Volcanic rocks from Rosemary Bank (Rockall Trough, NE Atlantic)

Abstract

A collection of basalts dredged from the southern flank of Rosemary Bank in the Rockall Trough is described. All samples are highly altered, the introduction of large amounts of CaCO 3 into the rocks being particularly notable. Normative calculations suggest that the basalts are transitional or mildly alkaline in character. Several trace elements appear to have been immobile during the process of secondary alteration and are used to infer the tectonic setting of Rosemary Bank at the time of its formation. Employing the discrimination techniques of Pearce and Cann, the basalts are shown to have oceanic affinities. However, caution has to be exercised in interpreting the trace element results in terms of sea-floor spreading in the Rockall Trough since some Scottish basalts extruded on to continental crust have similar compositions. A minimum age of Eocene has been obtained for Rosemary Bank.