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Metal-silicate segregation is one of the most fundamental mechanisms in planetary differentiation, with primitive achondrites offering important constraints on this process. Brachinites and brachinite-like achondrites (BLA) are olivine-dominated primitive achondrites that experienced up to ∼20% partial melt removal under relatively oxidized (ΔIW ∼ −1) conditions within an initially chondritic parent body and represent residues after inefficient metal-loss. We present bulk rock and in situ lithophile and highly siderophile element (HSE) abundance systematics as well as 187Re-187Os data for five olivine-rich primitive achondrites. These new data confirm classification of Reid 013 as a brachinite, three of the samples as BLA (Northwest Africa [NWA] 6874, NWA 7499, and Miller Range 090805), and the final sample as an ungrouped primitive olivine-rich achondrite (NWA 7680). An aliquot of MIL 090805 shows amongst the highest total HSE contents (>35 ppm) and the highest Pt content (∼23 ppm) of any primitive achondrite. Compiled HSE data for brachinites and BLA show correlations between total HSE abundance, Pt enrichment, and average olivine Fo. This correlation can be explained by variable melting (∼10–20%) of an H ordinary chondrite-like protolith, with retention of both Fe-metal and a Pt-rich alloy phase distinct from the observed Fe-metal phases in more depleted residues. Such a Pt-alloy phase is likely stabilized by elevated abundances of the HSE during chondrite melting and the low solubility of HSE in melts. Rhenium-Os isotope data in the studied samples has been modified by recent mobilization of Re during terrestrial weathering, with the limited range of measured 187Os/188Os in brachinites and BLA supporting minor fractionation of Re/Os during melting and an ancient (∼4.5 Ga) partial melting event to explain their compositions. These results indicate that models of planetary differentiation should consider the low solubility of Pt in chondrite melts and the potential for alloy formation to modify HSE abundances of silicate mantles. [ABSTRACT FROM AUTHOR]

• HSE data for high-3He/4He picrites formed during opening of north and south Atlantic. • Large degree partial melts from peridotite mantle with chondritic Os isotope character. • Atlantic LIP show evidence for deep mantle contributions during ocean basin formation. • Recycled components in high-3He/4He OIB consistent with lower degrees of partial melting. Osmium isotope and highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re) abundance data are reported for picrites and basalts from the ∼132 Ma Etendeka large igneous province (LIP) and the ∼60 Ma North Atlantic Igneous Province (NAIP). Picrite dykes of the Etendeka LIP have HSE abundances and 187Os/188Os (0.1276 to 0.1323; γOs i = -0.5 to +3.1) consistent with derivation from high-degree partial melting (>20 %) of a peridotite source with chondritic to modestly supra-chondritic long-term Re/Os. High-3He/4He NAIP picrites from West Greenland represent large-degree partial melts with similarly elevated HSE abundances and 187Os/188Os (0.1273 to 0.1332; γOs i = -0.2 to +3.9). Broadly chondritic Os isotope ratios have also been reported for the ∼132 Ma Paraná LIP and the ∼201 Ma Central Atlantic Magmatic Province (CAMP). Consequently, LIP associated with Atlantic Ocean opening derive, at least in part, from partial melting of peridotite mantle distinct from the depleted mantle associated with mid-ocean ridge basalt volcanism. Modern locations with high-3He/4He (>25R A) include ocean island basalts (OIB) from Ofu (Samoa), Loihi (Hawaii) and Fernandina (Galapagos) in the Pacific Ocean, and from Iceland, which is considered the modern manifestation of NAIP magmatism. Unlike Etendeka and NAIP picrites, these modern OIB have Sr-Nd-Pb-Os isotopes consistent with contributions of recycled oceanic or continental crust. The lower degree of partial melting responsible for modern high-3He/4He OIB gives higher proportions of fusible recycled crustal components to the magmas, with radiogenic 187Os/188Os and low-3He/4He. The high-3He/4He, incompatible trace element-depleted mantle component in both LIP and OIB therefore also has long-term chondritic Re/Os, which is consistent with an early-formed reservoir that experienced late accretion. Atlantic LIP (CAMP; Paraná-Etendeka; NAIP) provide geochemical evidence for a prominent role for mantle plume contributions during continental break-up and formation of the Atlantic Ocean, a feature hitherto unrecognized in other ocean basin-forming events. [ABSTRACT FROM AUTHOR]

The Marquesas islands are an age-progressive volcanic chain in French Polynesia formed by partial melting above a mantle plume. Previous studies have demonstrated the presence of an enriched mantle (EM2) endmember mixed with a high-3He/4He (up to 14.4 R A) component in Marquesas post-shield lavas. In contrast, Marquesas shield lavas sample a dilute high-μ (HIMU) type component with lower 3He/4He (∼8 R A). We report new incompatible trace element and highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re) abundances and osmium isotope data for bulk rocks from the islands of Fatu Hiva, Hiva Oa and Nuku Hiva, for which He, Sr, Nd and Pb isotope compositions have been reported previously (Castillo et al., 2007). As the HSE are chiefly hosted in sulfide phases in the mantle and all but Re are compatible during partial melting, they offer information on both sulfide-rich and melt-depleted mantle lithologies within the Marquesas plume. Primitive mantle-normalized HSE abundances show depletions in Ru and Pd, and fractionated (Ir/Os) N in fourteen of the seventeen analyzed samples. Ruthenium depletions and Ir-Os fractionations are likely caused by parental magma fractional crystallization. Palladium depletions are not easily explained by magmatic or secondary alteration processes and are instead likely to be a feature of the source mantle which was partially depleted in the more incompatible HSE by previous melting events within the Marquesas plume. Osmium isotopic systematics are mildly radiogenic relative to chondrites and are identical within uncertainties for shield-building Fatu Hiva (γOs = +2.9 ± 1.6; 2 SD; n = 7) and post-shield Hiva Oa (+2.7 ± 2.2; n = 9), showing no evidence for significant assimilation of radiogenic oceanic crust. The osmium budget of Marquesas lavas is controlled by a volumetrically dominant peridotite endmember that is incompatible element depleted while the Sr, Nd, and Pb budgets are strongly influenced by a volumetrically minor, incompatible element enriched EM2 component. The Nd-Sr-Os isotope systematics of the lavas can be explained by mixing of 0.3–0.7% of an EM2 type melt into the Marquesas source. Marquesas lavas offer further support that the high-3He/4He "focus zone" (FOZO) mantle has 187Os/188Os mildly more radiogenic than the depleted upper mantle, similar to estimates of the primitive mantle. Osmium isotope systematics offer a useful tool with which to characterize more depleted components within the ocean island basalt-source mantle that may be difficult to detect using lithophile isotope signatures. [ABSTRACT FROM AUTHOR]

