Bulk chondrite variability in mass independent magnesium isotope compositions – Implications for initial solar system 26Al/27Al and the timing of terrestrial accretion

Luu, Tu-Han; Hin, Remco C.; Coath, C. D.; Elliott, Tim

doi:10.1016/j.epsl.2019.06.033

Cited by 21 publications

(29 citation statements)

References 47 publications

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“…As discussed above, our measurements argue against the validity of this value. Moreover, subsequent work on bulk chondrites has illustrated that their variable ′ 26 Mg can be explained by their variable Al/Mg from a common canonical initial ′ 26 Mg and 26 Al/ 27 Al (37,38). Thus, the arguments made in (9) appear no longer relevant.…”

Section: Resultsmentioning

confidence: 99%

Primordial formation of major silicates in a protoplanetary disc with homogeneous ²⁶ Al/ ²⁷ Al

et al. 2020

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Understanding the spatial variability of initial 26Al/27Al in the solar system, i.e., (26Al/27Al)0, is of prime importance to meteorite chronology, planetary heat production, and protoplanetary disc mixing dynamics. The (26Al/27Al)0 of calcium-aluminum–rich inclusions (CAIs) in primitive meteorites (~5 × 10−5) is frequently assumed to reflect the (26Al/27Al)0 of the entire protoplanetary disc, and predicts its initial 26Mg/24Mg to be ~35 parts per million (ppm) less radiogenic than modern Earth (i.e., Δ′26Mg0 = −35 ppm). Others argue for spatially heterogeneous (26Al/27Al)0, where the source reservoirs of most primitive meteorite components have lower (26Al/27Al)0 at ~2.7 × 10−5 and Δ′26Mg0 of −16 ppm. We measured the magnesium isotope compositions of primitive meteoritic olivine, which originated outside of the CAI-forming reservoir(s), and report five grains whose Δ′26Mg0 are within uncertainty of −35 ppm. Our data thus affirm a model of a largely homogeneous protoplanetary disc with (26Al/27Al)0 of ~5 × 10−5, supporting the accuracy of the 26Al→26Mg chronometer.

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Section: Resultsmentioning

confidence: 99%

Primordial formation of major silicates in a protoplanetary disc with homogeneous ²⁶ Al/ ²⁷ Al

et al. 2020

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“…In order to assess the effect of a sampling bias on our Ni isotope measurements, we have measured two separate samples of CI1 chondrite Orgueil (both provided by the NHM). In addition, we have measured both a bulk sample (46.7 mg) of L3.7 chondrite Ceniceros and four subsamples microdrilled from two polished mounts (5-10 mg material; see Luu et al, 2019 and Table 2 for more details).…”

Section: Chondritic Meteoritesmentioning

confidence: 99%

“…The majority of the meteorite Ni isotope measurements were carried out on aliquots from larger sample dissolutions that were measured for Mg isotope composition by Hin et al (2017) and Luu et al (2019).…”

