A reassessment of the iron isotope composition of the Moon and its implications for the accretion and differentiation of terrestrial planets

Poitrasson, Franck; Zambardi, Thomas; Magna, Tomáš; Neal, C. R.

doi:10.1016/j.gca.2019.09.035

Cited by 24 publications

(9 citation statements)

References 139 publications

(278 reference statements)

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“…In these contexts, calculations agree that there is no significant Fe isotope fractionation between silicate minerals. This inference is supported by experimental determination of isotopic partitioning (Prissel et al, 2018) and interplanetary comparisons (Poitrasson et al, 2019). However, considering the upper crust formation, our results evidence significant iron isotope fractionation between Fe 2+ -bearing minerals, even with similar Fe-O bond lengths.…”

Section: -Geochemical Implications On Magmatic Differentiationsupporting

confidence: 79%

“…This is a critical parameter of the modeling that calls for a thorough investigation of the melt isotopic properties by first-principles molecular dynamics. Therefore, and although unknowns remain, such as the actual  factors of the evolving silicate melts, this modeling, involving new and self-consistent theoretical mineral Fe isotope fractionation factors to reduce the under-constrained nature of such multi-parametric modeling (Dauphas et al, 2017;Poitrasson et al, 2019), suggests that fractional crystallization is a viable way to interpret the global Fe isotope trend observed among terrestrial igneous rocks (Fig. 7).…”

Section: -Geochemical Implications On Magmatic Differentiationmentioning

confidence: 99%

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First-principles calculation of iron and silicon isotope fractionation between Fe-bearing minerals at magmatic temperatures: The importance of second atomic neighbors

Rabin

Blanchard

Pinilla

et al. 2021

Geochimica et Cosmochimica Acta

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In order to elucidate the processes involved in iron and silicon isotopes partitioning during magmatic differentiation, it is essential to know the precise value of equilibrium fractionation factors between the main minerals present in the evolving silicic melts. In this study, we performed first-principles calculations based on the density functional theory to determine the equilibrium iron and silicon isotopes fractionation factors between eleven relevant silicate or oxide minerals in the context of magmatic differentiation, namely: aegirine, hedenbergite, augite, diospide, enstatite, fayalite, hortonolite, Fe-rich and Fe-free forsterites, magnetite and ulvospinel. Results show that Fe 2+ -bearing silicate minerals display significant differences in iron isotope fractionation factors that cannot be neglected, even at high temperature (1000°C). Various physical and chemical parameters control the iron isotopic fractionation of silicate minerals. However, the main parameter, after temperature and the iron oxidation state, is the nature and number of iron second neighbors (i.e. the local chemical composition around Fe atoms). This conclusion is also valid for silicon isotopes. In the investigated nesosilicates and inosilicates, silicon isotope reduced partition function ratios (also called -factors) show no correlation with the average Si-O bond length, which remains almost constant, but Si factors are correlated with the local chemical composition of the minerals. Fractional crystallization is one of the mechanisms, which could explain the evolution of iron isotopic compositions during magmatic differentiation. Using the present theoretical set of equilibrium fractionation factors allows us to assess the impact of inter-mineral isotopic fractionations, and shows that pyroxene appears to be the main mineral phase driving the isotopic evolution to a heavier signature in the most evolved lavas.

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Section: -Geochemical Implications On Magmatic Differentiationsupporting

confidence: 79%

Section: -Geochemical Implications On Magmatic Differentiationmentioning

confidence: 99%

First-principles calculation of iron and silicon isotope fractionation between Fe-bearing minerals at magmatic temperatures: The importance of second atomic neighbors

Rabin

Blanchard

Pinilla

et al. 2021

Geochimica et Cosmochimica Acta

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“…Previous studies observed a bimodal distribution of δ 57 Fe values for lunar low-Ti and high-Ti basalts: higher δ 57 Fe values in high-Ti basalts were attributed to the presence of ilmenite during partial melting (Sossi and Moynier, 2017;Sossi and O'Neill, 2017), which is consistent with experimental studies (Longhi, 1992 and references therein) as well as our Ta/Hf and δ 49 Ti data. However, intra-group variation in δ 57 Fe of low-Ti basalts was not observed (Weyer et al, 2005;Sossi and Moynier, 2017;Poitrasson et al, 2019) as the δ 57 Fe of low-Ti basalts is mainly controlled by fractional crystallisation of olivine and pyroxene, which would preferentially incorporate light Fe isotopes, similar to ilmenite (Δ 57 Fe Ilm-Ol = +0.01 ‰; Sossi and O'Neill, 2017). Thus, δ 49 Ti appear more appropriate to discriminate better between the petrogenetic processes culminating in lunar basalts.…”

Section: Discussionmentioning

confidence: 99%

Unravelling lunar mantle source processes via the Ti isotope composition of lunar basalts

Horan¹,

Hilton

McCoy-West

et al. 2020

Geochem. Persp. Let.

