• 主要是2000年之后发表在Nature、Science上有关Element partitioning论文

1. 地球的形成过程

地球的形成大约在46亿年前，通过一个被称为凝聚的过程。以下是地球形成过程的简化概述：

• 太阳星云： 太阳系开始于一个巨大的、旋转的气体和尘埃盘，被称为太阳星云。

• 坍缩和旋转： 由于引力作用，太阳星云向内坍缩。随着坍缩，由于角动量守恒，它开始自旋。

• 原恒星形成： 在坍缩的太阳星云中央形成了一个致密区域，被称为原恒星。最终，这个原恒星演变成了我们的太阳。

• 原行星盘： 在旋转的盘中，余下的物质开始聚集，形成小型原行星或行星体在一个原行星盘内。

• 凝聚： 随着时间的推移，这些小行星相互碰撞并粘合在一起，通过凝聚的过程逐渐增长。

• 分化： 随着形成中的原地球继续吸积物质，它开始发生分化，重元素沉降到地球的中心，而轻元素上浮到表面。

• 地球层的形成： 这个分化过程导致了地球内部不同的层次，如地核、地幔和地壳的形成。

• 最终阶段： 地球形成的最后阶段涉及来自大型天体的碰撞，其中一次碰撞被认为导致了月球的形成。

通过数百万年的凝聚和分化过程，最终形成了我们今天所知的地球。

The differentiation of the Earth refers to the process by which the Earth's interior became layered with distinct compositional and physical zones. This process occurred early in the planet's history, primarily through the separation of materials based on their density. Here's a brief overview:

• Core Formation: The heaviest elements, such as iron and nickel, migrated toward the center of the Earth due to their higher density. This process formed the Earth's metallic core. The outer core is molten, while the inner core is solid due to intense pressure.

• Mantle Formation: Lighter elements, including silicates and other rocky materials, remained in the outer layers, forming the Earth's mantle. The mantle is mostly solid but has pockets of semi-molten rock that contribute to processes like plate tectonics.

• Crust Formation: The lightest materials, including silicate rocks, moved toward the surface, forming the Earth's crust. The crust is divided into the rigid plates that float on the semi-fluid asthenosphere, and it's where geological processes like volcanic activity and mountain building occur.

This differentiation process led to the formation of the Earth's distinct layers: the solid inner core, the molten outer core, the solid mantle, and the solid and rigid crust.

The differentiation of the Earth is crucial for the development of its geological and geophysical processes, including the generation of a magnetic field, plate tectonics, and the overall structure of the planet.

2. 关键词句

• element Partitioning, partition coefficients,

• the differentiation of the Earth, Highly siderophile elements (HSE), planet formation, core-mantle differentiation

• chemical differentiation, partitioning behaviour, planetary magmatic processes, the evolution and contemporary dynamics of the core

• coupled partitioning behavior, distribution of Au and As between hydrothermal fluid and pyrite, Coupled partitioning of Au and As into pyrite controls formation of giant Au deposits, simple partitioning (and the underlying process of adsorption) is the major depositional process

• Platinum group elements are invaluable tracers for planetary accretion and differentiation and the formation of PGE sulfide deposits. MANY geochemical processes, such as crystallization of silicate magmas or planetary differentiation. Late accretion of chondritic components to Earth after core formation has been invoked as the main source of mantle HSE.

3. 论文摘要

1. Element Partitioning: The Role of Melt Structure and Composition (Science, 2006)

• https://www.science.org/doi/10.1126/science.1126690

We segregated coexisting gabbroic and granitic melts by centrifuging them at high pressures and temperatures and measured the trace element compositions of the melts by laser ablation inductively coupled plasma mass spectrometry. Our results demonstrate that the effect of melt structure contributes about one order of magnitude to crystal/melt partition coefficients. Partitioning of alkali and alkaline earth elements strongly depends on field strength: Amphoteric and lone pair electron elements partition into the polymerized granitic melt; and rare earth, transition, and high field strength elements coordinated by nonbridging oxygens partition remarkably similar into the gabbroic melt. A regular solution model predicts these effects.

