Scourie Bay
Geological Conservation Review site | GCR #2461 | Structural and Metamorphic Geology | Lewisian
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Summary
Classic locality in the for establishing the history of the Lewisian, involving the early gneisses, intruded by the regional mafic dyke swarm that are then deformed again. The site of "Teall's shear zone" - fundament for understanding strain localisation in metamorphic rocks.
These are the type localities of the Scourie dyke suite; they have historical significance as the dykes were first studied by Teall in the 19th century. The dyke to the north of the bay is an iron-rich quartz dolerite with clinopyroxene, autometamorphic garnet, orthopyroxene and hornblende. Some parts of the dyke contact are undeformed and these truncate Scourian granulite facies gneisses; the margin here is fine-grained but not glassy. Other parts of the contact are affected by shear zones, which also crosscut the dyke. Deformation within these shear zones has retrogressed the dolerite to amphibolite and produced LS fabrics. The shearing was recognised by Teall, with strain localisation related to the retrogression in the shear zone - an early (but then lost) recognition of reaction-enhanced ductility. The dyke to the south of the bay contains a garnetifierous assemblage formed during autometamorphism, when the dyke was intruded and then cooled at depth within the earth's crust. This dyke has been the subject of much geochemical and mineralogical study. In addition, Rb-Sr ages of 2,930my have been obtained, and a study of palaeomagnetic pole directions carried out.
Site information
Further information
https://earthwise.bgs.ac.uk/index.php/Scourie_Mòr,_North-we…
Excursion guide for this locality, from Goodenough & Krabbendam, 2011. A geological excursion guide to the North-west Highlands of Scotland. Edinburgh : Edinburgh Geological Society in association with NMS Enterprises.
Related geosites
Overlaps with:
Con Gillen
Locality map for Scourie Bay from the excursion guide edited by Goodenough & Krabbendam, 2011. This is a coloured version from the GCR Lewisian volume, edited by Mendum et. al (2009).
Con Gillen
Oct. 17, 2015
Another view of 'THE' Scourie Dyke - type locality at Craig a' Mhàil, Scourie Bay. The dyke can be seen cutting granulite facies gneisses, which dip at about 30 degrees to the southwest. From Poll Eòrna.
Alex Gabriel
Garnetiferous rock, Poll Eòrna
Alex Gabriel
Banded Lewisian Gneiss, Poll Eòrna
Alex Gabriel
Mylonized rock exhibiting bands and boudins, Poll Eòrna
Alex Gabriel
The Scourie Dyke at Poll Eòrna. Northwest view