The Moon is thought to have been covered initially by a deep magma ocean, its gradual solidification leading to the formation of the plagioclase-rich highland crust. We performed a high-pressure, high-temperature experimental study of lunar mineralogical and geochemical evolution during magma ocean solidification that yields constraints on the presence of water in the earliest lunar interior. In the experiments, a deep layer containing both olivine and pyroxene is formed in the first ~50% of crystallization, β-quartz forms towards the end of crystallization, and the last per cent of magma remaining is extremely iron rich. In dry experiments, plagioclase appears after 68 vol.% solidification and yields a floatation crust with a thickness of ~68 km, far above the observed average of 34–43 km based on lunar gravity. The volume of plagioclase formed during crystallization is significantly less in water-bearing experiments. Using the relationship between magma water content and the resulting crustal thickness in the experiments, and considering uncertainties in initial lunar magma ocean depth, we estimate that the Moon may have contained at least 270 to 1,650 ppm water at the time of magma ocean crystallization, suggesting the Earth–Moon system was water-rich from the start.
At a glance
- The magma ocean concept and lunar evolution. Annu. Rev. Earth Planet. Sci. 13, 201–240 (1985).
- A chemical model for generating the sources of mare basalts: combined equilibrium and fractional crystallization of the lunar magmasphere. Geochim. Cosmochim. Acta 56, 3809–3823 (1992). , &
- Making the Moon from a fast-spinning Earth: a giant impact followed by resonant despinning. Science 338, 1047–1052 (2012). &
- Forming a Moon with an Earth-like composition via a giant impact. Science 338, 1052–1055 (2012).
- Lunar core formation: new constraints from metal-silicate partitioning of siderophile elements. Earth Planet. Sci. Lett. 388, 343–352 (2014). &
- New geochemical models of core formation in the Moon from metal-silicate partitioning of 15 siderophile elements. Earth Planet. Sci. Lett. 441, 1–9 (2016). , , , &
- Thermal and magmatic evolution of the Moon. Rev. Mineral. Geochem. 60, 365–518 (2006). et al.
- Model of early lunar differentiation. Proc. Lunar Planet. Sci. Conf. 11, 289–315 (1980).
- 1990). & Origin of the Earth (Oxford Univ. Press,
- Lunar magma ocean crystallization revisited: bulk composition, early cumulate mineralogy, and the source regions of the highlands Mg-suite. Geochim. Cosmochim. Acta 75, 3024–3045 (2011). , &
- The origin of KREEP. Rev. Geophys. Space Phys. 17, 73–88 (1979). &
- The Moon: a Taylor perspective. Geochim. Cosmochim. Acta 70, 5904–5918 (2006). , &
- Volatile content of lunar volcanic glasses and the presence of water in the Moon’s interior. Nature 454, 192–195 (2008). et al.
- Nominally hydrous magmatism on the Moon. Proc. Natl Acad. Sci. USA 107, 11223–11228 (2010). et al.
- Lunar apatite with terrestrial volatile abundances. Nature 466, 466–469 (2010). et al.
- Water in lunar anorthosites and evidence for a wet early Moon. Nat. Geosci. 6, 177–180 (2013). , , &
- High pre-eruptive water contents preserved in lunar melt inclusions. Science 333, 213–215 (2011). , , , &
- Water, fluorine, and sulfur concentrations in the lunar mantle. Earth Planet. Sci. Lett. 427, 37–46 (2015). et al.
- The lunar magma ocean: reconciling the solidification process with lunar petrology and geochronology. Earth Planet. Sci. Lett. 304, 326–336 (2011). , &
- Joint inversion of seismic and gravity data for lunar composition and thermal state. Geophys. J. Int. 168, 243–258 (2007). , , &
- The composition of the Earth. Chem. Geol. 120, 223–253 (1995). &
- Mineralogy and petrology of some Apollo 16 rocks and fines: general petrologic model of Moon. Geochim. Cosmochim. Acta 1, 519–536 (1973). &
- Formation and evolution of a lunar core from ilmenite-rich magma ocean cumulates. Earth Planet. Sci. Lett. 292, 139–147 (2010). , &
- The crust of the Moon as seen by GRAIL. Science 339, 671–675 (2013). et al.
- Simulating planetary igneous crystallization environments (SPICEs): a suite of igneous crystallization programs. Lunar Planet. Sci. Conf. 45, abstr. 1111 (2014). , , , &
- Experimental investigations of the role of H2O in calc-alkaline differentiation and subduction zone magmatism. Contrib. Mineral. Petrol. 113, 143–166 (1993). &
- Solubility of molecular hydrogen in silicate melts and consequences for volatile evolution of terrestrial planets. Earth Planet. Sci. Lett. 345–348, 38–48 (2012). , , &
- Oxygen fugacity, temperature reproducibility, and H2O contents of nominally anhydrous piston-cylinder experiments using graphite capsules. Am. Mineral. 93, 1838–1844 (2008). , , &
- Apatites in lunar KREEP basalts: the missing link to understanding the H isotope systematics of the Moon. Geology 42, 363–366 (2014). et al.
- Experimental study of trace element partitioning between lunar orthopyroxene and anhydrous silicate melt: effects of lithium and iron. Chem. Geol. 285, 1–14 (2011). , &
- Mapping the thermal structure of solid-media pressure assemblies. Contrib. Mineral. Petrol. 142, 640–652 (2002). , , &
- The thermodynamics of iron and magnesium partitioning between olivine and liquid: criteria for assessing and predicting equilibrium in natural and experimental systems. Contrib. Mineral. Petrol. 149, 22–39 (2005).
- Fractionation of pyroxene-phyric MORB at low-pressure: An experimental-study. Contrib. Mineral. Petrol. 84, 293–309 (1983). &
- Primary magmas of mid-ocean ridge basalts 1. Experiments and methods. J. Geophys. Res. 97, 6885–6906 (1992). &
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