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H2O and Other Volatiles in the Moon, 50 Years and on Youxue Zhang*

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ABSTRACT: In the 50 years since the first lunar sample return, the investigation of H2O in the Moon has experienced several stages of developments and paradigms. In the early years since Apollo sample return, only bulk soil and bulk rock samples were analyzed for H2O as well as other volatiles. From 1970 to 2007, it was thought that the Moon is essentially devoid of innate H2O, containing probably less than 1 ppb. New technologies gradually enabled the measurements of H2O in lunar glass beads, soil glass, minerals such as apatite and anorthite, and olivine-hosted melt inclusions. The advancements in measurement techniques led to improved data and new fi insights. Starting from 2008, signi cant H2O in deep-sourced lunar rocks has been reported, resulting in a paradigm shift from a bone-dry Moon to a fairly wet Moon, although there is still debate about whether the bulk silicate Moon contains ∼100 ’ ppm of H2O (similar to that in the Earth s MORB mantle) or only a few ppm H2O. The advances on our knowledge of H2O in the Moon is accompanied by increased understanding of other volatiles in the Moon. Gradually, the degrees of depletion of various volatiles in the Moon relative to the Earth were inferred. Using assessed data from available lunar samples, mostly the melt inclusions, and also bulk rock analyses, it is found that the inferred degrees of depletion for volatile elements in the Moon relative to the Earth do not vary much and are independent of the condensation temperature. It is proposed that an early veneer delivered the volatiles to both the Earth and the Moon, but the Moon received proportionally less of the early veneer planetesimals. In addition to fi H2O in the interior of the Moon, signi cant surface H2O in the form of ice in lunar polar regions and structural OH in agglutinate glass in lunar regolith originating from solar wind implantation has also been gradually quantified. KEYWORDS: lunar volatiles, early veneer and late veneer, relative volatile depletion of the Moon compared to the Earth, volatile/refractory elemental ratios, water in the Moon, fluorine in the Moon, sulfur in the Moon, chlorine in the Moon, copper in the Moon, cesium in the Moon

■ INTRODUCTION dry, with less than one ppb water”. In just 2 years, this “new ” 14 fi Fifty years ago, in 1969, astronauts of the Apollo 11 mission view became an old view of the Moon. Saal et al. rst brought back lunar samples and offered humankind the discovered a measurable amount of H2O in lunar volcanic glasses. Numerous subsequent reports (some were planned opportunity for the first time to analyze lunar rocks and to well before 2008 and some inspired by the study of Saal et investigate the Moon to unprecedented detail. Later Apollo 14 Downloaded via UNIV OF MICHIGAN ANN ARBOR on September 29, 2020 at 04:37:57 (UTC). fi See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles. al. ) showed signi cant H O and other volatiles in lunar missions and the discovery of lunar meteorites provided more − 2 apatite,15 30 plagioclase crystallized from the lunar magma lunar samples. Extensive research was carried out on H O and 2 ocean (LMO),31,32 and lunar mare basalt and hence lunar other volatiles in lunar rocks because they provide key 33−40 − interior, and shifted the paradigm of a bone-dry Moon constraints on the origin of the Moon,1 7 on understanding 8−10 with less than 1 ppb H2O to a fairly wet Moon. The paradigm the evolution of the Moon, and for assessing future human 5−7 11 shift led to new thinking about the origin of the Moon and exploration of the Moon. It was known before the Apollo − the evolution of the Moon.8 10 In addition, new studies further program that liquid water cannot exist on the surface of the − constrained lunar surface H O content,41 52 and also supplied Moon because the surface is essentially under a vacuum. The 2 more reliable concentration data on other volatile elements, very first analyses of the Apollo 11 samples revealed significant 33−37,53,54 including C, F, S, Cl, Zn, Cu, and Ga, etc. depletion of volatiles, including a K/U ratio in lunar rocks lower than that in terrestrial rocks by a factor of about 4 to 5.12 fi Received: November 19, 2019 Because H2O is highly volatile, signi cant depletion is expected in lunar samples. Early (1970−2007) studies did not Revised: July 27, 2020 Accepted: July 28, 2020 convincingly reveal any innate lunar H2O, leading to the notion of a completely dry Moon. For example, in the 2006 Published: July 28, 2020 volume of Reviews in Mineralogy and Geochemistry titled “New Views of the Moon”, Taylor et al.13 wrote that “the Moon is

© 2020 American Chemical Society https://dx.doi.org/10.1021/acsearthspacechem.9b00305 1480 ACS Earth Space Chem. 2020, 4, 1480−1499 ACS Earth and Space Chemistry http://pubs.acs.org/journal/aesccq Review

a Table 1. Whole-Rock or Glass Bead Composition (Oxide wt %) of Lunar Rocks That Have Been Investigated for H2O and Other Volatile Elements Using Naturally Glassy or Homogenized Melt Inclusions

10020 12008 12040 15016 15647 74220 74235 age (Ga) 3.8 3.2 3.3 3.3 3.6 3.7 OHMIsb NPG + HG HG HG HG HG NG + HG NPG + HG

SiO2 40.8 42.75 43.89 44.3 44.4 39.2 38.62

TiO2 10.35 4.45 2.74 2.27 2.44 9.2 12.17

Al2O3 10.31 7.98 7.41 8.39 9 5.9 8.61

Cr2O3 0.30 0.61 0.70 0.66 0.63 0.63 0.51 FeO 18.79 21.94 20.9 22.95 22.36 22.3 19.32 MnO 0.27 0.3 0.26 0.29 0.28 0.29 0.28 MgO 7 12.33 16.1 11.65 10.04 14.5 8.35 CaO 11.99 8.97 7.87 9.2 9.65 7.4 10.7

Na2O 0.38 0.25 0.2 0.32 0.22 0.44 0.4

K2O 0.07 0.05 0.04 0.05 0.044 0.06 0.07

P2O5 0.12 0.07 0.07 0.06 0.065 0.04 0.05 − H2O ref 35, 37 35 37 37 37 33 37 37 aAge and compositions of whole rocks (for 74220, orange glass beads) are from Lunar Sample Compendium. (https://curator.jsc.nasa.gov/lunar/ lsc/). bOHMIs (olivine-hosted melt inclusions) that are naturally glassy (NG), naturally partially glassy (NPG), or homogenized (HG) have been studied.

The fifty year anniversary of returned lunar sample research lists the age and composition of some lunar rocks discussed in is a good time to look back at the discoveries and this review. fi accomplishments, and to review current debates on unsolved Below I rst discuss H2O in the Moon because H2O is the issues. A number of synthesis and review contributions with most extensively investigated volatile by using a number of − different focus have been published.34,55 57 I am fortunate to different approaches, including bulk rock analyses and SIMS have participated in this exciting paradigm shift. This work will (second ion mass spectrometry) and FTIR (Fourier transform review advances in our understanding of the abundance and infrared spectrometry) analyses on lunar minerals, glass beads, roles of H O and other volatiles in the Moon over the past 50 and melt inclusions. Then other volatiles will be examined. 2 fi years of lunar science, with more emphasis on the more recent Then the results will be synthesized, and their signi cance in work. understanding the origin of the Moon evaluated. Before in-depth discussion, some definitions and basic H O IN THE LUNAR INTERIOR AND IGNEOUS information are in order. H Oor“water” is defined to be ■ 2 2 ROCKS hydrogen bonded with oxygen, including H2O ice, structural OH in minerals and glass, but excluding hydrogen bonded with Early (Pre-2008) Studies of Apollo Samples on H2Oin itself, carbon, and nitrogen, etc. There is no liquid water on the Lunar Rocks. The Apollo 11 mission was the first human- Moon. The volatility of volatile elements is often characterized landing mission to the Moon and brought back 21.5 kg of lunar samples on July 24, 1969. These were the first recognized by the 50% condensation temperature, Tc, which may depend on the oxygen fugacity.58 Lodders59 provided T for H O and lunar samples available to humankind. One important feature c 2 fi all other elements, and Wood et al.60 provided an updated set revealed by the analyses of these rst lunar samples is the stronger depletion of volatile elements in the Moon than in the of Tc values except for H2O, C, N, and noble gases. For some 12,64,65 60 fi ff Earth. Hence, there was much expectation that H2O (an elements, the new Tc by Wood et al. is signi cantly di erent 59 even more volatile component) in the Moon would be highly from that of Lodders. In this work, new Tc values from Wood 66 60 depleted. Epstein and Taylor analyzed H2 and H2O content et al. are used, except for species whose Tc values were not 2 1 60 59 and H/ H isotope ratio in some of these Apollo soil and evaluated by Wood et al., for which T values from Lodders c breccia samples using stepwise heating of the bulk “rock” to are used. Volatile elements discussed in this work include H O, 2 release the gases. The concentration of H ranges from 22 to Cl, Pb, Cs, S, F, Zn, Rb, K, Ga, Cu, Na, and Li. Lunar rocks 2 50 μmol/g (or from 44 to 100 ppm) with δ2H ranging from discussed here include mare basalts and highland rocks (mostly − ‰ − ‰ 873 to 830 . The concentration of H2O ranges from anorthosites, which consist of mainly Ca-plagioclase). Lunar 8.9 to 11.6 μmol/g (or 160 to 209 ppm) with δ2H ranging basalts are subdivided into high-Ti basalts, low-Ti basalts, and − ‰ − ‰ ff fi from 412 to 257 . The authors concluded that (i) very-low-Ti basalts, but di erent de nitions can be found in H O was due to terrestrial contamination, (ii) H is of solar fi 61 2 2 the literature. One set of de nitions is by Taylor et al.: high- wind origin, and (iii) there was no detectable innate lunar − Ti (>9 wt % TiO2), low-Ti (1.5 9 wt % TiO2), and very-low- H O, but they cautioned that the possibility that lunar rocks fi 2 Ti (<1.5 wt % TiO2). Another set of de nitions is by Neal and may contain primary water with normal δ2H had not been 62 − Taylor: high-Ti (>6 wt % TiO2), low-Ti (1 6 wt % TiO2), eliminated. Subsequent work between 1970 and 2007 did not and very-low-Ti (<1 wt % TiO2). In this work, the latter challenge the conclusion but strengthened the notion that the fi fi de nition is adopted. Note that the de nitions do not mean Moon does not contain innate H2O. For example, Epstein and 67 68 that TiO2 distribution in mare basalts is bimodal or trimodal. Taylor and Beckinsale concluded that measured H2Oin Using spectral reflectance data, Giguere et al.63 showed that lunar bulk rock samples (ranging from 72 to 720 ppm) was the distribution of TiO2 concentration in mare basalts is likely entirely due to terrestrial contamination, including the continuous, probably close to log-normal distribution. Table 1 rusty rock 66095. In order to avoid terrestrial contamination, it

