Title: On the timing and nature of magmatism in the North Atlantic Igneous Province: New implications from basaltic rocks of the Faroe Islands
Abstract: New 40Ar/39Ar ages representing a number of basaltic sills and a key lava flow from the Faroe Islands are presented in this contribution and utilised in order to assess the igneous history of parts of this region. In turn, the acquired ages are contrasted against other Faroese rocks of known ages as well as against other comparable igneous regions in the North Atlantic area. Altogether, the novel ages obtained in this work enable us to put new constraints on the timing of late stage magmatic activity and hence lithospheric extension within this part of the North Atlantic Igneous Province, which the Faroe Islands form part of. Even though the main stages of igneous activity within the North Atlantic Igneous Province generally took place within a time span of ~61 Ma to ~55 Ma, examples of more recent magmatism have been documented for W Greenland, E Greenland, the Norwegian – Greenland Sea, igneous centres at the eastern fringes of the Rockall Plateau and in the Rockall trough, thus testifying that lithospheric extension off rift axes continued for some noticeable time following onset of regional seafloor spreading. In this research we present new ages as young as ~50.5 Ma for some of the smallest Faroese sills and demonstrate that the larger and oldest sills of the Faroe Islands, grouped into the Streymoy/Kvívík sills and the Eysturoy/Sundini sills respectively (~55.5 Ma), likely formed just subsequent to the formation of the uppermost parts of the Enni Formation, which represent the latest stages of local surface magmatism at ~55.8 Ma. Gradually decreasing volumes of Faroese sills coupled with sequentially younger ages point to systematic decrease of local igneous activity with increasing distances to active regional rifting zones in the Early Paleogene Period, as the young Faroese lava plateau gradually drifted away from the then active regional rift axis. Similar scenarios in other parts of the North Atlantic Igneous Province support our inferences that it was commonplace within this large igneous province to experience relatively small-scale lithospheric extension and magmatism at some distances from zones/axes of active seafloor-spreading. Age variations between igneous products of the Faroe Islands versus those of the central E Greenland point to a somewhat diachronous evolution pattern within this part of the North Atlantic Igneous Province subsequent to ~57.5 Ma. Accordingly, our study does not preclude the existence of a contemporaneous Icelandic microcontinent between Faroe Islands and central E Greenland.