The Dalradian Supergroup in Scotland, Shetland and Ireland

Harris, A. L.; Haselock, P. J.; Kennedy, Michael J.; Mendum, J. R.; Long, C. B.; Winchester, J. A.; Tanner, Peter

doi:10.1144/sr22.4

Cited by 90 publications

(36 citation statements)

References 72 publications

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“…Lithostratigraphic correlation is hampered by the almost complete absence of stratigraphically useful fossils, complex polyphase deformation and rapid lateral facies changes. Despite these difficulties, a coherent lithostratigraphy has been established from western Ireland through mainland Scotland to the Shetland Islands (Harris et al 1994), comprising four groups -Grampian, Appin, Argyll and Southern Highland. The Dalradian Supergroup was deformed during the Grampian Orogeny (ca.…”

Section: Scotland and Irelandmentioning

confidence: 99%

The Ocean – Continent Transition Zones Along the Appalachian – Caledonian Margin of Laurentia: Examples of Large-Scale Hyperextension During the Opening of the Iapetus Ocean

Chew

Staal

2014

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A combination of deep seismic imaging and drilling has demonstrated that the ocean-continent transition (OCT) of present-day, magma-poor, rifted continental margins is a zone of hyperextension characterized by extreme thinning of the continental crust that exhumed the lowermost crust and/or serpentinized continental mantle onto the seafloor. The OCT on present-day margins is difficult to sample, and so much of our knowledge on the detailed nature of OCT sequences comes from obducted, magma-poor OCT ophiolites such as those preserved in the upper portions of the Alpine fold-and-thrust belt. Allochthonous, lens-shaped bodies of ultramafic rock are common in many other ancient orogenic belts, such as the Caledonian – Appalachian orogen, yet their origin and tectonic significance remains uncertain. We summarize the occurrences of potential ancient OCTs within this orogen, commencing with Laurentian margin sequences where an OCT has previously been inferred (the Dalradian Supergroup of Scotland and Ireland and the Birchy Complex of Newfoundland). We then speculate on the origin of isolated occurrences of Alpine-type peridotite within Laurentian margin sequences in Quebec – Vermont and Virginia – North Carolina, focusing on rift-related units of Late Neoproterozoic age (so as to eliminate a Taconic ophiolite origin). A combination of poor exposure and pervasive Taconic deformation means that origin and emplacement of many ultramafic bodies in the Appalachians will remain uncertain. Nevertheless, the common occurrence of OCT-like rocks along the whole length of the Appalachian – Caledonian margin of Laurentia suggests that the opening of the Iapetus Ocean may have been accompanied by hyperextension and the formation of magma-poor margins along many segments.SOMMAIREDes travaux d’imagerie sismique et des forages profonds ont montré que la transition océan-continent (OCT) de marges continentales de divergence pauvre en magma exposée de nos jours, correspond à une zone d’hyper-étirement tectonique caractérisée par un amincissement extrême de la croûte continentale, qui a exhumé sur le fond marin, jusqu’à la tranche la plus profonde de la croûte continentale, voire du manteau continental serpentinisé. Parce qu’on peut difficilement échantillonner l’OCT sur les marges actuelles, une grande partie de notre compréhension des détails de la nature de l’OCT provient d’ophiolites pauvres en magma d’une OCT obduite, comme celles préservées dans les portions supérieures de la bande plissée alpine. Des masses lenticulaires de roches ultramafiques allochtones sont communes dans de nombreuses autres bandes orogéniques anciennes, comme l’orogène Calédonienne-Appalaches, mais leur origine et signification tectonique reste incertaine. Nous présentons un sommaire des occurrences d’OCT potentielles anciennes de cet orogène, en commençant par des séquences de la marge laurentienne, où la présence d’OCT a déjà été déduites (le Supergroupe Dalradien d’Écosse et d'Irlande, et le complexe de Birchy de Terre-Neuve). Nous spéculons ensuite sur l'origine de cas isolés de péridotite de type alpin dans des séquences de marge des Laurentides du Québec-Vermont et de la Virginie-Caroline du Nord, en nous concentrant sur les unités de rift d'âge néoprotérozoïque tardif (pour éviter les ophiolites du Taconique). La conjonction d’affleurements de piètre qualité et de la déformation taconique omniprésente, signifie que l'origine et la mise en place de nombreuses masses ultramafiques dans les Appalaches demeureront incertaines. Néanmoins, la présence fréquente de roches de type OCT tout le long de la marge Calédonnienne-Appalaches de Laurentia suggère que l'ouverture de l'océan Iapetus peut avoir été accompagnée d’hyper-étirement et de la formation de marges pauvres en magma le long de nombreux segments.

