A new study published in Science Advances by researchers from the Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (GIG-CAS), and international collaborators reveals that deeply subducted carbonates can cause strong redox heterogeneity in Earth’s mantle, influencing the formation of sublithospheric diamonds and the long-term evolution of ancient continental keels known as cratons.

Using high-pressure experiments simulating depths of 250 to 660 kilometers, the team investigated how carbonatite melts from subducted slabs interact with metallic iron–bearing mantle rocks. Their findings suggest that in “nonplume” settings, carbonatite melts are progressively reduced, forming immobile diamonds and stabilizing the craton. In contrast, in hotter, plume-influenced environments, carbonatite melts oxidize the mantle, weaken the lithosphere, and may lead to lithosphere delamination, surface uplift, and widespread volcanism.

“The redox state of the deep mantle is a critical factor controlling how volatiles like carbon cycle between Earth’s surface and interior,” said Prof. Yu Wang, the study’s corresponding author. “Our experiments show that the fate of subducted carbon depends heavily on mantle temperature and redox conditions, which in turn shape how continents evolve over geological time.”

By comparing the compositions of experimentally produced minerals with natural diamond inclusions from cratons in Africa and South America, the study provides the clearest evidence yet that different mantle environments produce markedly distinct redox signatures. These redox conditions directly affect whether subducted carbon forms stable diamonds or contributes to destabilizing the lithosphere.

This work not only deepens our understanding of how carbon is stored and mobilized within Earth’s interior, but also has implications for interpreting diamond formation ages and predicting craton stability under future tectonic events.

The research was mainly supported by the National Natural Science Foundation of China, National Key R&D Program of China and the Strategic Priority Research Program of the CAS.

Fig. 1 Schematic illustration showing the role of slab carbonatite melt on mantle redox states, sublithospheric diamond formation, and craton evolution under nonplume and plume scenarios.