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Contrasting TiO2 Compositions in Early Cenozoic Mafic Sills of the Faroe Islands: An Example of Basalt Formation from Distinct Melting Regimes

Received: 14 August 2019    Accepted: 23 September 2019    Published: 09 October 2019
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Abstract

The Paleocene lava succession of the Faroe Islands Basalt Group (FIBG), which is a part of the North Atlantic Igneous Province (NAIP), is intruded by numerous basaltic sills. These can be grouped into three main categories according to their geochemical characteristics: A low-TiO2 sill category (TiO2 = 0.7-0.9), a relatively high-TiO2 sill category (TiO2 = 1.95-2.6) and an intermediate-TiO2 sill that displays major element compositions lying between the other two categories. Mantle normalised plots for the high-TiO2 and low-TiO2 sills display relatively uniform flat LREE trends and slightly steeper HREE slopes for high-TiO2 relative to low-TiO2 sills. The intermediate-TiO2 Morskranes Sill is LREE depleted. Mantle normalised trace elements of low-TiO2 sill samples define positive Eu and Sr anomalies, whereas high-TiO2 sill samples display negative anomalies for these same lements. Different Nb and Ta anomalies (positive versus negative) in many high-TiO2 versus low-TiO2 sill samples suggest various metasomatism of their sources prior to partial melting. The intermediate-TiO2 sill displays noticeably lower 87Sr/86Sr, 206Pb/204Pb and 208Pb/204Pb ratios relative to both the high-TiO2 and the low-TiO2 sill samples. Pb isotope compositions displayed by local contaminated basaltic lavas imply that some of these assimilated distinct crustal material from E Greenland or basement from NW Britain, while others probably assimilated only distinct E Greenland type of crustal material. A third crustal source of E Greenland or Rockall-type basement could be required in order to explain some of the range in lead isotopes displayed by the intermediate-TiO2 Morskranes Sill. Geochemical modelling suggest that Faroese high-TiO2 sills, could have formed by ~4 to 7.5% batch melting of moderately fertile lherzolites, while 16 to 21% batch melting fertile mantle sources could explain geochemical compositions of Faroese low-TiO2 sills. The intermediate-TiO2 sill samples could have formed by a range of 6 to 7% batch melting of a depleted mantle source, probably with a composition comparable to sources that gave rise to local low-TiO2 and intermediate-TiO2 host-rocks. Most Faroese sill samples probably developed outside the garnet stabilitry field and probably formed by batch melting of mantle materials comparable in composition to those reported for the sub-continental lithospheric mantle (SCLM) previously at depths of ≤ 85 km. Relative enrichments in LREE (and LILE in general), and their varying Nb and Ta anomalies point to sources affected by metasomatism.

DOI 10.11648/j.earth.20190805.11
Published in Earth Sciences (Volume 8, Issue 5, October 2019)
Page(s) 235-267
Creative Commons

This is an Open Access article, distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution and reproduction in any medium or format, provided the original work is properly cited.

Copyright

Copyright © The Author(s), 2024. Published by Science Publishing Group

Keywords

North Atlantic, Faroe Islands, Flood Basalts, Sill Intrusion, Partial Melting, Fractional Crystallisation, Mineral Accumulation, Crustal Contamination

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Author Information
  • Department of Earth Sciences, Durham University, Durham, United Kingdom

  • Department of Earth Sciences, Durham University, Durham, United Kingdom

  • The Centre for Earth Evolution and Dynamics (CEED), Oslo University, Oslo, Norway; Dougalearth Ltd., Solihull, United Kingdom; Earth, Environmental and Biological Sciences, Queensland University of Technology, Brisbane, Australia

  • Department of Earth Sciences, Durham University, Durham, United Kingdom

  • School of Environmental Science, University of Hull, Hull, United Kingdom

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    Jógvan Hansen, Jon Davidson, Dougal Jerram, Christopher Ottley, Mike Widdowson. (2019). Contrasting TiO2 Compositions in Early Cenozoic Mafic Sills of the Faroe Islands: An Example of Basalt Formation from Distinct Melting Regimes. Earth Sciences, 8(5), 235-267. https://doi.org/10.11648/j.earth.20190805.11

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    Jógvan Hansen; Jon Davidson; Dougal Jerram; Christopher Ottley; Mike Widdowson. Contrasting TiO2 Compositions in Early Cenozoic Mafic Sills of the Faroe Islands: An Example of Basalt Formation from Distinct Melting Regimes. Earth Sci. 2019, 8(5), 235-267. doi: 10.11648/j.earth.20190805.11

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    Jógvan Hansen, Jon Davidson, Dougal Jerram, Christopher Ottley, Mike Widdowson. Contrasting TiO2 Compositions in Early Cenozoic Mafic Sills of the Faroe Islands: An Example of Basalt Formation from Distinct Melting Regimes. Earth Sci. 2019;8(5):235-267. doi: 10.11648/j.earth.20190805.11

