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A new study in Science Advances by researchers from the Guangzhou Institute of Geochemistry of the Chinese Academy of Sciences (GIG-CAS), along with international collaborators, reveals that deeply subducted carbonates can cause significant variations in the redox states of Earth's mantle. This process influences the formation of sublithospheric diamonds and plays a role in the long-term evolution of cratons—ancient stable parts of the continental lithosphere.

The research team conducted high-pressure experiments simulating depths between 250 and 660 kilometers to investigate how carbonatite melts, derived from subducted slabs, interact with metallic iron-bearing mantle rocks.

Their findings indicate that in "nonplume" environments (cooler mantle settings), carbonatite melts undergo progressive reduction, leading to the formation of immobile diamonds that help stabilize the craton. Conversely, under hotter, plume-influenced conditions, the carbonatite melts tend to oxidize the surrounding mantle, which weakens the lithosphere and may trigger lithosphere delamination, surface uplift, and widespread volcanic activity.

"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," said 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 the composition of minerals formed in their experiments with natural diamond inclusions from cratons in Africa and South America, the researchers found clear evidence that different mantle environments produce distinctly different redox signatures. These variations directly determine whether subducted carbon forms stable diamonds or contributes to lithospheric destabilization.

This study not only advances our understanding of deep carbon storage and mobility in Earth's interior, but also has implications for interpreting the ages of diamond formation and predicting craton stability in response to future tectonic events.