1481 https://dx.doi.org/10.1021/acsearthspacechem.9b00305 ACS Earth Space Chem. 2020, 4, 1480−1499 ACS Earth and Space Chemistry http://pubs.acs.org/journal/aesccq Review is best to use a microbeam method to analyze the interior of lunar apatite papers, Boyce et al.16 pointed out that “it is grains of collected samples, rather than heating or dissolving difficult, if not impossible, to learn anything about” the bulk rock samples. Fogel and Rutherford69 used microbeam conditions of the melt before apatite saturation because OH is FTIR to measure lunar volcanic glasses but found OH and C a structural component in apatite and because apatite strongly − − were below detection limits (10 50 ppm for H2O and 50 100 fractionates the OH/F ratio. Specifically, they said that “H-rich ” ppm for C) at the time. apatite cannot be cited as evidence for elevated H2O in the Numerous data also show significant depletion of many melt.16 Pernet-Fisher et al.28 also discussed complexities in 70,71 other volatiles in the Moon compared to the Earth. The using apatite to estimate H2O in the Moon. Nonetheless, notion that the Moon is moderately depleted in moderately apatite remains an important lunar mineral for constraining H volatile elements and extremely depleted in highly volatile and Cl isotope ratios of lunar igneous materials, origin of lunar elements was perfectly consistent with earlier thinking of the volatiles, evolution of lunar magma ocean, and possible − Giant Impact origin for the Moon, in which a Mars-sized body alteration/metasomatism of lunar rocks.17,21 27,29,30,75,76 collided with the proto-Earth, and the Moon was made of − Using Cl Isotopes in Lunar Materials to Infer Lunar H2O. ff 1 4 77 splashed-o high-temperature materials. It was thought that Sharp et al. reported Cl isotope ratios in lunar fire-fountain 1 H2O and other highly volatile components would be lost at glass beads, lunar apatite, and other lunar materials. They − 4 high temperatures of 3000 6000 K. Hence, even though found that δ37Cl/35Cl values in these lunar samples range from direct measurements never provided strong constraints that 0.0‰ to 24.5‰. On the other hand, δ37Cl values in typical 78 77 H2O was below 10 ppm, certainly not sub-ppm level, it was still terrestrial samples are 0 ± 0.5‰. Sharp et al. argued that thought widely that the Moon was essentially void of H2O. 13 because Cl is very hydrophilic, if H2O concentration were high, Taylor et al. claimed that “the Moon is dry, with less than 1 37 35 ” Cl would be in the form of HCl and Cl/ Cl isotope ppb water . Soon this claim would be shown to be incorrect. fractionation would be small, as in terrestrial samples. They Post-2008 Studies. Advancement in secondary ion mass hence thought that Cl must be degassed as metal chloride, spectrometry allowed the first accurate measurement of innate such as FeCl2 or ZnCl2, and estimated that H2O concentration H (interpreted to be H2O) in lunar igneous samples. Saal et 14 in the lunar mantle would be below 0.09 ppm. Further studies al. reported new microbeam SIMS measurements of H2O, F, of lunar apatite by numerous authors confirmed the very high Cl, and S concentrations and concentration profiles in lunar − ‰ fi Cl isotope fractionation, ranging from 4 to volcanic re-fountain glass beads. The highest H2O concen- ‰ 17,18,24,26,75,76 81 . However, the inference of low H2O tration was 46 ppm in a high-Ti basalt glass, which is 46,000 concentration in the lunar mantle by Sharp et al.77 using times 1 ppb in the claim by Taylor et al.13 The volcanic glasses large variability in Cl isotope ratios is debatable. For example, cooled on the surface of the Moon at presumably near-vacuum 79 Sharp et al. reported that δ37Cl in terrestrial volcanic conditions, and hence likely lost much H O and other volatiles. 2 fumaroles ranges from −4.0‰ to 18.8‰, demonstrating that This expectation is confirmed by measured concentration significant 37Cl/35Cl isotope fractionation of similar magnitude profiles of volatiles in a green glass bead:14 volatile element to that in lunar materials found in Sharp et al.77 can occur in concentrations are high in the center (29 ppm H O, 8.6 ppm 2 fumaroles in the presence of abundant H O. In addition, lunar F, 262 ppm S, and 0.27 ppm Cl) and smoothly decreases 2 apatite containing significant OH also shows a large range of toward the surface of the glass bead (14 ppm H2O, 5.2 ppm F, δ37 17,18,21−27,75,76 216 ppm S, and 0.14 ppm Cl near the surface). This trend Cl values, inconsistent with the claim that the demonstrates that H O in glass beads is not due to terrestrial presence of H2O would prohibit large Cl isotope fractiona- 2 tion.77 Various mechanisms and processes have since been contamination, which would have resulted in higher H2O ff δ37 concentration near the bead surface and lower concentration at o ered to explain the large range of Cl values, including the the center. Saal et al.14 modeled the volatile element following: (1) degassing of the lunar magma ocean leading to δ37 concentration profiles and estimated pre-eruptive H O in the elevated Cl in urKREEP, the last residue of the lunar magma 2 ocean, which later mixed with less fractionated Cl reser- glass bead to be likely 745 ppm, but uncertainties in the 17,24 assumed thermal history and diffusivities and other model voir; (2) metasomatism of lunar samples by volatile-rich fl δ37 75 issues made the estimation debatable.72,73 A flurry of uid phase with high Cl; and (3) Cl isotope fractionation occurring in the early and dry stage of Moon formation contributions followed, determining H2O content in various followed by late accretion of hydrous components.76 In lunar samples and inferring H2O concentration in the lunar mantle using different approaches. addition, extensive post-eruptive degassing of Cl on the lunar H2O in Lunar Apatite. Lunar apatite has been shown to surface (see eq 1 later) is a mechanism to produce large Cl fi isotope ratio fractionation in lunar volcanic rocks. contain signi cant H2O since 2008. Early work used electron microprobe data to calculate OH concentrations in lunar H2O in Olivine-Hosted Melt Inclusions. Because lunar bulk apatite from measured F and Cl concentrations by assuming rocks and volcanic glass beads might have lost H2O, and lunar 74 stoichiometry. Although the data showed significant OH in bulk rock data might be contaminated by terrestrial H2O, 33 apatite, the confidence level was not high and direct Hauri et al. used SIMS to measure concentrations of H2O measurement of H or OH in apatite is preferred. Boyce et and other volatiles in olivine-hosted melt inclusions (OHMIs) al.,15 McCubbin et al.,19 and Greenwood et al.20 used SIMS to and basalt glass beads in lunar soil sample 74220 containing measure H in apatite and reported that OH contents in lunar fire-fountain volcanic orange glass beads and olivine grains apatite are similar to those in terrestrial apatite. Initially, these with melt inclusions that are essentially glassy. Note that glass results were thought to support a wet Moon, and these authors beads in this fire-fountain deposit contain surface coating that 34,80−82 tried to use H2O concentration in apatite to estimate H2O is rich in volatiles. Hence, if whole beads or whole soil concentration in the melt in which apatite crystallized as well samples are dissolved, the concentrations of volatiles can be as the source region of the melt. However, in a later very high.34,77 On the other hand, microbeam SIMS analyses of publication coauthored by all first authors on these earlier glass beads can avoid the surface coating and reveal interior

1482 https://dx.doi.org/10.1021/acsearthspacechem.9b00305 ACS Earth Space Chem. 2020, 4, 1480−1499 ACS Earth and Space Chemistry http://pubs.acs.org/journal/aesccq Review

