Sedimentation and tectonics in the Scottish Dalradian

Abstract

Synopsis Sedimentological research on the Scottish Dalradian has progressed from the recognition of sedimentary structures in the 1930s, via the identification of sedimentary facies from the 1950s onwards, to the integration, in the 1970s, of sedimentological data with that from studies of stratigraphy, tectonics and volcanism. This has now led to an understanding of the pre-orogenic evolution of the Dalradian terrane in terms of progressive lithospheric stretching associated with the break-up of the Proterozoic Supercontinent. The Appin and Argyll Groups were deposited on the NW side of a late Precambrian marine gulf which developed over a complex zone of crustal thinning between the Laurentian and Baltic parts of the Super-continent. As extension accelerated, subsidence rates increased and the Dalradian area of the gulf evolved from a relatively shallow shelf into a series of turbidite basins. Thinning of the lithosphere gave rise, in Argyll Group times, to locally intense igneous activity. Subsequently, complete continental rupture along the gulf axis led to the birth of the Iapetus Ocean. By Southern Highland Group times the Dalradian terrane had become part of the new, thermally-subsiding, Laurentian continental margin. One can envisage the geometry and facies variations of many horizons within the Dalradian in terms of a pattern of numerous fault blocks defined by listric normal faults, dipping SE towards the site of continental rupture, and NW–SE trending transfer faults, which divided the gulf and subsequent margin into a series of compartments. It was movements on these faults that largely controlled Dalradian stratigraphic evolution. For example, pulses of rapid stretching, and consequent fault activity, produced basin-deepening sequences which mark the base of the Easdale and Crinan Subgroups.

Evidence from Rb–Sr mineral ages for multiple orogenic events in the Caledonides of Shetland, Scotland

“…The Yell Sound Group and the Westing Group are succeeded eastwards by the c. 14 km thick East Mainland Succession consisting of psammites, pelites and marbles with minor volcanic horizons (Flinn 1967), although the presumed intervening unconformity is obscured by high tectonic strain (Flinn 1988). The East Mainland Succession is partly time-equivalent to the Dalradian Supergroup (Prave et al 2009;Strachan et al 2013), and hence probably accumulated on the passive margin of Laurentia during continental break-up and development of the Iapetus Ocean (Anderton 1985;Strachan et al 2002). The Eleonore Bay Supergroup of East Greenland is broadly time-correlative with the Dalradian and East Mainland successions (Leslie et al 2008).…”

How the Neoproterozoic S-isotope record illuminates the genesis of vein gold systems: an example from the Dalradian Supergroup in Scotland

“…1). The sequence was deposited along the developing east Laurentian passive margin during a period of ocean widening (Anderton 1985). The Dalradian Supergroup has a depositional history spanning the Neoproterozoic (Cryogenian) to mid-Cambrian (Tanner & Sutherland 2007;Stephenson et al 2013) and comprises marineclastic sedimentary rocks with occasional carbonate beds and minor volcanic rocks (Stephenson et al 2013).…”

“…The overlying Appin Group is characterized by a limestone-pelite -quartzite assemblage deposited in a relatively stable shelf environment (Wright 1988). The Argyll and Southern Highland Groups, overlying the Appin Group, contain significant black slates and graphitic schists, and an increased incidence of mafic lavas and sills, grading upwards into coarse turbidite sequences (Harris et al 1978;Anderton 1985), with the Argyll Group host to locally developed stratabound exhalative mineralization (Stephenson et al 2013). The upper-Appin and lower-Argyll Group stratigraphy is absent in the Tyndrum area (Fig.…”

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

“…The Dalradian Supergroup, which is structurally and stratigraphically above the Moine Supergroup, is mainly composed of three Groups from structural bottom to top: the Appin, Argyll, and Southern Highland (e.g. Anderson, 1985). The Moine Supergroup is composed of six Groups from structural bottom to top: the Morar, Glenfinnan, Loch Eil Groups, the East Sutherland Moine, the Glen and Dava Successions, and the Grampian Group.…”