New 187Re-187Os, 87Rb-87Sr, triple O-isotope isotope, bulk rock highly siderophile- (HSE: Os, Ir, Ru, Pt, Pd, Re), major- and trace-element abundance data are reported for a variety of carbonaceous, ordinary and enstatite chondrite meteorites. In addition, new mineral chemical data are reported for the Chelyabinsk LL5 ordinary chondrite fall for comparison with existing chondrite data and to investigate element sequestration into metal and mineral phases within some chondrites. The focus of the study is to link the variations observed in the HSE abundances and Re-Os isotopes with other isotopic and elemental data to explore the relative roles of sample sizes, terrestrial alteration and parent body processes more fully on chondrite meteorite compositions. Trace element variations in Chelyabinsk silicate, oxide and metal grains highlight the importance of geochemical heterogeneity imparted by mineralogical variations and mode effects, as well as sample size. Using a range of sample powder aliquot sizes, it is possible to show that this becomes significant for the HSE at <0.1 g. Variations in high field strength elements relative abundances (HFSE: Ti, Zr, Nb, Ta, Hf) are also identified within individual aliquots of carbonaceous chondrite Ivuna, emphasizing the importance of complete dissolution of refractory phases. The range of fall and find meteorites examined here demonstrates that terrestrial alteration effects revealed for trace elements (e.g., Ba, U, Sr) do not correlate particularly well with Re/Os variations. Instead, the Re/Os ratios of carbonaceous chondrites are susceptible to disturbance, more so than indicated by incompatible trace element systematics, with the Murchison CM2 carbonaceous chondrite showing significant Re/Os fractionation between sample aliquots. For sample aliquots measured that do not show significant mode or terrestrial alteration effects, parent body processes appear to be largely restricted to thermal metamorphism and dehydration. Including data for this study, the combined published dataset for Re-Os isotope and HSE abundances now extends to 33 ordinary, 39 carbonaceous, 27 enstatite and 6 Rumuruti chondrites. The range in absolute HSE abundances among these meteorite groups is ∼30%, with all chondrites having, within uncertainties, the same average Os, Ir, Ru, Pt and Pd abundances. Notably, carbonaceous chondrites have long-term Re/Os ∼ 8% lower than for the other chondrite groups. If chondrite groups are representative of early planetary feedstocks, then the measured 187Os/188Os of ordinary chondrites make them a close match to the composition of the bulk silicate Earth. Assuming ∼0.5% late accretion of ordinary chondrites to Earth, this would result in a long-term Rb/Sr ratio ∼0.6% higher than from late accretion of carbonaceous chondrites, indicating that ordinary chondrites are a potentially attractive source for moderately volatile enrichment. [ABSTRACT FROM AUTHOR]

Impactors striking the Moon since the formation of its crust have left an indelible imprint on the lunar surface, in the guise of craters and associated impact rocks. The lunar crust has low intrinsic abundances of the highly siderophile elements (HSE: Re, Os, Ir, Ru, Pt, Rh, Pd, Au), at greater than 3000 times lower than in chondrite meteorites. Consequently, during impact, bolides with chondritic or differentiated iron-rich compositions should impart elevated HSE signatures to the lunar crust. Here we examine glassy lunar impact melt coats (IMC) from the outside rims of Apollo 16 cataclastic anorthosites (60015, 65325) and breccias (65035), as well as both fragments and powders of Antarctic anorthositic regolith breccia (ARB) meteorites (Miller Range 090034/36/70/75 and MacAlpine Hills 88105) for their petrography, mineral chemistry and bulk-rock compositions. The HSE concentrations for IMC range from ∼0.001 to 0.1 × CI chondrite, with measured 187Os/188Os between 0.1189 and 0.1366. Anorthositic regolith breccia meteorites, which have components with 2.6–4.1 Ga ages, have similar HSE concentrations to IMC, but typically have lower 187Os/188Os (0.1164–0.1284). These latter Os ratios are generally less radiogenic than those measured in ∼3.8–3.9 Ga Apollo impact melt breccias. The Apollo 16 IMC are not well-dated, but their KREEPy trace-element signatures and associated ages of 3.7 to 3.8 Ga for Apollo 16 glasses might imply, at least in part, an origin from the Imbrium or Serenitatis basin-forming impacts. Within the IMC, metal-schreibersite-troilite assemblages record significant inter-element HSE fractionation which is also reflected in bulk HSE patterns for both IMC and ARB meteorites. Variations in relative and absolute HSE compositions directly reflect the control of metal and sulfide segregation within and between impact melt and breccia lithologies. Collectively, IMC and ARB meteorites exhibit approximately 50% of the variation in Ru/Ir and 187Os/188Os observed in lunar impact melt breccias. These results imply that significant variations in inter-element compositions can occur during impact brecciation and melting and so some impact melt rock HSE compositions may not record the compositions of impactors that struck the Moon with fidelity. Nonetheless, the generally low 187Re/188Os of lunar impact melt rocks means that osmium isotope ratios provide evidence for impact composition, and a change from ordinary to carbonaceous-like impactors either with time – or location – striking the Moon. [ABSTRACT FROM AUTHOR]

New highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re) abundance and Os isotopic compositions, along with major- and trace-element abundance and Sr-Nd-Hf-Pb isotope data are reported for high-MgO (>8–17 wt.%) lavas from the islands of São Miguel, Terceira, Pico and Faial in the Azores archipelago. The lavas span the range of Sr-Nd-Hf-Pb isotope and trace-element abundance variability reported previously for the islands. Pico and Faial lavas preserve distinct absolute and relative HSE abundances and 187Os/188Os (Ʃ HSE = 2 ± 2 ng g−1; 2SD; 187Os/188Os in lavas with > 50 pg g−1 Os = 0.1255 ± 31; 2SD) compared with São Miguel and Terceira lavas (Ʃ HSE = 5 ± 3 ng g−1; 187Os/188Os 50pg = 0.1284 ± 48). Although HSE abundance variations in volcanic rocks from individual Azorean islands can be explained by sulfide crystallization, those between Pico and Faial and São Miguel and Terceira can only reasonably be attributed to partial melting of distinct mantle sources. Pico and Faial lava compositions are consistent with high degrees of sulfide melting (90–100%) from a sulfide-depleted mantle source (<100 ppm) with relatively unradiogenic 187Os/188Os (<0.126). São Miguel and Terceira lavas likely derive from a sulfide-enriched (300–600 ppm) mantle source that underwent lesser degrees of sulfide melting (1–15%), with more radiogenic 187Os/188Os (>0.128). Radiogenic sulfides are not solely linked to the enriched lithophile isotope signature found in eastern São Miguel. Instead, São Miguel and Terceira magmatism may collectively result from metasomatism associated with the recycling of old subducted oceanic lithosphere. Abundances of sulfide-hosted HSE, and 187Os/188Os, are decoupled from silicate-hosted Sr-Nd-Hf-Pb isotope compositions, in the mantle. Compositional variations of the HSE among global OIB suggest that, while distinct mantle domains are represented by heterogeneous sulfide mineralogy, comprising common metasomatic (enriched) and magmatic (depleted) compositions, these sulfide populations are distinct beneath different OIB due to their origin in different lithospheric materials (e.g., oceanic crust versus pelagic sediment), and to the degree of partial melting caused by variable mantle potential temperature or lithospheric thickness. [ABSTRACT FROM AUTHOR]

