Evidence for a late chondritic veneer in the Earth's mantle from high-pressure partitioning of palladium and platinum

Holzheid, Astrid; Sylvester, Paul J.; O’Neill, Hugh; Rubie, D. C.; Palme, H.

doi:10.1038/35019050

Cited by 140 publications

(107 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Currently, however, it is not possible to find either a set or range of pressure-temperature conditions where metal-silicate partitioning at a single f O 2 can explain concentrations of all three groups of siderophile elements (Wood et al 2006). Highly siderophile elements, for example, remain excessively depleted in a homogeneous accretion scenario and require the addition of a final late veneer of material that did not undergo core formation (Holzheid et al 2000). Although it has been proposed that at high temperatures and pressures slightly siderophile (e.g.…”

Section: The Evolution Of Mantle F Omentioning

confidence: 99%

The redox state of the mantle during and just after core formation

Frost

Mann

Asahara

et al. 2008

Phil. Trans. R. Soc. A.

View full text Add to dashboard Cite

Siderophile elements are depleted in the Earth's mantle, relative to chondritic meteorites, as a result of equilibration with core-forming Fe-rich metal. Measurements of metal-silicate partition coefficients show that mantle depletions of slightly siderophile elements (e.g. Cr, V ) must have occurred at more reducing conditions than those inferred from the current mantle FeO content. This implies that the oxidation state (i.e. FeO content) of the mantle increased with time as accretion proceeded. The oxygen fugacity of the present-day upper mantle is several orders of magnitude higher than the level imposed by equilibrium with core-forming Fe metal. This results from an increase in the Fe 2 O 3 content of the mantle that probably occurred in the first 1 Ga of the Earth's history. Here we explore fractionation mechanisms that could have caused mantle FeO and Fe 2 O 3 contents to increase while the oxidation state of accreting material remained constant (homogeneous accretion). Using measured metal-silicate partition coefficients for O and Si, we have modelled core-mantle equilibration in a magma ocean that became progressively deeper as accretion proceeded. The model indicates that the mantle would have become gradually oxidized as a result of Si entering the core. However, the increase in mantle FeO content and oxygen fugacity is limited by the fact that O also partitions into the core at high temperatures, which lowers the FeO content of the mantle. (Mg,Fe)(Al,Si)O 3 perovskite, the dominant lower mantle mineral, has a strong affinity for Fe 2 O 3 even in the presence of metallic Fe. As the upper mantle would have been poor in Fe 2 O 3 during core formation, FeO would have disproportionated to produce Fe 2 O 3 (in perovskite) and Fe metal. Loss of some disproportionated Fe metal to the core would have enriched the remaining mantle in Fe 2 O 3 and, if the entire mantle was then homogenized, the oxygen fugacity of the upper mantle would have been raised to its present-day level.

show abstract

Section: The Evolution Of Mantle F Omentioning

confidence: 99%

The redox state of the mantle during and just after core formation

Frost

Mann

Asahara

et al. 2008

Phil. Trans. R. Soc. A.

View full text Add to dashboard Cite

show abstract

“…The composition of the lithospheric mantle in terms of PGE and other chalcophile metals has been extensively documented and studied in the context of lithospheric age, tectonic/geodynamic setting, and the presence and composition of the late veneer event (e.g., Jagoutz et al, 1979;Morgan 1986;Pattou et al, 1996;Alard et al, 2000;Holzheid et al, 2000). Studies based on bulk rock geochemistry (e.g., Maier et al, 2012) may be prone to significant nugget effects because of the heterogeneous distribution of PGE-bearing microphases (Lorand et al, 2013), and thus detailed investigations that combine base metal sulphide petrography, mineral trace element compositions and isotopic systematics (particularly for the Re-Os system) are vital to assess the true complexity of the upper mantle sulphur and chalcophile element reservoir (e.g., Alard et al, 2000Alard et al, , 2005Aulbach et al, 2009;Griffin et al, 2002Griffin et al, , 2004Harvey et al, 2010;Lorand et al, 1990Lorand et al, , 2008Lorand et al, , 2010Luguet et al, 2003Luguet et al, , 2004Marchesi et al, 2013;Szabo et al, 1995;Wainwright et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Paradoxical co-existing base metal sulphides in the mantle: The multi-event record preserved in Loch Roag peridotite xenoliths, North Atlantic Craton