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Formation and crystallisation of the Lunar Magma Ocean (LMO) was one of the most incisive events during the early evolution of the Moon. Lunar Magma Ocean solidification concluded with the coeval formation of K-, REE-and P-rich components (KREEP) and an ilmenite-bearing cumulate (IBC) layer. Gravitational overturn of the lunar mantle generated eruptions of basaltic rocks with variable Ti contents, of which their δ 49 Ti variations may now reflect variable mixtures of ambient lunar mantle and the IBC. To better understand the processes generating the spectrum of lunar low-Ti and high-Ti basalts and the role of Ti-rich phases such as ilmenite, we determined the mass dependent Ti isotope composition of four KREEP-rich samples, 12 low-Ti, and eight high-Ti mare basalts by using a 47 Ti-49 Ti double spike. Our data reveal significant variations in δ 49 Ti for KREEPrich samples (+0.117 to +0.296 ‰) and intra-group variations in the mare basalts (-0.030 to +0.055 ‰ for low-Ti and +0.009 to +0.115 ‰ for high-Ti basalts). We modelled the δ 49 Ti of KREEP using previously published HFSE data as well as the δ 49 Ti evolution during fractional crystallisation of the LMO. Both approaches yield δ 49 Ti KREEP similar to measured values and are in excellent agreement with previous studies. The involvement of ilmenite in the petrogenesis of the lunar mare basalts is further evaluated by combining our results with element ratios of HFSE, U and Th, revealing that partial melting in an overturned lunar mantle and fractional crystallisation of ilmenite must be the main processes accounting for mass dependent Ti isotope variations in lunar basalts. Based on our results we can also exclude formation of high-Ti basalts by simple assimilation of ilmenite by ascending melts from the depleted lunar mantle. Rather, our data are in accord with melting of these basalts from a hybrid mantle source formed in the aftermath of gravitational lunar mantle overturn, which is in good agreement with previous Fe isotope data.

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“…Chromium isotope data are also compiled, since it has been suggested recently that Cr isotope fractionation between the Moon and Earth is a result of evaporative processes (Sossi et al 2018). For this reason, we have also compiled data from Mg and Fe isotopes (Poitrasson et al 2019;Sedaghatpour & Jacobsen 2019;Sossi & Moynier 2017), with similar 50% condensation temperatures as Cr. Finally, we have added Ca isotope data to the excel sheet as a reference for refractory element signatures (Valdes et al 2014).…”

Section: Limitations Within the Lunar Mve Datasetmentioning

confidence: 99%

Evidence for Transient Atmospheres during Eruptive Outgassing on the Moon

2020

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Events following the giant impact formation of the Moon are thought to have led to volatile depletion and concurrent mass-dependent fractionation of the isotopes of moderately volatile elements (MVE). The detailed processes and conditions surrounding this episode remain obscured and are not unified by a single model for all volatile elements and compounds. Using available data, including new Zn isotope data for eight lunar samples, we demonstrate that the isotopic fractionation of MVE in the Moon is best expressed by nonideal Rayleigh distillation, approaching the fractionation factor α using the reduced masses of the evaporated isotopologs. With these calculations, a best fit for the data is obtained when the lunar MVE isotope data are normalized to ordinary or enstatite chondrites ( ), rather than a bulk silicate Earth composition. This analysis further indicates that the parent body from which the Moon formed cannot have partitioned S into its core based on S isotope compositions of lunar rocks. The best fit between and modeled nonideal Rayleigh fractionation is defined by a slope that corresponds to a saturation index of 90% ± 4%. In contrast, the older Highland suite is defined by a saturation index of 75% ± 2%, suggesting that the vapor phase pressure was higher during mare basalt eruptions. This provides the first tangible evidence that the Moon was veiled by a thin atmosphere during mare basalt eruption events spanning at least from 3.8 to 3 billion years ago and implies that MVE isotope fractionation dominantly occurred after the Moon had accreted.

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A reassessment of the iron isotope composition of the Moon and its implications for the accretion and differentiation of terrestrial planets

Cited by 24 publications

References 139 publications

First-principles calculation of iron and silicon isotope fractionation between Fe-bearing minerals at magmatic temperatures: The importance of second atomic neighbors

First-principles calculation of iron and silicon isotope fractionation between Fe-bearing minerals at magmatic temperatures: The importance of second atomic neighbors

Unravelling lunar mantle source processes via the Ti isotope composition of lunar basalts

Evidence for Transient Atmospheres during Eruptive Outgassing on the Moon

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