Cockade breccia: product of mineralisation along dilational faults

Frenzel, Max and Woodcock, Nigel H. (2014) Cockade breccia: product of mineralisation along dilational faults. Journal of Structural Geology, 68 (Part A). pp. 194-206. ISSN ISSN: 0191-8141 DOI https://doi.org/10.1016/j.jsg.2014.09.001

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Abstract

Cockade breccias are fault fills in which individual clasts are completely surrounded by concentric layers of cement. They occur particularly in low-temperature near-surface hydrothermal veins. At least six mechanisms have been proposed for the formation of cockade breccia-like textures, but only two – repeated rotation–accretion, and partial metasomatic replacement of clast minerals – have been supported by detailed evidence. A typical example of cockade breccia from the Gower Peninsula (South Wales) shows clear evidence for the rotation–accretion mechanism: in particular, overgrown breakage points in cement layers – where cockades were previously touching each other – and rotated geopetal infills of haematitic sediment. Based on the available evidence, it is proposed that cockade textures result from low rates of cement growth compared to high rates of dilational fault slip. Seven criteria are given for the correct identification of cockade breccias.

Item Type:	Article
Uncontrolled Keywords:	2014AREP; IA68;
Subjects:	02 - Geodynamics, Geophysics and Tectonics
Divisions:	02 - Geodynamics, Geophysics and Tectonics 06 - Part-III Projects
Journal or Publication Title:	Journal of Structural Geology
Volume:	68
Page Range:	pp. 194-206
Identification Number:	https://doi.org/10.1016/j.jsg.2014.09.001
Depositing User:	Sarah Humbert
Date Deposited:	19 Sep 2014 18:11
Last Modified:	07 Nov 2014 20:15
URI:	http://eprints.esc.cam.ac.uk/id/eprint/3133

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