The Dalradian rocks of Scotland: an introduction

doi:10.1016/j.pgeola.2012.06.002

Proceedings of the Geologists' Association

Volume 124, Issues 1–2, January 2013, Pages 3-82

https://doi.org/10.1016/j.pgeola.2012.06.002 Get rights and content

Abstract

The Dalradian Supergroup and its basement rocks, together with younger plutons, underpin most of the Grampian Highlands and the islands of the Inner Hebrides between the Highland Boundary and Great Glen faults. The Dalradian is a mid-Neoproterozoic to early-Ordovician sequence of largely clastic metasedimentary rocks, with some volcanic units, which were deformed and metamorphosed to varying degrees during the Early Palaeozoic Caledonian Orogeny.

Sedimentation of the lower parts of the Dalradian Supergroup, possibly commencing about 730 million years ago, took place initially in fault-bounded rift basins, within the supercontinent of Rodinia and adjacent to sectors of continental crust that were later to become the foundations of North America, Greenland and Scandinavia. Later sedimentation reflected increased instability, culminating between 600 and 570 million years ago in continental rupture, volcanicity and the development of the Iapetus Ocean. This left the crustal foundations of Scotland, together with those of North America and Greenland, on a laterally extensive passive margin to the new continent of Laurentia, where turbiditic sedimentation continued for about 85 million years. Later plate movements led to closure of the Iapetus Ocean and the multi-event Caledonian Orogeny. Most of the deformation and metamorphism of the Dalradian strata peaked at about 470 million years ago, during the mid-Ordovician Grampian Event, which has been attributed to the collision of an oceanic arc with Laurentia. The later, mid-Silurian Scandian Event, attributed to the collision of the continent of Baltica with Laurentia and the final closure of the Iapetus Ocean, apparently had little effect on the Dalradian rocks but marked the start of late-orogenic uplift and extensive magmatism in the Grampian Highlands that continued until Early Devonian times.

The Dalradian rocks thus record a wide range of sedimentary environments (alluvial, tidal, deltaic, shallow marine, turbiditic, debris flow) and a complex structural and metamorphic history. In areas of low strain, original sedimentary and volcanic structures are well preserved, even at relatively high metamorphic grades. There is convincing evidence for glacial episodes of worldwide importance and economic deposits of stratiform barium minerals are unique. The Grampian Highlands include two of the World's type-areas for metamorphic zonation, Barrovian and Buchan, with spectacular examples of the key metamorphic minerals, and various stages of migmatite development. Polyphase folding is widespread on all scales and gives rise to a range of associated cleavages and lineations. Regional dislocations, both ductile and brittle, are associated with a range of shear fabrics, breccias, clay gouges and veining.

Section snippets

The Dalradian Supergroup

The Dalradian Supergroup is a mid-Neoproterozoic to Early Palaeozoic sequence of largely clastic sedimentary rocks, with some notable carbonate and volcanic units that were all deformed and metamorphosed to varying degrees during the mid-Ordovician Grampian Event of the Caledonian Orogeny. The Dalradian rocks, together with Caledonian intrusive igneous rocks, form the bedrock to most of the Grampian Highlands of Scotland and the islands of the Inner Hebrides between the Highland Boundary and

GCR site selection (D. Stephenson)

Metamorphic rocks in the more-sparsely populated areas of Great Britain are on the whole less prone to damage than sequences in the more-developed areas. They are none the less vulnerable to large-scale activities, some long established and obvious, such as quarrying and landfill, and others related to more-recent exploitation of the rural landscape such as coastal defences, hydro-electric schemes, wind farms and power transmission lines.

The greatest threat is undoubtedly the possibility of

Basement to the Dalradian basins (D. Stephenson)

Our knowledge of the immediate basement to the Dalradian rocks of the Grampian Highlands is limited to outcrops on the islands of Islay and Colonsay in the south-west (the Rhinns Complex) and in parts of the northern Grampian Highlands (the Badenoch Group, formerly known informally as the Dava and Glen Banchor successions) (Fig. 1). The existence of an unmodified contact with the basement is difficult to demonstrate in either area, but a stratigraphical and orogenic unconformity can be inferred

Dalradian lithostratigraphy (D. Stephenson)

The Dalradian Supergroup is dominated by well-differentiated sequences of variably metamorphosed marine clastic sedimentary rocks and metacarbonate rocks. Some fluvial interludes are recognized in the earliest parts and localized metavolcanic rocks occur in the later parts. The aggregate total thickness of the succession adds up to at least 25 km, although the complete thickness was never deposited at one place. It is more likely that depocentres migrated south-eastwards with time and individual

