Isotope mass fractionation during evaporation of Mg2Si04

Davis, A. M.; Hashimoto, Akihiko; Clayton, Robert N.; Mayeda, T. K.

doi:10.1038/347655a0

Cited by 191 publications

(124 citation statements)

References 8 publications

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“…Similar situation has been reported for the evaporation of forsterite; large isotopic mass fractionation was associated with evaporation of liquid forsterite, while not with evaporation of solid forsterite (Davis et al, 1990). The different behavior in the fractionation between the solid and liquid phases has been explained by the slow diffusivity of elements in the solid; isotopic com position of the crystal very close to the surface is changed by evaporation, but the isotopic compo sition of the crystal interior cannot be changed as long as the diffusion rate of the isotope species in the crustal is smaller than the evaporation rate (Davis et al, 1990). The present result can also be explained by the small diffusivity of S in the sulfide crystal, and suggests that mass dependent isotopic fractionation of S may not have occurred with incongruent evaporation of FeS in the primary solar nebula.…”

Section: Sulfur Isotopic Fractionation During Evaporationsupporting

confidence: 53%

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Incongruent evaporation experiments on iron sulfide (Fe1-.DELTA.S) under H2-rich (at 1 atm) and evacuated conditions.

1997

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JapanEvaporation experiments using pyrrhotite single crystals (Fe0.886S) were carried out at temperatures between 500 and 1300°C at 1 atm in an H2-CO2 gas flow (0.62-0.64 atm H2), and at 500 and 900°C un der an evacuated condition. Under the H2-rich condition, spongy metallic iron layer was formed on the sulfide crystal surface at temperatures below the Fe-FeS eutectic point as a result of incongruent evaporation, and developed inward almost conserving its original shape. The thickness of the iron layer increases linearly with time at constant temperatures (linear rate law) due to transportation of evaporated gas species through pores in the spongy iron layers. If incongruent evaporation is controlled by diffusion of element(s) in an evaporation residue layer, a parabolic rate law is expected. The linear rate law shows that FeS evaporates more efficiently than expected based on a parabolic rate law. The linear rate constant obtained at various temperatures obeys the Arrhenius relation: kFes = (1.61 ± 0.42) x 10-3exp(-115 ± 2 [kJ/mol]/RT) [m/sec]. A minor part of metallic iron in the surface layer diffused into the inner sulfide to form stoichio metric FeS (troilite) in the early evaporation stage. Thus, the experiments can be almost regarded as evaporation of troilite. Evaporation coefficients of FeS were obtained by comparing the experimental results with calculated rates using the Hertz-Knudsen equation. They are small (1.4 x 10-4 9.4 x 10-6) due to slow surface reaction and/or slow escape of S-bearing gas species into the gas flow. Mass-dependent isotopic fractionation of S by the evaporation was not detected within an error of ±3%o probably due to slow diffusivity of S in the sulfide crystal. In the evacuated experiments, evaporation occurred very slowly due to the absence of H2 gas, which acts as a reducing agent. Iron residue layer was very thin or sometimes not detected probably because the evaporation rate of S from FeS became comparable to the evaporation rate of metallic iron, which can be neglected under the H2-rich condition.

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Section: Sulfur Isotopic Fractionation During Evaporationsupporting

confidence: 53%

“…It has been known in laboratory experiments that isotopic mass fractionations occur during evaporation (e.g., Esat et al, 1986;Davis et al, 1990) and condensation (Uyeda et al, 1991). The isotopic mass fractionation reported in refractory inclusions in considered to be caused by evapora tion and/or condensation in the solar nebula.…”

Section: Introductionmentioning

confidence: 99%

Incongruent evaporation experiments on iron sulfide (Fe1-.DELTA.S) under H2-rich (at 1 atm) and evacuated conditions.

