New constraints on the genesis and long-term stability of Os-rich alloys in the Earth’s mantle

Fonseca, Raúl O. C.; Laurenz, Vera; Mallmann, Guilherme; Luguet, Ambre; Hoehne, Nadine; Jochum, Klaus Peter

doi:10.1016/j.gca.2012.04.002

Cited by 99 publications

(63 citation statements)

References 89 publications

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“…Further support for a non-residual origin for Group B comes from the presence of Pt-sulphide (cooperite) in Group B BMS, which implies a high sulphur fugacity (ƒS 2 ) -but not so high ƒS 2 as to lead Fonseca et al, 2012). The partition coefficient of Pt (D Pt ) decreases with decreasing ƒS 2 from S-oversaturated (pyrrhotite-rich) to S-undersaturated (Fe metal-rich) conditions (Mungall et al, 2005) and thus leads to PGE alloy nucleation.…”

Section: Accepted M Manuscriptmentioning

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

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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...

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Section: Accepted M Manuscriptmentioning

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

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“…Ballhaus et al, 2006). During partial melting of fertile mantle rocks, base metal sulfides melt to form a Cu-rich-sulfide melt and a more refractory sulfide solid-solution residue which concentrates the compatible PGE, namely Os, Ir, and Ru (Bockrath et al, 2004;Ballhaus et al, 2006;Luguet et al, 2007;Fonseca et al, 2012). Experimental work has shown that during high-degree mantle melting, at levels of complete or nearly complete sulfur removal from the rock, the residual sulfides can become saturated in the Os, Ir and Ru and exsolve these elements as alloys or as PGE-sulfides (Brenan & Andrews, 2001;Brenker et al, 2003;Ballhaus et al, 2006;Fonseca et al, 2012).…”

Section: The Formation Of Os-rich Alloysmentioning

confidence: 99%

“…During partial melting of fertile mantle rocks, base metal sulfides melt to form a Cu-rich-sulfide melt and a more refractory sulfide solid-solution residue which concentrates the compatible PGE, namely Os, Ir, and Ru (Bockrath et al, 2004;Ballhaus et al, 2006;Luguet et al, 2007;Fonseca et al, 2012). Experimental work has shown that during high-degree mantle melting, at levels of complete or nearly complete sulfur removal from the rock, the residual sulfides can become saturated in the Os, Ir and Ru and exsolve these elements as alloys or as PGE-sulfides (Brenan & Andrews, 2001;Brenker et al, 2003;Ballhaus et al, 2006;Fonseca et al, 2012). The degree of melting at which sulfides are removed from a peridotite residue depends on the sulfur concentration of the fertile starting material, but is typically 15%-25%; such high degrees of mantle melting are uncommon (Luguet et al, 2007;Fonseca et al, 2012) and should only occur under unusual circumstances such as hydrous re-melting of fore-arc mantle, or high-degree mantle melting in plume heads.…”

Section: The Formation Of Os-rich Alloysmentioning

confidence: 99%

“…Experimental work has shown that during high-degree mantle melting, at levels of complete or nearly complete sulfur removal from the rock, the residual sulfides can become saturated in the Os, Ir and Ru and exsolve these elements as alloys or as PGE-sulfides (Brenan & Andrews, 2001;Brenker et al, 2003;Ballhaus et al, 2006;Fonseca et al, 2012). The degree of melting at which sulfides are removed from a peridotite residue depends on the sulfur concentration of the fertile starting material, but is typically 15%-25%; such high degrees of mantle melting are uncommon (Luguet et al, 2007;Fonseca et al, 2012) and should only occur under unusual circumstances such as hydrous re-melting of fore-arc mantle, or high-degree mantle melting in plume heads. Therefore, such high-degree melting events should be associated with the production of discrete Os-rich Platinum-Group Minerals (PGM).…”

Section: The Formation Of Os-rich Alloysmentioning

confidence: 99%

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Osmium isotope compositions of detrital Os-rich alloys from the Rhine River provide evidence for a global late Mesoproterozoic mantle depletion event

