The geochronology of plutonism associated with the Great Glen Fault, northern Scottish Highlands

MacRae, Careen (2025) The geochronology of plutonism associated with the Great Glen Fault, northern Scottish Highlands. MSc(R) thesis, University of Glasgow.

Abstract

The Northern Highlands of Scotland contain Palaeozoic intrusions emplaced during collision of continents Baltica and Laurentia of the late Caledonian Scandian Orogeny. However, uncertainties remain regarding the accuracy of existing isotope dilution geochronology and understanding of the geodynamic history in relation to spatial and temporal distribution of intrusions. This study obtained emplacement dates by zircon U-Pb LA-ICP-MS (laser ablation-inductively coupled plasma-mass spectrometry) for the Strontian intrusion Sunart facies (423.5 ± 2.1 Ma), Strontian Sanda facies (418.2 ± 6.3 Ma), Helmsdale intrusion (417.0 ± 4.0 Ma) and Abriachan intrusion (418.2 ± 5.6 Ma). These dates provide confidence in existing literature, and a new date for the Abriachan intrusion. Further, use of in situ analysis produced evidence of antecrystic zircon and thus pre-emplacement magmatism in each sample up to a maximum age of c. 450 Ma, supportive of the lower crustal hot zone model for late Caledonian magmatism in the Northern Highlands. LA-ICP-MS zircon trace element data obtained for the Strontian Sunart facies similarly support open system magma evolution and homogenisation within a lower crustal hot zone prior to emplacement.

Spatially limited mid – upper crustal emplacement and thus limited mobilisation of hot zone material from c. 450 – c. 432 Ma is attributed to compression in the Laurentian margin induced by the initial stages of continental collision. Widespread mid – upper crustal emplacement from c. 432 – c. 423 Ma typically associated with regional transpression is interpreted as comprising new mantle derived melt and remobilised hot zone material. This widespread emplacement may have been triggered by lithospheric delamination, particularly the peak in emplacement at c. 425 Ma. A final phase of emplacement of evolved magmas is defined at c. 418 – c. 417 Ma and is highly spatially limited to the Great Glen Fault and related faults. This phase is interpreted to comprise remobilised hot zone material emplaced during a phase of strike slip displacement and may be related to continued uplift and the accretion of peri-Gondwanan terranes to Laurentia further southwest.

• Item Type: Thesis (MSc(R))
• Qualification Level: Masters
• Subjects: Q Science > Q Science (General); Q Science > QE Geology
• Colleges/Schools: College of Science and Engineering > School of Geographical and Earth Sciences
• Supervisor's Name: Neill, Dr. Iain and Einsle, Dr. Joshua Franz
• Date of Award: 2025
• Depositing User: Theses Team
• Unique ID: glathesis:2025-85196
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 17 Jun 2025 10:29
• Last Modified: 17 Jun 2025 13:04
• Thesis DOI: 10.5525/gla.thesis.85196
• URI: https://theses.gla.ac.uk/id/eprint/85196

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