Osmium isotopes and mantle convection

Abstract
The decay of 187Re to 187Os (with a half–life of 42 billion years) provides a unique isotopic fingerprint for tracing the evolution of crustal materials and mantle residues in the convecting mantle. Ancient subcontinental mantle lithosphere has uniquely low Re/Os and 187Os/188Os ratios due to large–degree melt extraction, recording ancient melt–depletion events as old as 3.2 billion years. Partial melts have Re/Os ratios that are orders of magnitude higher than their sources, and the subduction of oceanic or continental crust introduces into the mantle materials that rapidly accumulate radiogenic 187Os. Eclogites from the subcontinental lithosphere have extremely high 187Os/188Os ratios, and record ages as old as the oldest peridotites. The data show a near–perfect partitioning of Re/Os and 187Os/188Os ratios between peridotites (low) and eclogites (high).

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