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High Pre-Eruptive Water Contents Preserved in Lunar Melt Inclusions Erik H. Hauri,1* Thomas Weinreich,2 Alberto E. Saal,2 Malcolm C. Rutherford,2 James A. Van Orman3 1Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington DC 20015, USA. 2Department of Geological Sciences, Brown University, Providence, RI 02912, USA. 3Department of Geological Sciences, Case Western Reserve University, Cleveland, OH 44106, USA.

*To whom correspondence should be addressed. E-mail: [email protected]

The Moon has long been thought to be highly depleted in within crystals that grow in the magma prior to eruption. By volatiles such as water, and indeed published direct virtue of their enclosure within their host crystals, melt measurements of water in lunar volcanic glasses have inclusions are protected from loss of volatiles by degassing never exceeded 50 parts per million (ppm). Here, we during magma eruption. Melt inclusions have been used for report in situ measurements of water in lunar melt decades to determine pre-eruptive volatile contents of inclusions; these samples of primitive lunar magma, by terrestrial magmas from subduction zones (9, 10), hotspots virtue of being trapped within olivine crystals prior to (11, 12) and mid-ocean ridges (13, 14), as well as volatile volcanic eruption, did not experience post-eruptive contents of Martian magmas (15, 16). Using standard degassing. The lunar melt inclusions contain 615–1410 petrographic methods, we identified nine inclusion-bearing ppm water, and high correlated amounts of fluorine (50– olivine crystals (Fig. 1) and analyzed melt inclusions hosted 78 ppm), sulfur (612–877 ppm) and chlorine (1.5–3.0 within (17). The measured water contents of the melt ppm). These volatile contents are very similar to primitive inclusions range from 615 ppm up to a maximum of 1410 terrestrial mid-ocean ridge basalts and indicate that some ppm (Fig. 2); these water contents are up to one hundred parts of the lunar interior contain as much water as times higher than the water content of the matrix glass

Earth’s upper mantle. surrounding the olivine crystals (6–30 ppm H2O) and the centers of individual volcanic glass beads from the same The Moon is thought to have formed in a giant impact sample (4). The melt inclusions also contain high collision between a Mars-sized object and an early-formed concentrations of fluorine (50–78 ppm), sulfur (612–877 proto-Earth (1). Though all of the inner planets, including ppm) and chlorine (1.5–3.0 ppm) that are two to one hundred Earth, are depleted in water and other volatiles when times higher than the matrix glasses and individual glass compared with primitive meteorites, the more extreme beads from this sample (Fig. 3). Volatile contents corrected depletion of volatiles in lunar volcanic rocks has long been for post-entrapment crystallization are on average 21% lower taken as key evidence for a giant impact that resulted in high- than the measured concentrations (17), and represent the best temperature catastrophic degassing of the material that estimate of the pre-eruptive concentrations of volatiles in the formed the Moon (2, 3). However, recent work on rapidly 74220 magma. quenched lunar volcanic glasses has detected the presence of There are few descriptions in the literature of melt water dissolved in lunar magmas at concentrations up to 46 inclusions contained within olivine from lunar samples, but ppm (4), and water contents of lunar apatite grains from mare these existing observations provide important context for the basalts are consistent with similarly minor amounts of water volatile abundances we have observed. Roedder and Weiblen in primitive lunar magmas (5–7). These results indicate that (18–20) noted the presence of melt silicate inclusions in the the Moon is not a perfectly anhydrous planetary body, and very first samples returned from the Apollo 11, Apollo 12 and suggest that some fraction of the Moon’s observed depletion Luna 16 missions, and noted that many primary melt in highly volatile elements may be the result of magmatic inclusions contained a vapor bubble, requiring dissolved degassing during the eruption of lunar magmas into the near- volatiles to have been present in the melt at the time it was vacuum of the Moon’s surface. trapped within the host crystal. Klein & Rutherford (21) and In order to bypass the process of volcanic degassing, we Weitz et al. (22) found sulfur contents of 600–800 ppm, conducted a search for lunar melt inclusions in Apollo 17 similar to our measurements, and Cl contents of <50 ppm that sample 74220, a lunar soil containing ~99% high-Ti volcanic were limited by electron microprobe detection limits. glass beads, the so-called “orange glass” with 9–12 wt% TiO 2 Reheated Apollo 12 melt inclusions, containing medium-Ti (8). Melt inclusions are small samples of magma trapped

