Heavy iron in large gem diamonds traces deep subduction of serpentinized ocean floor.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 33789901.
- Also identified by DOI 10.1126/sciadv.abe9773 and PMC identifier 8011960.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Subducting tectonic plates carry water and other surficial components into Earth's interior. Previous studies suggest that serpentinized peridotite is a key part of deep recycling, but this geochemical pathway has not been directly traced. Here, we report Fe-Ni-rich metallic inclusions in sublithospheric diamonds from a depth of 360 to 750 km with isotopically heavy iron (δ<sup>56</sup>Fe = 0.79 to 0.90‰) and unradiogenic osmium (<sup>187</sup>Os/<sup>188</sup>Os = 0.111). These iron values lie outside the range of known mantle compositions or expected reaction products at depth. This signature represents subducted iron from magnetite and/or Fe-Ni alloys precipitated during serpentinization of oceanic peridotite, a lithology known to carry unradiogenic osmium inherited from prior convection and melt depletion. These diamond-hosted inclusions trace serpentinite subduction into the mantle transition zone. We propose that iron-rich phases from serpentinite contribute a labile heavy iron component to the heterogeneous convecting mantle eventually sampled by oceanic basalts.