A field guide to the Glenelg-Attadale Inlier, NW Scotland, with emphasis on the Precambrian high-pressure metamorphic history and subsequent retrogression

Abstract

SynopsisThe Glenelg-Attadale Inlier contains Proterozoic eclogites and Late Archaean mafic high-pressure granulites. Eclogites were formed both in the Palaeoproterozoic (around 1.75 Ga) and the Mesoproterozoic (around 1.1 Ga). The inlier is the only place in the British Isles that contains significant and unequivocal crustal eclogites and furthermore is one of the few places that retains clear evidence of having been strongly affected by the c. 1.1-1.0 Ga Grenvillian orogeny. The excursions provide an opportunity to study these rare rocks and gain insight into how they formed and how they were exhumed back to the surface.

Niobium mineralization of sedimentary carbonates, Lewisian Complex, UK

“…The Lewisian Complex is predominantly Archean, of igneous origin, but includes numerous supracrustal successions, of Palaeoproterozoic age. The limestone at Loch Shin is undated, but other marbles in Lewisian supracrustal assemblages date to ∼1.9 Ga, in accretionary subduction-related complexes (Park et al 2001; Whitehouse and Bridgwater 2001; Storey 2008). The supracrustal rocks include marbles whose sedimentary origin is evident from associated beds of mudrock and ironstone, entrained grains of quartz and mica, and carbon isotope data.…”

Caledonian and Knoydartian overprinting of a Grenvillian inlier and the enclosing Morar Group rocks: structural evolution of the Precambrian Proto-Moine Nappe, Glenelg, NW Scotland

“…Many eclogite bodies probably originated as mafic intrusions, but some thin, laterally extensive eclogite layers in paragneiss have gradational boundaries, and may have a volcanic or volcaniclastic origin. Felsic eclogite, comprising kyanite, quartz and K-feldspar occurs locally (Sanders 1988;Storey et al 2005;Storey 2008b). Rare ultramafic rocks include garnet-bearing websterite (Rawson et al 2001).…”

“…Felsic gneisses are reduced to fine-grained and finely laminated quartz-feldspar rocks while hornblendic and garnetiferous rocks are now seen as olive-grey banded ultramylonite. Strong deformation also affected the 'Median Strip' of Morar Group psammite between the main Western and Eastern Glenelg inliers (Storey et al 2004;Storey 2008b) and adjacent parts of the Western Glenelg gneiss, and also affects the Western Glenelg gneiss near Arnisdale; an example is shown in Figure 6c. A similar high-strain zone occurs on the eastern boundary of the Eastern Glenelg Inlier, near Beinn a'Chuirn; the Inverinate Shear Zone of Storey et al (2004).…”