Evidence for the formation of an iron meteorite at 3.8 × 10^9 years

Rb Sr isotopic analyses were made on silicate inclusions from Kodaikanal, a brecciated fine octahedrite. Twelve analyses of different mineral fractions and separate inclusions were made. The silicates in this iron meteorite are highly enriched in alkalis and show ^(87)Sr/^(86)Sr ratios ranging up to 8.8. The samples lie on a well defined isochron on the Sr-Rb evolution diagram and indicate an age of 3.8 ± 0.1 × 10^9 y and an initial ^(87)Sr/^(86)Sr ratio between 0.69 and 0.73. These data provide unambiguous evidence for the ‘formation’ of younger solid objects in the solar system in a process which demands extensive chemical differentiation. This is evidence for an intermediate history for some meteoritic objects of a different sort than has been previously observed