Classification of fault breccias and related fault rocks

Woodcock, N. H. and Mort, K. (2008) Classification of fault breccias and related fault rocks. Geological Magazine, 145 (3). pp. 435-440. ISSN 0016-7568 DOI https://doi.org/10.1017/S0016756808004883

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Abstract

Despite extensive research on fault rocks, and on their commercial importance, there is no non-genetic classification of fault breccias that can easily be applied in the field. The present criterion for recognizing fault breccia as having no ‘primary cohesion’ is often difficult to assess. Instead we propose that fault breccia should be defined, as with sedimentary breccia, primarily by grain size: with at least 30% of its volume comprising clasts at least 2 mm in diameter. To subdivide fault breccias, we advocate the use of textural terms borrowed from the cave-collapse literature – crackle, mosaic and chaotic breccia – with bounds at 75% and 60% clast content. A secondary breccia discriminant, more difficult to apply in the field, is the ratio of cement to matrix between the clasts. Clast-size issues concerning fault gouge, cataclasite and mylonite are also discussed.

Item Type:	Article
Uncontrolled Keywords:	08AREP IA55, Part III
Subjects:	02 - Geodynamics, Geophysics and Tectonics
Divisions:	02 - Geodynamics, Geophysics and Tectonics
Journal or Publication Title:	Geological Magazine
Volume:	145
Page Range:	pp. 435-440
Identification Number:	https://doi.org/10.1017/S0016756808004883
Depositing User:	Sarah Humbert
Date Deposited:	16 Feb 2009 13:04
Last Modified:	23 Jul 2013 09:54
URI:	http://eprints.esc.cam.ac.uk/id/eprint/813

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