Ophiolite-Hosted Diamond: A New Window for Probing Carbon Cycling in the Deep Mantle Review uri icon

DCO ID 11121/7038-1417-4245-4676-CC

is Contribution to the DCO

  • Yes

year of publication

  • 2019

abstract

  • As reported in our prior work, we have recovered microdiamonds and other unusual minerals, including pseudomorph  stishovite , moissanite, qingsongite, native elements, metallic  alloys , and some crustal minerals (i.e., zirconquartzamphibole , and rutile) from ophiolitic peridotites  and chromitites . These ophiolite-hosted microdiamonds display different features than kimberlitic, metamorphic, and meteoritic diamonds  in terms of isotopic values and mineral inclusions. The characteristic of their light carbon isotopic composition  implies that the material source of ophiolite-hosted diamonds is surface-derived organic matter. Coesite inclusions coexisting with kyanite  rimming an FeTi  alloy from the Luobusa ophiolite  show a polycrystalline  nature and a prismatic habit, indicating their origin as a replacement of stishovite. The occurrence in kyanite and coesite with inclusions of qingsongite, a cubic boron nitride  mineral, and a high-pressure polymorph  of rutile  (TiO2 II) point to formation pressures  of 10–15 GPa at temperatures ∼1300 °C, consistent with depths greater than 380 km, near the mantle transition zone (MTZ). Minerals such as moissanite, native elements, and metallic alloys in chromite  grains indicate a highly reduced environment for ophiolitic peridotites and chromitites. Widespread occurrence of diamonds in ophiolitic peridotites and chromitites suggests that the oceanic mantle may be a more significant carbon reservoir  than previously thought. These ophiolite-hosted diamonds have proved that surface carbon can be subducted into the deep mantle, and have provided us with a new window for probing deep carbon cycling.

volume

  • 5

issue

  • 3