Abstract
The measured 187Os/186Os of uncontaminated oceanic peridotites and basalts ranges between 1.0032 ± 0.0072 and 1.111 ± 0.011 (2σx). This range reflects chemical fractionation of the incompatible parent element Re from compatible Os in the mantle during crust production and subsequent isolation of the Re depleted regions of the mantle for time periods in excess of 1000 Ma. The 187Os/186Os of subcontinental mantle samples also reflects ancient Re depletion events. A material balance for osmium isotopes in the silicate fraction of the earth is made based on the premise that the average silicate earth 187Os/186Os is 1.10. The calculated amount of Re depleted mantle that was caused by the extraction of the continental crust is small, probably less than 3%, and is comparable to the mass of the subcontinental lithosphere that has been depleted with respect to major elements. This calculation illustrates that a complementary relationship may exist between the continental crust and the subcontinental lithosphere wi...
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