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Amsellam, E, Moynier F, Pringle EA, Bouvier A, Chen H, Day JMD.  2017.  Testing the chondrule-rich accretion model for planetary embryos using calcium isotopes. Earth and Planetary Science Letters. 469:75-83.   10.1016/j.epsl.2017.04.022   Abstract

Understanding the composition of raw materials that formed the Earth is a crucial step towards
understanding the formation of terrestrial planets and their bulk composition. Calcium is the fifth most
abundant element in terrestrial planets and, therefore, is a key element with which to trace planetary
composition. However, in order to use Ca isotopes as a tracer of Earth’s accretion history, it is first
necessary to understand the isotopic behavior of Ca during the earliest stages of planetary formation.
Chondrites are some of the oldest materials of the Solar System, and the study of their isotopic
composition enables understanding of how and in what conditions the Solar System formed. Here we
present Ca isotope data for a suite of bulk chondrites as well as Allende (CV) chondrules. We show that
most groups of carbonaceous chondrites (CV, CI, CR and CM) are significantly enriched in the lighter Ca
isotopes (δ44/40Ca= +0.1 to +0.93) compared with bulk silicate Earth (δ44/40Ca= +1.05 ± 0.04,
Huang et al., 2010) or Mars, while enstatite chondrites are indistinguishable from Earth in Ca isotope
composition (δ44/40Ca = +0.91 to +1.06). Chondrules from Allende are enriched in the heavier
isotopes of Ca compared to the bulk and the matrix of the meteorite (δ44/40Ca = +1.00 to +1.21).
This implies that Earth and Mars have Ca isotope compositions that are distinct from most carbonaceous
chondrites but that may be like chondrules. This Ca isotopic similarity between Earth, Mars, and
chondrules is permissive of recent dynamical models of planetary formation that propose a chondrulerich
accretion model for planetary embryos.

Amsellam, E, Moynier F, Day JMD, Moriera M, Puchtel IS, Teng F-Z.  2018.  The stable strontium isotopic composition of ocean island basalts, mid-ocean ridge basalts, and komatiites. Chemical Geology. 483:595-602.   Abstract

The radiogenic 87Rb-87Sr system has been widely applied to the study of geological and planetary processes. In contrast, the stable Sr isotopic composition of the bulk silicate Earth (BSE) and the effects of igneous differentiation on stable Sr isotopes are not well-established. Here we report the stable Sr isotope (88Sr/86Sr, reported as δ88/86Sr, in parts per mil relative to NIST SRM 987) compositions for ocean islands basalts (OIB), mid-ocean ridge basalts (MORB) and komatiites from a variety of locations. Stable Sr isotopes display limited fractionation in a OIB sample suite from the Kilauea Iki lava lake suggesting that igneous processes have limited effect on stable Sr isotope fractionation (±0.12‰ over 20% MgO variation; 2sd). In addition, OIB (δ88/86Sr = 0.16–0.46‰; average 0.28 ± 0.17‰), MORB (δ88/86Sr = 0.27–0.34‰; average 0.31 ± 0.05‰) and komatiites (δ88/86Sr = 0.20–0.97‰; average 0.41 ± 0.16‰) from global localities exhibit broadly similar Sr stable isotopic compositions. Heavy stable Sr isotope compositions (δ88/86Sr > 0.5‰) in some Barberton Greenstone belt komatiites may reflect Archean seawater alteration or metamorphic processes and preferential removal of the lighter isotopes of Sr. To first order, the similarity among OIBs from three different ocean basins suggests homogeneity of stable Sr isotopes in the mantle. Earth's mantle stable Sr isotopic composition is established from the data on OIB, MORB and komatiites to be δ88/86Sr = 0.30 ± 0.02‰ (2sd). The BSE δ88/86Sr value is identical, within uncertainties, to the composition of carbonaceous chondrites (δ88/86Sr = 0.29 ± 0.06‰; 2sd) measured in this study.

Barry, PH, Hilton DR, Day JMD, Pernet-Fisher JF, Howarth GH, Magna T, Agashev AM, Pokhilenko NP, Pokhilenko LH, Taylor LA.  2015.  Helium isotopic evidence for modification of the cratonic lithosphere during the Permo-Triassic Siberian flood basalt event. Lithos. 216-217:73-80.   10.1016/j.lithos.2014.12.001   Abstract

Major flood basalt emplacement events can dramatically alter the composition of the sub-continental lithospheric mantle (SCLM). The Siberian craton experienced one of the largest flood basalt events preserved in the geologic record — eruption of the Permo-Triassic Siberian flood basalts (SFB) at ~250 Myr in response to upwelling of a deep-rooted mantle plume beneath the Siberian SCLM. Here,we present helium isotope (3He/4He) and concentration data for petrologically-distinct suites of peridotitic xenoliths recovered from two temporally-separated kimberlites:
the 360 Ma Udachnaya and 160 Ma Obnazhennaya pipes, which erupted through the Siberian SCLM and bracket the eruption of the SFB. Measured 3He/4He ratios span a range from 0.1 to 9.8 RA (where RA = air 3He/4He) and fall into two distinct groups: 1) predominantly radiogenic pre-plume Udachnaya samples (mean clinopyroxene 3He/4He = 0.41 ± 0.30 RA (1σ); n = 7 excluding 1 outlier), and 2) ‘mantle-like’ post plume Obnazhennaya samples (mean clinopyroxene 3He/4He=4.20±0.90 RA (1σ); n=5 excluding 1 outlier). Olivine separates from both kimberlite pipes tend to have higher 3He/4He than clinopyroxenes (or garnet). Helium contents in Udachnaya samples ([He] = 0.13–1.35 μcm3STP/g; n = 6) overlap with those of Obnazhennaya
([He]=0.05–1.58 μcm3STP/g; n = 10), but extend to significantly higher values in some instances ([He]=49–349 μcm3STP/g; n = 4). Uranium and thorium contents are also reported for the crushed material from which He was extracted in order to evaluate the potential for He migration from the mineral matrix to fluid inclusions. The wide range in He content, together with consistently radiogenic He-isotope values in Udachnaya peridotites suggests that crustal-derived fluids have incongruently metasomatized segments of the Siberian SCLM, whereas high 3He/4He values in Obnazhennaya peridotites show that this section of the SCLM has been overprinted by Permo-Triassic (plume-derived) basaltic fluids. Indeed, the stark contrast between pre- and post-plume 3He/4He ratios in peridotite xenoliths highlights the potentially powerful utility of He-isotopes for differentiating between various types of metasomatism (i.e., crustal versus basaltic fluids).