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Section: Scotland and Irelandmentioning

confidence: 99%

The Ocean – Continent Transition Zones Along the Appalachian – Caledonian Margin of Laurentia: Examples of Large-Scale Hyperextension During the Opening of the Iapetus Ocean

Chew

Staal

2014

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“…Based upon apparent stratigraphical, structural and metamorphic continuity in the Grampian Terrane, Harris et al (1978) extended the then tripartite Dalradian Supergroup downwards to include such lithologies, which were all assigned to a new Grampian Group. A number of constituent subgroups and formations were proposed by Winchester and Glover (1988) and the lithostratigraphical relationships were synthesized by Harris et al (1994) and Stephenson and Gould (1995).…”

Section: Grampian Group Lithostratigraphy and Basin Evolutionmentioning

confidence: 99%

“…These are the lowest strata recognized in the Grampian Group and form a geochemically distinct metasedimentary unit across the Northern Grampian Highlands (Haselock, 1994;Banks and Winchester, 2004).…”

Section: Descriptionmentioning

confidence: 99%

“…The lithological, metamorphic and structural correlation of the lowest Dalradian rocks of the Northern Grampian Highlands with the Moine Supergroup of the Northern Highlands has long been the subject of considerable debate (see reviews by Harris et al, 1994;Stephenson and Gould, 1995).…”

Section: Introductionmentioning

confidence: 99%

“…The Grampian Group rocks that underlie much of the Northern Grampian Highlands have been divided by Harris et al (1994) into the Glenshirra (oldest), Corrieyairack and Glen Spean (youngest) subgroups.…”

Section: Introductionmentioning

confidence: 99%

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The Dalradian rocks of the northern Grampian Highlands of Scotland

Leslie

Robertson

Smith

et al. 2013

Proceedings of the Geologists' Association

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Tectonic analysis of progressive secondary deformation in the hinge of a major Caledonian fold nappe, north-western Ireland

Alsop¹

1996

Geol. J.

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Polyphase deformation chronologies established within the mid-crustal portions of orogenic belts have classically been attributed to regional-scale 'events' which generate distinct structural sequences that can be directly correlated across large tracts of the orogenic belt. However, concepts of progressive deformation in which minor structures may be continually generated, amplified and redeformed within a unifying kinematic framework suggest that regional correlation of minor structures is both misguided and misleading. Detailed structural analysis of lower amphibolite facies Dalradian metasediments in north-west Ireland does, however, demonstrate that a coherent and meaningful deformation chronology can be established within the framework of individual fold nappes. Protracted deformation has resulted in the generation of a series of overprinting, secondary structures (D4-D9), which are kinematically linked to the continued structural evolution and south-east directed translation of the crustal-scale (D3) Ballybofey (fold) Nappe. Secondary (D4) crenulation axes initiated at an oblique angle to the direction of nappe transport both rotate and amplify into larger scale folds, which are subparallel to transport and demonstrate successive stages of diachronous folding. Continued nappe-related deformation induces southwards verging contractional (D5) folds, which are particularly well developed and focused into reactivated ductile (D3) thrust zones generated during the initial stages of nappe translation. Subsequent to thickening-induced ductile extension and collapse of the nappe, a return to contractional tectonics is marked by major episodes of broad, open buckle folding developed orthogonal to both the overturned limb (D,) and upper limb (Ds) of the nappe. Detailed structural analysis and investigation of secondary folds and overprinting fabrics provides a valuable insight into the protracted kinematic evolution of major fold nappes.

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The Dalradian Supergroup in Scotland, Shetland and Ireland

Cited by 90 publications

References 72 publications

The Ocean – Continent Transition Zones Along the Appalachian – Caledonian Margin of Laurentia: Examples of Large-Scale Hyperextension During the Opening of the Iapetus Ocean

The Ocean – Continent Transition Zones Along the Appalachian – Caledonian Margin of Laurentia: Examples of Large-Scale Hyperextension During the Opening of the Iapetus Ocean

The Dalradian rocks of the northern Grampian Highlands of Scotland

Tectonic analysis of progressive secondary deformation in the hinge of a major Caledonian fold nappe, north-western Ireland

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