Homogeneous and glassy volcaniclastic debris of excellent preservation was cored during IKU shallow drilling south west of Bjørnøya in 1989. The present paper focuses on the age and origin of the volcaniclastics based on petrological and isotopic studies of glasses and whole-rocks and their occurrence in relation to the sediments. Chemical analyses of ash, lapilli and blocks all show fairly similar, relatively alkali-rich subalkaline basaltic composition. Sm-Nd and Rb-Sr isotopic signatures are comparable with melting from anomalously enriched mantle or alternatively modification by interaction with anomalously enriched mantle or lower crustal components. 40Ar-39Ar dating by the stepwise heating technique detennined a crystallization age of ca. 2.3 Ma for the volcanic eruptions. The activity was tenninated by sliding and re-sedimentation of both the volcanics and older Tertiary sedimentary deposits at the Western Barents Shelf margin. The present data are used to constrain the timing of the thermal-tectonic evolution and the erosional history in the vicinity of the Vestbakken Volcanic Province and Stappen High areas.

M. B. E. Mørk, IKU, 7034 Trondheim, Norway;
R. A. Duncan, Oregon State University, Corvallis, OR 97331-5503, USA