Influence of redox processes on the germanium isotopic composition of ordinary chondrites

Florin, Guillaume; Luais, Béatrice; Rushmer, Tracy; Alard, Olivier

doi:10.1016/j.gca.2019.10.038

Cited by 12 publications

(16 citation statements)

References 89 publications

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“…This could be interpreted as evidence for preaccretion hydration processes in different regions of the protoplanetary disk. Whereas there is no clear limit between the H contents of unequilibrated and equilibrated OCs, the observed decrease in H contents with increasing metamorphism is in line with the progressive increase of %Fa and the loss of Fe-Ni metal during metamorphism (Florin et al, 2020).…”

Section: Ordinary Chondritesmentioning

confidence: 60%

“…The percentage of fayalite (%Fa) in ordinary chondrites increases from H to L to LL groups and is considered a robust proxy of the degree of hydration (i.e., the water content) of their respective parent bodies (Rubin, 2005;Florin et al, 2020). However, the lack of variation between the H contents of the different groups of OCs (Fig.…”

Section: Ordinary Chondritesmentioning

confidence: 99%

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Hydrogen in chondrites: Influence of parent body alteration and atmospheric contamination on primordial components

Vacher

Piani

Rigaudier

et al. 2020

Geochimica et Cosmochimica Acta

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Hydrogen occurs at the near percent level in the most hydrated chondrites (CI and CM) attesting to the presence of water in the asteroid-forming regions. Their H abundances and isotopic signatures are powerful proxies for deciphering the distribution of H in the protoplanetary disk and the origin of Earth's water. Here, we report H contents and isotopic compositions for a set of carbonaceous and ordinary chondrites, including previously analyzed and new samples analyzed after the powdered samples were degassed under vacuum at 120°C for 48 hours to remove adsorbed atmospheric water. By comparing our results to literature data, we reveal that the H budgets of both H-poor and H-rich carbonaceous chondrites are largely affected by atmospheric moisture, and that their precise quantification requires a specific pre-degassing procedure to correct for terrestrial contamination. Our results show that indigenous H contents of CI carbonaceous chondrites usually considered the more hydrated meteorites are almost a factor of 2 lower than those previously reported, with uncontaminated D/H ratios differing significantly from that of Earth's oceans. Without pre-degassing, the H concentrations of H-poor samples (e.g., CVs chondrites) are also affected by terrestrial contamination. After correction for contamination, it appears that the amount of water in chondrites is not controlled by the matrix modal abundance, suggesting that the different chondritic parent bodies accreted variable amounts of water-ice grains. Our results also imply that (i) thermal metamorphism play an important role in determining the H content of both CV and ordinary chondrites but without affecting drastically their H isotopic composition since no clear D enrichment is observed with the increase of petrographic type and (ii) the D enrichment of ordinary chondrites does not result from the loss of isotopically light H 2 induced by metal oxidation but is rather linked to the persistence of a thermally resistant D-rich component.

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Section: Ordinary Chondritesmentioning

confidence: 60%

Section: Ordinary Chondritesmentioning

confidence: 99%

Hydrogen in chondrites: Influence of parent body alteration and atmospheric contamination on primordial components

Vacher

Piani

Rigaudier

et al. 2020

Geochimica et Cosmochimica Acta

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“…After full digestion, remaining silicate grains enclosed in the metal were removed by centrifugation and cleaned for 10 min with 2 mL of cold 2 M HNO 3 in an ultrasonic bath to fully recover the digested metal solution. Florin et al (2020) demonstrated that silicates are not digested using this protocol. in grain M 2 .…”