Structure of the Grampian Highlands (D. Stephenson)

Current structural interpretations of the Grampian Highlands are still based upon those proposed by C.T. Clough and E.B. Bailey, which drew upon the results of the primary mapping by the Geological Survey. In a series of papers, from 1910 to 1938, Bailey demonstrated that the rocks of the south-west and central Grampian Highlands are disposed in large, Alpine-scale recumbent folds. He proposed that the long limbs of many of these folds are partly replaced by low-angled faults, termed ‘slides’,

Metamorphism of the Grampian Highlands (D.J. Fettes and A.G. Leslie)

The metamorphic grade expressed in the Dalradian rocks of the Grampian Highlands was initially referred to index minerals in pelitic rocks. Barrow, 1893, Barrow, 1912, working in the south-east of the Grampian Highlands, was the first to establish a zonal sequence in such rocks, indicative of progressive metamorphic grade. This scheme, slightly modified by Tilley (1925), became the classical Barrovian zones (chlorite → biotite → garnet → staurolite → kyanite → sillimanite). Subsequently, Read (1952)

Dating the Dalradian sedimentation (D. Stephenson)

The age of the sediments that became the Dalradian Supergroup is poorly constrained. Fossils are rare, are poorly preserved, and where species have been identified they have a wide stratigraphical range. Tillites and other possible glacigenic deposits raise various possibilities of correlation with global glacial events. As yet few radiometric age determinations have been made on the undoubted interbedded volcanic rocks and most available dates relate to intrusions or later tectonothermal

Tectonic evolution of the Dalradian basins (D. Stephenson and A.G. Leslie)

For much of Proterozoic time, the crustal foundations of Scotland were part of a continental block that also incorporated parts of present-day North America and Greenland. At the beginning of Neoproterozoic time, this block was included within the large supercontinent of Rodinia, where it lay adjacent to blocks that later became the Baltic shield and South America (Fig. 13). It was only towards the end of Neoproterozoic time that Rodinia became fragmented and the three blocks became,

Acknowledgements

This special issue is the combined work of 22 authors, listed with the paper titles, many of whom, in addition to their own site descriptions, have made valuable comments on other aspects of the work. Sadly, John Roberts and Steve Robertson both died during the early stages of preparation and their contributions have been completed by P.W.G. Tanner and M. Smith respectively. Peter Thomas, Derek Flinn and Robert Scott died whilst the special issue was being prepared for publication. All made

References (572)

J.J. Ague et al.
Brief thermal pulses during mountain building recorded by Sr diffusion in apatite and multicomponent diffusion in garnet
Earth and Planetary Science Letters
(2007)
C.J. Banks et al.
Provenance of intra-Rodinian basin-fills: the lower Dalradian Supergroup, Scotland
Precambrian Research
(2007)
A.M. Bell
Vergence: an evaluation
Journal of Structural Geology
(1981)
M. Cannat
Late Caledonian northeastward ophiolite thrusting in the Shetland Islands, U.K.
Tectonophysics
(1989)
Agrell, S.O., 1942. 1. A petrological investigation of the adinoles at Dinas Head, Cornwall. 2. A petrofabric study of...
A. Allison
Loch Awe succession and tectonics-Kilmartin-Tayvallich-Danna
Quarterly Journal of the Geological Society, London
(1941)
I. Allison et al.
An Excursion guide to the Moine Geology of the Scottish Highlands
(1988)
G.I. Alsop et al.
A review and revision of Dalradian stratigraphy in central and southern Donegal, Ireland
Irish Journal of Earth Sciences
(1990)
G.I. Alsop et al.
Cleaved clasts in Dalradian conglomerates: possible evidence for Neoproterozoic compressional tectonism in Scotland and Ireland?
Geological Journal
(2000)
Amos, B.J., 1960. The geology of the Bowmore district, Islay. Unpublished PhD Thesis. University of London, Imperial...

