Timing of regional deformation and development of the Moine Thrust Zone in the Scottish Caledonides: constraints from the U–Pb geochronology of alkaline intrusions

Abstract

12The Moine Thrust Zone in the Scottish Highlands developed during the Scandian 13Event of the Caledonian Orogeny, and now forms the boundary between the 14 Caledonian orogenic belt and the undeformed foreland. The Scandian Event, and the 15 formation of the Moine Thrust Zone, have previously been dated by a range of 16 isotopic methods, and relatively imprecise ages on a suite of alkaline intrusions 17 localised along the thrust zone have provided the best age constraints for deformation. 18Recent BGS mapping has improved our understanding of the structural relationships 19 of some of these intrusions, and this work is combined with new U-Pb dates in this 20 paper to provide significantly improved ages for the Moine Thrust Zone. Our work 21shows that a single early intrusion (the Glen Dessarry Pluton) was emplaced within 22 the orogenic belt to the east of the Moine Thrust Zone at 447.9 ± 2.9 Ma. A more 23 significant pulse of magmatism centred in the Assynt area, which temporally 24 overlapped movement in the thrust zone, occurred at 430.7 ± 0.

The mantle of Scotland viewed through the Glen Gollaidh aillikite

“…425 Ma; Stone et al 1993) with the suture between the prior supercontinents of Laurentia and Avalonia lying in what is now the Southern Uplands Terrane of southern Scotland. Caledonian metamorphism associated with the Moine Thrust largely ceased around the same time (429 Ma; Goodenough et al 2011) with the Loch Borralan intrusion (39 km south-west of Glen Gollaidh) dated to 430 ± 4 (2σ) Ma (Van Breeman et al 1979) and the Loch Loyal syenite complex (18 km east north-east of Glen Gollaidh) dated to 426 ± 9 (2σ) Ma (Halliday et al 1987). However, the subducting Avalonia slab continued to progress northwards, first reflected in minor magmatism near the Iapetus suture and subsequently within the regions affected by the Caledonian Orogeny.…”

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

“…ages reported for peak-metamorphic deformation ('D2') and pegmatite intrusions in the northern Moine Nappe Kocks et al 2006;Alsop et al 2010;Goodenough et al 2011). Within the Moine Nappe, 'D2' thus appear to be diachronous: whether this is because of a distinctly separate late-Ordovician 'Grampian II' event (e.g.…”

“…deformation and magmatism appears to be mainly restricted to the higher Sgurr Beag and Naver nappes (Kinny et al 1999;Cutts et al 2010). Scandian (c. 440-420 Ma) deformation was the last major phase, affecting much of the Moine succession and culminating in major displacement along the Moine Thrust (Freeman et al 1998;Kinny et al 2003;Alsop et al 2010;Goodenough et al 2011). However, the separation between 'Grampian' and 'Scandian' events may not be so clear-cut as previously thought, as there is increasing evidence of tectonothermal activity around 450 Ma specifically in the southern Moine Nappe Bird et al 2013, Cawood et al in press),.…”

Chemical composition and K–Ar age of Phengite from Barrovian metapelites, Loch Leven, Scotland

“…Moreover, the K-Ar age of the Eilde Flags is closer to the age of movement on the Moine Thrust (ca. 437-408 Ma; Freeman et al, 1998;Goodenough et al, 2011), and the Fort William Slide bounds the Eilde Flags and overlying Formations (Fig. 2).…”