Constraints on Earth accretion deduced from noble metals in the oceanic mantle

Snow, J. E.; Schmidt, Gerhard

doi:10.1038/34396

Cited by 126 publications

(94 citation statements)

References 23 publications

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“…Xenoliths with atmarenth chondritic PdPGE ratios have been analyzed from the Cameroon line, Africa (Rehkamper et af., 1997) and eastern Australia (Morgan et al, 198 1 ;Handler et af., 1997;. HSE data for abyssal peridotites from several localities have also been reported (Snow and Reisberg, 1995;Snow and Schmidt, 1998;Rehkamper et al, 1999;Brandon el af., 2000).…”

Section: Terrestrial Upper Mantlementioning

confidence: 85%

“…These studies raise two important questions. First, in some sample suites, deviations in PGE from CI ratios are noted, in particular a "non-chondritic" PdAr ratio (Morgan et al, 198 1;Morgan, 1986;Pattou, et al, 1996;Snow and Schmidt, 1998). Some deviations may be due to analytical bias and an over-literal interpretation of "chondritic" as meaning identical to CI chondrites.…”

Section: Introductionmentioning

confidence: 99%

“…From this and more recent work we have selected for closer review and synthesis several data sets for orogenic and xenolithic spinel lherzolites (Morgan, 1986;Pattou et al, 1996;Rehkamper ef al., 1997;Handler et al, 1997; and for abyssal peridotites (Snow and Reisberg, 1995;Snow and Schmidt, 1998;Rehkamper et al, 1999;Brandon et al, 2000). These studies raise two important questions.…”

Section: Introductionmentioning

confidence: 99%

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Siderophile elements in Earth's upper mantle and lunar breccias: Data synthesis suggests manifestations of the same late influx

Morgan

Walker

Brandon

et al. 2001

Meteorit & Planetary Scien

124

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Abstract-The platinum group elements (PGE; Ru, Rh, Pd, Os, Ir, Pt), Re and Au comprise the highly siderophile elements (HSE). We reexamine selected isotopic and abundance data sets for HSE in upper mantle peridotites to resolve a longstanding dichotomy. Re-0s and Pt-0s isotope systematics, and approximately chondritic proportions of PGE in these rocks, suggest the presence in undepleted mantle of a chondrite-like component, which is parsimoniously explained by late influx of large planetisimals after formation of the Earth's core and the Moon. But some suites of xenolithic and orogenic spinel lherzolites, and abyssal peridotites, have a CI-normalized PGE pattern with enhanced Pd that is sometimes termed "non-chondritic". We find that this observation is consistent with other evidence of a late influx of material more closely resembling enstatite, rather than ordinary or carbonaceous, chondrites. Regional variations in HSE patterns may be a consequence of a late influx of very large objects of variable composition.Studies of many ancient (>3.8 Ga) lunar breccias show regional variations in A d I r and suggest that "graininess" existed during the early bombardment of the Earth and Moon. Reliable Pd values are available only for Apollo 17 breccias 73215 and 73255, however. Differences in HSE patterns between the aphanitic and anorthositic lithologies in these breccias show fractionation between a refractory group (Re, 0 s and Ir) and a normal (Pd, Ni, and Au) group and may reflect the compositions of the impacting bodies. Similar fractionation is apparent between the EH and EL chondrites, whose PGE patterns resemble those of the aphanitic and anorthositic lithologies, respectively.The striking resemblance of HSE and chalcogen (S, Se) patterns in the Apollo aphanites and highPd terrestrial peridotites suggest that the "non-chondritic" abundance ratios in the latter may be reflected in the composition of planetisimals striking the Moon in the first 700 Ma of Earth-Moon history. Most notably, high Pd may be part of a general enhancement of HSE more volatile than Fe suggesting that the Au abundance in at least parts of the upper mantle may be 1.5 to 2x higher than previously estimated.The early lunar influx may be estimated from observed basin-sized craters. Comparison of relative influx to Earth and Moon suggests that the enrichment of HSE is limited to the upper mantle above 670 km. To infer enrichment of the whole mantle would require several large lunar impacts not yet identified.