E.M. Anderson

The geology of the schists of the Schiehallion district

Quarterly Journal of the Geological Society, London

(1923)

E.M. Anderson

The Dynamics of Faulting

(1951)

J.G.C. Anderson

The stratigraphical order of the Dalradian schists near the Highland Border in Angus and Kincardineshire

Transactions of the Geological Society of Glasgow

(1942)

J.G.C. Anderson

The geology of the Highland Border, Stonehaven to Arran

Transactions of the Royal Society of Edinburgh

(1947)

J.G.C. Anderson

The Kinlochlaggan Syncline, southern Inverness-shire

Transactions of the Geological Society of Glasgow

(1947)

J.G.C. Anderson

Stratigraphic nomenclature of Scottish metamorphic rocks

Geological Magazine

(1948)

J.G.C. Anderson

The Moinian and Dalradian rocks between Glen Roy and the Monadhliath Mountains, Inverness-shire

Transactions of the Royal Society of Edinburgh

(1956)

Anderton, R., 1974. Middle Dalradian sedimentation in Argyll, with particular reference to the Jura quartzite, Scarba...

R. Anderton

Tidal-shelf sedimentation: an example from the Scottish Dalradian

Sedimentology

(1976)

R. Anderton

The Dalradian rocks of Jura

Scottish Journal of Geology

(1977)

R. Anderton

Slopes, submarine fans and syn-depositional sedimentology of parts of the Middle and Upper Dalradian in the S.W. Highlands of Scotland

The British Caledonides – Reviewed

Special Publication of the Geological Society, London

(1979)

R. Anderton

Distinctive pebbles as indicators of Dalradian provenance

Scottish Journal of Geology

(1980)

R. Anderton

Dalradian deposition and the late Precambrian–Cambrian history of the N Atlantic region: a review of the early evolution of the Iapetus Ocean

Journal of the Geological Society, London

(1982)

R. Anderton

Sedimentation and tectonics in the Scottish Dalradian

Scottish Journal of Geology

(1985)

R. Anderton

Dalradian slides and basin development: a radical interpretation of stratigraphy and structure in the SW and Central Highlands of Scotland

Journal of the Geological Society, London

(1988)

W.A. Ashcroft et al.

Major shear zones and autochthonous Dalradian in the northeast Scottish Caledonides

Nature (London)

(1984)

Ashworth, J.R., 1972. Migmatites of the Huntly-Portsoy area, north-east Scotland. Unpublished PhD Thesis. University of...

J.R. Ashworth

The sillimanite zones of the Huntly–Portsoy area in the north-east Dalradian, Scotland

Geological Magazine

(1975)

J.R. Ashworth

Petrogenesis of migmatites in the Huntly–Portsoy area, north-east Scotland

Mineralogical Magazine

(1976)

J.R. Ashworth

Comparative petrography of deformed and undeformed migmatites from the Grampian Highlands of Scotland

Geological Magazine

(1979)

M.P. Atherton

The metamorphism of the Dalradian rocks of Scotland

Scottish Journal of Geology

(1977)

E.B. Bailey

Recumbent folds in the schists of the Scottish Highlands

Quarterly Journal of the Geological Society, London

(1910)

E.B. Bailey

The Islay anticline (Inner Hebrides)

Quarterly Journal of the Geological Society, London

(1917)

E.B. Bailey

The structure of the South West Highlands of Scotland

Quarterly Journal of the Geological Society, London

(1922)

E.B. Bailey

Perthshire tectonics: Loch Tummel, Blair Atholl and Glen Shee

Transactions of the Royal Society of Edinburgh

(1925)

E.B. Bailey

New light on sedimentation and tectonics

Geological Magazine

(1930)

E.B. Bailey

West Highland tectonics: Loch Leven to Glen Roy

Quarterly Journal of the Geological Society, London

(1934)

E.B. Bailey

Eddies in mountain structure

Quarterly Journal of the Geological Society, London

(1938)

E.B. Bailey

The Geology of Ben Nevis and Glencoe and the Surrounding Country

(1960)

E.B. Bailey et al.

Perthshire tectonics: Schiehallion to Glen Lyon

Transactions of the Royal Society of Edinburgh

(1937)

E.B. Bailey et al.

The Glen Orchy Anticline, Argyllshire

Quarterly Journal of the Geological Society, London

(1912)

A.J. Baker

Pressures and temperatures of metamorphism in the eastern Dalradian

Journal of the Geological Society, London

(1985)

A.J. Baker

Models for the tectonothermal evolution of the eastern Dalradian of Scotland

Journal of Metamorphic Geology

(1987)

Banks, C.J., 2005. Neoproterozoic Basin Analysis: a combined sedimentological and provenance study in the Grampian...

C.J. Banks

Exceptional preservation of sedimentary structures in metamorphic rocks: an example from the upper Grampian Group, Creag Stalcair, Perthshire

Scottish Journal of Geology

(2007)

C.J. Banks et al.