Figure 1. Volatile versus refractory element concentration in OHMIs in lunar Apollo basalt 10020. The solid line in each panel represents the constant ratio given along the line. H2O/Ce and F/Nd ratios are roughly constant in an experimentally homogenized OHMI, and the glassy part of the partially glassy natural MIs (two of them, but one was measured at multiple points). On the other hand, S/Dy ratio in the glassy part of the partially crystallized MIs is significantly lower than that in the homogenized MI, indicating crystallization of sulfide. The homogenized MI has a μ 36 diameter of 83 m, and hence H2O loss during heating is negligible (see Figure 2). Data are from refs 35 and 37. concentrations of volatiles. Surface coating is not an issue when entrapment bubble growth and diffusion through the host melt inclusions in olivine grains are measured. mineral would decrease the concentrations of volatiles. Hence, A melt inclusion is a small pocket of melt that is trapped by measured volatile element concentrations in melt inclusions an advancing crystal growing in magma. Such a melt inclusion are still a minimum. is able to better preserve the concentrations of volatiles due to Because olivine host provides some protection against H O −2 protection by the host crystal. Hence, melt inclusions are loss from melt inclusions, albeit imperfect protection,36,91 95 widely used in studying pre-eruptive volatiles in terrestrial OHMIs offer a better environment than exposed glass or rock 83−85 volcanic rocks. There may also be complexities of using to preserve pre-eruptive H2O content. Concentration 35−37,96 melt inclusions, which have been addressed in the literature. data show evidence that H2O can be lost from lunar (1) Because the trapped melt is in the boundary layer of a melt inclusions if cooling is slow. The OHMIs in 74220 are growing crystal, there may be concern about whether a melt essentially glassy, meaning that the glass beads and olivine inclusion represents the bulk melt at the time of extrapment, or crystals in 74220 are among the most rapidly quenched lunar whether there would have been significant enrichment or volcanic samples. Estimated cooling rates of glass beads in depletion of elements due to diffusion through the boundary 74220 are 1−K/s,97,98 and that of the larger olivine grains layer. Lu et al.86 investigated melt inclusions of 50−400 μm containing melt inclusions (MIs) is about 1 K/s.36 Hauri et 33 diameter and concluded that the composition of melt al. found up to 1410 ppm H2O in OHMIs in 74220. inclusions in minerals crystallizing from rhyolite melt is Assuming that the degree of partial melting that produced indistinguishable from the bulk melt. This study concerns 74220 basalt is 5−30%, Hauri et al.33 estimated that the source ff − OHMIs in lunar basalts, in which elemental di usivities are mantle contains 79 409 ppm H2O, ranging from slightly greater than those in rhyolite,87 implying that the effect of below to about 4 times that in the terrestrial MORB mantle.99 boundary layer enrichment or depletion would be smaller than Subsequently, Saal et al.33 reported that hydrogen isotopes in in rhyolite. Hence, boundary layer effect is deemed negligible. lunar volcanic glasses and OHMIs reveal a carbonaceous (2) Melt inclusion composition may also be modified by (i) chondritic heritage. post-entrapment crystallization, most often due to the growth In order to bypass the need to (i) estimate the degree of of the host mineral inward into a melt inclusion,88,89 (ii) post- partial melting and (ii) evaluate whether the mantle source is entrapment bubble growth,90 and (iii) post-entrapment primitive or differentiated, Chen et al.35 measured both − diffusion of elements through the host mineral.91 94 In this volatiles and refractory elements in lunar samples and used work, appropriate elemental ratios will be used to circumvent elemental ratios to infer concentrations of volatiles in the lunar the need to correct for post-entrapment crystallization. Post- mantle. The ratios, H2O/Ce, F/Nd, and S/Dy, have been

1483 https://dx.doi.org/10.1021/acsearthspacechem.9b00305 ACS Earth Space Chem. 2020, 4, 1480−1499 ACS Earth and Space Chemistry http://pubs.acs.org/journal/aesccq Review shown to be roughly constant during mantle partial melting Ni et al.36 investigated diffusive loss of volatiles from 100−106 and basalt evolution in terrestrial MORB and OIB, OHMIs in 74220 and found that H2O can be lost by short- meaning that the ratio in basalts also represents the ratio in the duration heating (Figure 2), in agreement with literature mantle, regardless of its degree of depletion. Limited data on 35,37 lunar basalts by my group also verify that H2O/Ce and F/ Nd ratios are constant during lunar basalt fractionation. For example, H2O versus Ce, F versus Nd, and S versus Dy data in a homogenized melt inclusion (39 wt % SiO2, 18.1 wt % FeO, and 6.5 wt % MgO; near the melt composition at the incorporation of the MI) and in the glass of two partially glassy − MIs (glass composition: 55 wt % SiO2, 5.6 7.4 wt % FeO, and 1.7−2.3 wt % MgO; representing evolved melt) in lunar sample 10020 are plotted in Figure 1. The H2O/Ce ratio in both partially glassy and homogenized melt inclusions in this sample is 8.1 (solid line in Figure 1a), even though the partially glassy MIs are 69% crystallized based on Ce concentration increase in the melt. The F/Nd ratio is also constant (3.1, Figure 1b). However, the S/Dy ratio in evolved melt is significantly lower and variable (Figure 1c), indicating a variable degree of sulfide crystallization from the melt.

Therefore, the H2O/CeandF/Ndratiosdonotvary Figure 2. H2O/Ce ratio in natural and homogenized (reheated) significantly in lunar basalts even with significant differentiation OHMIs in lunar sample 74220. Data are from refs 35 and 36. For (at least up to 55 wt % SiO2 and down to 2 wt % MgO), but reference, H2O/Ce ratio in orange glass beads in 74220 is about 0.6. fi ff Data in refs 33 and 34 are not used because H2O concentration in the S/Dy ratio can decrease signi cantly with di erentiation. ∼ Before further discussion on H O, it is important to their work at a given MI diameter is systematically higher by 40% 2 than the data in refs 35 and 36, probably due to different emphasize that OHMIs in lunar soil sample 74220 do not calibrations.36 Adapted from 36. contain a coating of volatile-rich materials, and they show similar volatile/refractory elemental ratios for most other elements as other lunar OHMIs (see later sections) except for 92−95 the H O/Ce ratio. Chen et al.35 studied volcanic materials in work, whereas F, Cl, and S in OHMIs are not much 2 affected by short-duration heating. For a heating duration of 2 lunar soil samples 74220 (containing orange glass beads) and ° 15421 (containing green glass beads) and mare basalts 10020, min at about 1300 C to homogenize OHMIs, loss of H2Ois noticeable if the melt inclusion diameter is less than 50 μm 12008, and 15016. The glass beads in 74220 and 15421 are 36 glassy, indicating that they are the most rapidly quenched lunar (black solid triangles and dashed curve in Figure 2). Ni et al. volcanic samples with cooling rate of ≥1 K/s.36,97,98 No olivine also found that H2O/Ce ratio in naturally glassy OHMIs in grains were found in 15421. Of all lunar samples examined so 74220 decreases as MI diameter decreases (orange solid circles in Figure 2), indicating that the smaller naturally glassy far, only 74220 contains olivine with essentially glassy MIs. OHMIs in 74220 also lost significant H O during cooling on Mare basalts 10020, 12008, and 15016 contain completely 2 the lunar surface even though this is one of the most rapidly crystalline to partially glassy OHMIs due to slower cooling quenched samples. As shown in Figure 2, the trend for rates. Effort to analyze H O in crystalline MIs using large 2 homogenized MIs is below that for natural MIs due to beams resulted in highly scattered H2O/Ce ratios as well as 35 additional loss during homogenization. Because the heating other volatile/refractory ratios (one reason is that volatile history is roughly the same for the homogenization experi- and refractory elements are not analyzed at the same session, ments, using the black dashed curve in Figure 2, loss of H O meaning that they are not analyzed on the same material35). 2 35 fi during laboratory heating (homogenization) may be roughly Hence, Chen et al. rst homogenized the crystalline MIs by corrected. For example, if the diameter of an OHMI is 26 μm, heating MI-bearing olivine grains to above the liquidus of the about half of H2O in the MI would be lost by homogenization. MI for a couple of minutes, and then the quenched glassy MIs On the other hand, the trend for natural MIs defined by the fi were analyzed by SIMS. In addition, to con rm that H orange solid circles and line is specific for the rapidly cooled analyzed by SIMS is indeed in the form of OH, a large olivine grains in 74220 and cannot be used to correct for H2O homogenized OHMI was first analyzed by FTIR and then by 35 concentration in other lunar samples. Nonetheless, the data do SIMS for the H2O concentration. The rough agreement in indicate that OHMIs in even the most rapidly cooled lunar the obtained H O concentrations between FTIR, which 2 samples lost noticeable amounts of H2O, meaning that OHMIs measures OH in glass, and SIMS, which measured total H in in the slower cooled volcanic samples must have lost even 35 the glass, is reassuring. Chen et al. found that the naturally more H O unless the host olivine is surrounded by melt ∼ 2 glassy MIs in 74220 contain the highest H2O/Ce ratio ( 55), containing roughly the same concentration of H2O as in the followed by OHMIs in 10020 (both naturally partially glassy or OHMI. ∼ homogenized) with H2O/Ce ratio of 8, and followed by even In addition to the major role of the diameter of the OHMIs lower ratios (≤4) in homogenized crystalline MIs in 12008. examined in Figure 2, the diameter of the host olivine grain,36 The glassy embayments and glass beads in 74220 contain even whether the MI is in the center or near the surface of the host lower H2O/Ce ratios. Hence, even slowly cooled OHMIs olivine grain, the orientation of the olivine grain, and possible preserve volatiles better than rapidly quenched but unpro- presence of invisible cracks, also play a role in determining the tected glass beads. loss during heating in the laboratory. These factors are not