1997

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“…Loss of K from the surface takes place with accompanying isotopic fractionation, while diffusion homogenizes the melt, resulting in Rayleigh fractionation. This has been demonstrated experimentally for evaporation of melts with the compositions of forsterite (Mg, Si, 0), chondrite (Mg, Si, 0), and Fe0 (Fe, 0) by Davis et al (1990) and Wang et al ( 1994a,b). Since the physics is the same for the evaporation of K, the results of these experiments are taken to indicate that potassium, too, will fractionate following the Rayleigh law with an exponent that is the inverse square root of the masses.…”

Section: Nebular Processing-chondrules and Dust Grainsmentioning

confidence: 98%

Potassium isotope cosmochemistry: Genetic implications of volatile element depletion

Humayun

Clayton

1995

Geochimica et Cosmochimica Acta

306

185

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“…Based on the large scale Si/Mg variations throughout the Semarkona (LL3.0) type I chondrule suite which are uncorrelated with grain size, and hence the inferred degree of melting, Hewins (1997) also argued against volatilization of SiO 2 during chondrule formation. Additionally, if Si/Mg fractionation was due to evaporation from chondrule melts, one might expect to find mass-dependent Si isotopic fractionation in the rim materials (Davis et al 1990). Huss et al (1996) measured Mg and Si isotopes in olivines and pyroxenes from the rims and cores of two layered chondrules from the El Djouf 001 chondrite.…”

Section: Fractionation Of Common and Moderately Volatile Elements Durmentioning

confidence: 99%

Silica‐rich igneous rims around magnesian chondrules in CR carbonaceous chondrites: Evidence for condensation origin from fractionated nebular gas

Krot

Libourel

Goodrich

et al. 2004

Meteorit & Planetary Scien

128

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Silica-rich igneous rims around magnesian chondrules in CR carbonaceous chondrites: Evidence for condensation origin from fractionated nebular gasAlexander N. KROT Abstract-The outer portions of many type I chondrules (Fa and Fs <5 mol%) in CR chondrites (except Renazzo and Al Rais) consist of silica-rich igneous rims (SIRs). The host chondrules are often layered and have a porphyritic core surrounded by a coarse-grained igneous rim rich in low-Ca pyroxene. The SIRs are sulfide-free and consist of igneously-zoned low-Ca and high-Ca pyroxenes, glassy mesostasis, Fe, Ni-metal nodules, and a nearly pure SiO 2 phase. The high-Ca pyroxenes in these rims are enriched in Cr (up to 3.5 wt% Cr 2 O 3 ) and Mn (up to 4.4 wt% MnO) and depleted in Al and Ti relative to those in the host chondrules, and contain detectable Na (up to 0.2 wt% Na 2 O). Mesostases show systematic compositional variations: Si, Na, K, and Mn contents increase, whereas Ca, Mg, Al, and Cr contents decrease from chondrule core, through pyroxene-rich igneous rim (PIR), and to SIR; FeO content remains nearly constant. Glass melt inclusions in olivine phenocrysts in the chondrule cores have high Ca and Al, and low Si, with Na, K, and Mn contents that are below electron microprobe detection limits. Fe, Ni-metal grains in SIRs are depleted in Ni and Co relative to those in the host chondrules. The presence of sulfide-free, SIRs around sulfide-free type I chondrules in CR chondrites may indicate that these chondrules formed at high (>800 K) ambient nebular temperatures and escaped remelting at lower ambient temperatures. We suggest that these rims formed either by gas-solid condensation of silica-normative materials onto chondrule surfaces and subsequent incomplete melting, or by direct SiO (gas) condensation into chondrule melts. In either case, the condensation occurred from a fractionated, nebular gas enriched in Si, Na, K, Mn, and Cr relative to Mg. The fractionation of these lithophile elements could be due to isolation (in the chondrules) of the higher temperature condensates from reaction with the nebular gas or to evaporation-recondensation of these elements during chondrule formation. These mechanisms and the observed increase in pyroxene/olivine ratio toward the peripheries of most type I chondrules in CR, CV, and ordinary chondrites may explain the origin of olivine-rich and pyroxene-rich chondrules in general.

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Isotope mass fractionation during evaporation of Mg2Si04

Cited by 191 publications

References 8 publications

Incongruent evaporation experiments on iron sulfide (Fe1-.DELTA.S) under H2-rich (at 1 atm) and evacuated conditions.

Incongruent evaporation experiments on iron sulfide (Fe1-.DELTA.S) under H2-rich (at 1 atm) and evacuated conditions.

Potassium isotope cosmochemistry: Genetic implications of volatile element depletion

Silica‐rich igneous rims around magnesian chondrules in CR carbonaceous chondrites: Evidence for condensation origin from fractionated nebular gas

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