• Melting and crystallization control trace element contents in Juan Fernandez lavas. • Osmium isotopic compositions are unaffected by shallow petrogenetic processes. • Distinct isotope ratios in two islands main shield lavas imply heterogeneous plume. • A noble gas-impregnated lithospheric mantle contaminated the rejuvenated lavas. Mantle plume models have been widely applied to explain the formation of ocean island basalts (OIB), with high-3He/4He in their lavas being explained by sampling of a primitive deep mantle source. The Juan Fernandez Islands have 3He/4He (7.8–18 R A) similar to or higher than in mid-ocean ridge basalts (MORB; 8 ± 1 R A) and have been used to both support and refute the mantle plume hypothesis. Ambiguity regarding the origin of the Juan Fernandez Islands primarily originates from interpretation of mantle source signatures between the lava series from the two main islands, Robinson Crusoe and Alexander Selkirk. To examine this issue, we report new whole-rock and olivine separate 187Os/188Os ratios and major-, trace-, and highly siderophile-element (HSE: Re, Pd, Pt, Ru, Ir, Os) abundances. The HSE and trace element abundances in Juan Fernandez main shield lavas can be explained by up to 30% olivine removal, together with spinel crystallization at 1–5 kbar, whereas Robinson Crusoe rejuvenated lavas can be reproduced by higher-pressure fractional crystallization (up to 10 kbar). An assemblage of 30 modal % olivine and 1–5 modal % spinel, combined with the additional contribution of primary melt trapped in olivine inclusions reproduces the range of HSE compositions observed in Juan Fernandez Archipelago olivine grains. Ratios of 187Os/188Os for Juan Fernandez lavas are generally less radiogenic than global OIB and show no correlation with indices of fractionation, indicating that they reflect mantle source compositions. Younger basanite lavas from Robinson Crusoe represent rejuvenated volcanism dominantly from a depleted lithospheric mantle source (187Os/188Os < 0.13) mixed with a high-3He/4He component from the main shield building stage. These lavas are similar in origin and composition to other Pacific rejuvenated lavas (e.g., Samoa, Hawaii). Robinson Crusoe main shield lavas are from a high-3He/4He (>18 R A) and enriched mantle source (187Os/188Os = 0.1312) similar to the 'C' or 'FOZO' component, whereas Alexander Selkirk lavas are consistent with a dominant contribution from a depleted, low-3He/4He (<10 R A) mantle component. The mantle sources of the shield lavas yield subtle variations in Sr-Nd-Os-Pb isotope space and have no clear variations with relative or absolute abundances of the HSE or trace elements. These results are consistent with a heterogeneous mantle plume model, with initial eruption of lavas from a primitive high-3He/4He mantle source ∼4 million years ago (Ma) to form Robinson Crusoe Island, which also led to 3He enrichment of the oceanic lithosphere, followed by eruption of Alexander Selkirk lavas from a more depleted mantle source at ∼2 Ma. Juan Fernandez lavas show that mantle heterogeneity preserved in OIB can occur over short-timescales (<2 Ma) and can impact lithospheric compositions, leading to eruption of rejuvenated lavas with unusual isotopic characteristics. [ABSTRACT FROM AUTHOR]

Mantle lithosphere influences rift system tectonic evolution, yet the age and composition of rifted lithosphere is typically difficult to constrain due to limited sampling. In the West Antarctic Rift System (WARS), Cenozoic to recent alkaline volcanic rocks yield a variety of peridotite and pyroxenite xenoliths that allow sampling of lithosphere. We report osmium and helium isotope data, elemental abundances, and petrology, for a suite of xenoliths and lavas from the Hut Point Peninsula of Ross Island. Recently (<1.3 Ma) erupted basanites yield fresh dunite and harzburgite (olivine forsterite [Fo] 90.1–88.2), lherzolite (Fo 90.6–87.4), and pyroxenite xenoliths (Fo 89.3–87.3). The basanite lavas contain abundant large olivine xenocrysts (Fo 89.7–88.0), with more ferroan matrix olivine grains (Fo 83.7–81.2) and have HIMU-like incompatible trace-element signatures. The 3He/4He ratios (6.8 ± 0.3R A ; 2SD) defined by co-existing He-rich xenoliths indicate a mantle source distinct from high-3He/4He plume mantle. Pyroxenite and lherzolite xenoliths have similar relative abundances of incompatible trace elements to host lavas, whereas dunite xenoliths have refractory compositions. Melt-rock reaction occurring in the xenoliths is demonstrated by replacement by amphibole or clinopyroxene to form pyroxenite and lherzolite lithologies, or as amphibole-impregnated dunites. The 187Re 187Os systematics of the lavas, pyroxenites and lherzolites define an apparent isochron, with an initial 187Os/188Os ratio of 0.1286 ± 0.0001. The initial 187Os/188Os ratio is within uncertainty of dunite and harzburgite xenolith Os isotope compositions (0.1279–0.1303). Pervasive evidence for melt-rock interaction indicates that the straight-line relationship in 187Re/188Os-187Os/188Os space is a mixing line between high Re/Os lavas with radiogenic 187Os/188Os, and dunite and harzburgite. Petrological and geochemical evidence indicates that dunite and harzburgite xenoliths represent young lithosphere, with rhenium depletion ages up to ~250 Ma. The timing of formation and composition of the Hut Point Peninsula xenoliths are consistent with both destruction and creation of mantle lithosphere during or after subduction along the Gondwana margin, prior to WARS formation. Modification of mantle lithosphere by subduction is also consistent with generation of HIMU-like metasomatized mantle reservoirs that fed Cenozoic to recent alkali volcanism of Mount Erebus and the WARS. The presence of young lithosphere within the WARS has collateral implications for rift dynamics and melting processes, especially beneath Mount Erebus, contrasting with older lithospheric mantle beneath the Trans-Antarctic Mountains and Marie Byrd Land. Unlabelled Image • Melt-rock reaction between lithosphere and basanite melts at Hut Point Peninsula • Straight-line relationship in 187Re/188Os-187Os/188Os space represents mixing of melts and lithosphere • Dunite and harzburgite xenoliths are lithosphere formed during or after subduction along Gondwana margin • Subduction-generated mantle likely source of HIMU signatures, influencing West Antarctic Rift System dynamics and melting processes [ABSTRACT FROM AUTHOR]