Bottke, WF, Walker RJ, Day JMD, Nesvorny D, Elkins-Tanton L.  2010.  Stochastic Late Accretion to Earth, the Moon, and Mars. Science. 330:1527-1530.   10.1126/science.1196874   AbstractWebsite

Core formation should have stripped the terrestrial, lunar, and martian mantles of highly siderophile elements (HSEs). Instead, each world has disparate, yet elevated HSE abundances. Late accretion may offer a solution, provided that >= 0.5% Earth masses of broadly chondritic planetesimals reach Earth's mantle and that similar to 10 and similar to 1200 times less mass goes to Mars and the Moon, respectively. We show that leftover planetesimal populations dominated by massive projectiles can explain these additions, with our inferred size distribution matching those derived from the inner asteroid belt, ancient martian impact basins, and planetary accretion models. The largest late terrestrial impactors, at 2500 to 3000 kilometers in diameter, potentially modified Earth's obliquity by similar to 10 degrees, whereas those for the Moon, at similar to 250 to 300 kilometers, may have delivered water to its mantle.

Brandon, AD, Puchtel IS, Walker RJ, Day JMD, Irving AJ, Taylor LA.  2012.  Evolution of the martian mantle inferred from the Re-187-Os-187 isotope and highly siderophile element abundance systematics of shergottite meteorites. Geochimica Et Cosmochimica Acta. 76:206-235.   10.1016/j.gca.2011.09.047   AbstractWebsite

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 Re-187-Os-187 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 Os-187/Os-188 are well correlated with the initial Nd-143/Nd-144. Shergottites from mantle sources with long-term melt-depleted characteristics (initial epsilon Nd-143 of + 36 to + 40) have chondritic initial gamma Os-187 ranging from -0.5 to + 2.5. Shergottites with intermediate initial epsilon Nd-143 of + 8 to + 17 have a range in initial gamma Os-187 of -0.6 to + 2.3, which overlaps the range for depleted shergottites. Shergottites from long-term enriched sources, with initial epsilon Nd-143 of similar to-7, are characterized by suprachondritic gamma Os-187 values of + 5 to + 15. The initial gamma Os-187 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 epsilon Nd-143 and gamma Os-187 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. 4.5 Ga. 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. (C) 2011 Elsevier Ltd. All rights reserved.

Cabral, RA, Jackson MG, Koga KT, Rose-Koga EF, Hauri EH, Whitehouse MJ, Price AA, Day JMD, Shimizu N, Kelley KA.  2014.  Volatile cycling of H2O, CO2, F, and Cl in the HIMU mantle: A new window provided by melt inclusions from oceanic hot spot lavas at Mangaia, Cook Islands. Geochemistry, Geophysics, Geosystems. 15(11):4445-4467.   10.1002/2014GC005473   Abstract

Mangaia hosts the most radiogenic Pb-isotopic compositions observed in ocean island basalts and represents the HIMU (high m5238U/204Pb) mantle end-member, thought to result from recycled oceanic crust. Complete geochemical characterization of the HIMU mantle end-member has been inhibited due to a lack of deep submarine glass samples from HIMU localities. We homogenized olivine-hosted melt inclusions separated from Mangaia lavas and the resulting glassy inclusions made possible the first volatile abundances to be obtained from the HIMU mantle end-member. We also report major and trace element abundances and Pb-isotopic ratios on the inclusions, which have HIMU isotopic fingerprints. We evaluate the samples for processes that could modify the volatile and trace element abundances postmantle melting, including diffusive Fe and H2O loss, degassing, and assimilation. H2O/Ce ratios vary from 119 to 245 in the most pristine Mangaia inclusions; excluding an inclusion that shows evidence for assimilation, the primary magmatic H2O/Ce ratios vary up to 200, and are consistent with significant dehydration of oceanic crust during subduction and long-term storage in the mantle. CO2 concentrations range up to 2346 ppm CO2 in the inclusions. Relatively high CO2 in the inclusions, combined with previous observations of carbonate blebs in other Mangaia melt inclusions, highlight the importance of CO2 for the generation of the HIMU mantle. F/Nd ratios in the inclusions (3069; 2r standard deviation) are higher than the canonical ratio observed in oceanic lavas, and Cl/K ratios (0.07960.028) fall in the range of pristine mantle (0.02–0.08).

