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Caledonian hot zone magmatism in the ‘Newer Granites’: insight from the Cluanie and Clunes plutons, Northern Scottish Highlands

Milne, Eilidh J.M.; Neill, Iain; Bird, Anna F.; Millar, Ian L.; McDonald, Iain; Dempsey, Edward D.; Olive, Valerie; Odling, Nic; Waters, Emma C.


Eilidh J.M. Milne

Iain Neill

Ian L. Millar

Iain McDonald

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Dr Eddie Dempsey
Senior Lecturer in Structural Geology and Geohazards

Valerie Olive

Nic Odling

Emma C. Waters


Scottish ‘Newer Granites’ record the evolution of the Caledonides resulting from Iapetus subduction and slab breakoff during the Silurian–Devonian Scandian Orogeny, but relationships between geodynamics, petrogenesis and emplacement are incomplete. Laser ablation U–Pb results from magmatic zircons at the Cluanie Pluton (Northern Highlands) identify clusters of concordant Silurian data points. A cluster with a weighted mean206 Pb/238 U age of 431.6 ± 1.3 Ma (2σ confidence interval, n = 6) records emplacement whilst older points (clustered at 441.8 ± 2.3 Ma, n = 9) record deep crustal hot zone magmatism prior to ascent. The Cluanie Pluton, and its neighbour the c. 428 Ma Clunes tonalite, have adakite-like high Na, Sr/Y, La/Yb and low Mg, Ni and Cr characteristics, and lack mafic facies common in other ‘Newer Granites’. These geochemical signatures indicate the tapping of batches of homogenized, evolved magma from the deeper crust. The emplacement age of the Cluanie Pluton confirms volumetrically modest subduction-related magmatism occurred beneath the Northern Highlands before slab breakoff, probably restricted by crustal thickening during the c. 450 Ma Grampian 2 event. Extensive new in situ geochemical–geochronological studies for this terrane may further substantiate the deep crustal hot zone model and the association between Caledonian magmatism and potentially metallogenesis. The term ‘Newer Granites’ is outdated as it ignores geochronology, petrography and tectonic setting. Hence, ‘Caledonian intrusions’ would be a more appropriate generic term to cover those bodies related to either Iapetus subduction or to slab breakoff.


Milne, E. J., Neill, I., Bird, A. F., Millar, I. L., McDonald, I., Dempsey, E. D., …Waters, E. C. (2023). Caledonian hot zone magmatism in the ‘Newer Granites’: insight from the Cluanie and Clunes plutons, Northern Scottish Highlands. Journal of the Geological Society, 180(2), Article jgs2022-076.

Journal Article Type Article
Acceptance Date Nov 17, 2022
Online Publication Date Nov 28, 2022
Publication Date Mar 1, 2023
Deposit Date Nov 29, 2022
Publicly Available Date Nov 30, 2022
Journal Journal of the Geological Society
Print ISSN 0016-7649
Electronic ISSN 2041-479X
Publisher Geological Society
Peer Reviewed Peer Reviewed
Volume 180
Issue 2
Article Number jgs2022-076
Keywords Adakite; Caledonian; Geochemistry; Geochronology; Scotland
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Copyright Statement
© 2022 The Author(s). This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 License ( Published by The<br /> Geological Society of London. Publishing disclaimer:

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