Komatiites osmium isotopes

Figure 54 Comparison of present-day osmium isotopic compositions of eclogite xenoliths from Udachnaya, Yakutia (Pearson et ah, 1995c) and S. Africa (Pearson et al, 1992 Menzies et al, 1999 Shirey et ah, 2001) with continental crust, oceanic basalts (Shirey and Walker, 1998), and Archean komatiites and basalts (Walker et al, 1989b). Udachnaya peridotite data from Pearson et al (1995a).

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... 

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