1484 https://dx.doi.org/10.1021/acsearthspacechem.9b00305 ACS Earth Space Chem. 2020, 4, 1480−1499 ACS Earth and Space Chemistry http://pubs.acs.org/journal/aesccq Review ff corrected even though MIs too far o the center of olivine because H2O is lost only after oversaturation at very low grains or with visible cracks are avoided. pressures. Among the seven Apollo samples that have been 37 Ni et al. examined volatile elements in OHMIs for more investigated for H2O/Ce ratio, only four have cooling rates lunar basalts. In total, OHMIs in three high-Ti basalts and four reported. Even though the cooling rate for 10020 has not been low-Ti basalts have been investigated in the literature: high-Ti- investigated, the fact that there are natural partially glassy MIs − basalts in OHMIs in lunar soil sample 74220,33 37 high-Ti in 10020 indicates that the cooling rate should be higher than mare basalts 10020,35,37 and 7423537 and low-Ti mare basalt 12008 that has no natural partially glassy MIs, but lower than 12008,35 12040,37 15016,35,37 and 15647.37 The compositions that of 74235 because the glass in OHMIs in 10020 is more of these basalts are listed in Table 1. evolved than that in 74235. Figure 3 shows that there exists a Unlike F/Nd and S/Dy ratios, which are roughly constant in lunar melt inclusions of different lunar samples, available data 34−37 on H2O/Ce ratio in lunar OHMIs show wide variability. In order to interpret the data, it is necessary to understand post-eruptive H2O loss in lunar OHMIs. A number of observations show H2O loss from lunar volcanic rocks: (1) H2O concentration in orange glass beads in sample 74220 14,34,35,37 ranges from 5 to 14 ppm, whereas H2O concentration in OHMIs in 74220 with diameter ≥ 40 μm ranges from 900 − to 1400 ppm,33 37 indicating that even rapidly quenched glass samples on the lunar surface have lost about 99% of their pre- eruptive H2O, and that olivine host provides some protection against H2O loss for melt inclusions. (2) OHMIs that are essentially glassy in 74220 with cooling rate ∼ 1 K/s36 still show a trend of decreasing H2O with decreasing MI diameter (orange solid circles and line in Figure 2), indicating that the protection of a melt inclusion by the olivine host is not perfect Figure 3. Dependence of highest H2O/Ce ratio (after correction for even for rapidly quenched lunar glassy melt inclusions in homogenization loss) in each lunar sample as a function of post- olivine. For slowly cooled lunar samples, it is expected that eruptive cooling rate q.H2O/Ce data are from refs 35 and 37 but with more H2O would be lost from OHMIs, although OHMIs are correction for H2O loss during laboratory homogenization using the still expected to provide some protection. Expected loss of blue dashed curve in Figure 2. The data by refs 33 and 34 on 74220 H O from OHMIs includes (2a) loss due to diffusion through are not used due to interlaboratory inconsistency and would give a 2 ∼ the olivine host during post-eruptive cooling, (2b) additional H2O/Ce ratio of 70. Cooling rates are from refs 36, 113, and 115. loss for small MIs, and (2c) additional loss for MIs near a crack or a crystal surface. (3) H2O can also be lost from OHMIs rough inverse relation between the H2O/Ce ratio in OHMIs during the short-duration heating to homogenize MIs and post-eruptive cooling rates in these five samples, consistent ff 37 depending on the MI diameter (black solid triangles and with di usive loss of H2O. This trend is consistent with dashed curve in Figure 2), and this loss can be roughly qualitative conclusions by others.35,96 Hence, it may be corrected using the black dashed curve relative to the orange concluded that the sample with the highest cooling rate line in Figure 2. (74220) best represents the pre-eruptive H2O/Ce ratio in To address H2O loss from lunar volcanic samples discussed lunar basalts, and hence in the lunar mantle. Assuming that the above, we use OHMIs to avoid the no. 1 cause of H2O loss lunar primitive mantle contains the same Ce concentration as 123 (high H2O loss due to lack of protection). When homogenized the terrestrial mantle (1.675 ppm ), the H2O concentration +50 OHMIs are used, the loss of H2O due to homogenization in in the primitive lunar mantle is inferred to be 90−30 ppm. 53 the laboratory, the no. 3 cause for H2O loss, can be roughly Albarede et al. offered a different interpretation of the data. ff corrected using Figure 2. To minimize the e ect of loss due to They argued that sample 74220 with high H2O/Ce ratios in nos. 2b and 2c above, we use the two highest values of H2O/ OHMIs is a local anomaly and the lower H2O/Ce ratios are Ce measured in multiple MIs in a given lunar sample to more representative of the lunar mantle. Arguments against represent the ratio in the sample (two instead of one so as to volcanic OHMI materials in 74220 being a local anomaly − avoid outliers). Hence, the only cause that is not accounted for enriched in volatiles include the following:34 37 (1) Other is no. 2a, diffusive loss through the olivine host during cooling volatiles (such as F, S, and Cl) in OHMIs in 74220 are not after eruption, which is expected to depend on the post- higher than in homogenized OHMIs from other mare basalts; eruption cooling rate. For many lunar basalts, cooling rates at (2) high-Ti basalt glass beads are among the most primitive various stages of magma differentiation have been stud- magmas from the lunar mantle; (3) ingassing or coating of 36,73,97,98,107−121 fi ied. A volcanic rock typically rst cools slowly H2O into OHMIs in 74220 can be ruled out on the basis of the in its magma reservoir, more rapidly in the conduit, and then observed H2O/Ce ratio versus MI diameter trend for natural much more rapidly after eruption to the surface. Degassing of MIs (orange solid circles and line) in Figure 2; and (4) limited H2O mostly occurs at the surface or very shallow depths data show that the high H2O/Ce ratio can be correlated well because H2O solubility in melts is high at high pressures. For with cooling rate in Figure 3.Hence,ourpreferred example, the saturation pressure for 1000 ppm H2O (about the interpretation is that OHMIs in 74220 best preserve and highest H2O measured in lunar melt inclusions) in a basaltic represent pre-eruptive H2O/Ce ratios in lunar basalts, even melt at 1473 K is 0.2 MPa,122 or a lunar magma depth of 43 m. though more extensive data are needed to settle the debate. Hence, we use post-eruptive cooling rates (the fastest cooling Interestingly, in retrospect, the H2O contents extracted from 66−68 stage) as a parameter in assessing H2O loss from OHMIs bulk rock samples are about the same order of magnitude

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−2 ′ as our new estimate of H2O concentration in lunar basalts. cm . Even though the I value almost doubled, because both Hence, some of these bulk rock measurements appear to have Hui et al.31 and Hamada et al.138 used the old calibration136 done a superb job in avoiding terrestrial contamination and when measuring H2O concentration in plagioclase, using the fl 139 plag 31 might re ect innate H2O in lunar basalts even though all of new calibration lowers CH2O in Hui et al. to 3.3 ppm, but these earlier data were discounted by their original authors as plag plag/melt 138 also lowers CH2O and DH2O in Hamada et al. by the same being due to terrestrial contamination. ∼ ± Lunar mare basalts in which OHMIs are studied are factor, leading to the same 130 65 ppm of H2O in the bulk “ ” − silicate Moon (BSM), which are consistent with H2O relatively young lunar rocks, 3.2 3.7 Ga (Table 1). Hence, +50 concentration of 90− ppm in the primitive lunar mantle on inferred H O concentrations in lunar basalts and the lunar 30 2 the basis of studies of OHMIs.35,37 mantle may not reflect primary H O in the Moon, but H O 2 2 More experiments were carried out to investigate H O due to postformation bombardment of meteorites/asteroids 2 partitioning between plagioclase and mafic melts.140,141 These after the LMO. To estimate H O concentration in the Moon 2 new data are inconsistent with earlier data138 and appear to during the LMO, it is necessary to examine older lunar rocks, show Dplag/melt as two different functions of Cmelt, one for Cmelt such as highland anorthosites and troctolites (4.29−4.47 H2O H2O H2O 124−128 melt Ga ). < 0.7 wt % and one for CH2O > 0.7 wt %. However, when all H2O in Plagioclase of Lunar Anorthosite. It was thought experimental data are examined by a concentration plot, the that immediately after Moon formation, much of the Moon new data in ref 141 (red solid circles in Figure 4) do not follow was melted and there was a global LMO of peridotite − composition.129 133 Olivine crystallized first, followed by pyroxenes. The mafic minerals sank. At 70−80% crystalliza- tion, plagioclase began to form and floated to the sur- − face.9,10,129 135 Lunar anorthosites are thought to represent floated plagioclase cumulates from the LMO and hence the oldest crustal rock in the Moon. Therefore, if H2O concentration in plagioclase in lunar highland anorthosite can be measured, it may be used to infer H2O concentration in the LMO when the Moon had not solidified yet. Hui et al.31 used Fourier transform infrared spectrometer to determine H2O concentration in plagioclase crystals in lunar highland anorthosites and troctolites. Because plagioclase is anisotropic, it is necessary to take FTIR spectra at three mutually perpendicular directions that are also the extinction directions. The high degree of transparency of lunar plagioclase helps in such measurements because thick (e.g., millimeter thick) samples can be used to accumulate more transmission 31 Figure 4. Literature experimental data on H2O partitioning between signal. The limited data in Hui et al. showed that plagioclase plagioclase and mafic melt. Concentration data in the two phases are in highland anorthosite has a total (summing three directions) directly plotted to examine whether Henry’s law is obeyed. Data are ≈ −2 138 140 141 integrated absorption area Atot 98 cm . This IR signal can from Hamada et al., Caseres et al., and Lin et al., but those of plag Hamada et al.138 are recalculated using the new calibration.139 The be converted to H2O concentration in plagioclase (CH2O) if the absorption coefficient, I′,isknown.FromC plag ,HO dashed curve is based on assuming (1) constant OH partition H2O 2 coefficient and (2) constant equilibrium constant for reaction melt ⇌ 122 concentration in the magma ocean (CH2O) from which the H2O(melt) + O(melt) 2OH(melt). plagioclase crystal formed may be inferred if H2O partition coefficient between plagioclase and melt (Dplag/melt) is known. H2O ’ plag melt Henry s law that CH2O should be roughly proportional to CH2O. Then, H2O concentration in the initial magma ocean (roughly 138 BSM In Figure 4, the whole data set of Hamada et al. is fairly self- the bulk silicate Moon), CH2O, may be inferred as if the degree fi consistent and can be well modeled (blue dashed curve in of crystallization, F, of the LMO is known when this speci c Figure 4) by assuming that OH partition coefficient between plagioclase grain formed. It turns out that all three parameters plagioclase and melt is constant and that the equilibrium (I′, Dplag/melt, and F) were somewhat uncertain at the time. H2O constant for reaction H O(melt) + O(melt) ⇌ 2OH(melt) is 31 − − 2 Hui et al. adopted I′ ≈ 15.3 ± 0.7 ppm 1 cm 2136 and constant.122,138,142 On the other hand, it is not clear why the plag/melt ≈ 137 plag ≈ ± 141 fi fl DH2O 0.004, leading to CH2O 6.4 0.3 ppm and new data do not de ne a consistent trend. The con icting melt C ≈ 1600 ± 73 ppm. Assuming F ≈ 0.8 at the time of results show that more investigation of H2O partition H2O ffi fi plagioclase formation, then H O in the bulk silicate Moon coe cients between plagioclase and ma c melts is needed. 2 Hui et al.32 continued the investigation of H Oin would be ∼320 ± 15 ppm. Since then, new studies have 2 plagioclase in lunar anorthosites and troctolites. They used improved both I′ and Dplag/melt. Hamada et al.138 published new H2O SIMS rather than FTIR to measure H in plagioclase and found experimental H O partition data with Dplag/melt ∼ 0.010 ± ± ± 2 H2O 4 1to5 1 ppm H2O in plagioclase in two lunar ≤ 0.005 when H2O in plagioclase is 100 ppm. Using this result anorthosites (15415, 60015) and one lunar troctolite (76535), fi 31 and again assuming F = 0.8, H2O in the bulk silicate Moon in general con rming the earlier FTIR results. In addition, would be ∼130 ± 65 ppm.35 Mosenfelder et al.139 recalibrated they made the extremely difficult SIMS measurement of ffi 2 1 the integrated absorption coe cient for H2Obandsin H/ H ratio in a lunar highland plagioclase, corrected for plagioclase and obtained an updated I′ = 29.3 ± 3.0 ppm−1 cosmic ray spallation, and used the datum combined with