Cabral, RA, Jackson MG, Rose-Koga EF, Koga KT, Whitehouse MJ, Antonelli MA, Farquhar J, Day JMD, Hauri EH.  2013.  Anomalous sulphur isotopes in plume lavas reveal deep mantle storage of Archaean crust. Nature. 496:490-+.   10.1038/nature12020   AbstractWebsite

Basaltic lavas erupted at some oceanic intraplate hotspot volcanoes are thought to sample ancient subducted crustal materials(1,2). However, the residence time of these subducted materials in the mantle is uncertain and model-dependent(3), and compelling evidence for their return to the surface in regions of mantle upwelling beneath hotspots is lacking. Here we report anomalous sulphur isotope signatures indicating mass-independent fractionation (MIF) in olivine-hosted sulphides from 20-million-year-old ocean island basalts from Mangaia, Cook Islands (Polynesia), which have been suggested to sample recycled oceanic crust(3,4). Terrestrial MIF sulphur isotope signatures (in which the amount of fractionation does not scale in proportion with the difference in the masses of the isotopes) were generated exclusively through atmospheric photochemical reactions until about 2.45 billion years ago(5-7). Therefore, the discovery of MIF sulphur in these young plume lavas suggests that sulphur-probably derived from hydrothermally altered oceanic crust-was subducted into the mantle before 2.45 billion years ago and recycled into the mantle source of Mangaia lavas. These new data provide evidence for ancient materials, with negative Delta S-33 values, in the mantle source for Mangaia lavas. Our data also complement evidence for recycling of the sulphur content of ancient sedimentary materials to the subcontinental lithospheric mantle that has been identified in diamond-hosted sulphide inclusions(8,9). This Archaean age for recycled oceanic crust also provides key constraints on the length of time that subducted crustal material can survive in the mantle, and on the timescales of mantle convection from subduction to upwelling beneath hotspots.

Clay, PL, Burgess R, Busemann H, Ruzie-Hamilton L, Joachim B, Day JMD, Ballentine CJ.  2017.  Halogens in chondritic meteorites and terrestrial accretion. Nature. 551:614-618.   10.1038/nature24625   Abstract

Volatile element delivery and retention played a fundamental part in Earth’s formation and subsequent chemical differentiation. The heavy halogens—chlorine (Cl), bromine (Br) and iodine (I)—are key tracers of accretionary processes owing to their high volatility and incompatibility, but have low abundances in most geological and planetary materials. However, noble gas proxy isotopes produced during neutron irradiation provide a high-sensitivity tool for the determination of heavy halogen abundances. Using such isotopes, here we show that Cl, Br and I abundances in carbonaceous, enstatite, Rumuruti and primitive ordinary chondrites are about 6 times, 9 times and 15–37 times lower, respectively, than previously reported and usually accepted estimates1. This is independent of the oxidation state or petrological type of the chondrites. The ratios Br/Cl and I/Cl in all studied chondrites show a limited range, indistinguishable from bulk silicate Earth estimates. Our results demonstrate that the halogen depletion of bulk silicate Earth relative to primitive meteorites is consistent with the depletion of lithophile elements of similar volatility. These results for carbonaceous chondrites reveal that late accretion, constrained to a maximum of 0.5 ± 0.2 per cent of Earth’s silicate mass2,3,4,5, cannot solely account for present-day terrestrial halogen inventories6,7. It is estimated that 80–90 per cent of heavy halogens are concentrated in Earth’s surface reservoirs7,8 and have not undergone the extreme early loss observed in atmosphere-forming elements9. Therefore, in addition to late-stage terrestrial accretion of halogens and mantle degassing, which has removed less than half of Earth’s dissolved mantle gases10, the efficient extraction of halogen-rich fluids6 from the solid Earth during the earliest stages of terrestrial differentiation is also required to explain the presence of these heavy halogens at the surface. The hydropilic nature of halogens, whereby they track with water, supports this requirement, and is consistent with volatile-rich or water-rich late-stage terrestrial accretion5,11,12,13,14.

Day, JMD, Brandon AD, Walker RJ.  2016.  Highly Siderophile Elements in Earth, Mars, the Moon, and Asteroids. Reviews in Mineralogy and Geochemistry. 81:161-238.   10.2138/rmg.2016.81.04   Abstract

The highly siderophile elements (HSE: Os, Ir, Ru, Rh, Pt, Pd, Re, Au) are key tracers of planetary accretion and differentiation processes due to their affinity for metal relative to silicate. Under low-pressure conditions the HSE are defined by having metal–silicate partition coefficients in excess of 104 (e.g., Kimura et al. 1974; Jones and Drake 1986; O’Neill et al. 1995; Borisov and Palme 1997; Mann et al. 2012). The HSE are geochemically distinct in that, with the exception of Au, they have elevated melting points relative to iron (1665 K), low vapour pressures, and are resistant to corrosion or oxidation. Under solar nebular conditions, Re, Os, Ir, Ru, Rh, and Pt, along with the moderately siderophile elements (MSE) Mo and W, condense as refractory-metal alloys. Palladium and Au are not as refractory and condense in solid solution with FeNi metal (Palme 2008). Assuming abundances of the HSE in materials that made up the bulk Earth were broadly similar to modern chondrite meteorites, mass balance calculations suggest that >98% of these elements reside in the metallic core (O’Neill and Palme 1998). In practical terms, the resultant low HSE abundance inventories in differentiated silicate crusts and mantles enables the use of these elements in order to effectively track metallic core formation and the subsequent additions of HSE-rich impactors to planets and asteroids (Fig. 1). In detail, the absolute and relative abundances of the HSE in planetary materials are also affected by mantle and crustal processes including melting, metasomatism, fractional crystallization, and crust-mantle remixing, as well as later impact processing, volatility of Re under oxidizing conditions, and low-temperature secondary alteration (cf., Day 2013; Gannoun et al. 2016, this volume). In the absence of metal, the HSE are chalcophile, so these elements are also affected by processes

