Deep mantle carbon flow influences diamond formation and craton stability

Using high-pressure experiments that simulate depths from 250 to 660 kilometers, the team examined how carbonatite melts from subducted tectonic slabs interact with mantle rocks rich in metallic iron. The research shows that in cooler, nonplume regions of the mantle, these melts reduce over time, forming stable, immobile diamonds that help preserve the structural integrity of ancient continental roots known as cratons.

In contrast, under hotter, plume-influenced mantle conditions, the same carbonatite melts oxidize the mantle. This oxidation can weaken the lithosphere, potentially triggering delamination, uplift of the Earth's surface, and extensive volcanic episodes.

"The redox state of the deep mantle is a critical factor controlling how volatiles, such as carbon, cycle between Earth's surface and its interior," stated Prof. YU Wang, the study's corresponding author. "Our experiments show that the fate of subducted carbon is heavily influenced by mantle temperature and redox conditions, shaping continent evolution over geological time."

By comparing their laboratory results with natural diamond inclusions from African and South American cratons, the researchers confirmed that mantle redox conditions leave distinct mineralogical signatures. These signatures help determine whether subducted carbon is locked into diamonds or promotes geological instability.

Beyond enhancing knowledge of deep-Earth carbon processes, the study provides new insights into the formation timelines of diamonds and the resilience of continental lithosphere under changing tectonic regimes.

Research Report:Variable mantle redox states driven by deeply subducted carbon