Kinematic and thermal constraints on the reactivation of the Outer Hebrides Fault Zone, NW Scotland

A. G. Szulc, G. I. Alsop, G. J. H. Oliver

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

The Outer Hebrides Fault Zone is a major easterly dipping reactivated shear zone which displaces Lewisian gneiss of the Laurentian craton, NW Scotland. Despite a number of detailed field studies, the fault zone remains poorly understood with regard to both its age of inception and precise conditions of reactivation. The island of Scalpay in the northern portion of the Outer Hebrides Fault Zone provides exceptional exposures through a variety of reactivated fault rock types and therefore represents an ideal location to investigate fault zone evolution via fluid inclusion studies of syntectonic quartz veins. This fluid inclusion study constrains reactivation temperatures more precisely than hitherto possible with top-to-the-NW ductile thrusting occurring at 500 +/- 30 degrees C. Subsequent phyllonitization is associated with oblique sinistral top-to-the-NE strike-slip at 230 +/- 20 degrees C, followed by a discrete system of top-to-the-NE/SE extensional detachments at 150 +/- 20 degrees C. Other recent fluid inclusion studies in the southern portion of the Outer Hebrides Fault Zone constrain phyllonitization associated with top-to-the-E displacement to 370 +/- 20 degrees C, with subsequent top-to-the-NE extensional detachments operating at 150-210 degrees C. Thus, late-stage extensional detachment systems record consistent conditions of reactivation along the strike length of the Outer Hebrides Fault Zone. However, our results also clearly emphasize that conditions of earlier fault zone reactivation and phyllonitization were highly heterogeneous between the northern and southern portions, thus suggesting a spatial and temporal variation in the deformation and/or fluid flux system.

Original languageEnglish
Pages (from-to)623-636
Number of pages14
JournalGeological Magazine
Volume145
Issue number5
Early online date22 Jul 2008
DOIs
Publication statusPublished - Sep 2008

Keywords

  • deformation
  • fault
  • fluid inclusions
  • fluids
  • Scotland
  • Lewisian Gneiss Complex
  • crustal-scale fault
  • evolution
  • pseudotachylite
  • reappraisal

Cite this

Kinematic and thermal constraints on the reactivation of the Outer Hebrides Fault Zone, NW Scotland. / Szulc, A. G.; Alsop, G. I.; Oliver, G. J. H.

In: Geological Magazine, Vol. 145, No. 5, 09.2008, p. 623-636.

Research output: Contribution to journalArticle

@article{ff4c093a8c6c4cef97a552f40ec69d4c,
title = "Kinematic and thermal constraints on the reactivation of the Outer Hebrides Fault Zone, NW Scotland",
abstract = "The Outer Hebrides Fault Zone is a major easterly dipping reactivated shear zone which displaces Lewisian gneiss of the Laurentian craton, NW Scotland. Despite a number of detailed field studies, the fault zone remains poorly understood with regard to both its age of inception and precise conditions of reactivation. The island of Scalpay in the northern portion of the Outer Hebrides Fault Zone provides exceptional exposures through a variety of reactivated fault rock types and therefore represents an ideal location to investigate fault zone evolution via fluid inclusion studies of syntectonic quartz veins. This fluid inclusion study constrains reactivation temperatures more precisely than hitherto possible with top-to-the-NW ductile thrusting occurring at 500 +/- 30 degrees C. Subsequent phyllonitization is associated with oblique sinistral top-to-the-NE strike-slip at 230 +/- 20 degrees C, followed by a discrete system of top-to-the-NE/SE extensional detachments at 150 +/- 20 degrees C. Other recent fluid inclusion studies in the southern portion of the Outer Hebrides Fault Zone constrain phyllonitization associated with top-to-the-E displacement to 370 +/- 20 degrees C, with subsequent top-to-the-NE extensional detachments operating at 150-210 degrees C. Thus, late-stage extensional detachment systems record consistent conditions of reactivation along the strike length of the Outer Hebrides Fault Zone. However, our results also clearly emphasize that conditions of earlier fault zone reactivation and phyllonitization were highly heterogeneous between the northern and southern portions, thus suggesting a spatial and temporal variation in the deformation and/or fluid flux system.",
keywords = "deformation, fault, fluid inclusions, fluids, Scotland, Lewisian Gneiss Complex, crustal-scale fault, evolution, pseudotachylite, reappraisal",
author = "Szulc, {A. G.} and Alsop, {G. I.} and Oliver, {G. J. H.}",
year = "2008",
month = "9",
doi = "10.1017/S0016756808004925",
language = "English",
volume = "145",
pages = "623--636",
journal = "Geological Magazine",
issn = "0016-7568",
publisher = "Cambridge University Press",
number = "5",

}

TY - JOUR

T1 - Kinematic and thermal constraints on the reactivation of the Outer Hebrides Fault Zone, NW Scotland

AU - Szulc, A. G.