1486 https://dx.doi.org/10.1021/acsearthspacechem.9b00305 ACS Earth Space Chem. 2020, 4, 1480−1499 ACS Earth and Space Chemistry http://pubs.acs.org/journal/aesccq Review fi 146 other data to infer that the Moon lost a signi cant amount of ppm H2O. Johnson and Rossman showed that terrestrial H2O during its magma ocean stage. feldspars (e.g., in pegmatite) may contain structural OH, H2O, ffi + The uncertainty in the value of F is more di cult to address. and NH4 , but volcanic feldspars contain only structural OH. 39 Model calculation depends on the assumed BSM composition. Mills et al. suggested that their measured H represents H2O In addition, plagioclase crystallizes in a range of F values (e.g., or OH that was incorporated into the alkali feldspar during − F ≥ 0.75,9,10,130 135 For example, assuming F = 0.9 when the crystallization from a silicic melt containing 0.5−2.0 wt % fi ∼ ± speci c plagioclase crystallized leads to 65 33 ppm H2Oin H2O. They thought that this silicic magma represents a the BSM. Therefore, there is a need to further investigate how distilled component of the urKREEP reservoir, reflecting a 10− H O concentration in plagioclase in lunar highland troctolites 100 times enrichment in H2O. They then estimated that 2 ∼ ∼ and anorthosites varies with the degree of crystallization in granitoid containing 1wt%H2O makes up 0.1% of the plag/melt LMO. Despite the uncertainties in F and DH O , the bulk silicate Moon, leading to a contribution of 10 ppm H2O 2 to the bulk silicate Moon. Because other minerals do not measurement of H2O in lunar highland plagioclase demon- fi fi contain signi cant H2O, they argued that the lunar mantle had strates that the Moon already had signi cant H2O at the 39 40 magma ocean stage, which is important in the discussion of the <100 ppm H2O for most of its history. Simon et al. origin of H O in the Moon as well as the origin of the Moon. continued the study and reached a similar conclusion but 2 seemed to have confused HconcentrationandHO In future studies, to bypass the need to estimate F, both H O 2 2 concentration (a factor of 9 difference in concentrations). and other highly incompatible elements in lunar highland The uncertainty in their order of magnitude estimate of H O plagioclase can be measured. 2 content in the lunar mantle40 is difficult to assess due to the Using Lunar Zn Concentrations to Infer H2O. Zinc is a 60 various assumptions, uncertain parameters, as well as possible moderately volatile element with Tc = 704 K and is also 70 confusion of H and H2O concentrations. chalcophile. Wolf and Anders reported that average Zn 52 Other Studies. Milliken and Li analyzed the near-infrared concentration in lunar basalts is about 0.013 times that in reflectance spectra acquired by the Moon Mineralogy Mapper terrestrial basalts (a depletion factor of 77) on the basis of bulk 53 instrument and found hundreds of ppm of H2O in large rock analyses. Albarede et al. used LA-ICP-MS to measure pyroclastic deposits, consistent with melt inclusion studies in the concentration of Zn and estimated Zn/Fe ratio in lunar 74220. Their results seem to imply that there are unsampled samples. They found that Zn/Fe ratio in lunar basalts is lower glass beads or minerals with much higher H O concentrations than that in terrestrial basalts by a factor of 10−500. They used 2 − (hundreds of ppm) than in currently available glass beads (<50 the degree of Zn depletion and assumed a log linear relation ppm)becausemeltinclusionsarenotexpectedtobe between the depletion factor and Tc to extrapolate H2O detectable by remote-sensing NIR reflectance spectra. concentration in the BSM to be sub-ppm level. As for the high 9 33−37 53 Lin et al. carried out experiments to simulate the H2O concentration measured in OHMIs, Albarede et al. crystallization of a 700 km thick LMO and found that a discounted the data as a local anomaly. completely dry Moon would produce a flotation anorthosite A number of authors argued against the notion that high crust with a thickness of ∼68 km, much thicker than the H2O concentration in OHMIs in 74220 is a local anomaly as − 147 34 geophysically observed average thickness of 34 43 km. Lin summarized earlier. In addition, Hauri et al. estimated a high et al.9 then estimated that the LMO needs to contain 270− Zn concentration in pre-eruptive source melt of 74220 glass 1650 ppm H2O at the time of LMO crystallization to produce beads by adding Zn in the surface coating back to the glass an anorthosite crust with the right thickness. It turned out that beads. Ni et al.37 showed that Zn concentration in an OHMI 9 the H2O concentrations in Lin et al. were incorrect. Lin et (presumably better representing pre-eruptive concentrations) al.148 corrected the data in Lin et al.9 and carried out additional is 5.6 times that in a glass bead in 74220. That is, even rapidly experiments, and concluded that the bulk silicate Moon quenched glass materials can experience significant Zn loss if − contained 45 354 ppm H2O at the time of crust formation. not inside a melt inclusion protected by a host mineral. Such +50 Their updated result is consistent with 90−30 ppm H2O on the loss may partially explain high variability of Zn concentrations basis of OHMIs.35,37 in lunar basalts (by about 2 orders of magnitude from 0.6 to 54 Syntheses: H O in Lunar Volcanic Rocks and in the Lunar 143−145 143,144 2 ppm ), as well as large Zn isotope ratio variability. Mantle and New Debate. In summary, H concentration has Hence, it is necessary to examine whether literature data on Zn been measured by SIMS and OH concentration has been concentration using bulk rock data suffered from post-eruptive measured by FTIR in lunar materials including apatite, OHMIs loss. in mare basalts, plagioclase in highland anorthosites and In addition, the log−linear relation between the depletion troctolites, and alkali feldspars in granitoid. H concentration factor in the Moon relative to the Earth and Tc used by measured by SIMS is interpreted to be OH, which is verified 53 Albarede et al. is an assumed and unproven relation, by direct comparison with FTIR data in at least three especially because Zn is also chalcophile and may go into instances.31,32,35,50 The measured H concentrations by SIMS 35 37 the lunar core. Both Chen et al. and Ni et al. used and OH concentrations by FTIR data are reported as H2O − fi fi measured data to show that there is no simple log linear concentrations and con rm the presence of signi cant H2Oin relation between the depletion factor and Tc for volatile lunar samples, clearly orders of magnitude higher than 1 ppb. 53 elements used by Albarede et al. to infer H2O concentration There are uncertainties and debates on how to use the data to in the lunar mantle. The debate is continuing. infer H2O concentration in the primitive lunar mantle. fi H2O in Lunar Silicic Rocks. In addition to ma c rocks, there On the basis of studies of H O in OHMIs in lunar − 2 are also rare silicic igneous rocks in the Moon. Mills et al.39 basalt33 37 and in plagioclase in highland anorthosite and 31,32 used SIMS to measure H in alkali feldspar and silica from troctolite, inferred H2O concentration in the bulk silicate +50 sample 15405,78 granitoid clast xenolith with an age of 4.3 Ga. Moon is 90−30 ppm starting from the late stage of the LMO. They found alkali feldspar contains H, equivalent to about 20 Crystallization experiments148 are consistent with this result.

