Os isotopic systematics of the MORB mantle: results from altered abyssal peridotites

摘要: Abstract Abyssal peridotites are fragments of the oceanic upper mantle. Previous studies have indicated that their Os isotopic compositions span a wide range, including values more radiogenic than most estimates average bulk Earth 187 188 ratio. This is difficult to reconcile with derivation as residues MORB partial melting. We present results suggest some this variation, particularly higher values, may be secondary origin. Comparison altered rims and unaltered cores two mylonitic reveal submarine weathering can increase ratios by 5%. Leaching experiments demonstrate presence radiogenic, easily leachable phase explained seawater-derived component. Thus, from abyssal must interpreted caution unless it shown effects seawater alteration were minor. develop criteria based on Sr Nd measurements, well major element compositional changes, allow strongly samples identified. Applying these criteria, we find 10 samples, literature data new analyses, apparently suffered only minimal alteration. These range in 0.1221 0.1270, mean 0.1246 standard deviation 0.0014. see no evidence for depleted mantle rocks enriched preferred value ∼ 0.127. Finally, if lost during weathering, provide significant source world's oceans.