AU - Alsop, G. I.

AU - Oliver, G. J. H.

PY - 2008/9

Y1 - 2008/9

N2 - The Outer Hebrides Fault Zone is a major easterly dipping reactivated shear zone which displaces Lewisian gneiss of the Laurentian craton, NW Scotland. Despite a number of detailed field studies, the fault zone remains poorly understood with regard to both its age of inception and precise conditions of reactivation. The island of Scalpay in the northern portion of the Outer Hebrides Fault Zone provides exceptional exposures through a variety of reactivated fault rock types and therefore represents an ideal location to investigate fault zone evolution via fluid inclusion studies of syntectonic quartz veins. This fluid inclusion study constrains reactivation temperatures more precisely than hitherto possible with top-to-the-NW ductile thrusting occurring at 500 +/- 30 degrees C. Subsequent phyllonitization is associated with oblique sinistral top-to-the-NE strike-slip at 230 +/- 20 degrees C, followed by a discrete system of top-to-the-NE/SE extensional detachments at 150 +/- 20 degrees C. Other recent fluid inclusion studies in the southern portion of the Outer Hebrides Fault Zone constrain phyllonitization associated with top-to-the-E displacement to 370 +/- 20 degrees C, with subsequent top-to-the-NE extensional detachments operating at 150-210 degrees C. Thus, late-stage extensional detachment systems record consistent conditions of reactivation along the strike length of the Outer Hebrides Fault Zone. However, our results also clearly emphasize that conditions of earlier fault zone reactivation and phyllonitization were highly heterogeneous between the northern and southern portions, thus suggesting a spatial and temporal variation in the deformation and/or fluid flux system.

AB - The Outer Hebrides Fault Zone is a major easterly dipping reactivated shear zone which displaces Lewisian gneiss of the Laurentian craton, NW Scotland. Despite a number of detailed field studies, the fault zone remains poorly understood with regard to both its age of inception and precise conditions of reactivation. The island of Scalpay in the northern portion of the Outer Hebrides Fault Zone provides exceptional exposures through a variety of reactivated fault rock types and therefore represents an ideal location to investigate fault zone evolution via fluid inclusion studies of syntectonic quartz veins. This fluid inclusion study constrains reactivation temperatures more precisely than hitherto possible with top-to-the-NW ductile thrusting occurring at 500 +/- 30 degrees C. Subsequent phyllonitization is associated with oblique sinistral top-to-the-NE strike-slip at 230 +/- 20 degrees C, followed by a discrete system of top-to-the-NE/SE extensional detachments at 150 +/- 20 degrees C. Other recent fluid inclusion studies in the southern portion of the Outer Hebrides Fault Zone constrain phyllonitization associated with top-to-the-E displacement to 370 +/- 20 degrees C, with subsequent top-to-the-NE extensional detachments operating at 150-210 degrees C. Thus, late-stage extensional detachment systems record consistent conditions of reactivation along the strike length of the Outer Hebrides Fault Zone. However, our results also clearly emphasize that conditions of earlier fault zone reactivation and phyllonitization were highly heterogeneous between the northern and southern portions, thus suggesting a spatial and temporal variation in the deformation and/or fluid flux system.

KW - deformation

KW - fault

KW - fluid inclusions

KW - fluids

KW - Scotland

KW - Lewisian Gneiss Complex

KW - crustal-scale fault

KW - evolution

KW - pseudotachylite

KW - reappraisal

U2 - 10.1017/S0016756808004925

DO - 10.1017/S0016756808004925

M3 - Article

VL - 145

SP - 623

EP - 636

JO - Geological Magazine

JF - Geological Magazine

SN - 0016-7568

IS - 5

ER -