🟢 Element partitioning between magmas and crystals is essential to the differentiation of the Earth. Early work on trace element partitioning related mineral/melt partition coefficients, D_crystal/melt, to the relative ionic radii of the trace and major elements (1, 2) and to melt composition (3, 4). The melt compositional term was simplified by normalizing to the partitioning of a major cation (3). By ascribing ideal mixing to the mineral component, which expresses the behavior of the major cation in the melt, trace element partitioning can be formulated in terms of the lattice strain model (2, 5). This model defines a parabolic relationship between cation radius and partition coefficients that is specified by the effective Young's modulus, E, the partition coefficient, D0, and the cation radius, r0, relevant to the strain-free state. Although D0 is dependent on melt composition, melt composition itself is not an explicit variable. Attempts to explicitly include melt composition in the lattice strain model were limited to specific compositional parameters such as H2O content (6) and Fe/Mg ratio (7). Studies of coexisting silicate melts (8, 9) and mineral-melt systems suggest a strong dependence of crystal-melt partitioning on melt composition (10–15), but a general model for this dependence remains to be formulated.

In this study, we investigated partitioning of 45 elements between coexisting gabbroic and granitic K2O-FeO-Al2O3-SiO2 melts (16, 17) to isolate the effect of melt composition and structure from crystallographic effects. We used an experimental apparatus consisting of a piston cylinder mounted in a centrifuge that can achieve pressure and temperature conditions of 1.8 GPa and 1600°C, respectively, under an acceleration of 3000 g. Centrifuging is necessary to segregate coexisting silicate melts into pools large enough for measurement by laser ablation techniques, which permit simultaneous measurement of a large number of elements at trace-level concentrations (e.g., 200 parts per million, ppm). The centrifuging piston cylinder itself consists of a 42-kg integrated single-stage piston cylinder (18) with a 14-mm bore and 36-mm furnace length, allowing for capsules with an outer diameter of 4 mm and a length of 6 mm. The piston cylinder is mounted on a rotating 860-kg table with a 1.4-m diameter. With the sample at a radius of 32 cm, maximal acceleration of 3000 g is reached at 2850 revolutions per minute (rpm); at this frequency, the outer table rim travels at 753 km hour^(-1).

CONCLUSION: Our data imply that a significant change in the shape of the lattice-strain model parabola will result for the alkalis. To quantify this effect, we used data sets of Dcpx/basalt (30, 31) for basalts analogous to the gabbroic melt of experiment Z10 and combine Dcpx/basalt with our Dbasalt/granite. The site parameters for monovalent cations calculated from Dcpx/granite with respect to Dcpx/basalt are characterized by a Young's modulus decreased by 16 to 35% and by a strain-free partition coefficient D0 increased by a factor of 2. This softening of the site is attributed to the effect of melt composition. For the cations coordinated to NBOs, the effect of melt composition will increase Dcrystal/melt, Do, and hence the position of the parabola with respect to the D coordinate (1, 5) by one order of magnitude when changing from basaltic to granitic melt compositions. This effect acts in concert with the changes in crystal composition that occur as a consequence of the change in melt composition. Melt composition will play a key role for elements whose crystal/melt partition coefficients are close to unity, because they may change from compatible to incompatible as a function of melt composition. Because of the relative uniformity of partition coefficients for traces of Ca, Mg, RE, transition, and high field strength elements, melt composition does not strongly affect the relative partition coefficients of these elements. The latter are in general well characterized by models describing relative crystal-melt partition coefficients solely in terms of crystal lattice strain, but to quantify individual partition coefficients an explicit melt compositional term such as in Eq. 4 is necessary. Gross exceptions to the above generality are Pb (Fig. 2), for which Dgabbro/granite is as much as two orders of magnitude different from other divalent cations, and to a lesser extent Ba, Zn, and Sn. Among the NBO-coordinated cations, variations of Dbasalt/granite up to a factor of 2 exist, a non-negligible effect in the context of geochemical melting models.

2. Prediction of crystal–melt partition coefficients from elastic moduli (Nature, 1994)

• https://doi.org/10.1038/372452a0

MANY geochemical processes, such as crystallization of silicate magmas or planetary differentiation, require a knowledge of the way in which elements become partitioned between coexisting crystal and liquid phases1,2. But quantitative prediction of crystal/melt partition coefficients from thermodynamic principles has not previously been possible. By studying the partitioning of 15 elements between silicate minerals and their coexisting melts, we show here that the partitioning behaviour of any series of isovalent cations can be rationalized in terms of a simple model in which the size and elasticity of the crystal lattice sites play a critical role. We find that elasticity varies linearly with the formal charge of the cation. This model allows us to predict element partitioning behav-iour solely from the physical characteristics of the cation sites in the crystal.

Partition coefficients may vary by several orders of magnitude even for the case of a single element entering a single mineral phase, as the conditions of crystallization are varied (2). As the Nernst partition coefficient (Di, defined as [ilmineral/[ilmelt]) is related to the equilibrium constant for an appropriate exchange or fusion reaction (4,5), much of this variation can be attributed to the combined effects of pressure (P), temperature (T), and phase composition. The importance of these variables is widely recognized and yet the quantitative links between them and partition coefficients are poorly understood. Consequently, although most processes of chemical differentiation occur under conditions of varying P, T, and composition, a lack of understanding of their effects obliges geochemists to adopt a largely empirical approach using constant average Di values in modeling.

