The volcanic sequence on Storøya, in tectonic contact with ultramafic and gabbroic rocks of the Leka Ophiolite Complex, consists of a sequence of dominantly submarine, basaltic volcanics with a minimum thickness of 600 m. The dominant rock type is pillow lava, but throughout the sequence massive Javas of variable thickness occur. Layers of fine-grained, laminated sediments and limestone are intercalated with the volcanic sequence. The volcanics are overlain by black shales and green volcaniclastic sediments. Systematic sampling through the volcanic sequence has revealed profound geochemical variations. Plotted in discrimination diagrams, the metabasalts vary from MORB to within-plate basalts, and appear to have formed from a source enriched in trace elements. The geochemical variations can best be explained by applying an open magma chamber model in which assimilation, crystallization and replenishment, together with dynamic metting, occur.

R. Tveit, Phillips Petroleum Company Norway, P.O. Box 220, 4056 Tananger, Norway;
H. Furnes & R.-B. Pedersen, Geologisk Institutt, Avd. A., Allégt. 41, 5007 Bergen, Norway.