Tertiary Picrites from the Faroe Islands CFB Province: Implications for MORB-type Components in the
Icelandic Mantle Plume

Paul M. Holm Geological Institute, University of Copenhagen, Oster Voldgade 10, DK-1350 Copenhagen, Denmark


Niels Hald Geological Museum, University of Copenhagen, Oster Voldgade 10, DK-1350 Copenhagen, Denmark

Jonathan Bown Bullard Laboratories, Cambridge University, Madingley Road, Cambridge, UK

Regin Waagstein Geological Survey of Denmark and Greenland, Thoravej 8, DK-2400 Copenhagen, Denmark

Basic rocks from the Tertiary continental flood basalt province of the Faroe Islands have been investigated. The Faroe Islands are presently situated at the eastern end of the Faroe-Iceland ridge. During continental break-up in the Paleocene the Faroes were close to central East Greenland and the proposed centre of the Proto-Icelandic mantle plume. The outcrops on the islands are entirely of basic igneous rocks but the lithosphere is continental. The analysed samples in this study are fresh dyke-rocks and some fresh lavas obtained from bore holes. They are representative of the entire compositional range of the province. Picritic and basaltic samples display a considerable variation in incompatible element enrichment, e.g. La/YbN varies from 0.6 to 3.7. Both enriched and depleted picrites occur but are MORB-like in their Sr, Nd and Pb isotopic compositions. Evolved incompatible element depleted basaltic samples evolved by low pressure fractional crystallisation and most assimilated crustal materal. Basaltic enriched samples have Icelandic Sr and Nd isotopic compositions but their Pb is more thorogenic. The MORB-like picritic samples are unique among the Tertiary igneous rocks of the North Atlantic margin. Forward modelling of the REEs show that the enriched samples could be derived from mantle peridotite by a few percent of fractional melting in both the garnet and spinel stability fields. The depleted picritic samples are modelled as large degree melts of a depleted source. Using REE inversion techniques, melt generation is indicated to have taken place in the depth interval of c. 50-100km in a c. 1450°C hot source both in the case of depleted and enriched samples. It is suggested that hot source component with MORB isotope signatures was part of the Icelandic mantle plume in the early stage of its activity. None of these source components have been observed in Iceland. The isotopic and elemental character of the primary magmas will be discussed in relation to suggest source compositions for recent magmas in the North Atlantic region.