Publications

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In Press
Deng, Z, Moynier F, van Zuilen K, Sossi P, Pringle EA, Chaussidon M.  In Press.  Lack of resolvable titanium stable isotopic variations in bulk chondrites. Geochimica et Cosmochimica Acta.   10.1016/j.gca.2018.06.016   Abstract

Titanium and calcium are both refractory lithophile elements. Significant stable isotopic variations on Ti and Ca have been documented within calcium, aluminum-rich inclusions (CAIs) in carbonaceous chondrites. To trace the condensation history of Ti in the solar nebula, we conducted a high-precision double-spike Ti stable isotopic study on a large set of chondrites. The studied chondrites have a homogeneous bulk Ti stable isotopic composition (δ49/47TiIPGP-Ti = −0.069 ± 0.018‰, 2se, n = 22, i.e., the per mil deviation of the 49Ti/47Ti ratios relative to the IPGP-Ti reference material). The homogeneity across eleven chondrite groups implies that chondrites have acquired, through the condensation sequence at equilibrium, the average stable isotopic composition of Ti in the refractory solids that condensed early in the solar nebula. In contrast, the light Ca stable isotopic compositions of bulk chondrites can be attributed to either the presence of CAIs (CV-, CM- and CO-type) or parent-body aqueous alteration (CR- and CI-type).

Mahan, B, Moynier F, Siebert J, Gueguen B, Agranier A, Pringle EA, Bollard J, Connelly J, Bizzarro M.  In Press.  Volatile element evolution of chondrules through time. Proceedings of the National Academy of Science USA.   10.1073/pnas.1807263115   Abstract

Chondrites and their main components, chondrules, are our guides into the evolution of the Solar System. Investigating the history of chondrules, including their volatile element history and the prevailing conditions of their formation, has implications not only for the understanding of chondrule formation and evolution but for that of larger bodies such as the terrestrial planets. Here we have determined the bulk chemical composition—rare earth, refractory, main group, and volatile element contents—of a suite of chondrules previously dated using the Pb−Pb system. The volatile element contents of chondrules increase with time from ∼1 My after Solar System formation, likely the result of mixing with a volatile-enriched component during chondrule recycling. Variations in the Mn/Na ratios signify changes in redox conditions over time, suggestive of decoupled oxygen and volatile element fugacities, and indicating a decrease in oxygen fugacity and a relative increase in the fugacities of in-fluxing volatiles with time. Within the context of terrestrial planet formation via pebble accretion, these observations corroborate the early formation of Mars under relatively oxidizing conditions and the protracted growth of Earth under more reducing conditions, and further suggest that water and volatile elements in the inner Solar System may not have arrived pairwise.

2018
Ducasse, T, Gourgiotis A, Pringle EA, Moynier F, Frugier P, Jollivet P, Gin S.  2018.  Alteration of synthetic basaltic glass in silica saturated conditions: Analogy with nuclear glass. Applied Geochemistry. 97:19-31.   10.1016/j.apgeochem.2018.08.001   Abstract

This study investigates the analogy between basaltic and borosilicate glasses of nuclear interest, by focusing on mechanisms controlling glass dissolution under silica saturation conditions. These conditions are representative of a non- or slowly renewed contacting solution, favouring the formation of a potentially passivating silica rich gel layer and secondary phases. Laboratory batch experiments were performed with synthetic basaltic glass altered at 90 °C, at pH 7 in a saturated 29Si-doped aqueous solution for more than 600 days. Using elemental and isotopic solution analysis and solid characterizations by SEM, TEM and ToF-SIMS, we show that basaltic glass corrodes at an unexpectedly high and constant dissolution rate of 4 × 10−3 g m−2 d−1 associated with the absence of passivating gel. Our results highlight the fact that the dissolution rate is controlled by the hydrolysis of the glassy network, sustained by the precipitation of clay-type minerals and amorphous silica. When tested in similar conditions, the International Simple Glass (ISG), a six oxide borosilicate glasses of nuclear interest displays a much lower rate limited by water diffusion through a passivating layer. The different behavior of the two glasses is explained by their ability to form secondary crystalline phases at the expense of an amorphous passivating film.