3. Site-ordering effects on element partitioning during rapid solidification of alloys (Nature, 1996)

• https://doi.org/10.1038/383150a0

WHEN an alloy solidifies, the component elements are often redistributed between the solid and liquid phases, so that the composition of the growing solid differs from that of the liquid. This effect, known as solute partitioning1, is the main cause of inhomogeneity in alloys, affecting both the nature and the mechanical properties (for example, brittleness) of the solidified material. If solidification is rapid, the solid-liquid interface is no longer in equilibrium, and it is generally accepted—and has been demonstrated2 for solid solutions—that this gives rise to reduced partitioning, in the limit leading to a solid having the same composition as the liquid through a process known as 'solute trapping'3. We have recently argued4 on theoretical grounds that, when the solidifying phase shows site ordering, the partitioning behaviour can be considerably more complex: rapid solidification might lead to increased partitioning, a change in the direction of partitioning, or an absence of partitioning at solidification rates much lower than expected. Here we report the experimental verification of this phenomenon by demonstrating inverted partitioning during rapid solidification of the intermetallic compound NiAl.

4. Trace Element Partition Coefficient in Ionic Crystals (Science, 1966)

• https://www.science.org/doi/abs/10.1126/science.152.3723.767

Partition coefficients of monovalent trace ions between liquids and either solid NaNO3 or KCl were determined. The isotropic elastic model of ionic crystals was used for calculating the energy change caused by the ionic substitutions. The observed values of partition coefficients in KCl are in good agreement with calculated values.

5. Coupled partitioning of Au and As into pyrite controls formation of giant Au deposits (Sci Adv, 2019)

• https://www.science.org/doi/10.1126/sciadv.aav5891

The giant Carlin-type Au deposits (Nevada, USA) contain gold hosted in arsenic-rich iron sulfide (pyrite), but the processes controlling the sequestration of Au in these hydrothermal systems are poorly understood. Here, we present an experimental study investigating the distribution of Au and As between hydrothermal fluid and pyrite under conditions similar to those found in Carlin-type Au deposits. We find that Au from the fluid strongly partitions into a newly formed pyrite depending on the As concentration and that the coupled partitioning behavior of these two trace elements is key for Au precipitation. On the basis of our experimentally derived partition coefficients, we developed a mass balance model that shows that simple partitioning (and the underlying process of adsorption) is the major depositional process in these systems. Our findings help to explain why pyrite in Carlin-type gold deposits can scavenge Au from hydrothermal fluids so efficiently to form giant deposits.

卡林型金矿床（美国内华达州）含有富含砷的铁硫化物（黄铁矿）中的金，但控制这些热液系统中金的封存过程尚不明确。在这里，我们提出了一项实验研究，研究了在类似卡林型金矿床条件下金和砷在热液流体和黄铁矿之间的分布。我们发现，金从流体中强烈地分配到新形成的黄铁矿中，取决于砷浓度，而这两种微量元素的耦合分配行为对金的沉淀至关重要。基于我们实验获得的分配系数，我们制定了一个质量平衡模型，显示在这些系统中，简单的分配（以及底层的吸附过程）是主要的沉积过程。我们的研究结果有助于解释为什么卡林型金矿床中的黄铁矿能够如此高效地从热液流体中清除金，形成巨大的矿床。

6. Breaking of Henry’s law for sulfide liquid–basaltic melt partitioning of Pt and Pd (Nat Commun, 2021)

• https://www.nature.com/articles/s41467-021-26311-x

Platinum group elements are invaluable tracers for planetary accretion and differentiation and the formation of PGE sulfide deposits. Previous laboratory determinations of the sulfide liquid–basaltic melt partition coefficients of PGE () yielded values of 102–109, and values of >105 have been accepted by the geochemical and cosmochemical society. Here we perform measurements of at 1 GPa and 1,400 °C, and find that increase respectively from 3,500 to 3.5 × 105 and 1,800 to 7 × 105, as the Pt and Pd concentration in the sulfide liquid increases from 60 to 21,000 ppm and 26 to 7,000 ppm, respectively, implying non-Henrian behavior of the Pt and Pd partitioning. The use of values of 2,000–6,000 well explains the Pt and Pd systematics of Earth’s mantle peridotites and mid-ocean ridge basalts. Our findings suggest that the behavior of PGE needs to be reevaluated when using them to trace planetary magmatic processes.

