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Enrichment of Rare Earth Elements during magmatic and postmagmatic processes: a case study from the Loch Loyal Syenite Complex, northern Scotland

Walters, Abigail S., Goodenough, Kathryn M., Hughes, Hannah S.R., Roberts, Nick M.W., Gunn, A. Gus, Rushton, Jeremy and Lacinska, Alicja 2013. Enrichment of Rare Earth Elements during magmatic and postmagmatic processes: a case study from the Loch Loyal Syenite Complex, northern Scotland. Contributions to Mineralogy and Petrology 166 (4) , pp. 1177-1202. 10.1007/s00410-013-0916-z

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Abstract

Concern about security of supply of critical elements used in new technologies, such as the Rare Earth Elements (REE), means that it is increasingly important to understand the processes by which they are enriched in crustal settings. High REE contents are found in syenite dominated alkaline complexes intruded along the Moine Thrust Zone, a major collisional zone in north-west Scotland. The most northerly of these is the Loch Loyal Syenite Complex, which comprises three separate intrusions. One of these, the Cnoc nan Cuilean intrusion, contains two mappable zones: a Mixed Syenite Zone in which mafic melasyenite is mixed and mingled with leucosyenite and a Massive Leucosyenite Zone. Within the Mixed Syenite Zone, hydrothermal activity is evident in the form of narrow altered veins dominated by biotite and magnetite; these are poorly exposed and their lateral extent is uncertain. The REE mineral allanite is relatively bundant in the melasyenite and is extremely enriched in the biotite–magnetite veins, which have up to 2 % total rare earth oxides in bulk rock analyses. An overall model for development of this intrusion can be divided into three episodes: (1) generation of a Light Rare Earth Element (LREE)-enriched parental magma due to enrichment of the mantle source by subduction of pelagic carbonates; (2) early crystallisation of allanite in melasyenite, due to the saturation of the magma in the LREE; and (3) hydrothermal alteration, in three different episodes identified by petrography and mineral chemistry, generating the intense enrichment of REE in the biotite–magnetite veins. Dating of allanite and titanite in the biotite–magnetite veins gives ages of c. 426 Ma,overlapping with previously published crystallisation ages for zircon in the syenite.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Environmental Sciences
Uncontrolled Keywords: Rare Earth Elements; Post-collisional; Syenite; Allanite; Hydrothermal alteration
Publisher: Springer Verlag
ISSN: 0010-7999
Funders: Natural Environment Research Council
Date of First Compliant Deposit: 30 March 2016
Last Modified: 17 May 2023 13:58
URI: https://orca.cardiff.ac.uk/id/eprint/59654

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