Carbonation of Mantle Peridotite: An Approach From Fluid Inclusion Analysis and Hydrothermal Experiments

Abstract

Carbonate rocks in serpentinites are called ophicarbonate. Seawater-like saline fluid inclusions in carbonate minerals are commonly observed in ophicarbonate as follows: (1) the Oman ophiolite, formed at a fast spreading ridge; (2) the Western Alps ophiolite, formed at a slow spreading ridge; (3) serpentinite mud volcanoes in the Izu Mariana forearc; and (4) the Sambagawa Belt, Chichibu, Japan. Hydrothermal experiments are also conducted to provide constraints to know effects of iron on the phase relation during the carbonation by comparison with thermodynamic calculation in the CaO-MgO-SiO₂-H₂O-CO₂ system. An assemblage of talc, antigorite, calcite and dolomite (Osawa, in progress) provides constraints on CO₂/(H₂O+CO₂) ratios of fluids lower than 0.03 at 0.1 GPa and 0.002 at 0.5 GPa. Combination of natural observation, experiments and calculation allows us to understand the conditions of mantle carbonation more precisely.