白金族元素是行星凝聚和分化以及PGE硫化物矿床形成的无价追踪器。先前的实验室测定PGE的硫化物液-玄武岩熔体分配系数（）的值为102-109，地球化学和宇宙化学学会接受了>105的值。在这里，我们在1 GPa和1,400°C下进行测量，并发现随着硫化物液中Pt和Pd浓度从60 ppm和26 ppm增加到21,000 ppm和7,000 ppm，分别增加到3,500至3.5×105和1,800至7×105，暗示了Pt和Pd分配的非亨利行为。使用2,000-6,000的值很好地解释了地球幔岩和中洋脊玄武岩的Pt和Pd系统。我们的研究结果表明，在使用PGE追踪行星岩浆过程时，需要重新评估PGE的行为。

7. Reconciling metal–silicate partitioning and late accretion in the Earth (Nat Commun, 2021)

• https://doi.org/10.1038/s41467-021-23137-5

Highly siderophile elements (HSE), including platinum, provide powerful geochemical tools for studying planet formation. Late accretion of chondritic components to Earth after core formation has been invoked as the main source of mantle HSE. However, core formation could also have contributed to the mantle’s HSE content. Here we present measurements of platinum metal-silicate partitioning coefficients, obtained from laser-heated diamond anvil cell experiments, which demonstrate that platinum partitioning into metal is lower at high pressures and temperatures. Consequently, the mantle was likely enriched in platinum immediately following core-mantle differentiation. Core formation models that incorporate these results and simultaneously account for collateral geochemical constraints, lead to excess platinum in the mantle. A subsequent process such as iron exsolution or sulfide segregation is therefore required to remove excess platinum and to explain the mantle’s modern HSE signature. A vestige of this platinum-enriched mantle can potentially account for 186Os-enriched ocean island basalt lavas.

高铁亲和元素（HSE），包括铂，为研究行星形成提供了强大的地球化学工具。地球核心形成后的晚期陨石成分追加被认为是地幔HSE的主要来源。然而，核心形成也可能对地幔的HSE含量有所贡献。我们通过激光加热金刚石夹具实验获得的铂金属-硅酸盐分配系数测量结果表明，在高压和高温下，铂的分配到金属中较低。因此，地幔在核-幔分化后可能富集了铂。结合这些结果并同时考虑其他地球化学约束的核心形成模型导致地幔中存在过量的铂。因此，需要后续的过程，如铁析出或硫化物分离，来去除过量的铂并解释地幔现代HSE特征。这种富含铂的地幔的痕迹可能解释了富含186Os的洋岛玄武岩熔岩。

8. Solid–liquid iron partitioning in Earth’s deep mantle（Nature, 2012）

• https://www.nature.com/articles/nature11294

Melting processes in the deep mantle have important implications for the origin of the deep-derived plumes believed to feed hotspot volcanoes such as those in Hawaii1. They also provide insight into how the mantle has evolved, geochemically and dynamically, since the formation of Earth2. Melt production in the shallow mantle is quite well understood, but deeper melting near the core–mantle boundary remains controversial. Modelling the dynamic behaviour of deep, partially molten mantle requires knowledge of the density contrast between solid and melt fractions. Although both positive and negative melt buoyancies can produce major chemical segregation between different geochemical reservoirs, each type of buoyancy yields drastically different geodynamical models. Ascent or descent of liquids in a partially molten deep mantle should contribute to surface volcanism or production of a deep magma ocean, respectively. We investigated phase relations in a partially molten chondritic-type material under deep-mantle conditions. Here we show that the iron partition coefficient between aluminium-bearing (Mg,Fe)SiO3 perovskite and liquid is between 0.45 and 0.6, so iron is not as incompatible with deep-mantle minerals as has been reported previously3. Calculated solid and melt density contrasts suggest that melt generated at the core–mantle boundary should be buoyant, and hence should segregate upwards. In the framework of the magma oceans induced by large meteoritic impacts on early Earth, our results imply that the magma crystallization should push the liquids towards the surface and form a deep solid residue depleted in incompatible elements.

