Compositional evolution osmium isotopes

Eclogite osmium isotope compositions are indicative of long-term evolution with basaltic/picritic Re/Os. 

Fewer reliable osmium isotopic data exist for Precambrian samples owing to the problems of disturbance of rhenium and osmium during alteration and metamorphism. Key points used to define mantle evolution are indicated in Figure 7. The osmium isotopic constraints on the composition of the Archean mantle are, in many cases, derived from Late Archean komatiite suites. Komatiites are high-MgO lavas that often form differentiated flow sequences, such that Re-Os isochrons can be determined chromite-rich layers are commonly present and provide a robust estimate of the initial osmium isotopic... 

In this section mantle evolution curves are presented for neodymium (Nd), hafnium (Hf), lead (Pb) and osmium (Os) isotopes. A summary of these isotopic systems is given in Text Box 3.2. Earlier studies based upon the study of Sr isotopes in the mantle (e.g. Bell et al., 1982) are now known to be unreliable because of its high geochemical mobility (Goldstein, 1988). The significance of the mantle evolution curves described here is that they demonstrate that the mantle does not operate as an isolated system but that it has evolved in its composition over time, in response to core formation, crust extraction, and the recycling of crustal material. 

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