The South Atlantic appears to be the locus of a broad boundary between two major geochemical provinces of the earth's mantle. The DUPAL anomaly centered over the South Atlantic may be the result of contamination of the asthenosphere either by delamination of sub- continental lithosphere during the breakup and scatter of Gondwanaland or from the dispersal of mantle plumes of deeper origin within the earth. A 38-day cruise to dredge the Mid- Atlantic Ridge and adjacent seamounts from about 41S to 52S will be conducted. The post-cruise analytical program will provide a means to study the isotopic and geochemical nature of the DUPAL boundary, delineate the possible effects of the Gough, Discovery, and Shona off-ridge hotspots on mid-ocean ridge volcanism and its budget, and further evaluate the merit of two competing hypotheses: the plume dispersion model and the delamination of the sub-Gondwana continental lithosphere.