9. The ‘zero charge’ partitioning behaviour of noble gases during mantle melting (Nature, 2003)

• https://www.nature.com/articles/nature01708

Noble-gas geochemistry is an important tool for understanding planetary processes from accretion to mantle dynamics and atmospheric formation1,2,3,4. Central to much of the modelling of such processes is the crystal–melt partitioning of noble gases during mantle melting, magma ascent and near-surface degassing5. Geochemists have traditionally considered the ‘inert’ noble gases to be extremely incompatible elements, with almost 100 per cent extraction efficiency from the solid phase during melting processes. Previously published experimental data on partitioning between crystalline silicates and melts has, however, suggested that noble gases approach compatible behaviour, and a significant proportion should therefore remain in the mantle during melt extraction5,6,7,8. Here we present experimental data to show that noble gases are more incompatible than previously demonstrated, but not necessarily to the extent assumed or required by geochemical models. Independent atomistic computer simulations indicate that noble gases can be considered as species of ‘zero charge’ incorporated at crystal lattice sites. Together with the lattice strain model9,10, this provides a theoretical framework with which to model noble-gas geochemistry as a function of residual mantle mineralogy.

10. Core formation and metal–silicate fractionation of osmium and iridium from gold (Nature Geosci, 2009)

• https://www.nature.com/articles/ngeo658

The abundances of the highly siderophile elements as well as their relative proportions1 in the mantle deviate from those predicted by equilibrium partitioning between metal and silicate during the formation of the Earth’s core. This discrepancy is generally explained by invoking the addition of a late veneer of extraterrestrial material to the mantle after core formation was complete2. Recently reported partition coefficients for gold, platinum and palladium3,4,5 could result in mantle abundances consistent with equilibrium partitioning. However, whether these results can be extrapolated to all highly siderophile elements, and thereby preclude the need for a late veneer, remains to be verified. Here we use high-temperature experiments to determine the metal–silicate partition coefficients for osmium, iridium and gold. On the basis of our estimates, equilibrium partitioning during core formation can explain the observed concentration of gold in the mantle, but not that of osmium and iridium. We conclude that not all highly siderophile elements were affected by core formation in the same way, and that the abundances of elements such as osmium and iridium require the addition of a late veneer.

11. Highly siderophile elements were stripped from Earth’s mantle by iron sulfide segregation (Science, 2016)

• https://doi.org/10.1126/science.aaf6919

Highly siderophile elements (HSEs) are strongly depleted in the bulk silicate Earth (BSE) but are present in near-chondritic relative abundances. The conventional explanation is that the HSEs were stripped from the mantle by the segregation of metal during core formation but were added back in near-chondritic proportions by late accretion, after core formation had ceased. Here we show that metal-silicate equilibration and segregation during Earth’s core formation actually increased HSE mantle concentrations because HSE partition coefficients are relatively low at the high pressures of core formation within Earth. The pervasive exsolution and segregation of iron sulfide liquid from silicate liquid (the “Hadean matte”) stripped magma oceans of HSEs during cooling and crystallization, before late accretion, and resulted in slightly suprachondritic palladium/iridium and ruthenium/iridium ratios.

12. The critical role of magma degassing in sulphide melt mobility and metal enrichment (Nat Commun, 2022)

• https://doi.org/10.1038/s41467-022-30107-y

Much of the world’s supply of battery metals and platinum group elements (PGE) comes from sulphide ore bodies formed in ancient sub-volcanic magma plumbing systems. Research on magmatic sulphide ore genesis mainly focuses on sulphide melt-silicate melt equilibria. However, over the past few years, increasing evidence of the role of volatiles in magmatic sulphide ore systems has come to light. High temperature-high pressure experiments presented here reveal how the association between sulphide melt and a fluid phase may facilitate the coalescence of sulphide droplets and upgrade the metal content of the sulphide melt. We propose that the occurrence of a fluid phase in the magma can favour both accumulation and metal enrichment of a sulphide melt segregated from this magma, independent of the process producing the fluid phase. Here we show how sulphide-fluid associations preserved in the world-class Noril’sk-Talnakh ore deposits, in Polar Siberia, record the processes demonstrated experimentally.

13. Primitive noble gases sampled from ocean island basalts cannot be from the Earth’s core (Nat Commun, 2022)

• https://doi.org/10.1038/s41467-022-31588-7

Noble gas isotopes in plumes require a source of primitive volatiles largely isolated in the Earth for 4.5 Gyrs. Among the proposed reservoirs, the core is gaining interest in the absence of robust geochemical and geophysical evidence for a mantle source. This is supported by partitioning data showing that sufficient He and Ne could have been incorporated into the core to source plumes today. Here we perform ab initio calculations on the partitioning of He, Ne, Ar, Kr and Xe between liquid iron and silicate melt under core forming conditions. For He our results are consistent with previous studies allowing for substantial amounts of He in the core. In contrast, the partition coefficient for Ne is three orders of magnitude lower than He. This very low partition coefficient would result in a 3He/22Ne ratio of ~103 in the core, far higher than observed in ocean island basalts (OIBs). We conclude that the core is not the source of noble gases in OIBs.