Day, JMD, Harvey RP, Hilton DR.  In Press.  Melt-modified lithosphere beneath Ross Island and its role in the tectono-magmatic evolution of the West Antarctic Rift System. Chemical Geology. Abstract

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 (Fo90.6-87.4), and pyroxenite xenoliths (Fo89.3-87.3). The basanite lavas contain abundant large olivine xenocrysts (Fo89.7-88.0), with more ferroan matrix olivine grains (Fo83.7-81.2) and have HIMU-like incompatible trace-element signatures. The 3He/4He ratios (6.8 ±0.3RA; 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 initial 187Os/188Os ratio of 0.1286 ±0.0001. The initial 187Os/188Os 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.

Day, JMD.  2013.  Hotspot volcanism and highly siderophile elements. Chemical Geology. 341:50-74.   10.1016/j.chemgeo.2012.12.010   AbstractWebsite

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 crysta! 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 similar to>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 Os-187/Os-188-Os-186/Os-188 systematics. The growing database for HSE abundances and Os-187/Os-188 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 d! 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 Os-188/Os-188 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 variati! 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 similar to 0.0002 (Moon), to similar to 0.007 (Mars), to similar to 0.009 (Earth) x 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 3.8 Ga for Earth, and even earlier based on evidence from the Moon (similar to 4.4 Ga), Mars (similar to 4.5 Ga) and asteroids (>4.56 Ga). (C) 2013 Elsevier B.V. All rights reserved.DELMON.A, 1972, AMERICAN JOURNAL OF SCIENCE, V272, P805

Day, JMD.  2016.  Siderophile Elements. Encyclopedia of Geochemistry. ( White WM, Ed.).: Springer   10.1007/978-3-319-39193-9_234-1  
Day, JMD, Waters CL, Schaefer BF, Walker RJ, Turner S.  2016.  Use of Hydrofluoric Acid Desilicification in the Determination of Highly Siderophile Element Abundances and Re-Pt-Os Isotope Systematics in Mafic-Ultramafic Rocks. Geostandards and Geoanalytical Research. 40(1):49-65.   DOI: 10.1111/j.1751-908X.2015.00367.x   Abstract

Properly combining highly siderophile element (HSE: Re,Pd, Pt, Ru, Ir, Os) abundance data, obtained by isotope dilution, with corresponding 187Os/188Os and 186Os/188Os measurements of rocks requires efficient digestion of finely-ground powders and complete spike-sample equilibration. Yet, because of the nature of commonly used methods for separating Os from a rock matrix, hydrofluoric acid (HF) is typically not used in such digestions. Consequently, some silicates are not completely dissolved, and HSE residing within these silicates may not be fully accessed. Consistent with this, some recent studies of basaltic reference materials (RMs) have concluded that an HF-desilicification procedure is required to fully access the HSE (Ishikawa et al. (2014)Chemical Geology, 384, 27–46; Li et al. (2015) Geostandards and Geoanalytical Research, 39, 17–30). Highly siderophile element abundance and Os isotope studies of intraplate basalts typically target samples with a range of MgO contents (< 8to> 18% m/m, or as mass fractions, < 8 to> 18 g per 100 g), in contrast to the lower MgO mass fractions (< 10 g per 100 g) of basalt and diabase RMs (i.e., BIR-1, BHVO-2, TDB-1). To investigate the effect of HF-desilicification on intraplate basalts, experiments were performed on finely ground Azores basalts (8.1–17 g per 100 g MgO) using a‘standard acid digestion’ (2:1 mixture of concentrated HNO3 and HCl), and a standard acid digestion, followed by HF-desilicification. No systematic trends in HSE abundances were observed between data obtained by standard acid digestion and HF-desilicification. Desilicifi-cation procedures using HF do not improve liberation ofthe HSE from Azores basalts, or some RMs (e.g., WPR-1).We conclude that HF-desilicification procedures are useful for obtaining total HSE contents of some young lavas, but this type of procedure is not recommended for studies where Re-Pt-Os chronological information is desired. The collateral effect of a standard acid digestion to liberate Os, followed by HF-desilicification to obtain Re and Pt abundances in samples, is that the measured Re/Os and Pt/Os may not correspond with measured 187Os/188Os or 186Os/188Os.

Day, JMD, Koppers AAP, Mendenhall BC, Oller B.  2018.  The ‘Scripps Dike’ and its implications for mid-Miocene volcanism and tectonics of the California Continental Borderland. From the Mountains to the Abyss: The California Borderland as an Archive of Southern California Geologic Evolution - SEPM Special Publication. 110: Society for Sedimentary Geology   10.2110/sepmsp.110.02   Abstract