In order to establish the role and expression of silicate-metal fractionation in early planetesimal bodies, we have conducted a highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re) abundance and 187 Re- 187 Os study of acapulcoite-lodranite meteorites. These data are reported with new petrography, mineral chemistry, bulk-rock major and trace element geochemistry, and oxygen isotopes for Acapulco, Allan Hills (ALHA) 81187, Meteorite Hills (MET) 01195, Northwest Africa (NWA) 2871, NWA 4833, NWA 4875, NWA 7474 and two examples of transitional acapulcoite-lodranites, Elephant Moraine (EET) 84302 and Graves Nunataks (GRA) 95209. These data support previous studies that indicate that these meteorites are linked to the same parent body and exhibit limited degrees (<2–7%) of silicate melt removal. New HSE and osmium isotope data demonstrate broadly chondritic relative and absolute abundances of these elements in acapulcoites, lower absolute abundances in lodranites and elevated (>2 × CI chondrite) HSE abundances in transitional acapulcoite-lodranite meteorites (EET 84302, GRA 95209). All of the meteorites have chondritic Re/Os with measured 187 Os/ 188 Os ratios of 0.1271 ± 0.0040 (2 St. Dev.). These geochemical characteristics imply that the precursor material of the acapulcoites and lodranites was broadly chondritic in composition, and were then heated and subject to melting of metal and sulfide in the Fe-Ni-S system. This resulted in metallic melt removal and accumulation to form lodranites and transitional acapulcoite-lodranites. There is considerable variation in the absolute abundances of the HSE, both among samples and between aliquots of the same sample, consistent with both inhomogeneous distribution of HSE-rich metal, and of heterogeneous melting and incomplete mixing of silicate material within the acapulcoite-lodranite parent body. Oxygen isotope data for acapulcoite-lodranites are also consistent with inhomogeneous melting and mixing of accreted components from different nebular sources, and do not form a well-defined mass-dependent fractionation line. Modeling of HSE inter-element fractionation suggests a continuum of melting in the Fe-Ni-S system and partitioning between solid metal and sulfur-bearing mineral melt, where lower S contents in the melt resulted in lower Pt/Os and Pd/Os ratios, as observed in lodranites. The transitional meteorites, EET 84302 and GRA 95209, exhibit the most elevated HSE abundances and do not follow modelled Pt/Os and Pd/Os solid metal-liquid metal partitioning trends. We interpret this to reflect metal melt pooling into domains that were sampled by these meteorites, suggesting that they may originate from deeper within the acapulcoite-lodranite parent body, perhaps close to a pooled metallic ‘core’ region. Petrographic examination of transitional samples reveals the most extensive melting, pooling and networking of metal among the acapulcoite-lodranite meteorites. Overall, our results show that solid metal-liquid metal partitioning in the Fe-Ni-S system in primitive achondrites follows a predictable sequence of limited partial melting and metal melt pooling that can lead to significant HSE inter-element fractionation effects in proto-planetary materials. [ABSTRACT FROM AUTHOR]

Abyssal peridotites are oceanic mantle fragments that were recently processed through ridges and represent residues of both modern and ancient melting. To constrain the nature and timing of melt depletion processes, and the composition of the mantle, we report high-precision Os isotope data for abyssal peridotites from three ocean basins, as well as for Os-rich alloys, primarily from Mesozoic ophiolites. These data are complemented by whole-rock highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re), trace- and major-element abundances for the abyssal peridotites, which are from the Southwest Indian (SWIR), Central Indian (CIR), Mid-Atlantic (MAR) and Gakkel Ridges. The results reveal a limited role for melt refertilization or secondary alteration processes in modifying abyssal peridotite HSE compositions. The abyssal peridotites examined have experienced variable melt depletion (2% to >16%), which occurred >0.5 Ga ago for some samples. Abyssal peridotites typically exhibit low Pd/Ir and, combined with high-degrees of estimated total melt extraction, imply that they were relatively refractory residues prior to incorporation into their present ridge setting. Recent partial melting processes and mid-ocean ridge basalt (MORB) generation therefore played a limited role in the chemical evolution of their precursor mantle domains. The results confirm that many abyssal peridotites are not simple residues of recent MORB source melting, having a more complex and long-lived depletion history. Peridotites from the Gakkel Ridge, SWIR, CIR and MAR indicate that the depleted MORB mantle has 186 Os/ 188 Os of 0.1198356 ± 21 (2SD). The Phanerozoic Os-rich alloys yield an average 186 Os/ 188 Os within uncertainty of abyssal peridotites (0.1198361 ± 20). Melt depletion trends defined between Os isotopes and melt extraction indices (e.g., Al 2 O 3 ) allow an estimate of the primitive mantle (PM) composition, using only abyssal peridotites. This yields 187 Os/ 188 Os (0.1292 ± 25), and 186 Os/ 188 Os of 0.1198388 ± 29, both of which are within uncertainty of previous primitive mantle estimates. The 186 Os/ 188 Os composition of the PM is less radiogenic than for some plume-related lavas, with the latter requiring sources with high long-term time-integrated Pt/Os. Estimates of primitive mantle HSE concentrations using abyssal peridotites define chondritic Pd/Ir, which differs from previous supra-chondritic estimates for Pd/Ir based on peridotites from a range of tectonic settings. By contrast, estimates of PM yield supra-chondritic Ru/Ir. The cause of enhanced Ru in the mantle remains enigmatic, but may reflect variable partitioning behavior of Ru at high pressure and temperature. [ABSTRACT FROM AUTHOR]