14. Terrestrial Accretion Under Oxidizing Conditions (Science, 2013)

• https://www.science.org/doi/10.1126/science.1227923

The abundance of siderophile elements in the mantle preserves the signature of core formation. On the basis of partitioning experiments at high pressure (35 to 74 gigapascals) and high temperature (3100 to 4400 kelvin), we demonstrate that depletions of slightly siderophile elements (vanadium and chromium), as well as moderately siderophile elements (nickel and cobalt), can be produced by core formation under more oxidizing conditions than previously proposed. Enhanced solubility of oxygen in the metal perturbs the metal-silicate partitioning of vanadium and chromium, precluding extrapolation of previous results. We propose that Earth accreted from materials as oxidized as ordinary or carbonaceous chondrites. Transfer of oxygen from the mantle to the core provides a mechanism to reduce the initial magma ocean redox state to that of the present-day mantle, reconciling the observed mantle vanadium and chromium concentrations with geophysical constraints on light elements in the core.

15. Partitioning of oxygen during core formation on the Earth and Mars (Nature, 2004)

• https://www.nature.com/articles/nature02473

Core formation on the Earth and Mars involved the physical separation of metal and silicate, most probably in deep magma oceans1,2,3,4. Although core-formation models explain many aspects of mantle geochemistry, they have not accounted for the large differences observed between the compositions of the mantles of the Earth (∼8?wt% FeO) and Mars (∼18?wt% FeO) or the smaller mass fraction of the martian core5,6,7. Here we explain these differences as a consequence of the solubility of oxygen in liquid iron-alloy increasing with increasing temperature. We assume that the Earth and Mars both accreted from oxidized chondritic material. In a terrestrial magma ocean, 1,200–2,000?km deep, high temperatures resulted in the extraction of FeO from the silicate magma ocean owing to high solubility of oxygen in the metal. Lower temperatures of a martian magma ocean resulted in little or no extraction of FeO from the mantle, which thus remains FeO-rich. The FeO extracted from the Earth's magma ocean may have contributed to chemical heterogeneities in the lowermost mantle8, a FeO-rich D″ layer9 and the light element budget of the core10,11.

16. Equilibrium Iron Isotope Fractionation at Core-Mantle Boundary Conditions (Science, 2009)

• https://www.science.org/doi/abs/10.1126/science.1166329

The equilibrium iron isotope fractionation between lower mantle minerals and metallic iron at core-mantle boundary conditions can be evaluated from the high-pressure 57Fe partial vibrational density of states determined by synchrotron inelastic nuclear resonant x-ray scattering spectroscopy using a diamond anvil. Ferropericlase [(Mg,Fe)O] and (Fe,Mg)SiO3–post-perovskite are enriched in heavy iron isotopes relative to metallic iron at ultrahigh pressures, as opposed to the equilibrium iron isotope fractionation between these compounds at low pressure. The enrichment of Earth and Moon basalts in heavy iron isotopes relative to those from Mars and asteroid Vesta can be explained by the equilibrium iron isotope fractionation during the segregation of Earth's core and the assumption that Earth was already differentiated before the Moon-forming “giant impact.”

17. Partitioning of palladium at high pressures and temperatures during core formation (Nature Geosci, 2008)

• https://www.nature.com/articles/ngeo180

An early equilibration of the Earth’s mantle with the metals that later formed the core may explain the concentrations of iron-loving (siderophile) elements in the mantle. However, a subset of these elements, the highly siderophile elements including palladium, are present in greater concentrations than expected. Moreover, their relative ratios are similar to those found in chondrites, that is, primitive solar-system materials1,2,3,4. On the basis of very high partition coefficients for these elements derived from experiments at low pressures and temperatures (for example, a coefficient for palladium >104), it has been argued that the high mantle concentrations of the highly siderophile elements and also of volatile elements originated from the addition of chondritic material after core formation as a ‘late veneer’1,2,3,4. Here we present experiments at higher pressures and temperatures that approximate the conditions of early Earth, and find much lower partition coefficients for palladium, about 480, consistent with an equilibration scenario. This obviates the need for a late veneer to explain the terrestrial-mantle palladium content, and calls into question traditional explanations for the origin of the Earth’s volatile elements.

