High field strength elements in chondrites and their refractory components

In geochemistry and cosmochemistry, chondrites provide important reference values for comparison with planetary compositions. Employing isotope dilution, we report a comprehensive high precision data set for the refractory high field strength elements (HFSEs; W-Nb-Ta-Zr-Hf) and Sm-Nd-Lu-U-Th in different types of chondrites and in refractory inclusions, mainly from CV3 chondrites. Except for U, parent body processes and terrestrial alteration appear to have negligible effects. The CI chondrite data allow calculation of canonical trace element ratios such as Nb/Ta, Zr/Nb, Zr/Hf, Hf/W or Th/U at unprecedented precision and accuracy. Enstatite chondrites exhibit resolvably lower Hf/W and Zr/Hf than carbonaceous and ordinary chondrites. Ratios of Nb/Ta are uniform between all chondrite classes and groups, except for CV chondrites, where Nb/Ta is lowered by admixture of refractory inclusions that display systematic depletions of the slightly less refractory and more siderophile Nb. Regarding parent-daughter ratios of the Lu-Hf, Sm-Nd, Hf-W, and Nb-Zr radioactive decay systems, the variations in chondrites and their refractory components must have already been established in the solar nebula by selective processing of metal and silicate components and condensation processes during CAI formation.