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

Lucy McKay, Zoe K. Shipton, Rebecca J. Lunn, Billy Andrews, Timothy D. Raub, Adrian J. Boyce

Research output: Contribution to journalArticle

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., 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 meter 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.
LanguageEnglish
Number of pages32
JournalJournal of the Geological Society
Publication statusAccepted/In press - 27 Aug 2019

Fingerprint

plate boundary
Wall rock
Clay
Rocks
Chemical analysis
Chemical reactions
Earthquakes
Mechanics
wall rock
Physical properties
clay
authigenesis
earthquake rupture
San Andreas Fault
serpentinite
microfossil
chemical reaction
clast
rock
mechanics

Keywords

  • Highland boundary
  • plate boundary faults
  • minerology

Cite this

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title = "Detailed internal structure and along-strike variability of the core of a plate boundary fault: the Highland boundary fault, Scotland",
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., 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 meter 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.",
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AU - McKay, Lucy

AU - Shipton, Zoe K.

AU - Lunn, Rebecca J.

AU - Andrews, Billy

AU - Raub, Timothy D.

AU - Boyce, Adrian J.

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N2 - 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., 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 meter 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.

AB - 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., 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 meter 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.

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