18. The Earth’s missing lead may not be in the core (Nature, 2008)

• https://www.nature.com/articles/nature07375

Relative to the CI chondrite class of meteorites (widely thought to be the ‘building blocks’ of the terrestrial planets), the Earth is depleted in volatile elements. For most elements this depletion is thought to be a solar nebular signature, as chondrites show depletions qualitatively similar to that of the Earth1. On the other hand, as lead is a volatile element, some Pb may also have been lost after accretion. The unique 206Pb/204Pb and 207Pb/204Pb ratios of the Earth’s mantle suggest that some lead was lost about 50 to 130 Myr after Solar System formation2,3,4. This has commonly been explained by lead lost via the segregation of a sulphide melt to the Earth’s core5,6,7, which assumes that lead has an affinity towards sulphide. Some models, however, have reconciled the Earth’s lead deficit with volatilization8. Whichever model is preferred, the broad coincidence of U–Pb model ages with the age of the Moon9,10,11 suggests that lead loss may be related to the Moon-forming impact. Here we report partitioning experiments in metal–sulphide–silicate systems. We show that lead is neither siderophile nor chalcophile enough to explain the high U/Pb ratio of the Earth’s mantle as being a result of lead pumping to the core. The Earth may have accreted from initially volatile-depleted material, some lead may have been lost to degassing following the Moon-forming giant impact, or a hidden reservoir exists in the deep mantle with lead isotope compositions complementary to upper-mantle values; it is unlikely though that the missing lead resides in the core.

19. Trace-element fractionation in Hadean mantle generated by melt segregation from a magma ocean (Nature, 2005)

• https://www.nature.com/articles/nature03827

Calculations of the energetics of terrestrial accretion indicate that the Earth was extensively molten in its early history1. Examination of early Archaean rocks from West Greenland (3.6–3.8 Gyr old) using short-lived 146Sm–142Nd chronometry indicates that an episode of mantle differentiation took place close to the end of accretion (4.46 ± 0.11 Gyr ago)2,3,4. This has produced a chemically depleted mantle with an Sm/Nd ratio higher than the chondritic value. In contrast, application of 176Lu–176Hf systematics to 3.6–3.8-Gyr-old zircons from West Greenland indicates derivation from a mantle source with a chondritic Lu/Hf ratio5,6,7. Although an early Sm/Nd fractionation could be explained by basaltic crust formation8, magma ocean crystallization2 or formation of continental crust, the absence of coeval Lu/Hf fractionation is in sharp contrast with the well-known covariant behaviour of Sm/Nd and Lu/Hf ratios in crustal formation processes5. Here we show using mineral–melt partitioning data for high-pressure mantle minerals that the observed Nd and Hf signatures could have been produced by segregation of melt from a crystallizing magma ocean at upper-mantle pressures early in Earth's history. This residual melt would have risen buoyantly and ultimately formed the earliest terrestrial protocrust.

20. Chemical feedbacks during magma degassing control chlorine partitioning and metal extraction in volcanic arcs (Nat Commun, 2021)

• https://doi.org/10.1038/s41467-021-21887-w

Hydrous fluids released from subducting oceanic lithosphere fuel arc magmatism and associated hydrothermal mineralization, including formation of porphyry copper deposits. Critical magma degassing parameters are the depth, chemistry and style of fluid release during magma ascent, notably the behaviour of chlorine, a key metal-transporting ligand. Currently, understanding is limited by restricted data on fluid-melt partitioning of chlorine as a function of pressure and magma chemistry, and the complex interplay between the two that occurs in polybaric magmatic systems. Here we present experimental determinations of chlorine partitioning as a function of fluid and melt composition at pressures from 50 to 800 MPa. We provide, for the first time, a quantitative understanding of chlorine and copper evolution that is valid for shallow, deep or transcrustal differentiation and degassing. Monte Carlo simulations using our new data reproduce the chemical evolution of melt inclusions from arc volcanoes and fluid inclusions from upper crustal intrusions and porphyry copper deposits. Our results not only provide a novel chemical framework for understanding magma degassing, but quantify the primacy of magmatic chlorine concentration at the point of fluid saturation in promoting efficient copper extraction from magmas.

21. Experimental evidence for hydrogen incorporation into Earth’s core (Nat Commun, 2021)

• https://doi.org/10.1038/s41467-021-22035-0

Hydrogen is one of the possible alloying elements in the Earth’s core, but its siderophile (iron-loving) nature is debated. Here we experimentally examined the partitioning of hydrogen between molten iron and silicate melt at 30–60 gigapascals and 3100–4600 kelvin. We find that hydrogen has a metal/silicate partition coefficient DH ≥ 29 and is therefore strongly siderophile at conditions of core formation. Unless water was delivered only in the final stage of accretion, core formation scenarios suggest that 0.3–0.6 wt% H was incorporated into the core, leaving a relatively small residual H2O concentration in silicates. This amount of H explains 30–60% of the density deficit and sound velocity excess of the outer core relative to pure iron. Our results also suggest that hydrogen may be an important constituent in the metallic cores of any terrestrial planet or moon having a mass in excess of ~10% of the Earth.

