Volcanic rock dredged from the flanks of four volcanic edifices in the Ratak chain of the Marshall Islands consist of alkalic lave that erupted above sea level or in shallow water. Compositions of recovered samples are predominantly differentiated alkalic basalt and hawaiite but include strongly alkalic melilitite. Whole rock 40Ar/39Ar total fusion and incremental heating ages of 87.3¿0.6 Ma and 82.2¿1.6 Ma determined for samples from Erikub Seamount and Ratak Guyot, respectively, are within the range predicted by plate rotation models but show no age progression consistent with a simple hot spot model. Whole rock major element, and mineral chemistry are similar to those of alkalic lavas from other oceanic islands, but isotopic and certain trace element ratios reveal distinctive mantle source characteristics. Zr/Nb ratios of ~3.0¿0.2 for Bikar and Ratak Guyot, compared to 5.2¿0.3 for Majuro Atoll and Erikub Seamount, at comparable degree of differentiation, suggest a more alkalic trend for the northern sites. The 143Nd/144Nd isotopic ratios range from 0.51283 to 0.51289 and 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios range from 20.55 to 21.11, 15.71 to 15.77, and 39.93 to 40.75, for samples from Erikub and Ratak. Variations in isotopic and some incompatible element ratios suggest interisland heterogeneity. Similar highly radiogenic lead isotopes, coupled with distinct incompatible element ratios, especially with low Ba/Nb ratios (~6), are observed for St. Helena in the South Atlantic and for Tubuai and Mangaia in the South Pacific. The similar mantle signature shown by lavas from Tubuai and Mangaia in the Austral-Cook chain, which are located at approximately the position where the Ratak edifices formed during the Late Cretaceous, indicates that this mantle anomaly is not of recent origin but has erupted distinctive lava compositions for at least 87 m.y. ¿ American Geophysical Union 1989