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Section: Terrestrial Upper Mantlementioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Siderophile elements in Earth's upper mantle and lunar breccias: Data synthesis suggests manifestations of the same late influx

Morgan

Walker

Brandon

et al. 2001

Meteorit & Planetary Scien

124

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“…As the Emeishan picrites are relatively low-degree partial melts , the high Os concentrations in the ELIP picrites cannot be explained by the mechanism proposed by Schaefer et al (2000). An alternative interpretation invokes a small contribution in the mantle source of Os derived from the outer core (e.g., Snow and Schmidt, 1998;Snow et al, 2000), and indeed would be required if core-derived materials were detectable in the lavas through their 186 Os-187 Os characteristics (e.g., Brandon et al, 1998). In addition, high Os concentration also may result from fractional crystallization.…”

Section: Pge Characteristics As Features Of the Emeishan Mantle Sourcementioning

confidence: 90%

Platinum group elements in the Emeishan large igneous province, SW China: Implications for mantle sources

et al. 2005

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We report concentrations of platinum group elements (PGE: Os, Ir, Ru, Rh, Pt and Pd) for picrite-basalt lavas of the Emeishan large igneous province, SW China. The absolute concentrations of Os in most of the Emeishan picrites are higher than in picrites from ocean islands and other continental flood basalt provinces, and in estimated primitive mantle. A roughly positive correlation between MgO and Cr and Ni, and no overall correlation of Os or Ir with MgO, show that no Cu-Ni sulfide fractionated during differentiation but rather that olivine and chromite fractionated, implying that the initial picritic magma was sulfide-undersaturated. In addition, Os/Ir ratios are unusually high, suggesting that the picritic magmas may have been contaminated by black shales. Modeling shows that a 7% partial melt of primitive mantle containing 0.01 wt% of sulfides can account for the observed Os, Ir and Ru concentrations in the most primitive picrite if the melt is contaminated by 10 wt% of black shale en route to the surface.

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“…• C) processes, for which is commonly taken place under very reducing conditions [31,32]. Büchl et al [33] demonstrated that the PGEs are also significantly fractionated by hydrothermal fluids.…”

Section: Discussionmentioning

confidence: 99%

Different Origins of the Fractionation of Platinum-Group Elements in Raobazhai and Bixiling Mafic-Ultramafic Rocks from the Dabie Orogen, Central China

Liu

Hou

Xie

et al. 2012

Journal of Geological Research

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Concentrations of the platinum group elements (PGEs), including Ir, Ru, Rh, Pt, and Pd, have been determined for both Raobazhai and Bixiling mafic-ultramafic rocks from the Dabie Orogen by fire assay method. Geochemical compositions suggest that the Raobazhai mafic-ultramafic rocks represent mantle residues after variable degrees of partial melting. They show consistent PGE patterns, in which the IPGEs (i.e., Ir and Ru) are strongly enriched over the PPGEs (i.e., Pt and Pd). Both REE and PGE data of the Raobazhai mafic-ultramafic rocks suggest that they have interacted with slab-derived melts during subduction and/or exhumation. The Bixiling ultramafic rocks were produced through fractional crystallization and cumulation from magmas, which led to the fractionated PGE patterns. During fractional crystallization, Pd is in nonsulfide phases, whereas both Ir and Ru must be compatible in some mantle phases. We suggest that the PGE budgets of the ultramafic rocks could be fractionated by interaction with slab-derived melts and fractional crystallization processes.

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Constraints on Earth accretion deduced from noble metals in the oceanic mantle

Cited by 126 publications

References 23 publications

Siderophile elements in Earth's upper mantle and lunar breccias: Data synthesis suggests manifestations of the same late influx

Siderophile elements in Earth's upper mantle and lunar breccias: Data synthesis suggests manifestations of the same late influx

Platinum group elements in the Emeishan large igneous province, SW China: Implications for mantle sources

Different Origins of the Fractionation of Platinum-Group Elements in Raobazhai and Bixiling Mafic-Ultramafic Rocks from the Dabie Orogen, Central China

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