Sedimentology and stratigraphic affinities of Neoproterozoic coarse clastic successions, Glenshirra Group, Inverness-shire Scotland

Scottish Journal of Geology

(2004)

B.A. Barreiro

U–Pb systematics on zircon from the Keith and Portsoy granites, Grampian Highlands, Scotland

(1998)

G. Barrow

On an intrusion of muscovite-biotite gneiss in the south-east Highlands of Scotland, and its accompanying metamorphism

Quarterly Journal of the Geological Society, London

(1893)

G. Barrow

Moine gneisses of the east central Highlands and their position in the Highland sequence

Quarterly Journal of the Geological Society, London

(1904)

G. Barrow

On the geology of Lower Deeside and the southern Highland border

Proceedings of the Geologists’ Association

(1912)

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Implications of new geochronological constraints on the Aberfeldy stratiform barite deposits, Scotland, for the depositional continuity and global correlation of the Neoproterozoic Dalradian Supergroup
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As stated above, volcanic rocks are scarce at this stratigraphic position in the central Highlands. 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. 2b).
The Dalradian Supergroup of largely clastic metasediments in Scotland and Ireland is a well-known record of Neoproterozoic to Cambrian sedimentation on the Laurentian margin. Its apparent long duration, from ∼ 800 to ∼ 500 Ma, has encouraged a search for tectonic breaks and unconformities within the sequence. One suggestion is that a break in sedimentation occurred within the upper part of the Argyll Group, specifically in the Easdale Subgroup. Here we report dates for demonstrably synsedimentary barite mineralization hosted by the Easdale Subgroup Ben Eagach Schist Formation. Bedded pyrite from the Foss and the Ben Eagach–Duntanlich barite deposits, stratigraphically < 100 m apart, yields Re-Os ages of 604.0 ± 7.2 Ma and 612.1 ± 18.6 Ma respectively with two-sigma overlap. These ages are similar to the previously constrained 601 ± 4 Ma Tayvallich Volcanic Formation lying 2–5 km stratigraphically above. The new ages suggest continuous sedimentation through this period and, in combination with existing time markers, increase the likelihood that the basal-Argyll, Port Askaig Formation diamictite represents the Marinoan glaciation rather than the Sturtian glacial episode which may not be represented in the Dalradian sequence. As such, we urge caution in using the Dalradian in global compilations of Neoproterozoic history until further geochronological constraints are obtained for the Cryogenian-Tonian parts of the stratigraphy, which is now a high priority.
Terrane history of the Iapetus Ocean as preserved in the northern Appalachians and western Caledonides
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The Iapetus Ocean was the first ancient ocean to be identified following the development of plate tectonics; its history has been fundamental in relating orogenesis and plate motion. The ocean probably formed following 3-way rifting between Laurentia, Baltica, and Amazonia – West Africa (a block that became incorporated in Gondwana). Closure of the ocean trapped numerous terranes during the development of the Appalachian–Caledonide Orogen. Subsequent deformation, including late Paleozoic strike slip, transpression, and transtension, and Mesozoic stretching during Pangea breakup, must be taken into account in models for orogen development.
Traditional analyses of Iapetan terranes have focussed on Cambrian sedimentary successions, and on isotopic criteria, to classify terranes into larger domains: Ganderia, Avalonia and Megumia. Detrital zircon data show that these domains did not cross the Iapetus as single entities, while paleomagnetic data reveal significant vertical-axis terrane rotations. We here review and interpret 17 paleomagnetic poles and >350 published detrital zircon data sets from the northern Appalachians and western Caledonides, using consistent and rigorous criteria for the selection and presentation of data. We place these data on an integrated stratigraphic chart to show timing relations and to seek constraints on the provenance and travel of terranes in the Iapetus Ocean. We distinguish groups of terranes that likely travelled together as terrane assemblages.
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Several of the terranes that were accreted to the Laurentian margin carried internal records of earlier deformation that took place near Amazonia – West Africa in Early Ordovician time and earlier (Monian/Penobscottian Orogeny). The Iapetus Ocean thus contained a complex array of terranes, small ocean basins, arcs, and previously emplaced ophiolites analogous to modern southeast Asia. It closed to form a complex array of sutures in an orogen within which no single Iapetus suture can be clearly identified.
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A notable difference between those regions, however, is that post-rift sediments are unknown from the Central Segment of Laurentia, whereas in Scotland-Ireland, sedimentation continued until the second rifting phase started at around ~635 Ma. The lack of post-rift sediments in the Central Segment has often led to the interpretation that rifting was aborted there (e.g. Aleinikoff et al., 1995), although curiously a broadly similar narrative is inferred in Scotland-Ireland despite the enduring accumulation of sediments (Stephenson et al., 2013). Unfortunately, a comparison of these different marginal histories against the potentially conjugate margin of western Amazonia is complicated by the fact that Cryogenian relics are almost entirely unknown from the latter.
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The Dalradian rocks of Scotland: an introduction

