The origin(s) and geodynamic significance of Archaean ultramafic-mafic bodies in the mainland Lewisian Gneiss Complex, North Atlantic Craton

Guice, G. L., McDonald, I., Hughes, H. S.R., MacDonald, J. M. and Faithfull, J. W. (2020) The origin(s) and geodynamic significance of Archaean ultramafic-mafic bodies in the mainland Lewisian Gneiss Complex, North Atlantic Craton. Journal of the Geological Society, (doi: 10.1144/jgs2020-013) (Early Online Publication)

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Abstract

The geodynamic regime(s) that predominated during the Archaean remains controversial, with the plethora of competing models largely informed by felsic lithologies. Ultramafic-mafic rocks displaying distinctive geochemical signatures are formed in a range of Phanerozoic geotectonic environments. These rocks have high melting points, making them potentially useful tools for investigating Archaean geodynamic processes in highly metamorphosed regions. We present field mapping, petrography, traditional bulk-rock geochemistry, and platinum-group element geochemistry for 12 ultramafic-mafic bodies in the Lewisian Gneiss Complex (LGC), which is a highly metamorphosed fragment of the North Atlantic Craton in northwest Scotland. Our data indicate that most of these occurrences are layered intrusions emplaced into the tonalite-trondhjemite-granodiorite (TTG)-dominated crust prior to polyphase metamorphism, representing a significant re-evaluation of the LGC's magmatic evolution. Of the others, two remain ambiguous, but one (Loch an Daimh Mor) has some geochemical affinity with abyssal/orogenic peridotites and may represent a fragment of Archaean mantle, although further investigation is required. The ultramafic-mafic bodies in the LGC thus represent more than one type of event/process. Compared with the TTG host rocks, these lithologies may preserve evidence of protolith origin(s), with potential to illuminate tectonic setting(s) and geodynamic regimes of the early Earth.

Item Type:Articles (Other)
Additional Information:G.L.G. would like to thank The Society of Economic Geologists (Graduate Fellowship Award) and The Geological Society (Timothy Jefferson Fund) for generous bursaries that provided funding for the fieldwork upon which this research is based.
Keywords:Metamorphism, Precambrian, Archaean, magmatism.
Status:Early Online Publication
Refereed:Yes
Glasgow Author(s) Enlighten ID:Faithfull, Dr John and MacDonald, Dr John
Authors: Guice, G. L., McDonald, I., Hughes, H. S.R., MacDonald, J. M., and Faithfull, J. W.
Subjects:Q Science > QE Geology
College/School:College of Science and Engineering > School of Geographical and Earth Sciences
University Services > Library and Collection Services > Museum and Art Gallery
Journal Name:Journal of the Geological Society
Journal Abbr.:Jour. Geol Soc.
Publisher:Geological Society of London
ISSN:0016-7649
ISSN (Online):2041-479X
Published Online:03 March 2020
Copyright Holders:Copyright © 2020 The Authors
First Published:First published in Journal of the Geological Society 2020
Publisher Policy:Reproduced in accordance with the publisher copyright policy
Data DOI:10.6084/m9.figshare.c.4878588

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