| Titre | Age and composition of gabbro samples dredged from the Alpha Ridge, Arctic Ocean |
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| Auteur | Williamson, M -C ;
Mosher, D C; Rayner, N; Wilton, D H C; Cutts, J; Dewing, K; Hadlari, T; Lawley, C J M; Zhang, S; Cousens, B L; Macdonald, D J; Petts, D; Polivchuk, M |
| Source | 2023 p. 1 |
| Liens | Online - En ligne
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| Image |  |
| Année | 2023 |
| Séries alt. | Ressources naturelles Canada, Contribution externe 20220673 |
| Éditeur | Association géologique du Canada |
| Document | livre |
| Lang. | anglais |
| Media | papier; numérique; en ligne |
| Formats | pdf |
| Province | Région extracotière |
| Région | Océan Arctique |
| Lat/Long OENS | -180.0000 -60.0000 90.0000 76.0000 |
| Sujets | gabbros; Bassin d'Arctic ; minéralogie |
| Programme | GEM-GéoNord : La géocartographie de l'énergie et des minéraux Coordination du programme GEM |
| Diffusé | 2023 05 01 |
| Résumé | (disponible en anglais seulement)
The Alpha-Mendeleev ridge complex (AMR) is the largest submarine feature mapped in the Arctic Ocean basin. Ice cover and remoteness of the AMR within the
Amerasia Basin present operational challenges that limit the direct sampling of bedrock by dredging. Recent marine surveys carried out under Article 76 of the United Nations Convention on the Law of the Sea (UNCLOS) have provided a wealth of new
geophysical data that constrain the nature and origin of the AMR. Geological samples of bedrock are rare but provide direct evidence of voluminous mafic volcanism at ~ 90 Ma that is characteristic of large igneous provinces (LIPs). We report
mineralogical, geochemical and geochronological data for sample ECS005041 recovered by dredging at Nautilus Spur by the US Coast Guard Ship Healy (3285 m depth). The samples consist of massive and medium-grained microgabbro in which sub-ophitic
plagioclase and pyroxene predominate. Whole rock geochemical data indicate that the major element composition is typical of subalkaline magmas emplaced in a continental setting. Rare, small zircon grains were analysed in thin section by sensitive
high resolution ion microprobe (SHRIMP) and yielded a 206Pb/238U age of 732.0 ± 7.8 Ma interpreted as the crystallization age of the microgabbro. This result falls within the range of published ages for intrusive rocks of the Franklin LIP in Arctic
Canada, although a recent study suggests rapid emplacement of the LIP between 719.86 ± 0.21 and 718.61 ± 0.30 Ma. Immobile trace element concentrations for sample ECS005041 are typical of transitional basalts with enriched mid-ocean ridge basalt
(E-MORB) geochemical signatures (e.g., Th/Yb and Nb/Yb ratios). Chondrite-normalized rare earth element (REE) patterns are negatively sloped with minor light-REE enrichment (i.e., 20x chondrite), but are generally depleted in comparison with those of
magmatic rocks emplaced in the Franklin LIP, and in other continental flood basalts provinces of Phanerozoic age. Isotopic analyses yielded 87Sr/86Sr ratios of 0.703815, ENd of +1.45, and EHf of +6.6. These results, and the HFSE trace element ratios,
fall within the range of values reported for Franklinian intrusive rocks suggesting that precursor magmatism may have extended geographically beyond the known distribution of dykes exposed in the Canadian Arctic Islands. |
| Sommaire | (Résumé en langage clair et simple, non publié)
Le complexe de dorsales Alpha-Mendeleev (DAM) est la plus grande caractéristique physiographique cartographiée dans le bassin de l'océan
Arctique. Des levés récents menés en vertu de l'article 76 de la Convention des Nations Unies sur le droit de la mer (UNCLOS) ont offert de nouvelles possibilités d'échantillonner les affleurements du socle. Les échantillons géologiques récupérés
lors du dragage de la dorsale Alpha sont rares mais, jusqu'à présent, ils fournissent la seule preuve directe d'un volcanisme mafique volumineux, caractéristique des grandes provinces ignées. En revanche, notre étude d'un échantillon dragué de
l'Éperon Nautilus , situé sur la dorsale Alpha, indique une origine intrusive et un âge de cristallisation qui correspond à celui de dykes de Franklin d'âge néoprotérozoïque affleurant dans les îles arctiques canadiennes. |
| GEOSCAN ID | 331756 |
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