The isotope composition of selenium in chondrites constrains the depletion mechanism of volatile elements in solar system materials

· by · in , ,

Hauke Vollstaedt, Klaus Mezger, Ingo Leya

Earth and Planetary Science Letters, Volume 450, 15 September 2016, Pages 372-380
Available online 15 July 2016

LINK

“Highlights
• The Se isotope composition of CC, OC, and EC is identical.
• Homogeneous Se isotopic composition of the solar nebula.
• No indication for Rayleigh-type Se incomplete condensation or partial evaporation.
• Thermal metamorphism redistributed volatile elements on the OC and EC parent bodies.”

“Solar nebula processes led to a depletion of volatile elements in different chondrite groups when compared to the bulk chemical composition of the solar system deduced from the Sun’s photosphere. For moderately-volatile elements, this depletion primarily correlates with the element condensation temperature and is possibly caused by incomplete condensation from a hot solar nebula, evaporative loss from the precursor dust, and/or inherited from the interstellar medium. Element concentrations and interelement ratios of volatile elements do not provide a clear picture about responsible mechanisms. Here, the abundance and stable isotope composition of the moderately- to highly-volatile element Se are investigated in carbonaceous, ordinary, and enstatite chondrites to constrain the mechanism responsible for the depletion of volatile elements in planetary bodies of the inner solar system and to define a δ82/78Seδ82/78Se value for the bulk solar system. The δ82/78Seδ82/78Se of the studied chondrite falls are identical within their measurement uncertainties with a mean of −0.20±0.26‰−0.20±0.26‰ (2 s.d., n=14n=14, relative to NIST SRM 3149) despite Se abundance depletions of up to a factor of 2.5 with respect to the CI group. The absence of resolvable Se isotope fractionation rules out a kinetic Rayleigh-type incomplete condensation of Se from the hot solar nebula or partial kinetic evaporative loss on the precursor material and/or the parent bodies. The Se depletion, if acquired during partial condensation or evaporative loss, therefore must have occurred under near equilibrium conditions to prevent measurable isotope fractionation. Alternatively, the depletion and cooling of the nebula could have occurred simultaneously due to the continuous removal of gas and fine particles by the solar wind accompanied by the quantitative condensation of elements from the pre-depleted gas. In this scenario the condensation of elements does not require equilibrium conditions to avoid isotope fractionation. The results further suggest that the processes causing the high variability of Se concentrations and depletions in ordinary and enstatite chondrites did not involve any measurable isotope fractionation. Different degrees of element depletions and isotope fractionations of the moderately-volatile elements Zn, S, and Se in ordinary and enstatite chondrites indicate that their volatility is controlled by the thermal stabilities of their host phases and not by the condensation temperature under canonical nebular conditions.”

Related posts (automatically generated):

  1. The Sn isotope composition of chondrites: implications for volatile element depletion in the Solar System
  2. The selenium isotopic variations in chondrites are mass-dependent; Implications for sulfide formation in the early solar system
  3. Potassium Isotope Compositions of Carbonaceous and Ordinary Chondrites: Implications on the Origin of Volatile Depletion in the Early Solar SystemOPEN ACCESS 
  4. Titanium isotope fractionation in solar system materials
  5. Origin of volatile element depletion among carbonaceous chondrites
  6. The chemical composition of carbonaceous chondrites: implications for volatile element depletion, complementarity and alterationOPEN ACCESS 
  7. The selenium isotope composition of lunar rocks: Implications for the formation of the Moon and its volatile loss
  8. Nucleosynthetic Sr–Nd Isotope Correlations in Chondrites: Evidence for Nebular Thermal Processing and Dust Transportation in the Early Solar System
  9. Selenium isotopes as tracers of a late volatile contribution to Earth from the outer Solar System
  10. Depletion of Moderately Volatile Elements by Open-system Loss in the Early Solar NebulaOPEN ACCESS 
Tags: , , , , , , ,