New field observations, petrology, geochemistry, and 40Ar/39Ar geochronology are reported for the Scripps Dike, which crops out at the coast north of La Jolla, California. The northeast–southwest-trending and laterally discontinuous dike has a basaltic–trachyandesite bulk composition,
with an emplacement age of 13.89 6 0.13 Ma. Modeling of the dike composition indicates that it formed from 0.5 to 1.5% partial melting of a primitive mantle-type source, metasomatized by slab fluids, predominantly in the garnet stability field. The composition of the dike, including relatively high MgO (6.6 wt.%) and Sr/Y (~105), makes it akin to magnesian andesites in Baja California, Mexico, termed ‘‘bajaites.’’ Field evidence indicates
that the current exposure of the dike is close to the original stalling depth, it was probably associated with explosive volcanism, and the dike flowed laterally. After accounting for alteration, the dike has an initial 87Sr/86Sr composition of 0.70390, with limited evidence for crustal contamination, consistent with derivation from a slab-fluid-metasomatized mantle source. The composition of the dike places it broadly in the range of Miocene California Continental Borderland (hereafter referred to as Borderland) volcanic rocks studied previously. A comparison of ages of volcanic rocks occurring along the Borderland margin reveals an approximately age-progressive trend to the southeast. This represents an opposite sense to the apparent ageprogressive trend for Miocene to Recent volcanic rocks north of the Western Transverse Ranges. Possible models to explain the compositions and age relationships of Miocene to Recent volcanic rocks of the Borderland region include southeasterly migration of volcanism in response to Rivera Triple Junction movement and slab window formation, or the presence of a weak ‘‘hotspot’’ that has been active since at least the Miocene. Identification of the process(es) responsible for Borderland volcanism is currently limited by dissection and northwestward movement of Borderland rocks in response to northwest–southeast shearing of the Pacific–North American plate boundary, and by the quality and quantity of reported age-dates and paleomagnetic information. The formation processes of volcanism in the Borderland have ramifications for palinspastic reconstruction of the margin, as well as for the thermal and magmatic evolution of western California in response to a change in plate motion in a subduction to transform setting. The Scripps Dike provides evidence that regions of the mantle beneath the California Continental Borderland were metasomatized by slab fluids in a manner similar to portions of mantle beneath central Baja California, Mexico.

Day, JMD, Walker RJ, James OB, Puchtel IS.  2010.  Osmium isotope and highly siderophile element systematics of the lunar crust. Earth and Planetary Science Letters. 289:595-605.   10.1016/j.epsl.2009.12.001   AbstractWebsite

Coupled (187)Os/(188)Os 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 +/- 0.3 pg g(-1) Os, 1.5 +/- 0.6 pg g(-1) Ir, 6.8 +/- 2.7 pg g(-1) Ru, 16 +/- 15 pg g(-1) Pt,33 +/- 30 pg g(-1) Pd and 0.29 +/- 0.10 pg g(-1) Re (similar to 0.00002 x Cl) and Re/Os ratios that were modestly elevated ((187)Re/(188)Os = 0.6 to 1.7) relative to Cl chondrites. MGS samples are, on average, characterised by more elevated HSE abundances (similar to 0.00007 x Cl) 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. (C) 2009 Elsevier B.V. All rights reserved.

Day, JMD, Taylor LA.  2007.  On the structure of mare basalt lava flows from textural analysis of the LaPaz Icefield and Northwest Africa 032 lunar meteorites. Meteoritics & Planetary Science. 42:3-17. AbstractWebsite

Quantitative textural data for Northwest Africa (NWA) 032 and the LaPaz (LAP) mare basalt meteorites (LAP 02205, LAP 02224, LAP 02226, and LAP 02436) provide constraints on their crystallization and mineral growth histories. In conjunction with whole-rock and mineral chemistry, textural analysis provides powerful evidence for meteorite pairing. Petrographic observations and crystal size distribution (CSD) measurements of NWA 032 indicate a mixed population of slowly cooled phenocrysts and faster cooled matrix. LaPaz basalt crystal populations are consistent with a single phase of nucleation and growth. Spatial distribution patterns (SDP) of minerals in the meteorites highlight the importance of clumping and formation of clustered crystal frameworks in their melts, succeeded by continued nucleation and growth of crystals. This process resulted in increasingly poor sorting, during competition for growth, as the melt crystallized. Based on CSD and SDP data, we suggest a potential lava flow geometry model to explain the different crystal populations for NWA 032 and the LaPaz basalts. This model involves crystallization of early formed phenocrysts at hypabyssal depths in the lunar crust, followed by eruption and flow differentiation on the lunar surface. Lava flow differentiation would allow for formation of a cumulate base and facilitate variable cooling within the stratigraphy, explaining the varied textures and modal mineralogies of mare basalt meteorites. The model may also provide insight into the relative relationships of some Apollo mare basalt suites, shallow-level crystal fractionation processes, and the nature of mare basalt volcanism over lunar history.

Day, JMD, Sossi PA, Shearer CK, Moynier F.  2019.  Volatile distributions in and on the Moon revealed by Cu and Fe isotopes in the ‘Rusty Rock’ 66095. Geochimica et Cosmochimica Acta.   10.1016/j.gca.2019.02.036   Abstract

