Evidence for oxygen-conserving diamond formation in redox-buffered subducted oceanic crust sampled as eclogite

Sonja Aulbach () and Thomas Stachel
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Sonja Aulbach: Goethe-Universität
Thomas Stachel: University of Alberta

Nature Communications, 2022, vol. 13, issue 1, 1-13

Abstract: Abstract Cratonic eclogite is the product of oceanic crust subduction into the subcontinental lithospheric mantle, and it also is a fertile diamond source rock. In contrast to matrix minerals in magma-borne xenoliths, inclusions in diamond are shielded from external fluids, retaining more pristine information on the state of the eclogite source at the time of encapsulation. Vanadium is a multi-valent element and a widely used elemental redox proxy. Here, we show that that xenolithic garnet has lower average V abundances than garnet inclusions. This partly reflects crystal-chemical controls, whereby higher average temperatures recorded by inclusions, accompanied by enhanced Na2O and TiO2 partitioning into garnet, facilitate V incorporation at the expense of clinopyroxene. Unexpectedly, although diamond formation is strongly linked to metasomatism and xenoliths remained open systems, V concentrations are similar for bulk eclogites reconstructed from inclusions and from xenoliths. This suggests an oxygen-conserving mechanism for eclogitic diamond formation, and implies that eclogite is an efficient system to buffer fO2 over aeons of lithospheric mantle modification by subduction-derived and other fluids.

Date: 2022
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DOI: 10.1038/s41467-022-29567-z

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