Vasgo - Strathan Bay
Geological Conservation Review site | GCR #2980 | Structural and Metamorphic Geology | Moine
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Summary
One of the World's really great sections through a "crustal" shear zone, an outcrop analogue for reflective tracts on deep seismic profiles and an opportunity to explore the geometry of folds and deformation kinematics.
This area is part of a unique coastal cross-section of the Moine orogen, ranging from the thrust zone at Whiten Head to the Halladale migmatites at Portskerra. Here typical non-migmatitic, dominantly psammatic, lithologies of the west Sutherland Moine are displayed in excellent outcrops. They are considered to represent the northern continuation of the Morar Division. The state of strain of these A'Mhoine psammites is extremely variable. At Loch Vasgo low strain, cross-bedded feldspathic psammites are preserved in a large, flat lying F2 fold at the roadside. In contrast, on the cliffs east of Port Vasgo there are high strain zones in the psammites together with F2 sheath folds and variably strained metabasic intrusives of the Precambrian Ben Hope Sill suite. At Strathan Bay a Moine conglomerate lies within a zone of intense strain, it contains intensely flattened, pink, quartzo-feldspathic and grey quartzitic pebbles now shaped like elongated pancakes. There are at least two types of folded metabasic intrusive within the Moine in this area: frequently garnetiferous early-moine amphibolites of the Ben Hope Sill suite and later microdioritic sheets. There are also areas of Lewisian basement gneisses ranging from highly feldspathic to mafic. The Strathan Bay conglomerate has been interpreted as a basal conglomerate overlying one of these Lewisian inliers. This site exemplifies the typical west Sutherland A'Mhoine Psammites, with a variety of sedimentary and tectonic structures illustrating the extreme heterogeneity of strain in this region.
Rob Butler
Deformed conglomerates from the lower part of the Moine metasedimentary succession at Strathan Bay.
Rob Butler
Large-scale view of the foliation forming cliff sections at Portvasgo. It is the large-scale simplicity of the fabric here that makes the site such a great analogue for reflectivity in crustal seismic profiles.
Rob Butler
Classic similar folds of Moine psammites (metasandstones) in the crustal shear zone at Portvasgo.
Rob Butler
Getting to grips with complex refolded fold patterns