The Apollo 16 ‘Rusty Rock’ impact melt breccia 66095 is a volatile-rich sample, with the volatiles inherited through vapor condensation from an internal lunar source formed during thermo-magmatic evolution of the Moon. We report Cu and Fe isotope data for 66095 and find that bulk-rocks, residues and acid leaches span a relatively limited range of compositions (3.0 ±1.3 wt.% FeO [range = 2.0-4.8 wt.%], 5.4 ±3.1 ppm Cu [range = 3-12 ppm], average δ56Fe of 0.15 ± 0.05‰ [weighted mean = 0.16‰] and δ65Cu of 0.72 ± 0.14‰ [weighted mean = 0.78‰]). In contrast to the extreme enrichment of light isotopes of Zn and heavy isotopes of Cl in 66095, δ65Cu and δ56Fe in the sample lie within the previously reported range for lunar mare basalts (0.92 ± 0.16‰ and 0.12 ± 0.02‰, respectively). The lack of extreme isotopic fractionation for Cu and Fe isotopes reflects compositions inherent to 66095, with condensation of a cooling gas from impact-generated fumarolic activity at temperatures too low to lead to the condensation of Cu and Fe, but higher than required to condense Zn. Together with thermodynamic models, these constraints suggest that the gas condensed within 66095 between 700 and 900 °C (assuming a pressure of 10-6 and an fO2 of IW-2). That the Cu and Fe isotopic compositions of sample 66095 are within the range of mare basalts removes the need for an exotic, volatile-enriched source. The enrichment in Tl, Br, Cd, Sn, Zn, Pb, Rb, Cs, Ga, B, Cl, Li relative to Bi, Se, Te, Ge, Cu, Ag, Sb, Mn, P, Cr and Fe in the ‘Rusty Rock’ is consistent with volcanic outgassing models and indicates that 66095 likely formed distal from the original source of the gas. The volatile-rich character of 66095 is consistent with impact-generated fumarolic activity in the region of the Cayley Plains, demonstrating that volatile-rich rocks can occur on the lunar surface from outgassing of a volatile-poor lunar interior. The ‘Rusty Rock’ indicates that the lunar interior is significantly depleted in volatile elements and compounds and that volatile-rich lunar surface rocks likely formed through vapor condensation. Remote sensing studies have detected volatiles on the lunar surface, attributing them dominantly to solar wind. Based on the ‘Rusty Rock’, some of these surface volatiles may also originate from the Moon’s interior.

Day, JMD, Walker RJ, Qin LP, Rumble D.  2012.  Late accretion as a natural consequence of planetary growth. Nature Geoscience. 5:614-617.   10.1038/ngeo1527   AbstractWebsite

Core formation should strip highly siderophile elements (HSEs) from planetary mantles according to the expected metal-silicate partitioncoefficients(1,2). However, studies of Earth(3), the Moon(4) and Mars(5) indicate mantles with HSE abundances in chondrite-relative proportions that exceed the values expected from metal-silicate partitioning. Competing hypotheses have been proposed to account for these observations, including metal-silicate partitioning at higher pressures and temperatures(6) and late accretion(7). Here we present petrological and geochemical analyses of diogenite meteorites that represent mantle and crustal materials from two or more differentiated asteroids. We find that diogenites show HSE abundances that are consistent with metal-silicate equilibration, followed by minor continued accretion. Isotope chronometry supports diogenite crystallization ages within 2-3 million years of Solar System formation, indicating that late accretion occurred earlier than postulated for Earth, the Moon and Mars. The early timing and occurrence on differentiated asteroids, as well as on the larger terrestrial planets, therefore ties late accretion to planetary growth. On asteroidal bodies, such as the diogenite parent bodies, variations in HSE compositions may reflect regional rather than global effects. In contrast, for Earth, the Moon and Mars, compositional variations in mantle materials seem to be consistent with more homogeneous distributions through prolonged melting and/or solid-state convection.

Day, JMD, Ash RD, Liu Y, Bellucci JJ, Rumble D, McDonough WF, Walker RJ, Taylor LA.  2009.  Asteroids and andesites. Nature. 459:E2.   doi:10.1038/nature08078   Abstract

Arculus et al.1 raise an important question regarding the use of terrestrial rock nomenclature to characterize extraterrestrial materials. Here the issue relates to the definition of ‘andesite’, and whether the felsic achondrite meteorites GRA 06128 and GRA 06129 (GRA 06128/9) can and should be classified using this term2. More broadly, the question is whether extraterrestrial rocks should be classified using standard petrologic and geochemical criteria, such as mineralogy and major-element bulk composition, developed for the description of terrestrial rocks3,4. The approach of Arculus et al.1 is that petrogenetic process is of equal or greater importance when classifying a rock. This question must ultimately be decided by the scientific community.

Day, JMD, Walker RJ.  2015.  Highly siderophile element depletion in the Moon. Earth and Planetary Science Letters. 423:114-124.   10.1016/j.epsl.2015.05.001   Abstract

Coupled 187Os/188Os and highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re) abundance data are reported for Apollo 12 (12005, 12009, 12019, 12022, 12038, 12039, 12040), Apollo 15 (15555) and Apollo 17 (70135) mare basalts, along with mare basalt meteorites La Paz icefield (LAP) 04841 and Miller Range (MIL) 05035. These mare basalts have consistently low HSE abundances, at ∼2×10−5 to 2×10−7 the chondritic abundance. The most magnesian samples have broadly chondrite-relative HSE abundances and chondritic measured and calculated initial 187Os/188Os. The lower abundances and fractionated HSE compositions of more evolved mare basalts can be reproduced by modeling crystal–liquid fractionation using rock/melt bulk-partition coefficients of ∼2 for Os, Ir, Ru, Pt and Pd and ∼1.5 for Re. Lunar mare basalt bulk-partition coefficients are probably higher than for terrestrial melts as a result of more reducing conditions, leading to increased HSE compatibility. The chondritic-relative abundances and chondritic 187Os/188Os of the most primitive high-MgO mare basalts cannot readily be explained through regolith contamination during emplacement at the lunar surface. Mare basalt compositions are best modeled as representing ∼5–11% partial melting of metal-free sources with low Os, Ir, Ru, Pd (∼0.1 ng g−1), Pt (∼0.2 ng g−1), Re (∼0.01 ng g−1) and S (∼75 μg g−1), with sulphide-melt partitioning between 1000 and 10,000.

