The high reactivity of dissolved carbon in aqueous fluids with the mantle has been demonstrated in natural occurrences of carbonated peridotites, including different tectonic settings such as ocean fracture zones and ophiolites. This suggests a significant contribution of mantle carbonation as a global carbon sink. In this proposal, we plan to drill the Horoman peridotite massif and inject CO₂ fluid into the borehole. The Horoman peridotite massif is characterized by exceptional freshness with a minor degree of serpentinization, and the reaction mechanisms may be different from those of highly altered peridotites such as the Oman ophiolite. Migration of carbonaceous fluids and carbon mineralization will be monitored by fluid chemistry and geophysical data for two years after the injection. By monitoring multiple physicochemical properties during the CO₂ injection experiments, we will develop a method for detecting carbon mineralization and apply such a method to improve quantifiable attribution of natural mantle alteration and carbonation to the global carbon cycle. The knowledge of carbon mineralization in the mantle can also be applicable to subsurface CO₂ sequestration, which represents the safe and long-term carbon storage mechanism due to its conversion to the stable solid form. 

Keywords: Asia, Japan, Mantle Drilling, Carbon Injection, Mantle Carbonation, Carbon Cycle