Mahan, B, Moynier F, Beck P, Pringle EA, Siebert J.  2018.  A history of violence: insights into post-accretionary heating in carbonaceous chondrites from volatile element abundances, Zn isotopes, and water contents. Geochimica et Cosmochimica Acta. 220:19-35.   10.1016/j.gca.2017.09.027   Abstract

Zinc metal–silicate fractionation provides experimental access to the conditions of core formation and Zn has been used to estimate the S contents of the Earth’s core and of the bulk Earth, assuming that they share similar volatility and that Zn was not partitioned into the Earth’s core. Therefore, Zn provides both direct and indirect information into the origin and eventual fate of volatile and siderophile elements on Earth. However, the partitioning of Zn between metal and silicate – as well as the associated isotopic fractionation – is not well known. We have conducted a suite of partitioning experiments to characterize Zn elemental partitioning and isotopic fractionation between metal and silicate as a function of time, temperature, and com- position. Experiments were conducted at 2 GPa and temperatures from 1473 K to 2273 K in a piston cylinder apparatus, with run durations from 5 to 240 min for four distinct starting materials. Chemical and isotopic equilibrium is achieved within 10 min of experimental outset. Zinc metal–silicate isotopic fractionation displays no resolvable dependence on temperature, composition, or oxygen fugacity within the data set. Therefore, the Zn isotopic composition of silicate phases can be used as a proxy for bulk telluric bodies. Partitioning results from this study and data from literature were used to robustly parameterize Zn metal–silicate partitioning as a function of temperature, pressure, and redox state. Using this parametric characterization and viable formation conditions, we have estimated a range of Zn contents in the cores of iron meteorite parent bodies (i.e. iron meteorites) of $0.1–150 ppm, in good agreement with natural observations. We have also calculated the first geochemical estimates for the Zn contents of the Earth’s core and of the bulk Earth, at 242 ± 107 ppm and 114 ± 34 ppm (respectively), that consider the slightly siderophile behavior of Zn. These estimates of the Zn contents of the Earth’s core and bulk Earth are significantly higher than previous estimates 0–30 ppm and 24–47 ppm, respectively. Assuming similar volatility for S and Zn, a chondritic S/Zn ratio, and considering our new estimates, we have calculated a geochemical upper bound for the S content of the Earth’s core of 6.3 ± 1.9 wt%. This indicates that S may be a major contributor to the density deficit of the Earth’s core or that the S/Zn ratio for the Earth is non-chondritic.

2017
Bollard, J, Connelly JN, Whitehouse MJ, Pringle EA, Bonal L, Jørgensen JK, Nordlund Å, Moynier F, Bizzarro M.  2017.  Early formation of planetary building blocks inferred from Pb isotopic ages of chondrules. Science Advances. 3:e1700407.   10.1126/sciadv.1700407   Abstract

The most abundant components of primitive meteorites (chondrites) are millimeter-sized glassy spherical chondrules formed by transient melting events in the solar protoplanetary disk. Using Pb-Pb dates of 22 individual chondrules, we show that primary production of chondrules in the early solar system was restricted to the first million years after the formation of the Sun and that these existing chondrules were recycled for the remaining lifetime of the protoplanetary disk. This finding is consistent with a primary chondrule formation episode during the early high-mass accretion phase of the protoplanetary disk that transitions into a longer period of chondrule reworking. An abundance of chondrules at early times provides the precursor material required to drive the efficient and rapid formation of planetary objects via chondrule accretion.

Pringle, EA, Moynier F.  2017.  Rubidium isotopic composition of the Earth, meteorites, and the Moon: Evidence for the origin of volatile loss during planetary accretion. Earth and Planetary Science Letters. 473:62-70.   10.1016/j.epsl.2017.05.033   Abstract

Understanding the origin of volatile element variations in the inner Solar System has long been a goal of cosmochemistry, but many early studies searching for the fingerprint of volatile loss using stable isotope systems failed to find any resolvable variations.

An improved method for the chemical purification of Rb for high-precision isotope ratio measurements by multi-collector inductively-coupled-plasma mass-spectrometry. This method has been used to measure the Rb isotopic composition for a suite of planetary materials, including carbonaceous, ordinary, and enstatite chondrites, as well as achondrites (eucrite, angrite), terrestrial igneous rocks (basalt, andesite, granite), and Apollo lunar samples (mare basalts, alkali suite). Volatile depleted bodies (e.g. HED parent body, thermally metamorphosed meteorites) are enriched in the heavy isotope of Rb by up to several per mil compared to chondrites, suggesting volatile loss by evaporation at the surface of planetesimals. In addition, the Moon is isotopically distinct from the Moon in Rb. The variations in Rb isotope compositions in the volatile-poor samples are attributed to volatile loss from planetesimals during accretion. This suggests that either the Rb (and other volatile elements) were lost during or following the giant impact or by evaporation earlier during the accretion history of Theia.

Amsellem, 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 chondrule- rich accretion model for planetary embryos.