Apollo 12 olivine-, pigeonite- and ilmenite normative mare basalts define an imprecise 187Re–187Os age of 3.0±0.9 Ga with an initial 187Os/188Os of 0.107±0.010. This age is within uncertainty of 147Sm–143Nd ages for the samples. The initial Os isotopic composition of Apollo 12 samples indicates that the source of these rocks evolved with Re/Os within ∼10% of chondrite meteorites, from the time that the mantle source became a system closed to siderophile additions, to the time that the basalts erupted. Similarity in absolute HSE abundances between mare basalts from the Apollo 12, 15 and 17 sites, and from unknown regions of the Moon (La Paz mare basalts, MIL 05035), indicates relatively homogeneous and low HSE abundances within the lunar interior. Low absolute HSE abundances and chondritic Re/Os of mare basalts are consistent with a late accretion addition of ∼0.02 wt.% of the Moon's mass to the mantle, prior to the formation of the lunar crust. Late accretion must also have occurred significantly prior to cessation of lunar mantle differentiation (>4.4 Ga), to enable efficient mixing and homogenization within the mantle. Low lunar HSE abundances are consistent with proportionally 40 times more late accretion to Earth than the Moon. Disproportional late accretion to the two bodies is consistent with the small 182W excess (∼21–28 ppm) measured in lunar rocks, compared to the silicate Earth.

Day, JMD, Corder CA, Cartigny P, M. SA, Assayag N, Rumble D, Taylor LA.  2017.  A carbon-rich region in Miller Range 091004 and implications for ureilite petrogenesis. Geochimica et Cosmochimica Acta. 198:379-395.   10.1016/j.gca.2016.11.026   Abstract

Ureilite meteorites are partially melted asteroidal-peridotite residues, or more rarely, cumulates that can contain greater than three weight percent carbon. Here we describe an exceptional C-rich lithology, composed of 34 modal% large (up to 0.8 mm long) crystalline graphite grains, in the Antarctic ureilite meteorite Miller Range (MIL) 091004. This C-rich lithology is embedded within a silicate region composed dominantly of granular olivine with lesser quantities of low-Ca pyroxene, and minor FeNi metal, high-Ca pyroxene, spinel, schreibersite and troilite. Petrological evidence indicates that the graphite was added after formation of the silicate region and melt depletion. Associated with graphite is localized reduction of host olivine (Fo88-89) to nearly pure forsterite (Fo99), which is associated with FeNi metal grains containing up to 11 wt.% Si. The main silicate region is typical of ureilite composition, with highly siderophile element (HSE) abundances ∼0.3 × chondrite, 187Os/188Os of 0.1260 to 0.1262 and Δ17O of -0.81 ±0.16‰. Mineral trace-element analyses reveal that the rare earth elements (REE) and the HSE are controlled by pyroxene and FeNi metal phases in the meteorite, respectively. Modelling of bulk-rock REE and HSE abundances indicates that the main silicate region experienced ∼6% silicate and >50% sulfide melt extraction, which is at the lower end of partial melt removal estimated for ureilites. Miller Range 091004 demonstrates heterogeneous distribution of carbon at centimeter scales and a limited range in Mg/(Mg+Fe) compositions of silicate grain cores, despite significant quantities of carbon. These observations demonstrate that silicate rim reduction was a rapid disequilibrium process, and came after silicate and sulfide melt removal in MIL 091004. The petrography and mineral chemistry of MIL 091004 is permissive of the graphite representing late-stage C-rich melt that pervaded silicates, or carbon that acted as a lubricant during anatexis and impact disruption in the parent body. Positive correlation of Pt/Os ratios with olivine core compositions, but a wide range of oxygen isotope compositions, indicates that ureilites formed from a compositionally heterogeneous parent body that experienced variable sulfide and metal melt-loss that is most pronounced in relatively oxidized ureilites with Δ17O between -1.5 and ∼0‰.

Day, JMD, Taylor LA, Floss C, McSween HY.  2006.  Petrology and chemistry of MIL 03346 and its significance in understanding the petrogenesis of nakhlites on Mars. Meteoritics & Planetary Science. 41:581-606. AbstractWebsite

Antarctic meteorite Miller Range (MIL) 03346 is a nakhlite composed of 79% clinopyroxene, similar to 1% olivine, and 20% vitrophyric intercumulus material. We have performed a petrological and geochemical study of MIL 03346, demonstrating a petrogenetic history similar to previously discovered naklilites. Quantitative textural study of MIL 03346 indicates long (> 1 x 10(1) yr) residence times for the Cumulus augite, whereas the skeletal Fe-Ti oxide, fayalite, and sulfide in the vitrophyric intercumulus matrix suggest rapid cooling, probably as a lava flow. From the relatively high forsterite contents of olivine (up to Fo(43)) compared with other nakhlites and compositions of augite cores (Wo(38-42)En(35-40)Fs(22-28)) and their hedenbergite rims, we suggest that MIL 03346 is part of the same or a similar Martian Cumulate-rich lava flow as other nakhlites. However, MIL 03346 has experienced less equilibration and faster cooling than other nakhlites discovered to date. Calculated trace element concentrations based upon modal abundances of MIL 03346 and its constituent minerals are identical to whole rock trace element abundances. Parental melts for augite have REE patterns that are approximately parallel with whole rock and intercumulus melt using experimentally defined partition coefficients. This parallelism reflects closed-system crystallization for MIL 03346, where the only significant petrogenetic process between formation of augite and eruption and emplacement of the nakhlite flow has been fractional crystallization. A model for the petrogenesis of MIL 03346 and the naklilites (Nakhla, Governador Valadares, Lafayette, Yamato-000593, Northwest Africa (NWA) 817, NWA 998) Would include: 1) partial melting and ascent of melt generated from a long-term LREE depleted mantle Source, 2) crystallization of cumulus augite (+/- olivine, +/- magnetite) in a shallow-level Martian magma chamber, 3) eruption of the crystal-laden naklilite magma onto the surface of Mars, 4) cooling, crystal settling, overgrowth, and partial equilibration to different extents within the flow, 5) secondary alteration through hydrothermal processes, possibly immediately succeeding or during emplacement of the flow. This model might apply to single-or multiple-flow models for the nakhlites. Ultimately, MIL 03346 and the other nakhlites preserve a record of magmatic processes in volcanic rocks oil Mars with analogous petrogenetic histories to pyroxene-rich terrestrial lava flows and to komatiites.

