Recent work by PhD student Zhengyu Long, under the supervision of Frédéric Moynier, and their colleagues from the Institut de physique du globe de Paris (IPGP/Université Paris Cité/CNRS) and CNRS has shed light on a mechanism involved in Earth's carbon cycle, linked to the subduction of oceanic plates.
Their study, published in Science Advances, indicates that carbonatites—rare volcanic rocks rich in carbonates—display a particular isotopic signature, likely inherited from subducted oceanic crust.
These results suggest the existence of a process recycling marine carbon into Earth's mantle, which could contribute to regulating the global carbon cycle and maintaining conditions favorable for life on Earth.
Modern carbonatite volcanism at Ol Doinyo Lengai, Tanzania. / @Wiki A process at the heart of deep carbon dynamics
Carbonate sediments sinking into subduction zones are often interbedded with clay layers or lie atop altered igneous oceanic crust. By studying carbonatites from various geological environments—oceanic and continental—over a period spanning two billion years, the team observed that their potassium isotopic composition appears to reflect the mantle origin of these rocks rather than secondary magmatic processes.
These observations suggest that the recycling of marine carbonates, particularly through the subduction of altered oceanic crust, could play a significant role in the dynamics of deep carbon reservoirs. The origin of carbonatites, long debated, now appears more closely linked to the partial melting of mantle reservoirs enriched with recycled carbonates.
New insights for a better understanding of the global carbon cycle
The carbonate inputs involved in this process could come from a deep mantle plume or result from an interaction between a plume and a lithospheric mantle containing carbonates. A very limited partial melting could then produce carbonatitic magmas. This mechanism of deep carbon transfer has likely been active for at least two billion years, including in warmer subduction contexts.
This work thus provides complementary insights for a better understanding of the global carbon cycle. It highlights the role of carbonatites in mantle dynamics and underscores the probable contribution of subducted oceanic crust to carbon recycling—an important process in maintaining Earth's surface conditions.