Pedogenesis of ultramafic xenoliths from Hawaii inferred from Sr, Nd, and Pb isotopes

Osamu Okano, Mitsunobu Tatsumoto

Research output: Chapter in Book/Report/Conference proceedingChapter

18 Citations (Scopus)


Isotopic compositions of Nd, Sr, and Pb in xenoliths in the Honolulu volcanic series from the Salt Lake Crater (H-type) are similar to those of the host post-erosional basalts, but are distinct from the magma sources of Koolau shield tholeiites and MORB. In contrast, one spinel lherzolite (K-type) has isotopic compositions of Nd and Sr that are close to those of Koolau tholeiite rather than to the other Hawaiian basalts. Previous studies have shown that Sr isotopic composition of the xenoliths and the host basalt and that trace element concentrations in minerals of garnet lherzolites from Honolulu basalt were nearly in equilibrium with the host magma, indicating that Honolulu volcanics were derived from garnet lherzolite or similar material. However, differences exist among the isotopic compositions (especially Nd) of the xenoliths indicating that they are accidental inclusions from upper layers. The similarity in isotopic compositions between xenoliths and Honolulu basalt suggests that the source areas in the mantle are chemically similar. Correlation of 238U/204Pb vs. 206Pb/206Pb of chrome diop-side separated from the H-type spinel lherzolites indicates that the xenoliths are 80 ± 36 Ma, which corresponds to the lithosphere age of the Hawaiian site. This age is consistent with petrological studies [e.g.. Sen and Leeman, 1991] which have found that the spinel lherzolite inclusions are derived from the lithosphere wall rocks. The εNd = ~+8 of the H-xenoliths is slightly lower than that for the East Pacific Rise MORB indicating that the xenoliths are derived from a trace element depleted source similar to the MORB residue. If the garnet lherzolite xenoliths are derived from mixture of spinel lherzolite with intrusive pyroxenite, then the source of the pyroxenite contained little plume component. The one exceptional spinel lherzolite xenolith may be a residue of Koolau-like tholeiitic magma or may have been meta-somatized by Koolau volcanism in the deep lithosphere. Isotopic compositions of gabbro in Kaupulehu are similar to MORB, indicating its derivation from the oceanic crust. The Sr and Nd isotopic compositions of dunite are similar to those of Hualalai alkaline magma, consistent with the theory that the dunite is a cumulate from the Hualalai magma.

Original languageEnglish
Title of host publicationEarth Processes
Subtitle of host publicationReading the Isotopic Code, 1996
EditorsS. Hart, A. Basu
PublisherBlackwell Publishing Ltd
Number of pages13
ISBN (Electronic)9781118664230
ISBN (Print)9780875900773
Publication statusPublished - 1995
Externally publishedYes

Publication series

NameGeophysical Monograph Series
ISSN (Print)0065-8448
ISSN (Electronic)2328-8779

ASJC Scopus subject areas

  • Geophysics


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