The Dalradian rocks of the central Grampian Highlands of Scotland

Abstract

The Central Grampian Highlands, as defined here, are bounded to the north-west by the Great Glen Fault, to the south-west by Loch Etive and the Pass of Brander Fault and to the south-east by the main outcrop of the Loch Tay Limestone Formation.The more arbitrary northern boundary runs north-west along the A9 road and westwards to Fort William.The detailed stratigraphy of the Dalradian Supergroup ranges from the uppermost Grampian Group through to the top of the Argyll Group, most notably seen in the two classic areas of Loch Leven-Appin and Schiehallion-Loch Tay; Southern Highland Group strata are preserved only in a small structural inlier south of Glen Lyon.Major F1 and F2 folds are complicated by co-axial northeasttrending F3 and F4 folding, as well as by locally important northor NW-trending folds. In the Loch Leven area, nappe-like F1 folds verge to the north-west, whereas to the south-east the major recumbent F1/F2 Tay Nappe verges to the south-east.The trace of the upright Loch Awe Syncline lies between the opposing nappes, but

Abundant sulphate in the Neoproterozoic ocean: implications of constant δ 34 S of barite in the Aberfeldy SEDEX deposits, Scottish Dalradian

“…Polyphase deformation which accompanied amphibolite facies metamorphism during the Grampian Orogeny (Treagus 2000;Treagus et al 2013) produced fold structures ranging in amplitude from kilometric, for example, the Creag na h-Iolaire Anticline that trends ENE through the centre of the area shown in Figure 1b, to millimetric crenulated foliation in pelitic metasediments and celsian rocks. Intense ductile deformation in some parts of the Foss deposit resulted in concertina folding and thickening of the barite in some places, for example, at the Foss Quarry, while elsewhere attenuation has reduced bed thicknesses such that it is not feasible or economic to mine.…”

“…5b), whereas Stephenson et al (2013) suggest that the formation is the most extensive of many sandy turbidites that episodically flowed into deep-water basins. The Ben Eagach Schist Formation also shows great variation in thickness, probably as a result of the infilling of fault-generated grabens generated during incipient rifting of the Rodinia continental margin that led eventually to the opening of the Iapetus Ocean Treagus et al 2013).…”

Implications of new geochronological constraints on the Aberfeldy stratiform barite deposits, Scotland, for the depositional continuity and global correlation of the Neoproterozoic Dalradian Supergroup

“…In the mid-Ordovician Grampian Orogeny, some ~ 130 Myr after deposition of the uppermost Dalradian strata, the beds were tilted and distorted by several phases of folding (Fig. 3f) and faulting, and subjected to medium-grade, amphibolite facies regional metamorphism (Treagus, 2000;Treagus et al, 2013). Timing of the metamorphic maxima varied across the Dalradian outcrop but in Perthshire the peak conditions, associated with porphyroblast growth, lasted about 10 Myr from c. 474 to c. 464 Ma followed by relatively rapid cooling and uplift (Dempster, 1985;Stephenson et al 2013).…”

“…Stratigraphic correlation of the Tayvallich lavas with the Loch Tay Limestone in the central Highlands is a long-held assumption, largely based on lateral continuity of calcareous formations (Craignish Phyllite, Ben Lawers Schist) and equivalence of the Crinan Grit with the Ben Lui Schist (Crinan Subgroup: Fig. 8a) (Stephenson et al, 1995;Stephenson et al, 2013;Treagus, 2000;Treagus et al, 2013). In the central Highlands, the main episode of mafic volcanism in the Argyll Group is represented by the Farragon Beds within the upper Easdale Subgroup (Fig.…”

“…Graphitic pelites of the Easdale Slate overlain by calcareous phyllites in the southwest of Scotland are correlated with the Ben Eagach Schist and Ben Lawers Schist respectively in the Aberfeldy area in Perthshire (Perth and Kinross District) in the central Grampian Highlands (Fig. 1b) (Harris et al, 1994;Stephenson and Gould, 1995;Stephenson et al, 2013;Treagus et al, 2013). Pyrite Re-Os dates have been obtained separately for two discrete stratiform barite deposits, Foss and Ben Eagach-Duntanlich, that are hosted within upper and lower levels respectively of the ~ 300 m thick Ben Eagach Schist Formation (Fig.…”