Pringle, EA, Moynier F, Beck P, Paniello R, Hezel DC.  2017.  The origin of volatile element depletion in early solar system material: Clues from Zn isotopes in chondrules. Earth and Planetary Science Letters. 468:62-71.   10.1016/j.epsl.2017.04.002   Abstract

Volatile lithophile elements are depleted in the different planetary materials to various degrees, but the origin of these depletions is still debated. Stable isotopes of moderately volatile elements such as Zn can be used to understand the origin of volatile element depletions. Samples with significant volatile element depletions, including the Moon and terrestrial tektites, display heavy Zn isotope compositions (i.e. enrichment of 66Zn vs. 64Zn), consistent with kinetic Zn isotope fractionation during evaporation. However, Luck et al. (2005) found a negative correlation between δ66Zn and 1/[Zn] between CI, CM, CO, and CV chondrites, opposite to what would be expected if evaporation caused the Zn abundance variations among chondrite groups.

We have analyzed the Zn isotope composition of multiple samples of the major carbonaceous chondrite classes: CI (1), CM (4), CV (2), CO (4), CB (2), CH (2), CK (4), and CK/CR (1). The bulk chondrites define a negative correlation in a plot of δ66Zn vs 1/[Zn], confirming earlier results that Zn abundance variations among carbonaceous chondrites cannot be explained by evaporation. Exceptions are CB and CH chondrites, which display Zn systematics consistent with a collisional formation mechanism that created enrichment in heavy Zn isotopes relative to the trend defined by CI–CK.

We further report Zn isotope analyses of chondrite components, including chondrules from Allende (CV3) and Mokoia (CV3), as well as an aliquot of Allende matrix. All chondrules are enriched in light Zn isotopes (∼500 ppm on 66Zn/64Zn) relative to the bulk, contrary to what would be expected if Zn were depleted during evaporation, on the other hand the matrix has a complementary heavy isotope composition. We report sequential leaching experiments in un-equilibrated ordinary chondrites, which show sulfides are isotopically heavy compared to silicates and the bulk meteorite by ca. +0.65 per mil on 66Zn/64Zn. We suggest isotopically heavy sulfides were removed from either chondrules or their precursors, thereby producing the light Zn isotope enrichments in chondrules.

Mahan, B, Siebert J, Pringle EA, Moynier F.  2017.  Elemental partitioning and isotopic fractionation of Zn between metal and silicate and geochemical estimation of the S content of the Earth’s core. Geochimica et Cosmochimica Acta. 196:252-270.   10.1016/j.gca.2016.09.013   Abstract

Zinc metal–silicate fractionation provides experimental access to the conditions of core formation and Zn has been used to estimate the S contents of the Earth’s core and of the bulk Earth, assuming that they share similar volatility and that Zn was not partitioned into the Earth’s core. Therefore, Zn provides both direct and indirect information into the origin and eventual fate of volatile and siderophile elements on Earth. However, the partitioning of Zn between metal and silicate – as well as the associated isotopic fractionation – is not well known. We have conducted a suite of partitioning experiments to characterize Zn elemental partitioning and isotopic fractionation between metal and silicate as a function of time, temperature, and composition. Experiments were conducted at 2 GPa and temperatures from 1473 K to 2273 K in a piston cylinder apparatus, with run durations from 5 to 240 min for four distinct starting materials. Chemical and isotopic equilibrium is achieved within 10 min of experimental outset. Zinc metal–silicate isotopic fractionation displays no resolvable dependence on temperature, composition, or oxygen fugacity within the data set. Therefore, the Zn isotopic composition of silicate phases can be used as a proxy for bulk telluric bodies. Partitioning results from this study and data from literature were used to robustly parameterize Zn metal–silicate partitioning as a function of temperature, pressure, and redox state. Using this parametric characterization and viable formation conditions, we have estimated a range of Zn contents in the cores of iron meteorite parent bodies (i.e. iron meteorites) of 0.1–150 ppm, in good agreement with natural observations. We have also calculated the first geochemical estimates for the Zn contents of the Earth’s core and of the bulk Earth, at 242 ± 107 ppm and 114 ± 34 ppm (respectively), that consider the slightly siderophile behavior of Zn. These estimates of the Zn contents of the Earth’s core and bulk Earth are significantly higher than previous estimates 0–30 ppm and 24–47 ppm, respectively. Assuming similar volatility for S and Zn, a chondritic S/Zn ratio, and considering our new estimates, we have calculated a geochemical upper bound for the S content of the Earth’s core of 6.3 ± 1.9 wt%. This indicates that S may be a major contributor to the density deficit of the Earth’s core or that the S/Zn ratio for the Earth is non-chondritic.
! 2016 Elsevier Ltd. All rights reserved.

