Contrasting mechanisms for crustal sulphur contamination of mafic magma: evidence from dyke and sill complexes from the British Palaeogene Igneous Province

Hughes, Hannah S. R., Boyce, Adrian J., McDonald, Iain ORCID: https://orcid.org/0000-0001-9066-7244, Davidheiser-Kroll, Brett, Holwell, David A., McDonald, Alison and Oldroyd, Anthony 2015. Contrasting mechanisms for crustal sulphur contamination of mafic magma: evidence from dyke and sill complexes from the British Palaeogene Igneous Province. Journal of the Geological Society 172 , pp. 443-458. 10.1144/jgs2014-112

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Abstract

The addition of crustal sulphur to magma can trigger sulphide saturation, a process fundamental to the developmentof some Ni–Cu–PGE deposits. In the British Palaeogene Igneous Province, mafic and ultramafic magmas intrude a thick sedimentary sequence offering opportunities to elucidate mechanisms of magma–crust interaction in a setting with heterogeneous S isotope signatures. We present S-isotopic data from sills and dykes on the Isle of Skye. Sharp contrasts exist between variably light δ34S in Jurassic sedimentary sulphide (−35‰ to −10‰) and a local pristine magmatic δ34S signature of −2.3 ± 1.5‰. Flat-lying sills have restricted δ34S (−5‰ to 0‰) whereas steeply dipping dykes are more variable (−0‰ to −2‰). We suggest that the mechanism by which magma is intruded exerts a fundamental control on the degree of crustal contamination by volatile elements. Turbulent flow within narrow, steep magma conduits, discordant to sediments, and developed by brittle extension or dilation have maximum contamination potential. In contrast, sill-like conduits emplaced concordantly to sediments show little contamination by crustal S. The province is prospective for Ni–Cu–PGE mineralization analogous to the sill-hosted Noril’sk deposit, and Cu/Pd ratios of sills and dykes on Skye indicate that magmas had already reached S-saturation before reaching the present exposure level.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Earth and Environmental Sciences
Subjects:	Q Science > QE Geology
Publisher:	Geological Society
ISSN:	0016-7649
Funders:	Natural Environment Research Council
Date of First Compliant Deposit:	30 March 2016
Date of Acceptance:	19 March 2015
Last Modified:	15 Dec 2023 07:21
URI:	https://orca.cardiff.ac.uk/id/eprint/73371

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