouge surrounding relict original grains. | |
8. cataclastic fault rock with fragment of original rock. |