This study is a geochemical investigation of ocean bottom rock samples obtained in 1985 from the Drake Passage and Bransfield Strait under a cooperative program with the Federal Republic of Germany on R/V POLARSTERN. The objectives concern the formation of back-arc and marginal basins and their associated volcanic rocks. Major elements and trace elements will be analyzed to establish the extent to which subducted sediment is incorporated into the generation of mantle basalts, and how the subducted material has affected the composition of the mantle beneath the Bransfield Strait and the South Shetland Islands. Mineral chemistry and glass inclusions of phenocrysts will be analyzed to evaluate the extent of magma mixing, the depth of magma chambers, and the kinetics of magma eruption. The rock samples to be studied were obtained by the principal investigator, and include fresh basalts recovered from two seamounts and from volcanic hills in the Bransfield Strait. Older more weathered basalts were dredged from the basin between Low and Deception Islands. The Bransfield Strait is a young marginal basin that was formed by rifting and subsidence of the Antarctic Peninsula. The geochemical processes associated with this subduction are not well understood; neither is the transport of material from the subducting slab to the arc magma system. The slab may melt and intrude into the overlying mantle wedge with the mixture forming the island arc magma source, or the source may be the subducting slab itself. It is expected that the trace element analysis will point to one or the other of these processes.