Section: Digestion and Ni Purificationmentioning

confidence: 99%

The non-chondritic Ni isotope composition of Earth’s mantle

Klaver

Ionov

Takazawa

et al. 2020

Geochimica et Cosmochimica Acta

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Nickel is a major element in the Earth. Due to its siderophile nature, 93 % of Ni is hosted in the core and the Ni isotope composition of the bulk silicate Earth might inform on the conditions of terrestrial core formation. Whether Earth's mantle is fractionated relative to the chondritic reservoir, and by inference to the core, is a matter of debate that largely arises from the uncertain Ni isotope composition of the mantle. We address this issue through high-precision Ni isotope measurements of fertile-to melt-depleted peridotites and compare these data to chondritic meteorites. Terrestrial peridotites that are free from metasomatic overprint display a limited range in δ 60/58 Ni (deviation of 60 Ni/ 58 Ni relative to NIST SRM 986) and no systematic variation with degree of melt depletion. The latter is consistent with olivine and orthopyroxene buffering the Ni budget and isotope composition of the refractory peridotites. As such, the average Ni isotope composition of these peridotites (δ 60/58 Ni = 0.115 ± 0.011 ‰) provides a robust estimate of the δ 60/58 Ni of the bulk silicate Earth. Peridotites with evidence for melt metasomatism range to heavier Ni isotope compositions where the introduction of clinopyroxene appears to drive an increase in δ 60/58 Ni. This requires a process where melts do not reach isotopic equilibrium with buffering olivine and orthopyroxene, but its exact nature remains obscure. Chondritic meteorites have variability in δ 60/58 Ni due to heterogeneity at the sampling scale. In particular, CI1 chondrites are displaced to isotopically lighter values due to sorption of Ni onto ferrihydrite during parent body alteration. Chondrites less extensively altered than the CI1 chondrites show no systematic differences in δ 60/58 Ni between classes and yield average δ 60/58 Ni = 0.212 ± 0.013 ‰, which is isotopically heavier than our estimate of the bulk silicate Earth. The notable isotopic difference between the bulk silicate Earth and chondrites likely results from the segregation of the terrestrial core. Our observations potentially provide a novel constraint on the conditions of terrestrial core formation but requires further experimental calibration.

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“…Mg have not been observed for bulk chondrites (e.g.,36,37) but are known in two ancient achondrites (NWA 7325: δ 26 Mg*0=0.093 ± 0.004‰(38); Asuka 881394: δ 26 Mg*0=0.070 ± 0.052‰, 39). They could result from metamorphic perturbations or redistributions(39), or correspond to the protolith isotopic composition in the case of remelting of a crustal reservoir(38,40).…”

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confidence: 99%

A 4,565-My-old andesite from an extinct chondritic protoplanet

Barrat

Chaussidon

Yamaguchi

et al. 2021

Proc. Natl. Acad. Sci. U.S.A.

120

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The age of iron meteorites implies that accretion of protoplanets began during the first millions of years of the solar system. Due to the heat generated by 26Al decay, many early protoplanets were fully differentiated with an igneous crust produced during the cooling of a magma ocean and the segregation at depth of a metallic core. The formation and nature of the primordial crust generated during the early stages of melting is poorly understood, due in part to the scarcity of available samples. The newly discovered meteorite Erg Chech 002 (EC 002) originates from one such primitive igneous crust and has an andesite bulk composition. It derives from the partial melting of a noncarbonaceous chondritic reservoir, with no depletion in alkalis relative to the Sun’s photosphere and at a high degree of melting of around 25%. Moreover, EC 002 is, to date, the oldest known piece of an igneous crust with a 26Al-26Mg crystallization age of 4,565.0 million years (My). Partial melting took place at 1,220 °C up to several hundred kyr before, implying an accretion of the EC 002 parent body ca. 4,566 My ago. Protoplanets covered by andesitic crusts were probably frequent. However, no asteroid shares the spectral features of EC 002, indicating that almost all of these bodies have disappeared, either because they went on to form the building blocks of larger bodies or planets or were simply destroyed.

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Bulk chondrite variability in mass independent magnesium isotope compositions – Implications for initial solar system 26Al/27Al and the timing of terrestrial accretion

Cited by 21 publications

References 47 publications

Primordial formation of major silicates in a protoplanetary disc with homogeneous ²⁶ Al/ ²⁷ Al

Primordial formation of major silicates in a protoplanetary disc with homogeneous ²⁶ Al/ ²⁷ Al

The non-chondritic Ni isotope composition of Earth’s mantle

A 4,565-My-old andesite from an extinct chondritic protoplanet

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Bulk chondrite variability in mass independent magnesium isotope compositions – Implications for initial solar system 26Al/27Al and the timing of terrestrial accretion

Cited by 21 publications

References 47 publications

Primordial formation of major silicates in a protoplanetary disc with homogeneous 26 Al/ 27 Al

Primordial formation of major silicates in a protoplanetary disc with homogeneous 26 Al/ 27 Al

The non-chondritic Ni isotope composition of Earth’s mantle

A 4,565-My-old andesite from an extinct chondritic protoplanet

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Primordial formation of major silicates in a protoplanetary disc with homogeneous ²⁶ Al/ ²⁷ Al

Primordial formation of major silicates in a protoplanetary disc with homogeneous ²⁶ Al/ ²⁷ Al