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Figure 5. Evaluation of post-eruptive loss of volatiles by ratioing volatile/refractory element ratios in glass beads and embayments to those in 60 59 OHMIs. The condensation temperature values are from Wood et al. except for those of H2O and C, which are from Lodders. (a) All data; (b) enlargement of part of panel a. Note scale change in panel b. Post-entrapment crystallization (PEC) is accounted for by using volatile/refractory elemental ratios rather than simple concentrations. Concentrations of volatiles in embayments are on average higher than in glass beads. Na/Ce ratios are mostly >0.3, and Cu/Fe ratios are <0.3. Data are from refs 33−37, 53, and 54.

On the basis of investigation of alkali feldspars in lunar glass beads to reconstruct the pre-eruptive concentrations. 39 35−37 granitoid, inferred H2O concentration in the primitive lunar Below, the melt inclusion approach is used. This approach mantle is 10−100 ppm. There are other much less direct assumes that the MIs and glass beads are from the same inferences leading to lower H2O concentrations (of the order 1 magma source with the same pre-eruptive concentrations of ppm) in the primitive lunar mantle,53,77 which is still 3 orders volatiles. In addition to the existence of olivine crystals and of magnitude more than 1 ppb in the pre-2008 years.13 Hence, glass beads in the same soil sample 74220, other lines of the paradigm shifted from an “essentially dry” Moon to a “fairly evidence include the following: (1) The composition of the ” wet Moon, but there is a new debate on whether H2O in the melt inclusions can be related to that of the glass beads by primitive lunar mantle is of the order 100 or 1 ppm. Currently, post-entrapment crystallization.33,34 (2) Fe−Mg exchange ∼ ffi the balance is tilting in favor of 100 ppm H2O in the bulk coe cient KD,Fe/Mg between olivine host crystals and glass silicate Moon. beads is ∼0.28, similar to the equilibrium value for the given 152 TiO2 concentration, consistent with olivine crystals having ■ OTHER VOLATILES IN LUNAR ROCKS grown in the source melt with composition the same as the glass beads. On the other hand, KD,Fe/Mg between olivine host Even though the investigation of H2O has taken much of the crystals and OHMIs ranges from 0.06 to 0.24, reflecting spotlight, investigation of other volatiles has also proceeded different degrees of post-entrapment crystallization. (3) The steadily. Pre-2008 measurements of these other volatiles were cooling rates of the olivine host crystals36 and glass beads98 are 71,149−151 also bulk rock analyses, and whether such data consistent. Nonetheless, there is a possibility that the OHMIs represent pre-eruptive concentrations needs verification. More and glass beads in 74220 do not come from the same magma recent determinations are microbeam analyses of grain source, which would argue against the results in this section. interiors or OHMIs. Glass beads and glassy OHMIs in To bypass the need to correct for post-entrapment 74220 have been investigated fairly extensively for volatile crystallization of OHMIs and to bypass the need to evaluate 54 33−37 elements C, F, S, and Cl. In addition to lunar sample whether a basalt came from a primitive or differentiated lunar 153,154 74220, a database is accumulating for F, S, and Cl in naturally mantle, volatile/refractory elemental ratios, C/Ba, H2O/ partially glassy or homogenized OHMIs in 10020, 12008, Ce,101,102 Zn/Fe,53,155,156 S/Dy, Pb/Ce, F/Nd, Cs/Ba, Rb/Ba, 35−37 12040, 15016, 15647, and 74235. Limited data are Cl/Ba, Ga/Dy, K/Ba, Cu/Fe, and Li/Yb35,100,157,158] are used 37 available for Cu, Zn, Ga, Rb, Cs, and Pb in lunar OHMIs. rather than volatile element concentrations. A refractory analog Due to measurement limitations, other highly volatile for Na is debatable. O’Neill71 estimated that its behavior elements, including noble gases, N, Hg, Tl, I, In, Br, Cd, Se, during magma evolution is similar to Sm. However, when Sn, Te, and Bi have not been examined yet by microbeam MORB data159 are used to examine which REE behaves similar techniques. Below, I first discuss post-eruptive loss of volcanic to Na, no good relation is found. Because Na is a minor volatiles by comparing glass beads and OHMIs in 74220. element in lunar basalts but a major element in terrestrial Then, individual volatile elements will be assessed. basalt, the partitioning behavior of Na in lunar basalt might Post-eruptive Loss of Volcanic Volatiles. Before pre- differ from that in terrestrial basalt. By plotting Na versus each eruptive concentrations can be estimated, the post-eruptive REE in lunar OHMIs, the limited data available suggest that loss of volatiles must also be assessed, similar to the case of Na/Ce varies the least among Na to REE ratio. Hence, Na/Ce 35−37 H2O. One approach is to use volatiles in OHMIs as pre- ratio is used in this work. Nonetheless, using either Na/Ce or eruptive concentration. Hence, post-eruptive loss of volatiles is Na/Sm ratio, the following results would be similar. Figure 5 assessed by comparing concentrations of volatiles in OHMIs shows ratios in glass beads and embayments normalized to and in unprotected glass beads in lunar soil sample 74220, for OHMIs, all in lunar sample 74220, plotted against the 50% 34 which there are extensive data. Another approach is to add condensation temperature. Data are extensive for H2O, F, S, volatiles in the coating of glass beads to the composition of the Cl, C, Li, Na, and K but limited for Zn, Pb, Rb, Cs, Ga, and

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Cu. The depletion factor of volatiles in glass beads relative to OHMIs in 74220 can be ordered as follows:

H2 O>>> Cl C Zn >> F Cu >> S Cs ≈ Rb > Ga > Na ≈ Pb ≈> K Li (negligible loss) 287>>>>≈>>≈>>≈≈> 65 14 8.9 7.4 6.8 2.4 2.0 2.0 1.7 1.5 1.4 1.3 1.08 (1) where the value below each volatile is the depletion factor homogenize OHMIs is also negligible.36 On the other hand, fi calculated as the ratio (e.g., H2O/Ce) chosen for OHMIs in H2O loss is signi cant for smaller OHMIs and also during 74220 divided by the geometric mean ratio in orange glass homogenization experiments,36 as discussed earlier. beads in 74220 (COHMI/CGB, where subscript GB stands for In summary, post-eruptive loss of volatiles can be very glass beads), and a higher value means more post-eruptive loss. significant in lunar volcanic rocks, which can be quantified by The depletion factor of Li is indistinguishable from 1 (no comparison of volatiles in OHMIs and glass beads in 74220. depletion) because the estimated ratio has an error of about Melt inclusions provide good protection for most volatiles. 10%. The depletion trend in eq 1 is similar to that in Ni et al.37 Concentrations of volatiles from bulk rock analyses must be because similar data are used to assess the trend, with very assessed (e.g., by comparison with melt inclusion data) before minor differences due to the use of ratios here rather than using them to gauge relative depletion of volatiles in the bulk concentrations in Ni et al.37 in assessing the depletion factor. silicate Moon relative to the bulk silicate Earth. On the basis of Figure 5 and eq 1, H, Cl, C, F, Zn, Cu, S, Ga, Volatiles in Lunar OHMIs and the Lunar Mantle. Cs, Rb, and Ga are prone to post-eruptive loss by degassing or Carbon. In terrestrial volcanic rocks, carbon is easily degassed, ff and hence pre-eruptive carbon concentrations are typically di usion even for rapidly quenched glassy samples. Therefore, 83−85 54 it is necessary to evaluate possible post-eruptive loss of these obtained by studying melt inclusions. Wetzel et al. elements when bulk rocks are analyzed. determined carbon concentration in lunar volcanic materials in Figure 5 shows that there is no consistent trend between lunar soil sample 74220: OHMI glass may contain up to 4 ppm − post-eruptive loss and the condensation temperature. Hence, C, but glass beads contain only 0.25 0.75 ppm C. Measured the empirical trend of post-eruptive loss of volatiles from carbon concentrations in OHMIs in 74220 show that the C/Ba ratio apparently decreases with decreasing OHMI diameter magmas on the lunar surface (eq 1) is not purely controlled by μ the condensation temperature. A number of publications (Figure 6), indicating that MIs with diameter < 30 m lost C. reported experimental evaporation loss of volatile ele- − ments.58,160 162 The trend due to melting and vaporization160 is Pb ≈ Zn > Cu ≈ In > Ga, whereas the lunar post-eruptive loss trend in eq 1 is Zn > Cu > Ga > Pb. The evaporation loss trend by heating an anorthite-diopside eutectic melt161 is Pb > Zn > Rb > Cu > K > Ga > Na > Li, whereas the lunar trend (eq 1) is Zn > Cu > Rb > Ga ≈ Na > Pb > K > Li. The evaporation loss trend during levitation laser heating of a terrestrial rhyolite162 is Pb ≈ Na > Zn > K, whereas the lunar trend summarized in eq 1 is Zn > Cu ≫ Ga ≈ Na > Pb > K. Hence, there is no exact match between the lunar trend and any of the experimental trends. Both Wulf et al.58 and Norris and Wood160 showed that the degree of elemental volatility during heating depends strongly on oxygen fugacity. The empirical loss trend of lunar orange glass beads in eq 1 is not identical to any of the experimental volatile element loss trends by Wulf et al.,58 but is more similar to their experimental trend Figure 6. Carbon concentration in OHMIs in 74220 versus MI diameter. Data (both measured and those corrected for post- at the most reducing condition at logfO2 ≈ IW-1.8: Zn ≈ Pb > 54 ≈ ≈ entrapment crystallization) are from Wetzel et al. Carbon Ga > Cu Na K. Hence, it appears that the trend of volatile concentration decreases with decreasing MI diameter, suggesting element loss during maficvolcaniceruptionsislargely that smaller OHMIs lost more carbon. The effect of shrinkage bubbles controlled by oxygen fugacity and second by the melt on C concentration is not accounted for here. composition and ambient pressure. On the basis of Figure 5, unprotected glass beads and The largest OHMIs contain up to 4−6 ppm C, with C/Ba ratio embayments in lunar surface volcanics do not preserve pre- ∼ 0.07. After accounting for shrinkage bubbles, the corrected eruptive volatiles well. Because the glassy samples in 74220 are carbon concentration is 44−64 ppm,54 with C/Ba ratio of among the most rapidly quenched, other more slowly cooled ∼0.7, which is less than the ratio in terrestrial basalts153 (∼36) mare basalts may also have lost volatiles. On the other hand, by a factor of ∼50. On the other hand, due to the low solubility melt inclusions provide some protection against loss of of CO2 and CO, degassing of CO2 and CO occurs at fairly high volatiles. By examining the concentrations of volatiles in pressures.163 For example, in terrestrial basalts, even typical OHMIs of different size, F, S, and Cl concentrations do not MORB glasses at hundreds of bar pressure do not preserve pre- 153,164 show noticeable variation with diameters of OHMIs, eruptive CO2 concentration. Hence, there was likely indicating, at least for the most rapidly quenched lunar basalt, significant C degassing even before the entrapment of melt loss of F, S, and Cl from OHMIs is negligible.36 In addition, inclusions in olivine, and the depletion factor of carbon in the loss of F, S, and Cl due to short-duration heating to Moon is difficult to assess using the currently available data.

