Classification of fault breccias and related fault rocks

Geological Magazine - Tập 145 Số 3 - Trang 435-440 - 2008
Nigel Woodcock1, Kate Mort1
1Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK

Tóm tắt

AbstractDespite 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.

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Geological Magazine

Tập 145 Số 3

435-440

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