Organic carbon-rich sediment assimilation by basaltic magmas leads to enhanced emission of greenhouse gases during continental flood basalt eruptions. A collateral effect of these interactions is the generation of low oxygen fugacities ( f O 2 ) (below the iron-wüstite [IW] buffer curve) during magmatic crystallization, resulting in the precipitation of native-iron. The occurrence of native-iron bearing terrestrial basaltic rocks are rare, having been identified at three locations: Siberia, West Greenland, and Central Germany. We report the first combined study of Re–Os isotopes, highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re), and trace-element abundances for these three occurrences, in addition to host sediments at West Greenland. To quantify the amount of crustal assimilation experienced by the magmas, we present combined crystallization and assimilation models, together with fractional crystallization models, to assess how relative abundances of the HSE have been modified during crystallization. The radiogenic osmium isotopic compositions ( γ Os initial +15 to +193) of mafic igneous samples are consistent with assimilation of old high Re/Os crustal contaminants with radiogenic 187 Os/ 188 Os, whereas the HSE inter-element fractionations (Pd/Os 2 to >10,000) suggest that some Siberian samples underwent an early stage of sulfide removal. Metalliferous samples from the Siberian intrusions of Khungtukun and Dzhaltul (associated with the Siberian flood basalts) yield internal 187 Re– 187 Os ages of 266 ± 83 Ma and 249 ± 50 Ma , respectively, reflecting late-Permian emplacement ages. These results imply that crustal assimilation took place prior to crystallization of native-Fe. In contrast, metalliferous samples from Disko Island and Bühl (associated with the West Greenland flood basalts, and the Central European Volcanic Province, respectively) have trends in 187 Re/ 188 Os– 187 Os/ 188 Os space corresponding to apparent ages older than their reported crystallization ages. These anomalous ages probably reflect concurrent assimilation of high Re/Os, radiogenic 187 Os crust during crystallization of native-Fe, consistent with the character of local West Greenland sediments. In all three locations, calculations of combined assimilation of crustal sediments and fractional crystallization indicate between 1–7% assimilation can account for the Os-isotope systematics. In the case of Siberian samples, incompatible trace-element abundances indicate that lower crustal assimilation may have also occurred, consistent with the suggestion that crustal assimilation took place prior to native-Fe precipitation. The extent of local crustal contamination at Siberia, West Greenland, and Bühl necessitates that significant quantities of CH 4 , CO, CO 2 , SO 2 and H 2 O were released during assimilation of carbonaceous sediments. Consequently, carbonaceous sediment–basalt melt interactions have collateral effects on total gas output from flood basalt volcanism into the atmosphere. However, the amount of carbonaceous sediment contamination experienced by melts forming the Khungtukun and Dzhaltul intrusions alone, cannot explain the major C-isotope excursions at the Permo–Triassic mass-extinction event. Instead, further unsampled intrusions that also experienced significant carbonaceous sediment–melt interactions would be required. Enhanced greenhouse gas-emission during the Permo–Triassic mass extinction may have been facilitated by a combination of mantle melting and carbonaceous sediment–melt interactions, together with other proposed mechanisms, including wildfires, or by microbial metabolic exhalation. [ABSTRACT FROM AUTHOR]

Abstract: Hotspot volcanic rocks are formed under conditions that differ from conventional plate tectonic boundary magmatic processes and are compositionally distinct from mid-oceanic ridge basalts. Hotspot volcanic rocks include – but are not limited to – ocean island basalts (OIB), continental flood basalts (CFB), komatiites, oceanic plateau and some intraplate alkaline volcanic rocks. Studies of the highly siderophile element (HSE) geochemistry of hotspot volcanic rocks have provided new perspectives into mantle convection, mantle heterogeneity, core-mantle interactions, crustal and mantle lithospheric recycling, melting processes and crust-mantle interactions. The HSE, comprising Os, Ir, Ru, Rh, Pt, Pd, Re and Au, have strong affinities for metal and sulphide relative to silicate. These elements also have variable partitioning behaviour between highly compatible Os, Ir, Ru and Rh relative to compatible Pt and Pd and to moderately incompatible Re and Au during melting and crystallisation. This exceptional geochemical behaviour, combined with the existence of the long-lived 187Re-187Os and 190Pt-186Os decay systems embedded within the HSE, make these elements powerful tracers of processes acting on magmas and their volcanic products. The HSE can be utilised to understand sub-aerial volcanic degassing and crustal assimilation processes in hotspot volcanic rocks such as CFB and OIB, as well as for quantitative assessment of fractional crystallisation. Mantle melting studies have highlighted the strong control of sulphide in the mantle prior to exhaustion of S and generation of Os±Ir±Ru metal alloys at ~>25% partial melting; a behaviour of the HSE that is fundamental to understanding terrestrial hotspot volcanism. Perhaps the most exciting utility of the HSE, however, lies in their ability to reveal both short- and long-term fractionation processes acting on hotspot volcanic sources from inter-element HSE fractionations and 187Os/188Os-186Os/188Os systematics. The growing database for HSE abundances and 187Os/188Os in hotspot volcanic rocks is consistent with their generation from a heterogeneous upper mantle generated by melt differentiation and recycling of crust and mantle lithosphere during plate subduction. 187Os/188Os variations (ratios up to 0.175) in high-Os abundance (>50ppt) HIMU (high 238U/206Pb) OIB indicate high long-term (>1 to 2Ga) Re/Os, supporting models for recycled oceanic lithosphere in the source of these volcanic rocks. In contrast, and despite elevated 87Sr/86Sr and low 143Nd/144Nd, enriched mantle (EM) OIB can have 187Os/188Os that dominantly reflect contributions from peridotite with only minor contributions from recycled sediment or continental crust and/or lithospheric mantle materials. The HSE provide geochemical evidence for how lithological and chemical heterogeneities are sampled within the mantle. Modeling of HSE abundances and Os isotopes show that large apparent recycled contributions (50% to 90%) in some OIB can be explained by the preferential melting of volumetrically minor (<10%) pyroxenite in their sources. Preferential melting of more fusible materials in the mantle also explains why low-degree partial melts, such as alkali basalts and basanites, may exhibit more extreme isotopic variations than tholeiites or komatiites, which likely contain a higher contribution from peridotite in a hybridised pyroxenite-peridotite mantle source. High-precision 186Os/188Os data for hotspot volcanism are limited, but the combined variations in long-term Re/Os and Pt/Os retained in some mantle sources may reflect either the long-term fractionation of Re and Pt from Os between the inner and outer core, or ancient sulphide segregation and lithological variations in the mantle caused by convection but unrelated to core-mantle interaction. Either mode-of-origin is important for a firmer understanding of processes occurring in Earth, and both suggest that some hotspot volcanic mantle sources have been isolated and have evolved with supra-chondritic Pt/Os over >2 to 3Ga time-scales. Study of the HSE in hotspot volcanic rocks from Solar System bodies also informs on planetary-scale processes, indicating that Earth, the Moon, Mars and fully differentiated asteroids all have HSE abundances in their mantles that are higher than expected from low-pressure metal-silicate partitioning. Furthermore, the HSE are in broadly chondritic-relative abundances for these planetary bodies, at ~0.0002 (Moon), to ~0.007 (Mars), to ~0.009 (Earth)×carbonaceous chondrite Ivuna (CI) composition. The timing of addition of the HSE to planetary bodies preserved in their magmas and volcanic products is consistent with Solar-System-wide late accretion no later than 3.8Ga for Earth, and even earlier based on evidence from the Moon (~4.4Ga), Mars (~4.5Ga) and asteroids (>4.56Ga). [Copyright &y& Elsevier]

