Genetics, age and crystallization history of group IIC iron meteorites

Hope A. Tornabene, Connor D. Hilton, Katherine R. Bermingham, Richard D. Ash, Richard J. Walker

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

The eight iron meteorites currently classified as belonging to the IIC group were characterized with respect to the compositions of 21 siderophile elements. Several of these meteorites were also characterized for mass independent isotopic compositions of Mo, Ru and W. Chemical and isotopic data for one, Wiley, indicate that it is not a IIC iron meteorite and should be reclassified as ungrouped. The remaining seven IIC iron meteorites exhibit broadly similar bulk chemical and isotopic characteristics, consistent with an origin from a common parent body. Variations in highly siderophile element (HSE) abundances among the members of the group can be well accounted for by a fractional crystallization model with all the meteorites crystallizing between ∼10 and ∼26% of the original melt, assuming initial S and P concentrations of 8 wt.% and 2 wt.%, respectively. Abundances of HSE estimated for the parental melt suggest a composition with chondritic relative abundances of HSE ∼6 times higher than in bulk carbonaceous chondrites, consistent with the IIC irons sampling a parent body core comprising ∼17% of the mass of the body. Radiogenic 182W abundances of two group IIC irons, corrected for a nucleosynthetic component, indicate a metal-silicate segregation age of 3.2 ± 0.5 Myr subsequent to the formation of Calcium-Aluminum-rich Inclusions (CAI). When this age is coupled with thermal modeling, and assumptions about the Hf/W of precursor materials, a parent body accretion age of 1.4 ± 0.5 Myr (post-CAI) is obtained. The IIC irons and Wiley have 100Ru mass independent “genetic” isotopic compositions that are identical to other irons with so-called carbonaceous chondrite (CC) type genetic affinities, but enrichments in 94,95,97Mo and 183W that indicate greater s-process deficits relative to most known CC iron meteorites. If the IIC irons and Wiley are of the CC type, this indicates variable s-process deficits within the CC reservoir, similar to the s-process variability within the NC reservoir observed for iron meteorites. Nucleosynthetic models indicate that Mo and 183W s-process variability should correlate with Ru isotopic variability, which is not observed. This may indicate the IIC irons and Wiley experienced selective thermal processing of nucleosynthetic carriers, or are genetically distinct from the CC and NC precursor materials.

Original languageEnglish (US)
Pages (from-to)36-50
Number of pages15
JournalGeochimica et Cosmochimica Acta
Volume288
DOIs
StatePublished - Nov 1 2020
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Geochemistry and Petrology

Keywords

  • Accretion age
  • Fractional crystallization
  • Genetics
  • Group IIC iron meteorites
  • Hf-W chronometry
  • Highly siderophile elements
  • Nucleosynthesis
  • Re-Os isotopes

Fingerprint

Dive into the research topics of 'Genetics, age and crystallization history of group IIC iron meteorites'. Together they form a unique fingerprint.

Cite this