The initiation and early tectonic significance of the Outer Hebrides fault zone, Scotland

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doi: 10.1017/S0016756802006969
Authors:Imber, J.; Strachan, R. A.; Holdsworth, R. E.; Butler, C. A.
Author Affiliations:Primary:
University of Durham, Department of Geological Sciences, Durham, Federal Republic of Germany
Other:
Oxford Brookes University, United States
Volume Title:Geological Magazine
Source:Geological Magazine, 139(6), p.609-619. Publisher: Cambridge University Press, London, United Kingdom. ISSN: 0016-7568
Publication Date:2002
Note:In English. 54 refs.; illus., incl. geol. sketch map
Summary:The Outer Hebrides Fault Zone (OHFZ) is a major ESE-dipping detachment exposed within basement gneisses of the Archaean-Palaeoproterozoic Lewisian complex. The fault zone was active during Proterozoic, end-Silurian, Carboniferous and Mesozoic times. The earliest deformation event preserved onshore was associated with top-to-the-NW ductile thrusting. A previous study showed that the thrust-related protomylonitic and mylonitic fabrics are cross-cut by amphibolites (Younger Basics) and Laxfordian granite and pegmatite sheets, and suggested that ductile thrusting occurred during the Palaeoproterozoic Inverian event at ∼ 2500 m.y. The observations demonstrate, however, that mylonitic fabrics within the ductile thrust zone are superimposed on all components of the gneiss complex including amphibolites and Laxfordian intrusions and thus the OHFZ cannot be older than ∼ 1685 m.y., the age of recently dated Laxfordian granites in the Outer Hebrides. Geochronological studies have shown that the basement blocks of the N Outer Hebrides and Scottish mainland have different geological histories and were amalgamated during Proterozoic times at or after ∼ 1700 m.y. It is suggested that early ductile thrusting along the OHFZ formed part of this amalgamation process leading to burial and reheating of the footwall gneisses in Lewis and N Harris. This would account for the ∼ 1100 m.y. thermal event recorded by previous workers and implies that ductile thrusting along the OHFZ is of Grenvillian age. [G.L.B.]
Sections:Petrology
Subsections:General
Subjects:Archean; Decollement; Fault zones; Faults; Gneisses; Grenvillian Orogeny; Laxfordian; Mesoproterozoic; Metamorphic rocks; Precambrian; Proterozoic; Reactivation; Tectonics; Thrust faults; Upper Precambrian; Europe; Great Britain; Hebrides; Outer Hebrides; Scotland; United Kingdom; Western Europe; Scalpay Island
Coordinates:N575000 N575000 W0064000 W0064000
Abstract Numbers:03M/3198
Record ID:2003027699
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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