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  • @article{10.11648/j.earth.20190805.11,
      author = {Jógvan Hansen and Jon Davidson and Dougal Jerram and Christopher Ottley and Mike Widdowson},
      title = {Contrasting TiO2 Compositions in Early Cenozoic Mafic Sills of the Faroe Islands: An Example of Basalt Formation from Distinct Melting Regimes},
      journal = {Earth Sciences},
      volume = {8},
      number = {5},
      pages = {235-267},
      doi = {10.11648/j.earth.20190805.11},
      url = {https://doi.org/10.11648/j.earth.20190805.11},
      eprint = {https://download.sciencepg.com/pdf/10.11648.j.earth.20190805.11},
      abstract = {The Paleocene lava succession of the Faroe Islands Basalt Group (FIBG), which is a part of the North Atlantic Igneous Province (NAIP), is intruded by numerous basaltic sills. These can be grouped into three main categories according to their geochemical characteristics: A low-TiO2 sill category (TiO2 = 0.7-0.9), a relatively high-TiO2 sill category (TiO2 = 1.95-2.6) and an intermediate-TiO2 sill that displays major element compositions lying between the other two categories. Mantle normalised plots for the high-TiO2 and low-TiO2 sills display relatively uniform flat LREE trends and slightly steeper HREE slopes for high-TiO2 relative to low-TiO2 sills. The intermediate-TiO2 Morskranes Sill is LREE depleted. Mantle normalised trace elements of low-TiO2 sill samples define positive Eu and Sr anomalies, whereas high-TiO2 sill samples display negative anomalies for these same lements. Different Nb and Ta anomalies (positive versus negative) in many high-TiO2 versus low-TiO2 sill samples suggest various metasomatism of their sources prior to partial melting. The intermediate-TiO2 sill displays noticeably lower 87Sr/86Sr, 206Pb/204Pb and 208Pb/204Pb ratios relative to both the high-TiO2 and the low-TiO2 sill samples. Pb isotope compositions displayed by local contaminated basaltic lavas imply that some of these assimilated distinct crustal material from E Greenland or basement from NW Britain, while others probably assimilated only distinct E Greenland type of crustal material. A third crustal source of E Greenland or Rockall-type basement could be required in order to explain some of the range in lead isotopes displayed by the intermediate-TiO2 Morskranes Sill. Geochemical modelling suggest that Faroese high-TiO2 sills, could have formed by ~4 to 7.5% batch melting of moderately fertile lherzolites, while 16 to 21% batch melting fertile mantle sources could explain geochemical compositions of Faroese low-TiO2 sills. The intermediate-TiO2 sill samples could have formed by a range of 6 to 7% batch melting of a depleted mantle source, probably with a composition comparable to sources that gave rise to local low-TiO2 and intermediate-TiO2 host-rocks. Most Faroese sill samples probably developed outside the garnet stabilitry field and probably formed by batch melting of mantle materials comparable in composition to those reported for the sub-continental lithospheric mantle (SCLM) previously at depths of ≤ 85 km. Relative enrichments in LREE (and LILE in general), and their varying Nb and Ta anomalies point to sources affected by metasomatism.},
     year = {2019}
    }
    

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  • TY  - JOUR
    T1  - Contrasting TiO2 Compositions in Early Cenozoic Mafic Sills of the Faroe Islands: An Example of Basalt Formation from Distinct Melting Regimes
    AU  - Jógvan Hansen
    AU  - Jon Davidson
    AU  - Dougal Jerram
    AU  - Christopher Ottley
    AU  - Mike Widdowson
    Y1  - 2019/10/09
    PY  - 2019
    N1  - https://doi.org/10.11648/j.earth.20190805.11
    DO  - 10.11648/j.earth.20190805.11
    T2  - Earth Sciences
    JF  - Earth Sciences
    JO  - Earth Sciences
    SP  - 235
    EP  - 267
    PB  - Science Publishing Group
    SN  - 2328-5982
    UR  - https://doi.org/10.11648/j.earth.20190805.11
    AB  - The Paleocene lava succession of the Faroe Islands Basalt Group (FIBG), which is a part of the North Atlantic Igneous Province (NAIP), is intruded by numerous basaltic sills. These can be grouped into three main categories according to their geochemical characteristics: A low-TiO2 sill category (TiO2 = 0.7-0.9), a relatively high-TiO2 sill category (TiO2 = 1.95-2.6) and an intermediate-TiO2 sill that displays major element compositions lying between the other two categories. Mantle normalised plots for the high-TiO2 and low-TiO2 sills display relatively uniform flat LREE trends and slightly steeper HREE slopes for high-TiO2 relative to low-TiO2 sills. The intermediate-TiO2 Morskranes Sill is LREE depleted. Mantle normalised trace elements of low-TiO2 sill samples define positive Eu and Sr anomalies, whereas high-TiO2 sill samples display negative anomalies for these same lements. Different Nb and Ta anomalies (positive versus negative) in many high-TiO2 versus low-TiO2 sill samples suggest various metasomatism of their sources prior to partial melting. The intermediate-TiO2 sill displays noticeably lower 87Sr/86Sr, 206Pb/204Pb and 208Pb/204Pb ratios relative to both the high-TiO2 and the low-TiO2 sill samples. Pb isotope compositions displayed by local contaminated basaltic lavas imply that some of these assimilated distinct crustal material from E Greenland or basement from NW Britain, while others probably assimilated only distinct E Greenland type of crustal material. A third crustal source of E Greenland or Rockall-type basement could be required in order to explain some of the range in lead isotopes displayed by the intermediate-TiO2 Morskranes Sill. Geochemical modelling suggest that Faroese high-TiO2 sills, could have formed by ~4 to 7.5% batch melting of moderately fertile lherzolites, while 16 to 21% batch melting fertile mantle sources could explain geochemical compositions of Faroese low-TiO2 sills. The intermediate-TiO2 sill samples could have formed by a range of 6 to 7% batch melting of a depleted mantle source, probably with a composition comparable to sources that gave rise to local low-TiO2 and intermediate-TiO2 host-rocks. Most Faroese sill samples probably developed outside the garnet stabilitry field and probably formed by batch melting of mantle materials comparable in composition to those reported for the sub-continental lithospheric mantle (SCLM) previously at depths of ≤ 85 km. Relative enrichments in LREE (and LILE in general), and their varying Nb and Ta anomalies point to sources affected by metasomatism.
    VL  - 8
    IS  - 5
    ER  - 

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