11:30 AM - 11:45 AM
[SCG46-04] Carbonation experiments of mantle minerals
Keywords:Serpentinization, Carbonation, Hydrothermal experiment, Seawater
Carbonate veins are observed in serpentinites, and locally carbonates fill the matrix of serpentinite breccias, as seen in ophicarbonates. Ophicarbonates are present in serpentinites of oceanic mantle origin that have risen near the seafloor in oceanic core complexes, and in serpentinites of mantle wedge origin in metamorphic belts. Carbonate ions are more soluble in saline fluids than in fresh water. On the other hand, when serpentinite is fully carbonated, it is transformed into a rock called listvenite. Well studied are the Oman ophiolite listvenites. To understand the conditions for carbonation of these serpentinites, experiments have been conducted in which mantle rocks have been reacted with H2O-CO2 fluids.
The starting materials (olivine, antigorite with/without diopside) are used. In addition to magnesite and talc, quartz is also found. Experiments with magnesium end components are largely consistent with previous work in the MgO-SiO2-H2O-CO2 system [Johannes (1969) American Journal of Science, 267, 1083-1104]. Various reactions have been observed in the olivine-diopside and serpentine-diopside systems.
The experimental results show that the carbonation of serpentine is accompanied by a dehydration reaction. Under all experimental conditions, the volume of the solid phase increases compared to that before the reaction. The addition of a carbon dioxide-containing fluid to serpentine causes both dehydration and an increase in solid volume.
Carbonate veins are commonly found in serpentinite in nature. At shallow depths near the seafloor, called oceanization metamorphism, and during plate subduction, some serpentinites are carbonated. In most cases, calcite veins are formed, but in the present experiments, only magnesite or dolomite was formed, at least at temperatures above 300°C. We conclude that low temperatures below 300°C or the fluids must carry Ca to form calcite veins. Possible sources of calcium are sedimentary rocks and basalts.
The starting materials (olivine, antigorite with/without diopside) are used. In addition to magnesite and talc, quartz is also found. Experiments with magnesium end components are largely consistent with previous work in the MgO-SiO2-H2O-CO2 system [Johannes (1969) American Journal of Science, 267, 1083-1104]. Various reactions have been observed in the olivine-diopside and serpentine-diopside systems.
The experimental results show that the carbonation of serpentine is accompanied by a dehydration reaction. Under all experimental conditions, the volume of the solid phase increases compared to that before the reaction. The addition of a carbon dioxide-containing fluid to serpentine causes both dehydration and an increase in solid volume.
Carbonate veins are commonly found in serpentinite in nature. At shallow depths near the seafloor, called oceanization metamorphism, and during plate subduction, some serpentinites are carbonated. In most cases, calcite veins are formed, but in the present experiments, only magnesite or dolomite was formed, at least at temperatures above 300°C. We conclude that low temperatures below 300°C or the fluids must carry Ca to form calcite veins. Possible sources of calcium are sedimentary rocks and basalts.