Geochemistry of sulfides in Hawaiian garnet pyroxenite xenoliths: Implications for highly siderophile elements in the oceanic mantle

186Os–187Os systematics of Hawaiian picrites revisited: New insights into Os isotopic variations in ocean island basalts

“…This problem is best demonstrated in Fig. 6, which shows that the average BMS compositions reported by previous studies cannot reproduce the Hawaiian data, although the most enriched BMS compositions may be capable of producing the 186 Os enrichments (Luguet et al, 2008a;Sen et al, 2010a). Mass balance constraints of peridotite, pyroxenite and associated sulfides in a mantle source region must be more thoroughly defined in order to expand from the grain to mantle source scale.…”

“…Much lower percentages of the enriched BMS (1-1.5%) are required to produce the observed enrichments in 186 Os relative to the pyroxenite examples, although for the two individual BMS samples shown here, 187 Os enrichments are produced more rapidly than 186 Os. Average BMS compositions calculated from Luguet et al (2008a) and Sen et al (2010a) are all characterized by low Pt/Re ratios and, in general, chondritic 186 Os/ 188 Os, suggesting that there may need to be an additional mechanism required to concentrate BMS phases that are highly enriched in Pt and/or 186 Os.…”

“…Mass balance constraints of peridotite, pyroxenite and associated sulfides in a mantle source region must be more thoroughly defined in order to expand from the grain to mantle source scale. Additional, comprehensive studies of the HSE abundances and Os isotopes in these materials, such as those by Luguet et al (2008a), van Acken et al (2010 and Sen et al (2010a) are necessary to address these topics and to provide a global perspective of the compositions of these materials.…”

“…5), using a chondritic initial isotopic composition at 2 Ga as defined previously, the reported Re/Os and Pt/Os ratios (Table 2) and aging the material until the presentday. The BMS end-member compositions were derived from: (1) the two most radiogenic samples (M2015-3 and M2015-9) from Luguet et al (2008a), (2) average BMS from the same study, and (3) average BMS data from Sen et al (2010a). Much lower percentages of the enriched BMS (1-1.5%) are required to produce the observed enrichments in 186 Os relative to the pyroxenite examples, although for the two individual BMS samples shown here, 187 Os enrichments are produced more rapidly than 186 Os.…”

Iron isotope tracing of mantle heterogeneity within the source regions of oceanic basalts

“…The degree of partial melting was calculated following Hellebrand et al (2001). phlogopite. Based on major and trace element modeling and their Sr, Nd, Hf, Pb, and Os isotope compositions they have been largely interpreted as high pressure (>2 GPa, >60 km) cumulates near the base of the Pacific lithosphere from melts similar to the Hawaiian alkali rejuvenated lavas (Bizimis et al, 2013Keshav et al, 2007;Sen et al, 2010). Some samples display ilmenite exsolutions within garnet (including samples NMNH-114959-20A and 77SL-582 analyzed here), majorite pseudomorphs and nanodiamonds and probably initially crystallized at >5 GPa (>150 km) (Keshav and Sen, 2001;Keshav et al, 2007), deeper than the 80-90 km seismically defined base of the lithosphere beneath Oahu (Li et al, 2004).…”