2016
Pringle, EA, Moynier F, Savage PS, Jackson MG, Moreira M, Day JMD.  2016.  Silicon isotopes reveal recycled altered oceanic crust in the mantle sources of Ocean Island Basalts. Geochimica et Cosmochimica Acta. 189:282-295.   10.1016/j.gca.2016.06.008   AbstractWebsite

The study of silicon (Si) isotopes in Ocean Island Basalts (OIB) has the potential to discern between different models for the origins of geochemical heterogeneities in the mantle. Relatively large (∼several per mil per atomic mass unit) Si isotope fractionation occurs in low-temperature environments during biochemical and geochemical precipitation of dissolved Si, where the precipitate is preferentially enriched in the lighter isotopes relative to the dissolved Si. In contrast, only a limited range (∼tenths of a per mil) of Si isotope fractionation has been observed from high-temperature igneous processes. Therefore, Si isotopes may be useful as tracers for the presence of crustal material within OIB mantle source regions that experienced relatively low-temperature surface processes in a manner similar to other stable isotope systems, such as oxygen. Characterizing the isotopic composition of the mantle is also of central importance to the use of the Si isotope system as a basis for comparisons with other planetary bodies (e.g., Moon, Mars, asteroids).

Here we present the first comprehensive suite of high-precision Si isotope data obtained by MC-ICP-MS for a diverse suite of OIB. Samples originate from ocean islands in the Pacific, Atlantic, and Indian Ocean basins and include representative end-members for the EM-1, EM-2, and HIMU mantle components. On average, δ30Si values for OIB (−0.32 ± 0.09‰, 2 sd) are in general agreement with previous estimates for the δ30Si value of Bulk Silicate Earth (−0.29 ± 0.07‰, 2 sd; Savage et al., 2014). Nonetheless, some small systematic variations are present; specifically, most HIMU-type (Mangaia; Cape Verde; La Palma, Canary Islands) and Iceland OIB are enriched in the lighter isotopes of Si (δ30Si values lower than MORB), consistent with recycled altered oceanic crust and lithospheric mantle in their mantle sources.

2015
Moynier, F, Pringle EA, Bouvier A, Moureau J.  2015.  Barium stable isotope composition of the Earth, meteorites, and calcium–aluminum-rich inclusions. Chemical Geology. 413:1-6.   10.1016/j.chemgeo.2015.08.002   Abstract

High-precision stable Ba isotope ratios are reported in a variety of terrestrial samples, undifferentiated primitive meteorites, and calcium–aluminum-rich inclusions (CAIs) from the Allende chondrite. All whole-rock terrestrial and meteorite samples are isotopically indistinguishable at a 50 parts per million (ppm) level per atomic mass unit (amu). Three CAIs are isotopically light, with δ138/137Ba (permil deviation of the 138Ba/137Ba ratio from a terrestrial standard) values down to −0.6‰ compared to whole-rock meteorites, whereas the matrix is enriched in heavy isotopes (δ138/137Ba: +0.2‰). Similar light isotope enrichments in CAIs have been previously observed for Eu, Sr, and Ca, while for most other elements CAIs are enriched in the heavier isotopes (e.g. Mg, Fe). Kinetic isotopic fractionation is a possible explanation for the enrichment in the lightest isotopes, either by condensation from a vapor phase enriched in light isotopes by kinetic effects or by kinetic fractionation during non-equilibrium condensation of an undercooled gas as suggested for Ca isotopes. However, the common property of Ba, Eu, and Sr is that they all have a low first ionization potential. We suggest that electromagnetic sorting of ionized species in the early Solar System is a possible alternative mechanism to explain the depletion in heavy isotopes observed in refractory inclusions for those elements.

Fujii, T, Pringle EA, Chaussidon M, Moynier F.  2015.  Isotope fractionation of Si in protonation/deprotonation reaction of silicic acid: A new pH proxy. Geochimica et Cosmochimica Acta. 168:193-205.   10.1016/j.gca.2015.07.003   Abstract

Isotopic fractionation of Si in protonation/deprotonation reactions of monomeric silicic acids was theoretically and experimentally studied. The reduced partition function ratio for Si (as 1000 ln b) complexes was theoretically estimated by ab initio methods. Three permil of isotope fractionation was estimated to be possible for the 28Si-30Si isotope pair. This prediction was experimentally demonstrated by multi-collector inductively coupled plasma mass spectrometer measurements of Si-bearing aqueous solutions, for which equilibrated Si(OH)4 and SiO(OH)3 were separated using an anionic exchange column. The results create a new possibility for the application of Si isotopes as proxies for paleo-pH in the 9 < pH < 12 range.