Day, JMD, Pearson DG, Nowell GM.  2003.  High precision rhenium and platinum isotope dilution analyses by plasma ionisation multi-collector mass spectrometry. Plasma Source Mass Spectrometry: applications and emerging technologies. ( Holland G, Tanner SD, Eds.)., London: RSC Publishing   10.1039/9781847551689  
Day, JMD, Hilton DR.  2011.  Origin of (3)He/(4)He ratios in HIMU-type basalts constrained from Canary Island lavas. Earth and Planetary Science Letters. 305:226-234.   10.1016/j.epsl.2011.03.006   AbstractWebsite

New helium isotope and abundance measurements are reported for olivine and clinopyroxene phenocrysts from HIMU-type (high-mu=elevated (238)U/(204)Pb) lavas and xenoliths spanning the stratigraphies of El Hierro and La Palma, Canary Islands. Some pyroxene phenocrysts have suffered post-eruptive modification, either by less than 1% assimilation of crustal-derived He, or by closed-system ageing of He. Olivine phenocrysts record mantle source (3)He/(4)He compositions, with the average (3)He/(4)He for La Palma olivine (7.6 +/- 0.8R(A), where R(A) is the atmospheric (3)He/(4)He ratio of 1.38 x 10(-6)) being within uncertainty of those for El Hierro (7.7 +/- 0.3R(A)), and the canonical mid-ocean ridge basalt range (MORB: 8 +/- 1R(A)). The new helium isotope data for El Hierro and La Palma show no distinct correlations with whole-rock (87)Sr/(86)Sr, (143)Nd/(144)Nd, (187)Os/(188)Os, or Pb isotopes, but (3)He/(4)He ratios for La Palma lavas correlate with (18)O/(16)O measured for the same phenocryst populations. Despite limited (3)He/(4)He variations for El Hierro and La Palma, their He-O isotope systematics are consistent with derivation from mantle sources containing distinct recycled oceanic basaltic crust (El Hierro) and gabbroic lithosphere (La Palma) components that have mixed with depleted mantle, and a high-(3)He/(4)He component (>9.7R(A)) in the case of La Palma. The new data are consistent with models involving generation of compositionally and lithologically (e.g., pyroxenite, eclogite, peridotite) heterogeneous mantle sources containing recycled oceanic crust and lithosphere entrained within upwelling high-(3)He/(4)He mantle that has been severely diluted by interaction with depleted mantle. We propose that the noble gas systematics of HIMU-type lavas and ocean island basalts (OIB) in general, are most simply interpreted as being controlled by the most gas-rich reservoir involved in mixing to generate their mantle sources. In this scenario, HIMU and enriched mantle (EM) sources are dominated by depleted mantle, or high-(3)He/(4)He mantle, because recycled crust and lithosphere have low He concentrations. Consequently, high-(3)He/(4)He OIB would predominantly reflect derivation from a less depleted mantle source with sub-equal to higher He contents than depleted mantle. The available coupled He-O isotope systematics measured for OIB lavas are consistent with this hypothesis. (C) 2011 Elsevier B.V. All rights reserved.

Day, JMD.  2015.  Planet formation processes revealed by meteorites. Geology Today. 31(1):12-20.   10.1111/gto.12082   Abstract

The history of the solar system is locked within the planets, asteroids and other objects that orbit the Sun. While remote observations of these celestial bodies are essential for understanding planetary processes, much of the geological and geochemical information regarding solar system heritage comes directly from the study of rocks and other materials originating from them. The diversity of materials available for study from planetary bodies largely comes from meteorites; fragments of rock that fall through Earth’s atmosphere after impact-extraction from their parent planet or asteroid. These extra-terrestrial objects are fundamental scientific materials, providing information on past conditions within planets, and on their surfaces, and revealing the timing of key events that affected a planet’s evolution. Meteorites can be sub-divided into four main groups: (1) chondrites, which are unmelted and variably metamorphosed ‘cosmic sediments’ composed of particles that made up the early solar nebula; (2) achondrites, which represent predominantly silicate materials from asteroids and planets that have partially to fully melted, from a broadly chondritic initial composition; (3) iron meteorites, which represent Fe-Ni samples from the cores of asteroids and planetesimals; and (4) stony-iron meteorites such as pallasites and mesosiderites, which are mixtures of metal and dominantly basaltic materials. Meteorite studies are rapidly expanding our understanding of how the solar system formed and when and how key events such as planetary accretion and differentiation occurred. Together with a burgeoning collection of classified meteorites, these scientific advances herald an unprecedented period of further scientific challenges and discoveries, an exciting prospect for understanding our origins.