A groundbreaking study from the Guangzhou Institute of Geochemistry of the Chinese Academy of Sciences reveals how deeply subducted carbonates influence Earth's mantle redox states. Published in Science Advances, the research highlights the role of these carbonates in sublithospheric diamond formation and craton evolution.
Researchers simulated conditions at depths of 250 to 660 kilometers. Their experiments showed that carbonatite melts from subducted slabs interact with metallic iron-bearing mantle rocks. The team discovered that in cooler, "nonplume" environments, carbonatite melts reduce, forming immobile diamonds that stabilize cratons.
Conversely, in hotter, plume-influenced conditions, carbonatite melts oxidize the mantle. This oxidation weakens the lithosphere, potentially causing delamination, uplift, and 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.
By comparing experimental minerals with natural diamond inclusions from African and South American cratons, researchers found distinct redox signatures. These variations determine whether subducted carbon forms stable diamonds or destabilizes the lithosphere. The findings advance our understanding of deep carbon storage and mobility.
The study also has implications for interpreting diamond formation ages and predicting craton stability. This research was supported by the National Natural Science Foundation of China, among other programs. It offers new insights into Earth's deep carbon cycle and its impact on geological processes.