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magmas (5–6 wt% TiO2), show sulfur contents that are 20% similar contents of fluorine, sulfur and chlorine associated higher than our data on average (23). In our data set, we with this water, a volatile abundance signature shared by both observe a correlation of all the volatiles with each other (Fig. bodies. 3) pointing toward the degassed compositions of the matrix These results show that the Moon is the only planetary glass rinds and volcanic glass beads (4). object in our solar system currently identified to have an The most important aspect of our volatile data on lunar internal reservoir with a volatile content that is similar to melt inclusions is their similarity to melt inclusions from Earth’s upper mantle, and that prior estimates of the lunar primitive samples of terrestrial mid-ocean ridge basalts inventory for highly volatile elements are biased to low (MORB), like those recovered from spreading centers located concentrations owing to the degassed nature of lunar samples within transform faults (24); the melt inclusions from 74220 thus far studied. The Moon has erupted a wide variety of bear a remarkable resemblance to melt inclusions from the magmas during its history, and it remains to be seen if other Siqueiros Fracture Zone on the East Pacific Rise, some of the lunar mantle sources are as volatile rich as the source of most primitive mid-ocean ridge magmas that have been Apollo 17 high-Ti magmas. Nevertheless, the hydrated nature measured (Fig. 3). These similarities suggest that the volatile of at least part of the Moon’s interior is a result that is not signature of the lunar mantle source of the high-Ti melt consistent with the notion that the Moon lost its entire volatile inclusions is very similar to that of the upper mantle source of inventory to the vacuum of space during degassing following MORB. a high-energy giant impact, which would be expected to leave It is important that we have made these measurements on a highly desiccated lunar interior. inclusions from olivine crystals contained within primitive If the bulk of the lunar interior has a volatile content lunar volcanic glasses. These inclusions were quenched similar to our estimate for the high-Ti mantle source, then our within a matter of minutes after their eruption (4), providing results present difficulties for late-accretion models that minimal opportunity for post-eruptive hydrogen diffusion out require volatile delivery to Earth and the Moon after their of the inclusions, and it means that we have a direct H2O formation, because these two bodies have very different measurement on primary lunar magma samples that have not accretion cross sections that would predict different internal experienced post-eruptive degassing and associated loss of volatile contents. An Earth-Moon similarity in volatiles could volatiles. The water concentrations that we measure are 20– indicate that chemical exchange of even the most volatile 100 times higher than previous direct measurements of the elements between the molten Earth and the proto-lunar disc lunar glass beads from this same sample, which was might have been pervasive and extensive, resulting in estimated to have suffered 95–98% loss of H2O via degassing homogenization at the very high temperatures expected (4), and they are higher than estimates derived from lunar following a giant impact; this could have been aided by the apatite measurements, which require a 95–99% correction for presence of a high-temperature convective atmospheric fractional crystallization to estimate primary magma volatile envelope surrounding Earth and the proto-lunar disc as the contents (5, 6). Our results are direct measurements on Moon solidified (29). Alternatively, it is conceivable that a primary lunar magma compositions that require no such portion of the lunar interior escaped the widespread melting extrapolations. expected in the aftermath of a giant impact, and simply Our melt inclusion data allow us to place some constraints inherited the inventory of water and other volatiles that is on the volatile content of the lunar mantle source that characteristic of Earth’s upper mantle. Any model for the generated the high-Ti picritic magmas. Using the most water- formation of Earth-Moon system must meet the constraints rich melt inclusion composition after correction for post- imposed by the presence of H2O in the lunar interior, with an entrapment crystallization, and an estimation that the high-Ti abundance similar to Earth’s upper mantle, and with a magmas originated from 5–30% batch partial melting with complement of fluorine, sulfur and chlorine also present at partitioning similar to terrestrial mantle-derived melts (17), terrestrial levels. To the extent that lunar formation models we estimate lunar mantle volatile concentrations of 79–409 predict very different volatile contents of Earth and the Moon, ppm H2O, 7–26 ppm F, 193–352 ppm S, and 0.14–0.83 ppm our results on the volatile content of lunar melt inclusions Cl. These estimates overlap most estimates for the volatile suggest that we lack understanding on some critical aspects of content of the terrestrial MORB mantle (24–27), and are the physics of planetary moon formation by collisional much higher than prior estimates for the lunar mantle based impact. on the volatile content of lunar apatite (5, 6) and the variation Our findings also have implications for the origin of water of Cl isotopes in lunar rocks (28) including the sample 74220 ice in shadowed lunar craters, which has been attributed to that we have studied here. The melt inclusions indicate cometary and meteoritic impacts (30). It is conceivable that definitively that some reservoirs within the interiors of Earth some of this water could have originated from magmatic and the Moon not only have similar water contents, but also degassing during emplacement and eruption of lunar magmas

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Acknowledgments: This work was supported by the Carnegie Institution of Washington, the NASA LASER and Cosmochemistry programs, the NASA Lunar Science Institute, and the NASA Astrobiology Institute. We thank J. Wang for NanoSIMS assistance, and L. Nittler and Z. Peeters for help with image processing software. All data can be found in supporting online materials available at Science Online.

Supporting Online Material www.sciencemag.org/cgi/content/full/science.1204626/DC1 Materials and Methods Figs. S1 and S2 Tables S1 and S2 References 32 to 37

21 February 2011; accepted 10 May 2011 Published online 26 May 2011; 10.1126/science.1204626

Fig. 1. (A to F) Optical photographs of olivines A1, A2, N3, N6, N8, and N9 from Apollo 17 sample 74220. Inclusions within circles indicate the inclusions that were imaged in Fig. 2. Scale bars are 10 µm in all photos. Fig. 2. (A to F) NanoSIMS scanning isotope images of olivines A1, A2, N3, N6, N8 and N9 from Apollo 17 sample 74220, showing the distribution of water within melt inclusions from the olivine grains shown in Fig. 1. The images show the distribution of the isotope ratio 16OH/30Si indicated by the color scale shown in (A), where dark regions correspond to low 16OH/30Si ratios (e.g. olivine surrounding melt inclusions), up to red regions within melt inclusions with 16OH/30Si ratios approaching 0.25 (corresponding to ~1400 ppm H2O). The color scale is the same in all images, and all images show a scale bar of 1 µm. Rectangular areas are regions of interest (ROIs) within which each isotope ratio is calculated and converted to concentrations. Fig. 3. (A to C) Volatile abundances for lunar melt inclusions (orange circle with black rims) and matrix glasses (orange circles) from Apollo 17 sample 74220. Melt inclusions show the highest concentrations (>600 ppm H2O) while matrix glasses show the lowest concentrations due to degassing (≤30 ppm H2O). The black curves show lunar magma degassing trends, scaled from the volatile-volatile correlations observed in core-rim NanoSIMS data on a lunar glass bead reported by

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