Peridotite xenoliths from the Polynesian Austral and Samoa hotspots: Implications for the destruction of ancient <SUP>187</SUP>Os and <SUP>142</SUP>Nd isotopic domains and the preservation of Hadean <SUP>129</SUP>Xe in the modern convecting mantle

The Re-Os systematics in 13 peridotite xenoliths hosted in young (<0.39 myr) rejuvenated lavas from the Samoan island of Savai'i and 8 peridotite xenoliths from 6 to 10 myr old lavas from the Austral island of Tubuai have been examined to evaluate the history of the oceanic mantle in this region. Modal mineralogy, trace element compositions and Os-187/Os-188 ratios suggest that these peridotites are not cognate or residual to mantle plumes but rather samples of Pacific oceanic lithosphere created at the ridge. Savai'i and Tubuai islands lie along a flow line in the Pacific plate, and provide two snapshots (separated by over 40 Ma in time) of Pacific mantle that originated in the same region of the East Pacific rise. Tubuai xenoliths exhibit Os-187/Os-188 from 0.1163 to 0.1304, and Savai'i (Samoa) xenoliths span a smaller range from 0.1173 to 0.1284. The Os-187/Os-188 ratios measured in Tubuai xenoliths are lower than (and show no overlap with) basalts from Tubuai. The Os-187/Os-188 of the Savai'i xenoliths overlap the isotopic compositions of lavas from the island of Savai'i, but also extend to lower Os-187/Os-188 than the lavas. 3 He/4 He measurements of a subset of the xenoliths range from 2.5 to 6.4 Ra for Tubuai and 10.8 to 12.4 Ra for Savai'i.