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Figure 7. F in lunar OHMIs. (a) Variation of F/Nd ratio in lunar OHMIs with MI diameter. For 74220, data in natural (Nat) and homogenized (Homo) OHMIs are shown using different symbols. An outlier point in 74220 is excluded. (b) F versus Nd in lunar OHMIs (for 74235, matrix glass data are included), in lunar whole rocks (WR), and in terrestrial MORB and OIB glasses (gray +). Data for lunar OHMIs are from refs 34−37. Solid symbols are for high-Ti basalts, and open symbols are for low-Ti basalts. Data for lunar whole rocks are for A15 low-Ti mare basalts and A17 high-Ti mare basalts.150,151 Data for terrestrial basalts are from GeoRoc (http://georoc.mpch-mainz.gwdg.de/georoc/). The values on each line indicate the F/Nd ratio.

Fluorine. Fluorine is a volatile element with a condensation primitive mantle123 is ∼20, which matches the terrestrial basalt temperature of 674 K.60 O’Neill71 inferred that F concen- ratio in Figure 7b within error. Hence, F/Nd ratio in lunar tration in the bulk silicate Moon was 0.012 times F in CI basalts (and hence the lunar mantle) is lower than the chondrites. Using F concentration of 60 ppm in CI chondrites terrestrial ratio by a factor of 5.0 ± 1.3.34,35,37 This new and 25 ppm in terrestrial primitive mantle,123 the Earth/Moon depletion factor is different from that of O’Neill71 by a factor of F concentration ratio would be about 35. Taking REE 7, and old literature data from bulk rock analyses of concentrations in the Moon to be the same as those in the basalts150,151 are consistent with the new result. 34 Earth, then the Moon would be depleted in F by a factor of Chen et al.35 reported SIMS analyses on crystalline MIs but 35 relative to the Earth according to this estimate. decided not to use such data because such ratios can be highly A new approach to estimate the Earth/Moon F ratio uses a scattered due to the heterogeneity of crystalline MIs, and measured F/Nd ratio in melt inclusions. As shown by Ni et 36 especially because volatiles and refractory elements are al. and in Figure 7a, the F/Nd ratio in natural OHMIs in analyzed in different sessions and hence on different materials. 74220 does not depend on the size of MIs (solid orange circles Greenwood et al.165 also reported a range of F/Nd ratios (as in Figure 7a), and homogenization heating does not cause well as Cl/Nb ratios) in crystalline OHMIs in 12004 and noticeable decrease in the F/Nd ratio in OHMIs (solid orange 35,37 12009. The F/Nd ratio in crystalline MIs in a single sample triangles in Figure 7a). In other lunar samples, there is also 165 fi 12004 ranges from 1 to about 80. The data on crystalline no signi cant variation of F/Nd ratio with MI diameter, except MIs35,165 are not considered here. for 12040, in which the smaller MIs have higher F/Nd ratios In summary, the F/Nd ratio in most lunar basalts is lower than the largest MI, which is unexpected. The lunar sample than the terrestrial ratio by a factor of 5.0 ± 1.3. 12040 is the slowest cooled sample among the lunar samples Sulfur. Sulfur is both volatile (T is 672 K60)and investigated so far (Figure 3). It is unclear whether the slower c chalcophile. Ni et al.37 showed that S concentration in natural cooling rate allowed additional processes to affect the F/Nd ratio in smaller OHMIs. OHMIs in 74220 does not depend on the size of MIs, and In Figure 7b, F concentration is plotted against Nd short-duration homogenization experiments do not change the concentration in OHMIs in lunar samples and in terrestrial S concentration. However, the scatter of S/Dy ratio in OHMIs in a single lunar sample may be as large as an order of MORB and OIB glasses. The unusually high F/Nd ratios in the fi smaller MIs in 12040 are similar to terrestrial basalts. Ignoring magnitude (Figure 1c), which is attributed to sul de the anomalously high F/Nd ratios in the smaller MIs in 12040, crystallization. Hence, in Figure 8, when S concentration is there is no discernible difference between high-Ti basalts (solid plotted against Dy concentration in OHMIs in lunar samples symbols) and low-Ti basalts (open symbols) in Figure 7. and in terrestrial MORB and OIB glasses, the obviously low S/ Literature bulk rock data on Apollo 15 low-Ti mare basalts and Dy ratios in lunar OHMIs (e.g., the low S/Dy points in Figure 37 Apollo 17 high-Ti mare basalts150,151 are also included in 1c) in each lunar sample are excluded. Ni et al. noted that Figure 7b. Bulk rock data on lunar soil and breccia samples are the OHMI data in Figure 8 appear to show that the not included. As shown in Figure 7b, the bulk rock data on undifferentiated S/Dy ratio in low-Ti basalts (open symbols basalts150,151 are similar to data from OHMIs, suggesting post- in Figure 8) is about 150 and that in high-Ti basalts (solid eruptive loss of F is insignificant from these crystallized whole symbols in Figure 8) is about 80. However, the bulk rock rocks in the Moon. Using the upper-limit F/Nd ratios in data150,151 do not show a difference in the S/Dy ratio between OHMIs in each lunar basalt, the pre-eruptive F/Nd ratio in lunar low-Ti and high-Ti basalts. The average S/Dy ratio in ± +40 lunar basalts is 4 1. The F/Nd ratio in the terrestrial lunar basalts is about 110−30. The S/Dy ratio in the bulk

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Figure 8. Comparison of S and Dy in lunar OHMIs (for 74235, matrix glass data are included), in lunar whole rocks (WR), and in Figure 9. Comparison of Cl and Ba in lunar OHMIs (for 74235, terrestrial MORB and OIB glasses. See Figure 7b for symbols, data matrix glass data are included), in lunar whole rocks (WR), and in sources, and explanation. The estimated ratio in the primitive terrestrial MORB and OIB glasses. See Figure 7b for symbols, data terrestrial mantle123 is 370. sources, and explanation. The estimated Cl/Ba ratio in primitive terrestrial mantle123 is 2.6. silicate Earth is about 370. Hence, lunar S/Dy ratio is lower +1.8 60 than that in terrestrial rocks by a factor of 3.4−1.2. Zinc. Zinc is both volatile (Tc is 704 K ) and chalcophile. Chlorine. Chlorine is a volatile element (Tc is 472 K by Hence, in addition to depletion related to its volatility, there Wood et al.,60 very different from 948 K by Lodders59). may be additional depletion related to its being chalcophile. O’Neill71 estimated that Cl concentration in the bulk silicate The Zn/Fe ratio in terrestrial basalts with MgO > 8.5 wt % and Moon was 0.0013 times that in CI chondrite. Because Cl in terrestrial mantle is not much fractionated, and is about 1.0 contentinthebulksilicateEarthis0.025timesCI × 10−3.155,156 Albarede et al.53 examined Zn/Fe ratios in lunar chondrite,123 Cl in the Moon would be depleted by a factor glass beads and olivine and pyroxene grains. The highest Zn/ of 19 relative to the Earth. Fe ratio is found in some green glass beads, with Zn/Fe ≈ Chlorine is extremely incompatible, with a compatibility 10−4. Orange glass beads, mineral grains, and other green glass index157,158 much more negative than other highly incompat- beads have Zn/Fe ratios ranging from 2 × 10−6 to 4 × 10−5.53 ible elements including Cs, Rb, Ba, and K (compatibility index They53 thus inferred that the Moon is depleted by 2 orders of CoI = −3.51 for Cl, −2.77 for Cs, −1.89 for Rb, −1.80 for Ba, magnitude in Zn compared to the Earth. Other authors also and −1.18 for K, Table S2 in Zhang and Gan158). Cl/Cs ratio reported bulk rock Zn concentration data in lunar basalts, and might be the best ratio for constancy in basalt, but Cs data in they similarly show a large degree of depletion (e.g., Zn/Fe of lunar rock are limited in the available data. Rb data are also 0.9 × 10−5 to 1.9 × 10−5 in ref 150 and 0.35 × 10−5 to 8.0 × limited. Hence, Cl/Ba ratio is used to assess Cl in lunar and 10−5 in ref 169). Even the most recent Zn concentration data − terrestrial basalts. Because Cl is prone to loss even from in lunar basalts by bulk rock analyses143 145 still show high OHMIs,35 the highest Cl/Ba ratios are used to represent each variability (by about 2 orders of magnitude from 0.6 to 54 − lunar sample. For terrestrial basalt glass used for comparison, ppm143 145) with Zn/Fe ratio ranging from 4 × 10−6 to 4 × because seawater assimilation may increase Cl concentration 10−4, probably reflecting post-eruptive loss (Figure 5) or gain significantly,166,167 only melt inclusion data in MORB and OIB (such as condensation81). There is only one Zn measurement (GeoRoc) are used. The Cl versus Ba data are plotted in in OHMIs37 with Zn/Fe ratio of 4.8 × 10−5 in an OHMI in Figure 9. The highest Cl/Ba ratios in OHMIs of all seven 74220, about 9 times the ratio in orange glass beads in 74220. − measured lunar samples34 37 as well as those in bulk rock On the basis of all of the available data, Zn in lunar basalts analyses of lunar basalts150,151 all fall in a narrow range relative to terrestrial basalts is tentatively estimated to be +30 between 0.05 and 0.1, which are lower than the ratio in depleted by a factor of 20−12, larger than the degree of terrestrial MORB and OIB by a factor of about 20. There is no depletion for H2O, F, and S. The much smaller Zn/Fe ratio or significant difference in Cl/Ba ratio in high-Ti (solid symbols) the much larger degree of depletion for Zn in lunar basalts versus low-Ti (open symbols) lunar basalts. Because Ba is not a compared to terrestrial basalts might be partially explained by good analog for Cl, the depletion factor of 20 for Cl in the high Zn/Fe ratio (1.8 × 10−4 to 0.031) in lunar highland Moon relative to the Earth is probably inaccurate, but anorthosites,169 by high FeO in lunar basalts, and also by nonetheless it is in good agreement with the earlier estimate possible high Zn/Fe ratio in the lunar core. More work is of O’Neill.71 necessary to constrain Zn concentration in lunar basalts and Greenwood et al.168 reported Cl and Ba concentrations in the lunar mantle. interstitial glass in a KREEP basalt 15382. The Cl/Ba ratio Copper. Copper is chalcophile and somewhat volatile (Tc is using the geometric mean concentration of Cl and Ba is 0.083, 1034 K60). MacDonough and Sun123 and Salters and Stracke99 which is roughly consistent with data in OHMIs. Considering inferred a Cu/Sc ratio of 1.85 in terrestrial primitive and all of the available data, the depletion factor for Cl in the Moon depleted mantle. When lunar bulk rock data are plotted +30 fi relative to the Earth is tentatively estimated to be about 20−12. (Figure 10), there is a signi cant scatter in the Cu/Sc ratio in

