Petrogenesis of the Voring Plateau volcanic sequence drilled on Leg 104: interaction of mantle and crustal derived melts during formation of a constructive plate margin

During ODP Leg 104 a 900 m thick sequence of volcanic rocks was drilled at Site 642E on the Vøring Plateau. It was subdivided into an Upper and a Lower Series separated by 7 m of estuarine volcaniclastic and epiclastic rocks. The Upper Series comprises transitional-type mid-oceanic ridge tholeiites with chemical affinities to the Faeroes and E Greenland plateau basalts and to Recent basalts from transitional segments of the mid-Atlantic ridge such as Reykjanes Ridge. The magmas are interpreted as having been derived from a secondarily LIL-element enriched, primarily strongly depleted mantle source. Some flows and dykes show evidence of minor contamination by upper continental crustal rocks. Interlayered tuffs are more differentiated and ferrobasaltic, and are interpreted to have been derived from a LIL-element enriched plume-type mantle source. The Lower Series contains 13 peraluminous dacite flows representing melts of upper crustal metasedimentary rocks such as shales and greywackes. The dacites overlie five basaltic andesite flows formed by mixing of LIL-element depleted tholeiitic magma with upper crustal melts.