Tectonostratigraphy of the Moine Supergroup: a synthesis

Abstract

The Neoproterozoic (early Riphean) Moine Supergroup crops out extensively in the Scottish Caledonides north of the Great Glen and is characterized by structural complexity and monotonous siliciclastic lithology with a lack of biostratigraphic control. Despite these problems, it has become possible to combine locally defined successions into a regional stratigraphic framework. This permits an evaluation of the tectonic setting of Moine deposition, in a subsiding tract that became the Scottish part of the Laurentian margin when Iapetus opened in the Vendian. Two major rift-basins are inferred, each of half-graben type, controlled by east-facing normal faults. The earlier Morar Group basin received a thick fill of dominantly shallow-marine arkosic sandstones, the Upper Morar Psammite forming a major regressive sequence. The Glenfinnan Group consists of mixed and muddy deposits that are interpreted partly as distal equivalents of the Morar Group, partly as a post-Morar transgressive thermal re-equilibration sequence. The Loch Eil Group, dominated by shallow marine arkosic and siliceous psammites, was deposited in a second, more easterly rift-basin that was subsequently juxtaposed with the Morar basin during Caledonian thrusting. Sediment dispersal in the major sandy sequences was northwards, and there is some evidence that provenance was, at least in part, from a mid-Proterozoic basement terrain to the south. The extension-dominated depositional setting of the Moine Supergroup, and basin geometry, are similar to those inferred for the other major Riphean clastic sequences of Scotland, the ‘Torridonian’ of the foreland and the Grampian Group to the southeast. The latter is followed by Upper Riphean transgressive strata of the Appin Group. Scottish Riphean stratigraphy records a major pre-Iapetan cycle of lithospheric extension and thermal recovery, with no regional scale unconformities yet identified that might constitute evidence for contemporary orogenesis.

Late Precambrian U–Pb titanite age for peak regional metamorphism and deformation (Knoydartian orogeny) in the western Moine, Scotland

“…2). Soper et al (1998), building on earlier work by Strachan (1986) and Glendinning (1988), have proposed that the Moine sequence was deposited in a pair of contiguous NNE-trending half-graben that faced to the SE.…”

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

“…In eastern Knoydart, a major thrust termed the 'Knoydart Slide' has been interpreted along the contact between the Barrisdale Psammite and the Morar Pelite Formation (Poole & Spring 1974;Powell 1974;Barr et al 1986;Soper et al 1998). Above this thrust, within the outcrop of the Morar Pelite Formation (= Ladhar Bheinn Pelite in east Knoydart, Figs.…”

Sedimentology of the early Neoproterozoic Morar Group in northern Scotland: implications for basin models and tectonic setting

“…Nonetheless, in some orogens it has proved possible to reconstruct the main depositional environments in areas where the structural setting is relatively straightforward and exposure is of good quality. In this context, much research has been carried out on the sedimentology and basin setting of the deformed and polymetamorphic Moine Supergroup of northern Scotland (Strachan 1986;Glendinning 1988;Soper et al 1998;Bonsor & Prave 2008;Krabbendam et al 2008;Bonsor et al 2010). This is one of a number of thick early Neoproterozoic siliciclastic successions that were deposited in the North Atlantic region during and after the amalgamation of Laurentia, Baltica and Amazonia that resulted in the Grenville orogeny and the formation of the Rodinia Supercontinent (Fig 1;Hoffman 1991;Li et al 2008).…”

“…It was interpreted as a shallow-marine rift basin (Strachan 1986;Glendinning 1988;Soper et al 1998), perhaps representing a 'failed rift' in the core of Rodinia ( Fig. 1a; Dalziel & Soper 2001).…”