| The moon is rich in energy and mineral resources, whether these energy and mineral resources can be fully utilized depends on the presence of water in the lunar environment. The existence and utilization of water on the moon have very important scientific interest and application prospect in lunar exploration program. New research using new chemical analysis technology to re-analyze the volcanic glass beads, olivine melt inclusions, apatite, and highland anorthosite in the Apollo lunar samples have detected the presence of large amounts of water, suggesting that some areas in the lunar interior may contain the same water content in Earth’s mantle. The electrical conductivity of rocks and minerals is very sensitive to water content, and theoretical and experimental studies have confirmed that water can greatly increase the electrical conductivity of rocks and minerals. The measurement of electrical conductivity of rocks and minerals under high temperature and high pressure has become a hotspot in deep geological-geophysical field in the last six years. It’s an effective way to infer the water content in the Earth’s interior by combining the laboratory electrical conductivity of rocks and minerals and the results of magnetotellurics and geomagnetic depth soundings.At present, the evidence about the presence of water in lunar interior are from geochemical methods. It’s uncertain to infer the water content in the lunar interior only by lunar surface samples collected during the Apollo-era. In this paper, we attempt to infer the water content in the lunar mantle by combining the laboratory electrical conductivity of the constituent minerals in the lower crust and the upper mantle, including olivine, pyroxenes, and garnet, and typical lunar conductivity-depth profiles obtained by lunar surface magnetometer. The main contents include the following aspects:(1) The presence of water on the moon and the status of electrical conductivity of rocks and minerals under high temperature and high pressure are reviewed.(2) The factors that influence the electrical conductivity of rocks and minerals under high temperature and high pressure are divided into external and internal factors, and the impact of these factors on the electrical conductivity of rocks and minerals are reviewed. The electrical conductivity increase with temperature, iron content, water content, and the melt volume fraction; with the increase in pressure and oxygen fugacity, the electrical conductivity respectively increase and decrease under anhydrous conditions, but quite the opposite under hydrous conditions; ignoring the influence of grain boundary; it’s necessary to consider the system equilibrium time and the iron loss during the electrical conductivity measurement.(3) The internal structure and constituent minerals in the lunar mantle, and the electrical conductivity of the constituent minerals(olivine, orthopyroxene, clinopyroxene, and garnet) in the lower crust and the upper mantle under hydrous and anhydrous conditions are reviewed.(4) The electrical conductivity models with similar chemical composition and constituent minerals applied to the temperature, pressure, and oxygen fugacity conditions in the lunar mantle are derived. Then, effective medium method is used to calculate the average conductivity of mixing mineral phases as a function of temperature and water content. The temperature-depth curves with different water content can be obtained by combining the typical conductivity-depth profiles from lunar surface magnetometer. In comparison with the temperature ranges inferred from lunar gravity and seismic data, the inferred total water content is less than lOppm, which is consistent with "Giant Impact Theory" related to the origin of the moon, the results of petrological modeling of lunar magma ocean, and chlorine isotope analysis results of lunar samples.(5) The main achievements of this paper are summarized, and certain deficiencies and improvements in the future are pointed out. |
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