The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Abstract -The processes that led to the onset and evolution of the North Atlantic Igneous Province (NAIP) have been a theme of debate in the past decades. A popular theory has been that the impingement on the lower lithosphere of a hot mantle plume (the 'Ancestral Iceland' plume) initiated the first voluminous outbursts of lava and initiated rifting in the North Atlantic area in Early Palaeogene times. Here we review previous studies in order to set the NAIP magmatism in a time-space context. We suggest that global plate reorganizations and lithospheric extension across old orogenic fronts and/or suture zones, aided by other processes in the mantle (e.g. local or regional scale upwellings prior to and during the final Early Eocene rifting), played a role in the generation of the igneous products recorded in the NAIP for this period. These events gave rise to the extensive Paleocene and Eocene igneous rocks in W Greenland, NW Britain and at the conjugate E Greenland-NW European margins. Many of the relatively large magmatic centres of the NAIP were associated with transient and geographically confined doming in Early Paleocene times prior to the final break-up of the North Atlantic area.

The Early Cenozoic igneous activity of the North Atlantic Igneous Province that generated widespread sill complexes in sedimentary basins at the NW European margins also generated various intrusive systems in the contemporaneous basaltic lava pile of the Faroe Islands. The Faroe Island Basalt Group comprises seven formations with a total thickness of about 6.5 km, of which four major formations are built up of tholeiitic lava flows, each being several hundred metres thick, and three thinner formations are mostly built up of volcaniclastic lithologies, each being a few metres to a few tens of metres thick. The largest sills are exposed as partly saucer-shaped bodies in the three uppermost formations, where inner gently dipping basal sill sections gradually give way to more steeply inclined discordant outer rims that commonly cut several hundred metres into overlying lava flows. Numerous subvertical and moderately inclined dykes ranging in thickness from c . 0.5 to c . 4.0 m intersect the areas affected by sill intrusion, but only inclined dykes or sheets have been positively identified as sill feeders. Locally controlled rotations of least principal stress axes σ 3 during initial sill intrusion or propagation may have been an important contributing factor in determining the overall geometry of the investigated intrusions.

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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 laying between the other two categories. Mantle normalised plots for the high-TiO2 and low-TiO2 sills display relatively uniform flat LREE trends, with (Ce/Sm)N ratios ranging from 1.11 to 1.27. Mantle normalised HREE trends representing the low-TiO2 sills show relatively low (Sm/Yb)N ratios ranging from 1.09 to 1.26, as compared to ratios of 1.59 to 2.38 for the high-TiO2 sills. The intermediate-TiO2 Morskranes Sill is LREE depleted with an average (Ce/Sm)N ratio of ~0.6, but displays a flat HREE trend with an average (Sm/Yb)N ratio of ~1.Mantle normalised trace elements of the low-TiO2 sill samples define positive Eu and Sr anomalies, whereas trace elements representing high-TiO2 sill samples display negative anomalies, thus probably indicating the involvement of plagioclase at some stage(s) during magma genesis. Different Nb and Ta anomalies (positive versus negative) in many high-TiO2 versus low-TiO2 sill samples indicate that their respective mantle sources were affected by metasomatism prior to partial melting. Two main isotope discriminators can be detected amongst the actual sill samples: 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. However, a third distinct crustal source of E Greenland or Rockall-type basement may be required in order to explain the range in compositions of some lead isotopes of the intermediate-TiO2 Morskranes Sill, unless these were caused by hitherto undetected isotopic heterogeneities in the mantle.Geochemical modelling indicates that primary melts, which subsequently evolved to Faroese high-TiO2 sills, could have formed by a range of ~4 to 7.5 % batch melting of moderately fertile lherzolitic sourches, while a range of 16 to 21 % batch melting of likewise fertile sources seems to be required in order to produce Faroese low-TiO2 sills. The moderately fertile source inferred for Faroese low-TiO2 sill samples in particular are at odds with the depleted sources envisaged for their low-TiO2 basaltic host-rocks. Primary melts that gave rise to 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. The modelling points to garnet-free residues during mantle melting in order to produce the primary melts that subsequently evolved to most of the Faroese sills. These are envisaged to have formed by batch melting of mantle materials comparable in composition to materials reported for the sub-continental lithospheric mantle (SCLM) at depths of 85 km. Their relative enrichments in LREE (and LILE in general), as well as their varying Nb and Ta anomalies, may well point to sources affected by metasomatism. These could have been caused by earlier Cenozoic local basaltic magmatism or by earlier events linked to the complex geologic history of the N Atlantic area.

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