Rhenium‐187—osmium‐187 in iron meteorites and the strange origin of the Kodaïkanal meteorite

Abstract— A set of iron meteorites was investigated for Re‐Os isotopes and provides a well‐defined isochron age of 4.624 ± 0.017 Ba and an initial 187Os/188Os ratio of 0.095636 ± 0.00009. Actual ages may be a few percent lower due to uncertainty on the 187Re decay constant. Within the small sample number presented here, there is no evidence for age differences between classes. A more detailed study of the meteorite Kodaïkanal shows that the metal reservoir of this meteorite formed approximately at the same time as the other iron meteorites, in contrast with the silicate inclusions which display a formation age of 3.67 Ba with all other chronometers. A collisional origin is in agreement with the data on this meteorite. Major secondary events do not affect the Re‐Os system at the bulk rock scale in metal as it is the sole significant reservoir of these two elements. A Re‐Os and Rb‐Sr investigation of meteoritic troilite exhibits disturbed chronometric systems, which we attribute to the terrestrial history of the meteorite.