Detailed internal structure and along-strike variability of the core of a plate boundary fault: the Highland Boundary fault, Scotland

McKay, L., Shipton, Z. K., Lunn, R. J., Andrews, B., Raub, T. D. and Boyce, A. J. (2019) Detailed internal structure and along-strike variability of the core of a plate boundary fault: the Highland Boundary fault, Scotland. Journal of the Geological Society, jsg2018226. (doi: 10.1144/jgs2018-226)

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Abstract

The Highland Boundary fault near Stonehaven, NE Scotland, provides a rare opportunity to study the internal fault structure of a well-exposed, along-strike section of an ancient plate boundary fault. As in many plate boundaries, serpentinite juxtaposes quartzo-feldspathic crustal rocks of distinct terranes. We report, for the first time, the complex internal structure of the Highland Boundary fault core, comprised of four structurally and chemically distinct clay-rich units that remain unmixed. Despite the evidence for internal strain, relatively intact clasts of wall rock and microfossils are preserved within the clay. The fault core clay minerology is consistent with a shallow, low-temperature authigenesis derived from shear-enhanced chemical reactions between wall rocks of contrasting chemistry during sinistral strike-slip. The observed structure is comparable to those of other major weak-cored plate boundaries (e.g. the San Andreas fault). Through detailed mapping, we demonstrate that the internal structure of a plate boundary fault core can vary in thickness and composition along-strike over centimetre- to metre-length scales. Earthquake rupture mechanics critically depend on the physical properties of fault rock assemblages. Therefore, models that investigate rupture propagation at active plate boundaries should incorporate, or else assess tolerance and sensitivity to, variable fault core thickness and composition.

Item Type:Articles
Additional Information:This work is funded by an Environmental and Physical Science Research Council (EPSRC) Doctoral Training Partnership (DTP) award (LM). TDR was supported initially by a grant from the Carnegie Foundation.
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Boyce, Professor Adrian
Authors: McKay, L., Shipton, Z. K., Lunn, R. J., Andrews, B., Raub, T. D., and Boyce, A. J.
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Journal of the Geological Society
Publisher:Geological Society of London
ISSN:0016-7649
ISSN (Online):2041-479X
Published Online:20 September 2019

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