2014
Pringle, EA, Moynier F, Savage PS, Badro J, Barrat JA.  2014.  Silicon isotopes in angrites and volatile loss in planetesimals. Proceedings of the National Academy of Sciences USA. 111(48):17029–17032.   10.1073/pnas.1418889111   Abstract

Inner solar system bodies, including the Earth, Moon, and asteroids, are depleted in volatile elements relative to chondrites. Hypotheses for this volatile element depletion include incomplete condensation from the solar nebula and volatile loss during energetic impacts. These processes are expected to each produce characteristic stable isotope signatures. However, processes of planetary differentiation may also modify the isotopic composition of geochemical reservoirs. Angrites are rare meteorites that crystallized only a few million years after calcium–aluminum-rich inclusions and exhibit extreme depletions in volatile elements relative to chondrites, making them ideal samples with which to study volatile element depletion in the early solar system. Here we present high-precision Si isotope data that show angrites are enriched in the heavy isotopes of Si relative to chondritic meteorites by 50–100 ppm/amu. Silicon is sufficiently volatile such that it may be isotopically fractionated during incomplete condensation or evaporative mass loss, but theoretical calculations and experimental results also predict isotope fractionation under specific conditions of metal–silicate differentiation. We show that the Si isotope composition of angrites cannot be explained by any plausible core formation scenario, but rather reflects isotope fractionation during impact-induced evaporation. Our results indicate planetesimals initially formed from volatile-rich material and were subsequently depleted in volatile elements during accretion.

2013
Pringle, EA, Savage PS, Jackson MG, Barrat JA, Moynier F.  2013.  Si isotope homogeneity of the Solar Nebula. The Astrophysical Journal. 779:123-127.   10.1088/0004-637X/779/2/123   Abstract

The presence or absence of variations in the mass-independent abundances of Si isotopes in bulk meteorites provides important clues concerning the evolution of the early solar system. No Si isotopic anomalies have been found within the level of analytical precision of 15 ppm in 29Si/28Si across a wide range of inner solar system materials, including terrestrial basalts, chondrites, and achondrites. A possible exception is the angrites, which may exhibit small excesses of 29Si. However, the general absence of anomalies suggests that primitive meteorites and differentiated planetesimals formed in a reservoir that was isotopically homogenous with respect to Si. Furthermore, the lack of resolvable anomalies in the calcium–aluminum-rich inclusion measured here suggests that any nucleosynthetic anomalies in Si isotopes were erased through mixing in the solar nebula prior to the formation of refractory solids. The homogeneity exhibited by Si isotopes may have implications for the distribution of Mg isotopes in the solar nebula. Based on supernova nucleosynthetic yield calculations, the expected magnitude of heavy-isotope overabundance is larger for Si than for Mg, suggesting that any potential Mg heterogeneity, if present, exists below the 15 ppm level.

Pringle, EA, Savage PS, Badro J, Barrat J-A, Moynier F.  2013.  Redox state during core formation on asteroid 4-Vesta. Earth and Planetary Science Letters. 373:75-82.   doi:10.1016/j.epsl.2013.04.012   Abstract

Core formation is the main differentiation event in the history of a planet. However, the chemical composition of planetary cores and the physicochemical conditions prevailing during core formation remain poorly understood. The asteroid 4-Vesta is the smallest extant planetary body known to have differentiated a metallic core. Howardite, Eucrite, Diogenite (HED) meteorites, which are thought to sample 4-Vesta, provide us with an opportunity to study core formation in planetary embryos.

Partitioning of elements between the core and mantle of a planet fractionates their isotopes according to formation conditions. One such element, silicon, shows large isotopic fractionation between metal and silicate, and its partitioning into a metallic core is only possible under very distinctive conditions of pressure, oxygen fugacity and temperature. Therefore, the silicon isotope system is a powerful tracer with which to study core formation in planetary bodies. Here we show through high- precision measurement of Si stable isotopes that HED meteorites are significantly enriched in the heavier isotopes compared to chondrites. This is consistent with the core of 4-Vesta containing at least 1 wt% of Si, which in turn suggests that 4-Vesta's differentiation occurred under more reducing conditions (ΔIW∼−4) than those previously suggested from analysis of the distribution of moderately siderophile elements in HEDs.