Abstract: Coupled 187Os/188Os compositions and highly-siderophile-element (HSE: Os, Ir, Ru, Pt, Pd, and Re) abundance data are reported for eight angrite achondrite meteorites that include quenched- and slowly-cooled textural types. These data are combined with new major- and trace-element concentrations determined for bulk-rock powder fractions and constituent mineral phases, to assess angrite petrogenesis. Angrite meteorites span a wide-range of HSE abundances from <0.005ppb Os (e.g., Northwest Africa [NWA] 1296; Angra dos Reis) to >100ppb Os (NWA 4931). Chondritic to supra-chondritic 187Os/188Os (0.1201–0.2127) measured for Angra dos Reis and quenched-angrites correspond to inter- and intra-sample heterogeneities in Re/Os and HSE abundances. Quenched-angrites have chondritic-relative rare-earth-element (REE) abundances at 10–15×CI-chondrite, and their Os-isotope and HSE abundance variations represent mixtures of pristine uncontaminated crustal materials that experienced addition (<0.8%) of exogenous chondritic materials during or after crystallization. Slowly-cooled angrites (NWA 4590 and NWA 4801) have fractionated REE-patterns, chondritic to sub-chondritic 187Os/188Os (0.1056–0.1195), as well as low-Re/Os (0.03–0.13), Pd/Os (0.071–0.946), and relatively low-Pt/Os (0.792–2.640). Sub-chondritic 187Os/188Os compositions in NWA 4590 and NWA 4801 are unusual amongst planetary basalts, and their HSE and REE characteristics may be linked to melting of mantle sources that witnessed prior basaltic melt depletion. Angrite HSE-Yb systematics suggest that the HSE behaved moderately-incompatibly during angrite magma crystallization, implying the presence of metal in the crystallizing assemblage. The new HSE abundance and 187Os/188Os compositions indicate that the silicate mantle of the angrite parent body(ies) (APB) had HSE abundances in chondritic-relative proportions but at variable abundances at the time of angrite crystallization. The HSE systematics of angrites are consistent with protracted post-core formation accretion of materials with chondritic-relative abundances of HSE to the APB, and these accreted materials were rapidly, yet inefficiently, mixed into angrite magma source regions early in Solar System history. [Copyright &y& Elsevier]

Abstract: New major- and trace-element abundances, highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re) abundances, and oxygen and rhenium–osmium isotope data are reported for oligoclase-rich meteorites Graves Nunataks 06128 and 06129 (GRA 06128/9), six brachinites (Brachina; Elephant Morraine 99402/7; Northwest Africa (NWA) 1500; NWA 3151; NWA 4872; NWA 4882) and three olivine-rich achondrites, which are referred to here as brachinite-like achondrites (NWA 5400; NWA 6077; Zag (b)). GRA 06128/9 represent examples of felsic and highly-sodic melt products from an asteroid that may provide a differentiation complement to brachinites and/or brachinite-like achondrites. The new data, together with our petrological observations, are consistent with derivation of GRA 06128/9, brachinites and the three brachinite-like achondrites from nominally volatile-rich and oxidised ‘chondritic’ precursor sources within their respective parent bodies. Furthermore, the range of Δ17O values (∼0‰ to −0.3‰) among the meteorites indicates generation from isotopically heterogeneous sources that never completely melted, or isotopically homogenised. It is possible to generate major- and trace-element compositions similar to brachinites and the three studied brachinite-like achondrites as residues of moderate degrees (13–30%) of partial melting of primitive chondritic sources. This process was coupled with inefficient removal of silica-saturated, high Fe/Mg felsic melts with compositions similar to GRA 06128/9. Melting of the parent bodies of GRA 06128/9, brachinites and brachinite-like achondrites halted well before extensive differentiation, possibly due to the exhaustion of the short-lived radionuclide 26Al by felsic melt segregation. This mechanism provides a potential explanation for the cessation of run-away melting in asteroids to preserve achondrites such as GRA 06128/9, brachinites, brachinite-like achondrites, acapulcoite-lodranites, ureilites and aubrites. Moderate degrees of partial melting of chondritic material and generation of Fe–Ni–S-bearing melts are generally consistent with HSE abundances that are within factors of ∼2–10×CI-chondrite abundances for GRA 06128/9, brachinites and the three brachinite-like achondrites. However, in detail, brachinite-like achondrites NWA 5400, NWA 6077 and Zag (b) are interpreted to have witnessed single-stage S-rich metal segregation, whereas HSE in GRA 06128/9 and brachinites have more complex heritages. The HSE compositions of GRA 06128/9 and brachinites require either: (1) multiple phases in the residue (e.g., metal and sulphide); (2) fractionation after generation of an initial melt, again involving multiple phases; (3) fractional fusion, or; (4) a parent body with non-chondritic relative HSE abundances. Petrological and geochemical observations permit genetic links (i.e., same parent body) between GRA 06128/9 and brachinites and similar formation mechanisms for brachinites and brachinite-like achondrites. [Copyright &y& Elsevier]

Abstract: We report the petrography, mineral and whole-rock chemistry (major-, trace-, and highly-siderophile element abundances, and osmium and oxygen isotope compositions) of a newly recognized lherzolitic shergottite, Yamato (Y) 984028. Oxygen isotopes (Δ17O = 0.218‰) confirm a martian origin for this meteorite. Three texturally distinctive internal zones and a partially devitrified fusion crust occur in the polished section of Y 984028 studied here. The zones include: 1) a poikilitic region with pyroxene enclosing olivine and chromite (Zone A); 2) a non-poikilitic zone with cumulate olivine, interstitial pyroxene, maskelynite and Ti-rich chromite (Zone B) and; 3) a monomict breccia (Zone C). The pyroxene oikocryst in Zone A is chemically zoned from Wo3–7En76–71 in the core region to Wo33–36En52–49 at the rim, and encloses more Mg-rich olivine (Fo74–70) in the core, as compared with olivines (Fo69–68) located at the oikocryst rim. Constraints from Fe–Mg partitioning between crystals and melt indicate that constituent minerals are not in equilibrium with the corresponding bulk-rock composition, implying that Y 984028 represents a cumulate. The whole-rock major- and trace-element compositions, and initial 187Os/188Os value (0.1281 ± 0.0002) of Y 984028 are similar to other lherzolitic shergottites and this sample is probably launch-paired with Y 793602, Y 000027, Y 000047, and Y 000097. The Os isotopic composition and highly-siderophile element (HSE) abundances of Y 984028 and other lherzolitic shergottites are consistent with derivation from a martian mantle source that evolved with chondritic Re/Os. [ABSTRACT FROM AUTHOR]

