期刊
JOURNAL OF THE GEOLOGICAL SOCIETY
卷 170, 期 5, 页码 737-752出版社
GEOLOGICAL SOC PUBL HOUSE
DOI: 10.1144/jgs2012-104
关键词
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资金
- Northern Ireland Department of Enterprise Trade and Investment
- Northern Ireland Environment Agency
- British Geological Survey (BGS University Funding Initiative)
- Dalradian Resources, Geological Survey of Northern Ireland
- University of Southampton
- Metallum Resources and Natural History Museum, London
- NERC [nigl010001, bgs05001] Funding Source: UKRI
- Natural Environment Research Council [bgs05001, nigl010001] Funding Source: researchfish
Recent Ar-Ar and U-Pb zircon geochronology from across the British and Irish Caledonides has revealed a prolonged period of arc-ophiolite formation (c. 514-464 Ma) and accretion (c. 490-470 Ma) to the Laurentian margin during the Grampian orogeny. The Slieve Gallion Inlier of Northern Ireland, an isolated occurrence of the Tyrone Volcanic Group, records the development of a peri-Laurentian island arc-backarc and its obduction to an outboard microcontinental block. Although a previous biostratigraphic age constraint provides a firm correlation of at least part of the volcanic succession to the Ca1 Stage of the Arenig (c. 475-474 Ma), there is uncertainty on its exact statigraphic position in the Tyrone Volcanic Group. Earliest magmatism is characterized by light rare earth element (LREE) depleted island-arc tholeiite. Overlying deposits are dominated by large ion lithophile and LREE-enriched, hornblende-phyric and feldspathic calc-alkaline basaltic andesites and andesitic tuffs with strongly negative epsilon Nd-t values. Previously published biostratigraphic age constraints, combined with recent U-Pb zircon geochronology and new petrochemical correlations, suggest that the Slieve Gallion Inlier is equivalent to the lower Tyrone Volcanic Group. Temporal and geochemical correlations between the Slieve Gallion Inlier and Charlestown Group of Ireland suggest that they may be part of the same arc system, which was accreted at a late stage (c. 470 Ma) in the Grampian orogeny. A switch from tholeiitic volcanism to calc-alkaline dominated activity within the Lough Nafooey Group of western Ireland occurred prior to c. 490 Ma, some 15-20 Myr earlier than at Tyrone and Charlestown.
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