Dijkstra

Dale

Oberthür

et al. 2016

Earth and Planetary Science Letters

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Citation for published item:hijkstrD eFrF nd hleD gFF nd yerth¤ urD F nd xowellD qFwF nd ersonD hFqF @PHITA 9ysmium isotope ompositions of detritl ysErih lloys from the hine iver provide evidene for glol lte wesoproterozoi mntle depletion eventF9D irth nd plnetry siene lettersFD RSP F ppF IISEIPPF Further information on publisher's website: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. AbstractWe report osmium isotopic compositions for 297 mantle-derived detrital Ru-Os-Ir alloy grains found in gold and platinumgroup mineral bearing placers of the Rhine River. These alloys were likely formed as a result of high degree melting in the convective mantle and derived from residual Paleozoic mantle peridotites in the Alps of Central Europe that were accreted as part of a collage of Gondwana-derived 'Armorican' terranes before the Variscan Orogeny. The 187 Os/ 188 Os isotope ratios of the Os-rich alloys show a wide distribution, with two modes at 0.1244 and 0.1205. These two modes correspond to rhenium depletion ages, interpreted to correspond with episodes of high-degree mantle melting, at ~0.5 and ~1.1 Ga. The data confirm the ability of the oceanic mantle to preserve evidence of ancient melting events. Our new data, in combination with published data on Os-rich alloys from the Urals and Tasmania and with data for abyssal peridotites, indicate a geographically widespread record of a major global Late Mesoproterozoic (1.0-1.2 Ga) high-degree melting event in Paleozoic oceanic mantle rocks. This model age peak is essentially absent from the crustal record of Central-Western Europe, but does coincide with the apparent peak in global continental crust zircon ages at this time. Thus, high-degree mantle melting peaking in the 1.0-1.2 Ga interval may have affected a large part of Earth's mantle. This interval occurred during a period of relative super-continental stability, which may have been accompanied in the oceanic realm by rapid seafloor spreading and extensive subduction, and by unusually high activity of mantle plumes forming two active mantle superswells.

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“…Fonseca et al, 2012), where the removal of sulfur in silicate melts 274 leads to a decrease in the proportion of sulfide in the source. All the while that sulfide remains 275 present the HSE are quantitatively retained, and can reach wt.…”

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confidence: 99%

Highly Siderophile Element and Os Isotope Systematics of Volcanic Rocks at Divergent and Convergent Plate Boundaries and in Intraplate Settings

Gannoun¹,

Burton²,

Day³

et al. 2016

Highly Siderophile and Strongly Chalcophile Elements in High-Temperature Geochemistry and Cosmochemistry

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mid-ocean ridge basalts (MORB), which account for more than eighty percent of Earth's volcanic 44 products and which are formed at divergent oceanic plate margins; intraplate volcanic rocks such as 45 ocean island basalts (OIB), continental flood basalts (CFB) and continental rift-related basalts, and 46 highly magnesian ultramafic volcanic rocks that dominantly occur in Archean terranes, termed 47 komatiites. All of these broadly basaltic rocks are considered to form by partial melting of the upper 48 mantle, followed by extraction from their source regions and emplacement at the Earth's surface. For 49 these reasons, basalts can be used to examine the nature and extent of partial melting in the mantle, 50 the compositions of mantle sources, and the interactions between Earth's crust and mantle. Because 51 much of Earth's mantle is inaccessible, basalts offer some of the best 'proxies' for examining mantle 52 composition, mantle convection and crust-mantle interactions. By contrast, at arcs, volcanism is 53 dominated by andesitic rock compositions. While some arcs do have basaltic and picritic magmatism, 54 these magma types are rare in convergent plate margin settings and reflect the complex fractional 55 crystallization and often associated concomitant assimilation processes occurring in arc settings. 56Despite the limited occurrence of high MgO magmas in arc volcanics, magmas from this tectonic 57 setting are also important for elucidating the behavior of the HSE from creation of basaltic 58 compositions at mid-ocean ridges to the subduction of this crust beneath arcs at convergent plate 59 margins. 60The highly siderophile elements (HSE; comprising Re and Au, along with the six platinum-61 group elements [PGE] Os, Ir, Ru, Rh, Pt and Pd) combined with the 187 Os and 190 Os 62 systems that are embedded within these elements, have found significant utility in the study of 63 basaltic rocks (e.g., Shirey & Walker, 1998;Carlson, 2005;Day, 2013). The greatest strengths of the 64 HSE lie in the fact that they strongly partition into metal or sulfide phases, and so record evidence for 65 processes that are not revealed from other isotope systems commonly used in high-temperature 66 geochemical studies (e.g., He-O-Sr-Nd-Hf-Pb). Partial melting over much of Earth's geological 67 history has resulted in significant fractionation of the HSE between the mantle and the crust (oceanic 68 and continental). The HSE show contrasting behavior during melting, with the platinum-PGE (PPGE; 69 Pt, Pd), Re and Au usually behaving as moderately compatible to moderately incompatible elements 70 during melting and crystallisation, and the iridium-PGE (IPGE; Os, Ir and Ru) acting as highly 71 compatible elements (Barnes et al., 1985). The differential response of the HSE to partial melting is 72 demonstrated by differences in both the absolute and relative abundances of the HSE in mantle-73 3 derived melts and in residual mantle rocks themselves. High degree melts, such as komatiites (e.g. 74Puchtel et al., 2009) show a smaller enr...

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New constraints on the genesis and long-term stability of Os-rich alloys in the Earth’s mantle

Cited by 99 publications

References 89 publications

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

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

Osmium isotope compositions of detrital Os-rich alloys from the Rhine River provide evidence for a global late Mesoproterozoic mantle depletion event

Highly Siderophile Element and Os Isotope Systematics of Volcanic Rocks at Divergent and Convergent Plate Boundaries and in Intraplate Settings

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