[SGC53-P05] Highly siderophile elements in Hawaiian xenoliths: Implications for the origin of low 187Os/188Os signatures in oceanic mantle
Keywords:Highly siderophile elements, Os isotopes, mantle xenoliths, peridotite, Hawaii
In this study, we investigated whole-rock abundances of highly siderophile elements (HSE: Os, Ir, Ru, Pt, Pd and Re) together with other major-trace lithophile elements in peridotites from Salt Lake Crater in Oahu Island (Hawaii) with the aim of examining whether peridotite xenoliths having low 187Os/188Os compositions (187Os/188Os < 0.120) represent (1) ancient depleted mantle domain produced by shallow melting, subsequently recycled back into deep mantle by subduction processes, or (2) lowermost mantle domain associated with ancient Re-depletion, possibly due to chemical interaction with metallic outer core and/or segregation of metallic materials. Our results demonstrate that refertilisation and melt-rock interaction are predominant mechanisms creating the observed major-trace element variations in Salt Lake Crater peridotites. By contrast, their HSE patterns are characterised by strong depletions in the Re, Pd and Pt relative to Ir-group platinum group elements (IPGE: Os, Ir, Ru), suggesting that refertilisation processes involving silicate melts can have little overall effect on the HSE compositions. This support the idea that their Os isotope records are strongly influenced by past melt depletion processes, and such ancient depleted materials are commonly embedded in deeply-derived mantle plumes.