Section: Bulk Metal Grainsmentioning

confidence: 97%

“…We adapted the chemistry procedure of Luais (2007Luais ( , 2012 to a larger metal sample mass to accommodate the low Ge concentrations in CB chondrites (around 1 ppm); further details are given in the supporting information. The Ge elemental and isotopic compositions of sample solutions in 0.5 M HNO 3 were analyzed using a NeptunePlus multicollector inductively coupled plasma mass spectrometer coupled with a hydride generator system (HG-MC-ICP-MS) at the Centre de Recherches Pétrographiques et Géochimiques (Nancy, France; see Rouxel and Luais [2017] and references therein; Florin et al 2020). 68 Zn, 69 Ga, 70 Ge, 71 Ga, 72 Ge, 73 Ge, and 74 Ge were analyzed in static mode on the L3, L2, L1, C, H1, H2, and H3 Faraday cups, respectively.…”

Section: Germanium Elemental and Isotopic Measurements By Hg-mc-icp-msmentioning

confidence: 99%

“…Germanium is a moderately siderophile and volatile element that condenses in Fe-Ni alloy (Sears 1978;Wai and Wasson 1979) at T 50 = 883 K and pH 2 O/ pH 2 = 4.2 × 10 −4 atm (Lodders et al 2009), and is therefore ideal for unraveling the low-temperature formation and evolution of CB chondrites. Germanium contents and isotopic compositions vary widely among meteorite groups and have been used to characterize iron meteorites (Wasson 1974;Luais 2007Luais , 2012; impact volatilization (Luais 2007); and, more recently, ordinary chondrite formation (Florin et al 2020). Therefore, we report a comprehensive Ge elemental and isotopic survey of the bulk metal and individual metal grains from CB a and CB b chondrites.…”

Section: Introductionmentioning

confidence: 99%

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Condensation and evaporation processes during CB chondrite formation: Insights from Ge isotopes and highly siderophile element abundances

Florin

Luais

Alard

et al. 2021

Meteorit & Planetary Scien

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We analyzed the highly siderophile element (HSE) contents and bulk Ge isotopic compositions of large metal grains in the CB chondrites Bencubbin (CB a ), Gujba (CB a ), and HaH 237 (CB b ). Our results suggest that the large grains were formed by the aggregation of smaller condensed grains, and the two Benccubinite groups are distinguishable based on their bulk metal δ 74/70 Ge mass-dependent isotopic values of 0.99 AE 0.30‰ (CB a ) and −0.65 AE 0.10‰ (CB b ). Based on our observations of these three samples, the isotopic compositions of metal in CB a chondrites are best explained by condensation at slow cooling rates in the center of an impact plume, whereas the metal in CB b chondrites formed under fast cooling rates along the plume edges. We also analyzed the Ge contents and isotopic compositions of the core, intermediate, and rim fractions of two Gujba metal grains, which were separated by sequential digestion. These results show a gradual decrease in δ 74/70 Ge and [Ge] from core to rim. We suggest that these δ 74 Ge zonations result from nearequilibrium condensation and evaporation processes in a heterogeneous plume. We propose a model for their formation in which (1) small grains (to become grain cores) condensed at equilibrium; (2) these grains were transported to a warmer region of the plume where they reached temperatures lower than that of Fe-Ni condensation, but high enough for the rapid evaporation of Ge; (3) Ge evaporation followed by slow cooling enriched the grains in heavy Ge isotopes and the surrounding gas in light Ge isotopes; and (4) equilibrium recondensation of metal from the gas and around the small grains formed the light Ge isotopic zonations observed in grain rims.

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Geochemistry and cosmochemistry of potassium stable isotopes

Wang

et al. 2021

Geochemistry

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Influence of redox processes on the germanium isotopic composition of ordinary chondrites

Cited by 12 publications

References 89 publications

Hydrogen in chondrites: Influence of parent body alteration and atmospheric contamination on primordial components

Hydrogen in chondrites: Influence of parent body alteration and atmospheric contamination on primordial components

Condensation and evaporation processes during CB chondrite formation: Insights from Ge isotopes and highly siderophile element abundances

Geochemistry and cosmochemistry of potassium stable isotopes

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