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Description
We report major and trace element abundances and Hf, Pb, and Nd isotopic ratios for eight of the youngest rejuvenation stage lavas from the Samoan Islands of Upolu and Savai'i. The extensive and voluminous amount of rejuvenation stage volcanism on the Samoan islands, especially on the islands of Savai'i and Upolu, has made these islands key in the understanding of rejuvenation magmatism. The six lavas from Upolu are basanites, whereas the two lavas from Savai'i are alkali basalts. With the exception of one basanite with 7.4 wt. % MgO, all of the samples are relatively primitive (MgO = 10.5 to 12.2 wt. %) and show little evidence of fractionation beyond olivine control. However, variations in major element abundances at a given MgO value indicate changes in the parental melt composition. This interpretation is confirmed by wide variations in ratios of incompatible trace elements (e.g., Nb/La or Ce/Yb). On a primitive mantle normalized trace element diagram, the lavas have relatively constant, low abundances of heavy rare-earth elements (e.g., Yb) due to the presence of residual garnet in the mantle source region. The _Nd (-0.26 to +2.93) and εHf (+3.82 to +7.17) values, and Pb isotope ratios (e.g., ___Pb/___Pb = 18.57-18.88) vary significantly but plot within the range of published data for rejuvenation stage lavas from these islands. On a plot of εNd vs. ___Pb/___Pb, the new Upolu and Savai'i analyses make a distinctive positive correlation that overlaps with previous analyses of rejuvenation stage lavas from these islands. Interestingly, this trend is distinct from the ones defined by many of the purported Upolu and Savai'i shield stage lavas. These data will help to better understand the origin of rejuvenation stage magmatism.
