The Great Glen Caledonian Igneous Suite: new geochemical and geochronological insights into the final stages of the Caledonian Orogeny

Milne, Eilidh Jean McLaren (2019) The Great Glen Caledonian Igneous Suite: new geochemical and geochronological insights into the final stages of the Caledonian Orogeny. MRes thesis, University of Glasgow.

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Abstract

The Caledonian Orogeny is responsible for the consolidation of British and Irish crust and the intrusion of an extensive suite of granite (sensu – lato) plutons and dykes. Said intrusions are collectively known as the Newer granites and are a natural laboratory for studying mid-crustal petrogenetic processes in a post- collisional setting. Recent workers have highlighted inconsistencies in the timeline of events for the final stages of the orogeny (the so-called ‘Scandian phase’), particularly regarding the timing and geodynamic processes associated with Newer granite magmatism. New single grain U – Pb zircon data from three undated Newer granite bodies (Glen Loy, Cluanie and Loch Linnhe), and whole rock geochemical data from five (Glen Loy, Cluanie, Loch Linnhe Clunes and Scaddle) will facilitate new insights into said issues.

Intrusions at Glen Loy, Cluanie and Loch Linnhe return ages of 433.6 +/- 3.9, 437.7 +/- 3.3 and 439.4 +/-3.1 respectively (+/- 2σ). Their emplacement therefore predates estimates for slab break–off, usually invoked as the mechanism behind Newer granite melt generation, which requires some explanation. The geochemical profiles for Scaddle and Loy strongly suggest a mantle source, which requires explanation given their emplacement coincides with what is traditionally accepted as peak crustal thickening - another contradictory set of circumstances. As detailed, the newly acquired data is largely inconsistent with previously accepted geodynamic timelines for so called ‘Scandian’ events and supports a growing array of data suggesting the demarking of Caledonian orogenic events has been erroneous. A new model is presented, which includes Baltica - Laurentia collision occurring far earlier than traditional estimates of c. 430 Ma; instead occurring at c. 450 Ma. All subsequent events and processes are associated with crustal thickening, slab rollback, and eventual slab break-off.

Item Type: Thesis (MRes)
Qualification Level: Masters
Keywords: Geology, geochemistry, Highland geology, Scottish geology, Earth Sciences.
Subjects: Q Science > QE Geology
Colleges/Schools: College of Science and Engineering > School of Geographical and Earth Sciences > Earth Sciences
Supervisor's Name: Neill, Dr. Iain
Date of Award: 2019
Depositing User: Miss Eilidh Jean Mclaren Milne
Unique ID: glathesis:2019-81522
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 15 Jul 2020 08:15
Last Modified: 15 Jul 2020 08:36
URI: http://theses.gla.ac.uk/id/eprint/81522

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