Hughes

McDonald

Loocke

et al. 2017

Lithos

View full text Add to dashboard Cite

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT AbstractThe role of the subcontinental lithospheric mantle as a source of precious metals for mafic magmas is contentious and, given the chalcophile (and siderophile) character of metals such as the platinumgroup elements (PGE), Se, Te, Re, Cu and Au, the mobility of these metals is intimately linked with that of sulphur. Hence the nature of the host phase(s), and their age and stability in the subcontinental lithospheric mantle may be of critical importance. We investigate the sulphide mineralogy and sulphide in situ trace element compositions in base metal sulphides (BMS) in a suite of spinel lherzolite mantle xenoliths from northwest Scotland (Loch Roag, Isle of Lewis). This area is situated on the margin of the North Atlantic Craton which has been overprinted by a Palaeoproterozoic orogenic belt, and occurs in a region which has undergone magmatic events from the Palaeoproterozoic to the Eocene.We identify two populations of co-existing BMS within a single spinel lherzolite xenolith (LR80) and which can also be recognised in the peridotite xenolith suite as a whole. Both populations consist of a mixture of Fe-Ni-Cu sulphide minerals, and we distinguished between these according to BMS texture, petrographic setting (i.e., location within the xenolith in terms of 'interstitial' or within feldspar-spinel symplectites, as demonstrated by X-ray Computed Microtomography) and in situ trace element composition. Group A BMS are coarse, metasomatic, have low concentrations of total PGE (< 40 ppm) and high (Re/Os) N (ranging 1 to 400). Group B BMS strictly occur within symplectites of spinel and feldspar, are finer-grained rounded droplets, with micron-scale PtS (cooperite), high overall total PGE concentrations (15-800 ppm) and low (Re/Os) N ranging 0.04 to 2. Group B BMS sometimes coexist with apatite, and both the Group B BMS and apatite can preserve rounded micron-scale Ca-carbonate inclusions indicative of sulphide-carbonate-phosphate immiscibility. This carbonate-phosphate metasomatic association appears to be important in forming PGE-rich sulphide liquids, although the precise mechanism for this remains obscure. As a consequence of their position within the symplectites, Group B BMS are particularly vulnerable to being incorporated in ascending A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPTmantle-derived magmas (either by melting or physical entrainment). Based on the cross-cutting relationships of the symplectites, it is possible to in...

show abstract

“…Recent experimental studies do not favor such high values for D Re (Ertel et al, 2001) and D Pt (Holzheid et al, 2000) compared with D Os (Borisov and Walker, 2000) but further experimental work is needed before a definitive answer can be given to this long-standing problem. Indeed, it was recently suggested that the abundance of moderately siderophile elements in Earth's mantle was set by equilibrium partitioning at model pressures (40 to 60 Gpa) and temperatures (2000 to 4000 K) much higher (Gessmann and Rubie, 2000;Li and Agee, 2001b) than those investigated by partitioning experiments of highly siderophile elements (Borisov and Walker, 2000;Holzheid et al, 2000;Ertel et al, 2001). One might also question whether metal segregated from silicate at uniform pressure and temperature.…”

Section: Discussionmentioning

confidence: 99%

An alternative explanation for the distribution of highly siderophile elements in the Earth.

Dauphas¹,

Reisberg²,

Marty³

2002

Geochem. J.

View full text Add to dashboard Cite

The presence of highly siderophile elements (Ru, Rh, Pd, Re, Os, Ir, Pt, and Au) in the mantle has been a long standing enigma in the Earth sciences. Highly siderophile elements exhibit extremely low silicate/ metal partition coefficients and so should have partitioned into the core, leaving the mantle depleted and fractionated compared with precursor material. Late accretion of undifferentiated material after completion of core formation may have overprinted the residue inherited from metal-silicate equilibrium partitioning. Here, we present a model based on the osmium isotopic composition of the mantle that sheds new light on the distribution of highly siderophile elements in Earth. As the Earth grew from the accretion of chondritic material of unspecified nature, gravitational and radioactive heating permitted early segregation of metal from silicate. This resulted in fractionation of highly siderophile element abundances in the residual mantle relative to chondritic abundances. After completion of core formation, the model supposes that a late carbonaceous veneer delivered biogenic and highly siderophile elements to the Earth. This late veneer was mixed inhomogeneously with the fractionated residue left over after core formation. Part of the deep mantle was isolated early from shallow convection and thus preserved primordial noble gas and highly siderophile element signatures. Allègre and Luck, 1980). This contradiction disappears (Morgan, 1986) if highly siderophile elements were delivered to the mantle by a late accreting veneer after completion of core formation (Morgan, 1986;Chyba, 1990;Dauphas et al., 2000). Nevertheless, recent theoretical (Murthy, 1991) and experimental (Li and Agee, 1996;Righter and Drake, 1997;Cottrell and Walker, 2002) studies on the high pressure/high temperature partition coefficients of moderately and highly siderophile elements have revived discussion of the idea that the distribution of highly siderophile INTRODUCTIONMetal/silicate differentiation was one of the most important events in early Earth history. However, we have a very poor understanding of the underlying mechanisms that governed this segregation (Stevenson, 1990). Low pressure experiments indicate that highly siderophile elements in the residual mantle left over after core formation should have been much more depleted and fractionated (Jones and Drake, 1986) than is observed (Kimura et al., 1974;Jagoutz et al., 1979; Os ratio among the various meteorite classes. This implies that it may be possible to deduce the ultimate source of mantle osmium from its isotopic composition (Morgan, 1985;Meisel et al., 1996;Walker et al., 2001). Analysis of fertile lherzolites suggests that the 187 Os/ 188 Os ratio of the primitive upper mantle that has not experienced melt extraction is 0.1296 ± 0.0008 ). This value, first proposed by Meisel et al. (1996), has been confirmed by numerous recent studies of lithospheric peridotite suites (McBride et al., 1996;Handler et al., 1997;Peslier et al., 2000;Reisberg et al., 2000;Snow ...

show abstract

Evidence for a late chondritic veneer in the Earth's mantle from high-pressure partitioning of palladium and platinum

Cited by 140 publications

References 23 publications

The redox state of the mantle during and just after core formation

The redox state of the mantle during and just after core formation

Paradoxical co-existing base metal sulphides in the mantle: The multi-event record preserved in Loch Roag peridotite xenoliths, North Atlantic Craton

An alternative explanation for the distribution of highly siderophile elements in the Earth.

Contact Info

Product

Resources

About