Abstract: Coupled 187Os/188Os and highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, and Re) abundance data are reported for pristine lunar crustal rocks 60025, 62255, 65315 (ferroan anorthosites, FAN) and 76535, 78235, 77215 and a norite clast in 15455 (magnesian-suite rocks, MGS). Osmium isotopes permit more refined discrimination than previously possible of samples that have been contaminated by meteoritic additions and the new results show that some rocks, previously identified as pristine, contain meteorite-derived HSE. Low HSE abundances in FAN and MGS rocks are consistent with derivation from a strongly HSE-depleted lunar mantle. At the time of formation, the lunar floatation crust, represented by FAN, had 1.4±0.3pgg−1 Os, 1.5±0.6pgg−1 Ir, 6.8±2.7pgg−1 Ru, 16±15pgg−1 Pt, 33±30pgg−1 Pd and 0.29±0.10pgg−1 Re (∼0.00002×CI) and Re/Os ratios that were modestly elevated (187Re/188Os=0.6 to 1.7) relative to CI chondrites. MGS samples are, on average, characterised by more elevated HSE abundances (∼0.00007×CI) compared with FAN. This either reflects contrasting mantle-source HSE characteristics of FAN and MGS rocks, or different mantle–crust HSE fractionation behaviour during production of these lithologies. Previous studies of lunar impact-melt rocks have identified possible elevated Ru and Pd in lunar crustal target rocks. The new results provide no supporting evidence for such enrichments. If maximum estimates for HSE in the lunar mantle are compared with FAN and MGS averages, crust–mantle concentration ratios (D-values) must be ≤0.3. Such D-values are broadly similar to those estimated for partitioning between the terrestrial crust and upper mantle, with the notable exception of Re. Given the presumably completely different mode of origin for the primary lunar floatation crust and tertiary terrestrial continental crust, the potential similarities in crust–mantle HSE partitioning for the Earth and Moon are somewhat surprising. Low HSE abundances in the lunar crust, coupled with estimates of HSE concentrations in the lunar mantle implies there may be a ‘missing component’ of late-accreted materials (as much as 95%) to the Moon if the Earth/Moon mass-flux estimates are correct and terrestrial mantle HSE abundances were established by late accretion. [Copyright &y& Elsevier]

Abstract: The Rum Layered Suite is a layered mafic–ultramafic body that was emplaced during Palaeogene North Atlantic margin rifting. It is a classic open-system magma chamber, constructed of 16 repeated coupled peridotite–troctolite units, some of which have laterally extensive ~2 mm-thick platinum-group element (PGE) enriched (~2 µg g−1) Cr-spinel seams at their bases. In order to investigate Cr-spinel seam petrogenesis and enrichment of the PGE, abundances of these elements and Re–Os isotopes have been determined at three stratigraphic levels of the Rum Layered Suite that represent major magma replenishment events. Individual units preserve a range of initial 187Os/188Os ratios, demonstrating heterogeneity in the composition of replenishing magmas. Data for both the Cr-spinel seams and overlying silicates reveal that the processes that formed the Cr-spinel also concentrated the PGE, following magma replenishment. There is no evidence for structurally-bound PGE in Cr-spinel. Instead, the PGE budget of the Rum Layered Suite is linked to base metal sulphides, especially pentlandite, and to PGE alloys contained within the Cr-spinel seams, but which exist as separate phases at Cr-spinel grain boundaries. The range in initial Os isotope compositions (γ Os =3.4 to 36) in the Rum Layered Suite can be successfully modelled by 5–8% assimilation of Lewisian gneiss coupled with changing PGE contents in the replenishing magmas associated with sulphide removal. Initial 187Os/188Os ratios for Rum rocks range from 0.1305 to 0.1349 and are atypical of the convecting upper mantle, but are within the range for recently erupted picrites and basalts from Iceland and Palaeogene picrites and basalts from Baffin Island, Greenland and Scotland. Thus, the Os isotope data suggest that the North Atlantic Igneous Province magmas were collectively produced from a mantle source with components that remained relatively unchanged in Os isotopic composition over the past 60 Ma, and that likely contain a recycled lithospheric component. [Copyright &y& Elsevier]

The Jurassic Coast Range Ophiolites, California, provide evidence for tectonic processes that formed the western margin of North America. Whether the ophiolites were formed in a mid-ocean ridge, back arc or forearc setting, however, remains unconstrained. To address this issue, a systematic grid sampling approach was taken to examine the mantle section of an archetypal ~161 Ma Coast Range Ophiolite at Point Sal, California. The Point Sal peridotites are serpentinized, with 187Re 187Os evidence for a localized Late Miocene alteration event in grids closest to the lowermost bounding fault of the ophiolite. This event is interpreted to be related to tectonic changes and hydration-dehydration reactions acting on the serpentinites in response to changes in the azimuth and rate of Pacific-North American plate motion. Alteration and serpentinization have not systematically affected highly siderophile element (HSE) abundances, especially Os, Ir or Ru which, together with rare earth element abundances, record significant melt depletion (>20%) of a fertile mantle protolith (187Os/188Os = ~0.129) during ophiolite formation. Peridotites subsequently experienced localized and heterogenous addition of Re, Pt, Pd and radiogenic 187Os/188Os from Cl-rich, oxidized (QFM) fluids. Geochemical features of both Point Sal peridotites, as well as associated basaltic lavas, are consistent with high degrees of partial melting and variable addition of fluids as also observed in global forearc peridotites. A forearc origin for the Point Sal Ophiolite Complex supports models for the dominant formation process of 153–166 Ma Coast Range Ophiolite infant Arc crust terranes within a single westward facing arc along the Sierra continental-margin. [ABSTRACT FROM AUTHOR]