22. The Earth’s core as a reservoir of water (Nat. Geosci, 2020)

• https://doi.org/10.1038/s41561-020-0578-1

Current estimates of the budget and distribution of water in the Earth have large uncertainties, most of which are due to the lack of information about the deep Earth. Recent studies suggest that the Earth could have gained a considerable amount of water during the early stages of its evolution from the hydrogen-rich solar nebula, and that a large amount of the water in the Earth may have partitioned into the core. Here we calculate the partitioning of water between iron and silicate melts at 20–135 GPa and 2,800–5,000 K, using ab initio molecular dynamics and thermodynamic integration techniques. Our results indicate a siderophile nature of water at core–mantle differentiation and core–mantle boundary conditions, which weakens with increasing temperature; nevertheless, we found that water always partitions strongly into the iron liquid under core-formation conditions for both reducing and oxidizing scenarios. The siderophile nature of water was also verified by an empirical-counting method that calculates the distribution of hydrogen in an equilibrated iron and silicate melt. We therefore conclude that the Earth’s core may act as a large reservoir that contains most of the Earth’s water. In addition to constraining the accretion models of volatile delivery, the findings may partially account for the low density of the Earth’s core implied by measured seismic velocities.

23. Low hydrogen contents in the cores of terrestrial planets (Sci Adv, 2018)

• https://doi.org/10.1126/sciadv.1701876

Hydrogen has been thought to be an important light element in Earth’s core due to possible siderophile behavior during core-mantle segregation. We reproduced planetary differentiation conditions using hydrogen contents of 450 to 1500 parts per million (ppm) in the silicate phase, pressures of 5 to 20 GPa, oxygen fugacity varying within IW-3.7 and IW-0.2 (0.2 to 3.7 log units lower than iron-wüstite buffer), and Fe alloys typical of planetary cores. We report hydrogen metal-silicate partition coefficients of ~2 × 10−1, up to two orders of magnitude lower than reported previously, and indicative of lithophile behavior. Our results imply H contents of ~60 ppm in the Earth and Martian cores. A simple water budget suggests that 90% of the water initially present in planetary building blocks was lost during planetary accretion. The retained water segregated preferentially into planetary mantles.

24. Helium in Earth’s early core (Nature Geosci, 2013)

• https://doi.org/10.1038/ngeo1959

The observed escape of the primordial helium isotope, 3He, from the Earth’s interior indicates that primordial helium survived the energetic process of planetary accretion and has been trapped within the Earth to the present day. Two distinct reservoirs in the Earth’s interior have been invoked to account for variations in the 3He/4He ratio observed at the surface in ocean basalts: a conventional depleted mantle source and a deep, still enigmatic, source that must have been isolated from processing throughout Earth history. The Earth’s iron-based core has not been considered a potential helium source because partitioning of helium into metal liquid has been assumed to be negligible. Here we determine helium partitioning in experiments between molten silicates and iron-rich metal liquids at conditions up to 16 GPa and 3,000 K. Analyses of the samples by ultraviolet laser ablation mass spectrometry yield metal–silicate helium partition coefficients that range between 4.7×10−3 and 1.7×10−2 and suggest that significant quantities of helium may reside in the core. Based on estimated concentrations of primordial helium, we conclude that the early core could have incorporated enough helium to supply deep-rooted plumes enriched in 3He throughout the age of the Earth.

25. I/Pu reveals Earth mainly accreted from volatile-poor differentiated planetesimals (Sci Adv, 2023)

• https://doi.org/10.1126/sciadv.adg9213

The observation that mid-ocean ridge basalts had ~3× higher iodine/plutonium ratios (inferred from xenon isotopes) compared to ocean island basalts holds critical insights into Earth’s accretion. Understanding whether this difference stems from core formation alone or heterogeneous accretion is, however, hindered by the unknown geochemical behavior of plutonium during core formation. Here, we use first-principles molecular dynamics to quantify the metal-silicate partition coefficients of iodine and plutonium during core formation and find that both iodine and plutonium partly partition into metal liquid. Using multistage core formation modeling, we show that core formation alone is unlikely to explain the iodine/plutonium difference between mantle reservoirs. Instead, our results reveal a heterogeneous accretion history, whereby predominant accretion of volatile-poor differentiated planetesimals was followed by a secondary phase of accretion of volatile-rich undifferentiated meteorites. This implies that Earth inherited part of its volatiles, including its water, from late accretion of chondrites, with a notable carbonaceous chondrite contribution.