E. Heptinstall, J. Parnell, Andrea Schito, Adrian J. Boyce, J. Armstrong, David Muirhead
{"title":"Graphitisation of Neoproterozoic sedimentary marbles in The Aird, Scottish Highlands","authors":"E. Heptinstall, J. Parnell, Andrea Schito, Adrian J. Boyce, J. Armstrong, David Muirhead","doi":"10.1144/sjg2023-013","DOIUrl":null,"url":null,"abstract":"\n Graphite occurs in Neoproterozoic (probable Loch Ness Supergroup) marbles of The Aird, in the Northern Highland Terrane, Scotland. The graphite occurs particularly in association with phlogopite mica, and also with other micas and Mg-chlorite. Although the graphite-phlogopite association is recorded widely elsewhere in mantle-derived rocks, our data suggests graphite at The Aird does not have a mantle origin. The carbon isotopic composition of the graphite (\n \n \n δ\n \n \n 13\n C, 0.4 to -1.6 ‰) indicates graphitisation occurred from a CO\n 2\n -rich fluid associated with decarbonation or devolatilisation reactions of a carbonate-silicate protolith. Graphite-phlogopite bearing marbles in the Aird underwent extensive brecciation and haematite deposition that preceded carbon-rich, mantle-derived (carbonatite) fluids. Pyrite in veins within The Aird marble has a sulphur isotope composition depleted in\n \n 34\n S\n \n (-15.5 to -16.6 ‰), suggesting a biogenic origin. Elsewhere in The Aird and in surrounding fenitised rocks\n \n 34\n S\n \n -enriched pyrite has sulphur isotope compositions between 7.7 to 6.1 ‰, outside the sulphur isotopic composition range of most carbonatite-hosted pyrite, suggesting pyrite veining was likely influenced by crustal fluid-rock interactions. The observations show that if the protolith has a carbonate-silicate composition, a graphite-phlogopite association can form without the need for mantle-derived fluids.\n \n \n Thematic collection:\n This article is part of the Early Career Research collection available at:\n https://www.lyellcollection.org/topic/collections/early-career-research\n","PeriodicalId":49556,"journal":{"name":"Scottish Journal of Geology","volume":null,"pages":null},"PeriodicalIF":0.5000,"publicationDate":"2024-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Scottish Journal of Geology","FirstCategoryId":"89","ListUrlMain":"https://doi.org/10.1144/sjg2023-013","RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"GEOLOGY","Score":null,"Total":0}
引用次数: 0
Abstract
Graphite occurs in Neoproterozoic (probable Loch Ness Supergroup) marbles of The Aird, in the Northern Highland Terrane, Scotland. The graphite occurs particularly in association with phlogopite mica, and also with other micas and Mg-chlorite. Although the graphite-phlogopite association is recorded widely elsewhere in mantle-derived rocks, our data suggests graphite at The Aird does not have a mantle origin. The carbon isotopic composition of the graphite (
δ
13
C, 0.4 to -1.6 ‰) indicates graphitisation occurred from a CO
2
-rich fluid associated with decarbonation or devolatilisation reactions of a carbonate-silicate protolith. Graphite-phlogopite bearing marbles in the Aird underwent extensive brecciation and haematite deposition that preceded carbon-rich, mantle-derived (carbonatite) fluids. Pyrite in veins within The Aird marble has a sulphur isotope composition depleted in
34
S
(-15.5 to -16.6 ‰), suggesting a biogenic origin. Elsewhere in The Aird and in surrounding fenitised rocks
34
S
-enriched pyrite has sulphur isotope compositions between 7.7 to 6.1 ‰, outside the sulphur isotopic composition range of most carbonatite-hosted pyrite, suggesting pyrite veining was likely influenced by crustal fluid-rock interactions. The observations show that if the protolith has a carbonate-silicate composition, a graphite-phlogopite association can form without the need for mantle-derived fluids.
Thematic collection:
This article is part of the Early Career Research collection available at:
https://www.lyellcollection.org/topic/collections/early-career-research
期刊介绍:
Although published only since 1965, the Scottish Journal of Geology has a long pedigree. It is the joint publication of the Geological Society of Glasgow and the Edinburgh Geological Society, which prior to 1965 published separate Transactions: from 1860 in the case of Glasgow and 1863 for Edinburgh.
Traditionally, the Journal has acted as the focus for papers on all aspects of Scottish geology and its contiguous areas, including the surrounding seas. The publication policy has always been outward looking, with the Editors encouraging review papers and papers on broader aspects of the Earth sciences that cannot be discussed solely in terms of Scottish geology.
The diverse geology of Scotland continues to provide an important natural laboratory for the study of earth sciences; many seminal studies in geology have been carried out on Scottish rocks, and over the years the results of much of this work had been published in the Journal and its predecessors.
The Journal fully deserves its high reputation worldwide and intends to maintain its status in the front rank of publications in the Earth sciences.