Project 649 - Diamonds and Recycled Mantle

Recent studies of ophiolites show the presence of diamonds in both chromitites and peridotites. These “ophiolite-hosted diamonds” represent a new occurrence of ultra high-pressure (UHP) minerals, whose estimated pressure-temperature conditions indicate crystallization at mantle depths of 150-300 km or more. Current models of oceanic lithosphere production presume shallow mantle depths (~60-80 km) of partial melting, and therefore the discovery of ophiolitic diamonds poses a significant conundrum. Relevant questions include: (1) Are diamonds ubiquitous in the mantle, or do they only exist in isolated mantle domains? (2) Where did the carbon for diamonds come from? (3) How did diamonds and other UHP minerals reach the surface? Answers to these questions require global studies, and would contribute significantly to our understanding of mantle dynamics and recycling, and the operation of the Earth as a heat engine. Our project is designed to address these questions. Our research team is a leader in the study of ophiolite-hosted diamonds and has in-house access to the necessary instrumentation to do this research. We will undertake systematic sampling of peridotites and chromitites in different ophiolites with a range in ages and geochemical affinities, to document the extent of diamond occurrence in the mantle.

Trace element–isotope geochemistry and precise geochronology will help us address Questions 2–3. We will organize thematic meetings and training workshops for students and early-career researchers as venues for knowledge transfer, international collaboration, and capacity building. These activities will contribute to training the next generations of geoscientists and will provide them with opportunities to utilize modern instrumentation and to acquire quantitative skills.

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