[S-GC32] Volatiles in the Earth - from Surface to Deep Mantle

[SGC32-03] Impact of mantle hydration on the global carbon cycle

★Invited Papers

*Ikuo Katayama¹ (1.Department of Earth and Planetary Systems Science, Hiroshima University)

Keywords:Carbon cycle, Mantle hydration

The long-term stabilization of the Earth's surface environment is likely controlled by the global carbon cycle through the negative feedback system. The oceanic plate can capture carbon dioxide from seawater through water-rock interactions in the crust and mantle, in addition to carbonates and organic matter deposited on the seafloor, which is responsible for carbon transport to the Earth's interior. In the uppermost part of the oceanic crust, carbonates are precipitated in the volcanic rocks, filling the fractures and voids, and the carbon content tends to increase with the age of oceanic plates (e.g., Alt and Teagle 1999). On the other hand, although the amount of carbon uptake in the deep crust and mantle is not well known, if seawater penetrates along faults, carbonates are likely to be precipitated by water-rock interactions. In particular, alteration of mantle rocks can promote carbonate precipitation via increasing pH of the aqueous fluids. Extensive carbonation of peridotites is evident in the Oman ophiolite; for example, listvenite is widespread in the lower part of the ophiolite, where serpentine is completely replaced by carbonate due to metamorphic sole-derived fluids (Kelemen et al. 2013). Mantle hydration has recently been suggested along the outer-rise faults that develop in the relatively old plate subduction, such as the Japan Trench, where seawater infiltrates to mantle and extensive serpentinization is expected to occur (e.g., Fujie et al. 2013). In such case, carbonation process may have occurred during the mantle hydration, and the amount of carbon uptake in the oceanic lithosphere may have increased significantly. Although the negative feedback system of carbon cycle has contributed to the stabilization of the surface environment throughout the geological history, the extensive mantle carbonation may break the feedback system and result in global cooling. We hope that the upcoming deep drilling project at off Hawaii (Umino et al. 2020) provides a clue to understand the carbon uptake process in the deep crust and mantle.