LATE CRETACEOUS BASALTS FROM ROSEMARY-BANK, NORTHERN ROCKALL TROUGH

A borehole drilled on the tap of Rosemary Bank (Rockall Trough, NE Atl antic), recovered 16.72m of basalts and volcaniclastic sediments benea th a 1.53m thick limestone with basalt clasts, biostratigraphically da ted as late Maastrichtian. Magnetostratigraphic data, constrained by t he biostratigraphy, indicate extrusion of Rosemary Bank basalts took p lace during magnetochron C31R (71-69 Ma), or possibly earlier. This pr ovides definite proof of pre-Tertiary volcanism in the Rockall Trough, and indicates that the onset of activity in the North Atlantic Igneou s Province took place at least 7Ma earlier than the Postulated arrival of the Icelandic plume at 62Ma. 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 manifest ation of the Icelandic plume, whether they were associated with a diff erent plume, or whether they were derived from enriched upper mantle w ithout a significant thermal anomaly.