[S-CG49] Hard-Rock Drilling Science: From Continental to Deep Sea Drilling, and Oman Project

[SCG49-04] Low-salinity aqueous fluid inclusions in dolomite veins of a listvenite of Oman Drilling Project Phase 1

*Tatsuhiko Kawamoto¹, Hiroki Sato², Toma Takahashi³, Juan Miguel Guotana⁴, Tomoaki Morishita⁴, Peter B Kelemen⁵, Jude Ann Coggon⁶, Michelle Harris⁷, Juerg Michael Matter⁶, Katsuyoshi Michibayashi⁸, Eiichi TAKAZAWA⁹, Damon A H Teagle⁶, The Oman Drilling Project Phase 1 Science Party (1.Department of Geoscience, Faculty of Science, Shizuoka University, 2.Faculty of Science, Kyoto University, 3.Faculty of Geosciences and Civil Engineering, Kanazawa University, 4.Division of Natural Sciences, Graduate School of Natural Science and Technology, Kanazawa University, 5.Lamont-Doherty Earth Observatory, Columbia University, 6.School of Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, 7.School of Geography, Earth and Environmental Sciences, Plymouth University, 8.Department of Earth Planetary Sciences, Graduate School of Environmental Studies, Nagoya University, 9.Institute of Science and Technology, Niigata University)

Keywords:seawater, carbon cycling, serpentinite, serpentine, carbonate, carbonation

There are numerous gas and liquid, two-phase inclusions in dolomite crystals in a white-green-colored listvenite recovered through Oman Drilling Project Phase 1 (specimen name z68w). Most of the fluid inclusions are tiny, <6 micrometer across and seems to be too small to provide detectable Raman spectra of fluids. Fluid inclusions >6 micrometer across in dolomite provide Raman spectra of H₂O, but they become dark possibly due to destruction during the cooling processes and usually prohibit from observation of melting ices. So far, Raman microscopy indicated that they are filled with H₂O and do not detect any other gasses such as CH₄ or CO₂. Melting temperature of ice in the tiny fluid inclusions, on a Linkam THM600 heating stage with a Nikon 100X objective lens indicates that they are filled with saline fluids with 1.1 ± 0.5 wt% NaCl equivalent (n=42, Figure 1), which is much lower than that of seawater (3.5 wt% NaCl). Homogenization temperature of vapor-liquid suggests that the fluid inclusions were formed at temperature >139 ± 31°C (n=8, Figure 2). The fluid inclusions are mainly in dolomite veins, which cut magnesite and quartz (Figure 3, Raman mapping of magnesite, quartz, and dolomite). The present data indicate that low-salinity aqueous fluids were available during the crystallization of dolomite veins after the formation of magnesite-quartz assemblage. If seawater carries carbon to form listvenite from peridotite or serpentinite, the present low-salinity data suggest that chlorine needs to be absorbed by some phases during the fluid migration or be diluted by mixing with meteoric water.