Geochemical evolution of Dalradian metavolcanic rocks: implications for the break-up of the Rodinia supercontinent

Fettes, D. J.; Macdonald, Ray; Fitton, J. Godfrey; Stephenson, David; Cooper, Mark

doi:10.1144/0016-76492010-161

Cited by 24 publications

(16 citation statements)

References 72 publications

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“…As such, the high‐grade Cairn Leuchan/Glen Muick mafic migmatites and metasediments are thus interpreted as representing a slice of exhumed Ordovician Grampian Terrane lower crust—not Precambrian basement—with their basaltic protoliths having formed during c . 570‐Ma volcanism associated with passive‐margin extension (Fitton, ) prior to the initiation of closure of the Iapetus Ocean (Fettes et al., ; Goodman & Winchester, ; Smith et al., ).…”

Section: Discussionmentioning

confidence: 99%

“…We interpret that they most likely formed during a subsequent period of volcanism at c . 570 Ma associated with passive‐margin extension (Fitton, ), synchronous with deposition of the Crinan Subgroup and prior to the onset of Iapetus Ocean closure (Fettes et al., ; Goodman & Winchester, ; Smith et al., ).…”

Section: U–pb Zircon Geochronologymentioning

confidence: 99%

“…Although initially interpreted as Precambrian basement (Ramsay & Sturt, 1979;Read, 1955;Smith, Goodman, & Robertson, 2002;Sturt, Ramsay, Pingle, & Teggin, 1977;Viete, Richards, Lister, Oliver, & Banks, 2010), these mafic gneisses and intercalated metapsammite, metapelite, and calcsilicate lithologies have recently been stratigraphically reassigned to the Crinan Subgroup of the Upper Dalradian Series (Stephenson, Mendum, Fettes, Smith, et al, 2013), and thus are considered contiguous with the rest of the lower grade Barrow zone sequence. Detailed structural investigation has shown that these metamorphosed basic sheets were intruded as dykes and sills before regional-scale Grampian deformation, although some fine-grained rocks exposed near the base of the Subgroup are regarded as metavolcanic (Fettes, MacDonald, Fitton, Stephenson, & Cooper, 2011;Stephenson, Mendum, Fettes, Smith, et al, 2013). Highresolution U-Pb spot secondary ion mass spectrometry dating of zircon from Glen Muick metapelites performed by Vorhies et al (2013) showed that peak metamorphism occurred at c. 468 AE 7 Ma (MSWD = 0.9), matching that reported from elsewhere in the Grampian Terrane (e.g., Baxter et al, 2002;Breeding, Ague, Grove, & Rupke, 2004;Viete et al, 2013), providing further evidence for their contemporaneous evolution.…”

Section: The Mid-ordovician Grampian Eventmentioning

confidence: 99%

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Origin, age, and significance of deep‐seated granulite‐facies migmatites in the Barrow zones of Scotland, Cairn Leuchan, Glen Muick area

Palin

Sayed

White

et al. 2018

Journal Metamorphic Geology

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Petrological modelling of granulite‐facies mafic and semipelitic migmatites from Cairn Leuchan, northeast Scotland, has provided new constraints on the pressure (P) and temperature (T) conditions of high‐grade metamorphism in the type‐locality Barrow zones. Phase diagrams constructed in the Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O2 system have constrained the P−T conditions of peak metamorphism in the Glen Muick region of the upper sillimanite zone (Sill+Kfs) to have been at least ∼840°C at ∼9 kbar (high‐P granulite facies). These conditions are ∼120°C and ∼3 kbar higher than those recorded by lower sillimanite zone (Sill+Ms) units located only a few kilometres away to the southeast at Glen Girnock, indicating the presence of a significant thermal and barometric high exposed within the Scottish Dalradian, and supporting previous suppositions of a potential tectonic break between the two regions. U–Pb zircon geochronology performed on these mafic migmatites produced ages of c. 540–470 Ma from grains with both igneous and metamorphic morphological characteristics. Their basaltic protoliths likely formed during a period of volcanism dated at c. 570 Ma, associated with passive‐margin extension prior to the onset of Iapetus Ocean closure, and high‐grade metamorphism and partial melting is interpreted to have taken place at c. 470 Ma, synchronous with sillimanite‐grade metamorphism recorded elsewhere in the Dalradian. These high‐grade Cairn Leuchan lithologies are interpreted as representing a fragment of Grampian Terrane lower crust that was exhumed via displacement along a steeply dipping tectonic discontinuity related to the Portsoy–Duchray Hill Lineament, and are not pre‐Caledonian Mesoproterozoic basement, as suggested by some previous studies. Veins within some mafic migmatites in the Cairn Leuchan area, composed almost entirely (>80%) of garnet, with minor quartz, plagioclase, amphibole, and clinopyroxene, are interconnected with leucosomes and are interpreted to represent former garnet‐bearing melt segregations that have been locally drained of almost all melt. Thus, mafic components of the lower crust, currently underlying relatively lower grade metasediments exposed to the southeast, may represent a potential source rock for widely documented, post‐orogenic felsic plutons, sills, and dykes that occur throughout the Grampian Terrane.

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Section: Discussionmentioning

confidence: 99%

Section: U–pb Zircon Geochronologymentioning

confidence: 99%

Section: The Mid-ordovician Grampian Eventmentioning

confidence: 99%

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Origin, age, and significance of deep‐seated granulite‐facies migmatites in the Barrow zones of Scotland, Cairn Leuchan, Glen Muick area

Palin

Sayed

White

et al. 2018

Journal Metamorphic Geology

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“…On the Scottish -Irish sector of the Laurentian margin, mafic volcanic activity in the Dalradian Supergroup occurred throughout deposition of the Argyll Group and the lower part of the Southern Highland Group, reaching its greatest development in the Easdale and Tayvallich subgroups of the Argyll Group (Fettes et al 2011). Absolute age constraints on the timing of volcanic activity are poor, with the only reliable geochronology being the U-Pb zircon dates of 595 ± 4 Ma on a keratophyre intrusion (Halliday et al 1989), and of 601 ± 4 Ma on a felsic tuff (Dempster et al 2002) from within the Tayvallich Volcanic Formation of the upper Argyll Group.…”

Section: Scotland and Irelandmentioning

confidence: 99%

“…Absolute age constraints on the timing of volcanic activity are poor, with the only reliable geochronology being the U-Pb zircon dates of 595 ± 4 Ma on a keratophyre intrusion (Halliday et al 1989), and of 601 ± 4 Ma on a felsic tuff (Dempster et al 2002) from within the Tayvallich Volcanic Formation of the upper Argyll Group. Easdale Subgroup volcanism has been suggested to have occurred at around 630 -620 Ma (Fettes et al 2011). …”

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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Magma storage of an alkali ultramafic igneous suite from Chamberlindalen, SW Svalbard

et al. 2016

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Geochemical evolution of Dalradian metavolcanic rocks: implications for the break-up of the Rodinia supercontinent

Cited by 24 publications

References 72 publications

Origin, age, and significance of deep‐seated granulite‐facies migmatites in the Barrow zones of Scotland, Cairn Leuchan, Glen Muick area

Origin, age, and significance of deep‐seated granulite‐facies migmatites in the Barrow zones of Scotland, Cairn Leuchan, Glen Muick area

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

Magma storage of an alkali ultramafic igneous suite from Chamberlindalen, SW Svalbard

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