ABSTRACT

The lead isotopic compositions and the uranium, thorium and lead contents of eclogite and harzburgite inclusions from South African kimberlite-pipes and lherzolite inclusions from Itinomegata crater, Japan and of their main mineral fractions have been determined. The observed ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²³⁵U/²⁰⁴Pb in lherzolite samples from Itinomegata range from 17.9 to 18.2, from 15.1 to 15.5 and from 1.9 to 23, respectively. The results suggest that the lherzolites were of recent crystallization. The observed data on eclogite inclusions show no consistent pattern and suggest that they have a complicated history. The observed lead isotopic compositions of harzburgite inclusions from kimberlitepipes are ²⁰⁸Pb/²⁰⁴Pb = 17.3 ∼ 19.0 and ²⁰⁷Pb/²⁰⁴Pb = 15.3 ∼ 15.6. These results are distributed in a wide range on two regression lines, suggesting that they had been formed from the same source material but with different ages or have been formed recently by mixing of two different source materials and host rock of kimberlite.