Multiple high-pressure metamorphic events and crustal telescoping in the NW Highlands of Scotland

Abstract

The Glenelg–Attadale Inlier is the largest basement inlier within the Caledonian orogen in NW Scotland. A Western Unit consists of trondhjemite–tonalite–granodiorite (TTG) gneisses and subordinate mafic intrusions with locally preserved mafic high-pressure granulite and eclogite assemblages. An Eastern Unit comprises TTG gneisses, Grenville-age ( c . 1.1 Ga) eclogite and metasediments. U–Pb zircon ages from the Western Unit TTG gneisses are highly disturbed with Neoarchaean upper intercepts and Palaeo- to Mesoproterozoic lower intercepts, suggesting strong reworking at these times. U–Pb zircon, Sm–Nd and Lu–Hf garnet–clinopyroxene dates from the Western Unit high-pressure granulite and eclogite yield Neoarchaean ( c . 2.6–2.8 Ga) and Palaeoproterozoic ( c . 1.75 Ga) ages, respectively. These ages correspond to the ages of partial resetting of the TTG gneisses. The eclogite in the Western Unit may represent the high-pressure convergent margin to the lower-pressure Laxfordian events within the Lewisian Gneiss Complex, whereas the Mesoproterozoic eclogites in the Eastern Unit may represent a farther eastward Grenville-age margin. Further east, Ordovician high-pressure granulites within the Moine Supergroup may represent another, later, Grampian convergent margin. These high-pressure belts were developed sequentially towards the east and telescoped westwards from Palaeoproterozoic to Early Palaeozoic times. Supplementary material: U–Pb analytical data and LA-ICP-MS trace element data are available at http://www.geolsoc.org.uk/SUP18389 .

Structure and stratigraphy of the Morar Group in Knoydart, NW Highlands: implications for the history of the Moine Nappe and stratigraphic links between the Moine and Torridonian successions

“…The Western Glenelg gneiss comprises felsic and mafic orthogneisses, commonly with well-preserved agmatitic textures; paragneiss is absent. It experienced high-pressure granulite-facies metamorphism during the Neoarchaean, followed by Palaeoproterozoic eclogite-facies metamorphism dated at c. 1.7 Ga (Storey et al 2010). In contrast, the Eastern Glenelg gneiss contains abundant paragneisses in addition to orthogneisses.…”

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

“…Western Glenelg gneiss is similar to gneisses exposed below the Moine Thrust near Lochcarron (Barber & May 1976) and a correlation with the Lewisian Gneiss Complex seems valid. Both the protolith of the felsic gneiss as well as an early granulite-facies metamorphism are of Archaean age (Friend et al 2008;Storey et al 2010). High-pressure granulite-to-eclogite facies metamorphism occurred at c. 1.75 Ga (Storey et al 2010), but there is no evidence for Grenvillian metamorphism.…”

“…The c. 1200-960 Ma Grenville-Sveconorwegian Orogen stretches from Mexico to Southern Sweden, and is one of the largest collisional belts on Earth (e.g., Rivers 1997Rivers , 2008Tollo et al 2004;Tohver et al 2004). The Archaean-Palaeoproterozoic Glenelg Inlier in Scotland and the Annagh Gneiss Complex in Ireland provide small but crucial links between the North American and Scandinavian parts of the orogen (Sanders et al 1984;Daly 1996;Brewer et al 2003;Storey et al 2010). The Glenelg Inlier of Scotland, however, occurs within the much later 470-400 Ma Caledonian Orogen (e.g., McKerrow et al 1991;Woodcock & Strachan 2012;Chew & Strachan 2014;Dewey et al 2015) and has thus been strongly reworked.…”

“…Consequently, the structural setting and tectonic evolution of the Glenelg Inlier within the larger framework of the Scottish Caledonides has remained elusive (cf. Sanders et al 1997;Storey 2008a;Storey et al 2010;Barber 2011).…”

Meso-Neoproterozoic Grenville-Sveconorwegian intracontinental orogen: history, tectonics, geodynamics

“…Оценки параметров деком-прессионной стадии (~1.00 млрд лет) равны ~13 кбар и 650-700 °C. В западной части тектонического окна среди тоналит-трондьемит-гранодиоритовых гнейсов известны также несколько тел палеопро-терозойских (~1.75 млрд лет) мафитовых пород, в которых локально сохранились минеральные ассо-циации эклогитовой фации [Storey et al, 2010].…”