Abstract

A borehole drilled on the top of Rosemary Bank (Rockall Trough, NE Atlantic), recovered 16.72m of basalts and volcaniclastic sediments beneath a 1.53m thick limestone with basalt clasts, biostratigraphically dated as late Maastrichtian. Magnetostratigraphic data, constrained by the biostratigraphy, indicate extrusion of Rosemary Bank basalts took place during magnetochron C31R (71–69 Ma), or possibly earlier. This provides definite proof of pre-Tertiary volcanism in the Rockall Trough, and indicates that the onset of activity in the North Atlantic Igneous Province took place at least 7 Ma earlier than the postulated arrival of the Icelandic plume at 62 Ma. Geochemical and isotopic data suggest there was an enriched component to the magmatic source. Present data cannot resolve whether the Rosemary Bank basalts are an early manifestation of the Icelandic plume, whether they were associated with a different plume, or whether they were derived from enriched upper mantle without a significant thermal anomaly.

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