The Siberian sub-continental lithospheric mantle (SCLM) is regionally heterogeneous due to the complex modification of ancient cratonic material by various metasomatic fluids and interaction with the Siberian plume at ∼250 Ma. Here, we assess the extent and origin of this heterogeneity by analysis of helium isotopes, rhenium-osmium isotopes, trace-element, and highly siderophile element [HSE: Os, Ir, Ru, Pt, Pd, Re] abundances in a suite of mantle-derived megacrystalline dunite xenoliths from the 360 Ma Udachnaya East kimberlite pipe, Siberia. This enables assessment of the style and extent of metasomatism acting to modify the volatile budget of the Siberian SCLM. The olivine megacrysts have 3He/4He values that range from 2.3 to 7.4 R A (where R A = the 3He/4He of air), outside the canonical range for the lithospheric mantle (6.1 ± 2.1 R A ; Day et al., 2015). High [He] and low U + Th concentrations in these olivine megacrysts indicate that the Udachnaya megacrystalline dunite xenolith suite has undergone minimal post-eruptive modification of He isotopes by 4He recoil. We instead interpret He isotope variations to reflect pre- or syn-eruptive metasomatic signatures during kimberlite emplacement. The dunites can be divided into two groups, ultimately reflecting modification by two distinct metasomatic styles. Group 1 dunites are characterized by highly unradiogenic Os isotope compositions (γOs 360Ma −16 to −13) and ancient melt depletion ages (∼3 Ga) typical of ancient cratonic lithospheric mantle; yet display a range of He isotope ratios (2.3–5.9 R A). This indicates that group 1 dunites have been modified by gas-rich metasomatic fluids acting to change He abundances and isotope ratios, while preserving unradiogenic Os isotope and HSE abundance systematics. Group 2 dunites extend to significantly more radiogenic Os isotope signatures and higher He isotope values (γOs 360Ma > −5 to +53; 3He/4He from 3.7 to 7.4 R A). These two groups define a negative hyperbolic array between Os and He isotopes which we interpret to result from metasomatism by variable mixtures between: (1) a gas-rich and HSE-poor fluid (similar to the fluids acting to modify Group 1 dunites) with helium isotope compositions above the MORB range (>8 R A) derived from the asthenosphere, and: (2) strongly radiogenic fluids (∼2 R A ; 187Os/188Os > 0.25) likely sourced from within the SCLM. The Udachnaya megacrystalline dunite xenolith suite provides insight into how mantle-plume derived fluids interact with metasomatic fluids within the SCLM. [ABSTRACT FROM AUTHOR]

Osmium isotope and highly siderophile element (HSE: Os, Ir, Ru, Rh, Pt, Pd, Re, Au) abundance analysis provides a new methodology for examining the origins of ancient iron production in the Eastern Mediterranean, a current scholarly lacuna. Here we present results from a two-stage campaign of laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) followed by thermal ionization mass spectrometry and solution ICP-MS to measure mixed iron-copper chunks and iron objects from the Faynan region of Jordan. Faynan is a copper-ore resource zone with a rich history of copper smelting. The combination of sophisticated copper metallurgy and iron artifacts in the archaeological record of Iron Age Faynan (10th-9th centuries BCE) offers an exceptional opportunity to investigate the hypothesis that iron production originally developed as an adventitious byproduct of advanced copper smelting technologies. Based on the results, we find no connection from HSE abundances and inter-element ratios, or osmium isotopes, between the iron objects (Pt/Os = 2–7; 187Os/188Os = 1.15 to 2.50) and mixed metal chunks from the furnaces (Pt/Os = 7.7–35; 187Os/188Os = 2.15 to 8.96) excavated in Faynan, indicating that the objects were not locally produced. This conclusion provides additional evidence that iron production in the Levant was probably not directly developed from copper smelting. In turn, osmium isotopes and siderophile element abundances in artifacts and products from metal production can also offer a new line of evidence for examining exchange networks in the Iron Age Eastern Mediterranean and elsewhere. • Application of combined LA-ICP-MS and TIMS methodology in archaeology. • Osmium isotopes and HSE abundances are used to provenance iron objects. • Iron objects were not locally produced from iron-copper chunks in Faynan, Jordan. • Evidence that iron production did not originate from copper smelting technology. [ABSTRACT FROM AUTHOR]

Abstract: Shergottite meteorites are a suite of mafic to ultramafic igneous rocks whose parental magmas probably derived from the martian mantle. In this study, a suite of 23 shergottites, spanning their known range in bulk compositions, Rb–Sr, Sm–Nd, and Lu–Hf isotopes, were measured for 187Re–187Os isotopic systematics and highly siderophile element abundances (HSE: including Os, Ir, Ru, Pt, Pd, Re). The chief objective was to gain new insight on the chemical evolution of the martian mantle by unraveling the long-term HSE budget of its derivative melts. Possible effects upon HSEs related to crustal contamination, as well as terrestrial and/or martian surface alteration are also examined. Some of the shergottites are hot arid-desert finds. Their respective acetic acid leachates and residues show that both Re and Os display open-system behavior during sample residence at or near the martian and/or terrestrial surfaces. In some meteorites, the alteration effects can be circumvented by analysis of the leached residues. For those shergottites believed to record robust Re–Os isotopic systematics, calculated initial 187Os/188Os are well correlated with the initial 143Nd/144Nd. Shergottites from mantle sources with long-term melt-depleted characteristics (initial ε143Nd of +36 to +40) have chondritic initial γ187Os ranging from −0.5 to +2.5. Shergottites with intermediate initial ε143Nd of +8 to +17 have a range in initial γ187Os of −0.6 to +2.3, which overlaps the range for depleted shergottites. Shergottites from long-term enriched sources, with initial ε143Nd of ∼−7, are characterized by suprachondritic γ187Os values of +5 to +15. The initial γ187Os variations for the shergottites do not show a correlation with indices of magmatic differentiation, such as MgO, or any systematic differences between hot arid-desert finds, Antarctic finds, or observed falls. The strong correlation between the initial ε143Nd and γ187Os in shergottites from approximately +40 and 0 to −7 and +15, respectively, is assessed in models for mixing depleted mantle-derived melts with ancient crust (modeled to be similar to evolved shergottite in composition), and with assimilation-fractional crystallization. These models show that the correlation is unlikely to result from participation of martian crust. More likely, this correlation relates to contributions from depleted and enriched reservoirs formed in a martian magma ocean at ca. 4.5Ga. These models indicate that the shergottite endmember sources were generated by mixing between residual melts and cumulates that formed at variable stages during solidification of a magma ocean. The expanded database for the HSE abundances in shergottites suggests that their martian mantle sources have similar HSE abundances to the terrestrial mantle, consistent with prior studies. The relatively high HSE abundances in both planetary mantles likely cannot be accounted for by high pressure–temperature metal–silicate partitioning at the bases of magma oceans, as has been suggested for Earth. If the HSE were instead supplied by late accretion, this event must have occurred prior to the crystallization of the last martian magma ocean. [Copyright &y& Elsevier]