[SIT26-P07] Chromium isotopes of basalts from the Ontong Java Plateau and Samoan Ocean Islands: Implications for the core-mantle interaction
Keywords:Chromium isotope, core-mantle interaction, LIPs, OIBs
Results & Discussion: We prepared OJP drill core samples provided by the Ocean Drilling Program and basalt samples from the Samoan Island of Tutuila. The chemical separation and purification of Cr from the samples were made following the procedure described by . The recoveries of Cr were 90-100% for all samples. We have measured Cr stable isotope compositions of the samples processed through the separation scheme by thermal ionization mass spectrometry (TIMS). The external reproducibilities achieved here were ± 5 ppm and ± 11 ppm for 53Cr and 54Cr, which are markedly smaller than isotope variation among planetary materials (53Cr ~1ε; 54Cr ~2ε). The Cr isotope analyses so far yielded ε53Cr = 0.03 ± 0.05, ε54Cr = 0.02 ± 0.10 (2SE) for the OJP basalts, and ε53Cr = 0.03 ± 0.05, ε54Cr = –0.03 ± 0.11 ~ 0.05 ± 0.11 for the Samoan basalts. The results for both the OJP and Samoan basalts reveal that there is no resolvable 53, 54Cr excess or deficit in their source. Our results suggest that there’s no systematical contribution to Cr isotope signatures in the source of OJP and Samoan islands from the material with the anomalous Cr isotope compositions. Therefore, the chemical interaction between the core and the LIPs and OIBs sources is not detectable in terms of the Cr isotopes. This implies that, unlike W, the difference in the Cr concentrations of the core and the mantle might not be so large, or that Cr in the core does not necessarily diffuse in the mantle.
 Mundl et al. (2017) Science, 356, 66-69,  Willbold et al. (2011) Nature, 477, 195-199,  Rizo et al. (2019) GRL, 11, 6-11,  Mundl et al. (2017) Science, 356, 66-69.  Kleine et al. (2009) GCA, 73, 5150-5188,  McDonough et al. (2003) ToG2, 568, 559-575,  Chabot and Agee (2003) GCA, 67, 2077–2091,  Hibiya et al. (2019) GGR, 43, 133-145.