Abstract

Section snippets

The Dalradian Supergroup

GCR site selection (D. Stephenson)

Basement to the Dalradian basins (D. Stephenson)

Dalradian lithostratigraphy (D. Stephenson)

Structure of the Grampian Highlands (D. Stephenson)

Metamorphism of the Grampian Highlands (D.J. Fettes and A.G. Leslie)

Dating the Dalradian sedimentation (D. Stephenson)

Tectonic evolution of the Dalradian basins (D. Stephenson and A.G. Leslie)

Acknowledgements

Earth and Planetary Science Letters

Precambrian Research

Journal of Structural Geology

Tectonophysics

Loch Awe succession and tectonics-Kilmartin-Tayvallich-Danna

Quarterly Journal of the Geological Society, London

An Excursion guide to the Moine Geology of the Scottish Highlands

A review and revision of Dalradian stratigraphy in central and southern Donegal, Ireland

Irish Journal of Earth Sciences

Cleaved clasts in Dalradian conglomerates: possible evidence for Neoproterozoic compressional tectonism in Scotland and Ireland?

Geological Journal

The geology of the schists of the Schiehallion district

Quarterly Journal of the Geological Society, London

The Dynamics of Faulting

The stratigraphical order of the Dalradian schists near the Highland Border in Angus and Kincardineshire

Transactions of the Geological Society of Glasgow

The geology of the Highland Border, Stonehaven to Arran

Transactions of the Royal Society of Edinburgh

The Kinlochlaggan Syncline, southern Inverness-shire

Transactions of the Geological Society of Glasgow

Stratigraphic nomenclature of Scottish metamorphic rocks

Geological Magazine

The Moinian and Dalradian rocks between Glen Roy and the Monadhliath Mountains, Inverness-shire

Transactions of the Royal Society of Edinburgh

Tidal-shelf sedimentation: an example from the Scottish Dalradian

Sedimentology

The Dalradian rocks of Jura

Scottish Journal of Geology

Slopes, submarine fans and syn-depositional sedimentology of parts of the Middle and Upper Dalradian in the S.W. Highlands of Scotland

The British Caledonides – Reviewed

Special Publication of the Geological Society, London

Distinctive pebbles as indicators of Dalradian provenance

Scottish Journal of Geology

Dalradian deposition and the late Precambrian–Cambrian history of the N Atlantic region: a review of the early evolution of the Iapetus Ocean

Journal of the Geological Society, London

Sedimentation and tectonics in the Scottish Dalradian

Scottish Journal of Geology

Dalradian slides and basin development: a radical interpretation of stratigraphy and structure in the SW and Central Highlands of Scotland

Journal of the Geological Society, London

Major shear zones and autochthonous Dalradian in the northeast Scottish Caledonides

Nature (London)

The sillimanite zones of the Huntly–Portsoy area in the north-east Dalradian, Scotland

Geological Magazine

Petrogenesis of migmatites in the Huntly–Portsoy area, north-east Scotland

Mineralogical Magazine

Comparative petrography of deformed and undeformed migmatites from the Grampian Highlands of Scotland

Geological Magazine

The metamorphism of the Dalradian rocks of Scotland

Scottish Journal of Geology

Recumbent folds in the schists of the Scottish Highlands

Quarterly Journal of the Geological Society, London

The Islay anticline (Inner Hebrides)

Quarterly Journal of the Geological Society, London

The structure of the South West Highlands of Scotland

Quarterly Journal of the Geological Society, London

Perthshire tectonics: Loch Tummel, Blair Atholl and Glen Shee

Transactions of the Royal Society of Edinburgh

New light on sedimentation and tectonics

Geological Magazine

West Highland tectonics: Loch Leven to Glen Roy

Quarterly Journal of the Geological Society, London

Eddies in mountain structure

Quarterly Journal of the Geological Society, London

The Geology of Ben Nevis and Glencoe and the Surrounding Country

Perthshire tectonics: Schiehallion to Glen Lyon

Transactions of the Royal Society of Edinburgh

The Glen Orchy Anticline, Argyllshire

Quarterly Journal of the Geological Society, London