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60 For Cs (a moderately volatile element with Tc of 593 K ), there is disagreement in the literature about its degree of depletion in the Moon. O’Neill71 concluded that Cs/Ba ratio in lunar basalts is about the same as in terrestrial MORB, meaning no Cs depletion in the Moon relative to the Earth. However, McDonough et al.171 concluded that Cs/Rb ratio in lunar samples is about 0.045, slightly larger than the Cs/Rb ratio of 0.036 in the bulk silicate Earth, which would lead to Cs depletion in the Moon relative to the Earth by a factor of 3.6 ± 0.4 because Rb in the Moon is depleted relative to the Earth. Righter172 stated that the abundance of Na, K, Rb, and Cs in the bulk silicate Moon is lower than the bulk silicate Earth by a factor of 4−5. To evaluate the discrepancy on Cs depletion in the Moon relative to the Earth, in Figure 11, Cs/Ba ratio

Figure 10. Comparison of Cu and Sc in lunar basalts (whole-rock analyses) and in terrestrial MORB glasses. Whole-rock data for lunar basalts are from ref 173. MORB data are from ref 159. A11, Apollo 11; A12, Apollo 12; and so on. lunar basalts, likely related to post-eruptive Cu loss (see Figure 5) or condensation enrichment, or analytical error. It is difficult to choose a representative Cu/Sc ratio for the lunar mantle. Because the bulk rock data for Cu versus Sc in lunar basalts are highly scattered with both high and low Cu/Sc ratios, I examine melt inclusion data. However, no lunar melt inclusions have been measured for both Cu and Sc. Therefore, Cu/Fe ratio is used to evaluate Cu depletion. Cu/Fe ratio in terrestrial basalts and terrestrial mantle is about 4.8 × 10−4.99,123 As shown by Ni et al.37 and Figure 5,Cu concentration in the interior of glass beads is on average Figure 11. Cs/Ba ratio versus Ba concentration in terrestrial about a factor of 7 lower than in OHMIs in 74220. That is, MORB159 and lunar basalts from Apollo missions 11, 12, 14, 16, 173 even rapidly quenched lunar basalt has lost most of its Cu. The and 17 (data from Mare Basalt Database ). significant post-eruptive loss of Cu might be partially attributed to the high diffusivity of univalent Cu+ (as high as Na versus Ba concentration is plotted using the newer and larger diffusivity) in basalt melt.170 The highest Cu/Fe ratio in database for MORB159 and the Mare Basalt Database.173 All of OHMIs and matrix glass falls in a narrow range: 2.6 × 10−4 in these data are bulk rock analyses (there is only one Cs 12040, 1.4 × 10−4 in 15016, 2.8 × 10−4 in 15647, 4.5 × 10−5 in concentration datum in OHMI37). The plot shows that the × −4 37 +3.8 74220, and 1.1 10 in 74235, a factor of 3.5−1.8 below the Cs/Ba ratio in most MORB falls in a narrow range but that in terrestrial ratio. Using this depletion factor, lunar Cu/Sc ratio lunar basalts is more scattered. Visual examination of the figure would be 0.53. This ratio is plotted in Figure 10 and is within cannot distinguish the difference in Cs/Ba ratio in the Moon data scatter but toward the higher part of the Cu/Sc ratio. versus the Earth. However, the geometric mean Cs/Ba ratio in +3.8 Hence, this depletion factor 3.5−1.8 is tentatively adopted here. MORB is 0.0028 (whether or not the outliers are included More data are needed to assess Cu depletion in the Moon does not significantly affect the geometric mean), whereas the relative to the Earth. geometric mean Cs/Ba ratio in all lunar basalts is 0.00097. Li, Na, K, Rb, Cs, Ga, and Pb. For these elements, either Hence, the Cs/Ba ratio in terrestrial basalt is ∼2.9 times that in there are only limited data on lunar OHMIs (for Rb, Cs, Ga, lunar basalts, which is similar to the results of McDonough et ff 171 +3.0 and Pb) and/or the di erence between OHMIs and orange al. Hence, a depletion factor of 3.0−1.5 is adopted for Cs in glass beads in 74220 is not large enough (Li, K, Pb, and Na) to lunar basalts and bulk silicate Moon relative to terrestrial warrant a reexamination of their degree of depletion using counterparts. 60 60 OHMI data. Lithium (slightly volatile, with Tc of 1148 K )in Galium is both volatile (Tc is 1010 K ) and chalcophile. the Moon is not depleted relative to the Earth (and to Righter172 examined Ga/Al ratio in lunar basalts (bulk rock refractory lithophile elements) on the basis of a similar Li/Yb data) and terrestrial basalts and concluded that Ga is depleted ratio in lunar basalts and terrestrial MORB and OIB.71 by a factor of 4. 60 Comparison of Li concentrations in OHMI and in glass beads Lead is both volatile (Tc is 495 K ) and chalcophile. The in 74220 show also negligible post-eruptive Li loss in the radiogenic contribution to 206Pb, 207Pb, and 208Pb complicates 60 Moon (Figure 5). Sodium (Tc is 1035 K ) in the Moon is the evaluation of Pb depletion. Hence, it is best to use the 34 204 depleted relative to the Earth by a factor of 3. Potassium (Tc abundance of the stable and nonradiogenic isotope of Pb to is 993 K60) in the Moon is depleted relative to the Earth by a evaluate Pb depletion in the Moon relative to the Earth. 53,71,171 174 238 204 +59 factor of about 5 on the basis of K/U ratios. Rubidium Nemchin et al. inferred a U/ Pb ratio of 141−41 for the 60 238 204 ± (Tc is 752 K ) in the Moon is depleted relative to the Earth by primitive lunar mantle. Using a U/ Pb ratio of 9 1 for a factor of 4.5 ± 0.5on the basis of Rb/Ba ratios.53,71 the bulk silicate Earth,174 the bulk silicate Moon is depleted in

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204 +9.3 Pb by a factor of 15.7−5.7 relative to elements in the bulk silicate Moon will be further discussed the bulk silicate Earth. That is, the degree of depletion for in a later section. 204Pb in the Moon is similar to that for Zn and is much greater than for H2O, F, S, K, Rb, Cs, and Ga. ■ SURFACE H2O ON THE MOON Noble Gas Elements, N, Hg, Tl, I, In, Br, Cd, Se, Sn, Te, Bi, The preceding sections focused on H O and other volatiles in Ge, B, Sb, Ag, Au, and As. 2 There are no OHMI data to assess the interior of the Moon. The presence of H O on the surface the post-eruptive loss of these elements as well as the pre- 2 172 of the Moon has also been extensively investigated because it is eruptive concentrations. Righter reviewed literature bulk a critical resource for lunar exploration. For completeness, rock analyses of lunar basalts and concluded that As, In, Br, fl studies on lunar surface H2O are brie y summarized here. It Cd, Bi, and Tl (all chacophile and volatile) are depleted by a has been known for a long time that, due to the absence of an factor of about 100 compared to terrestrial basalts, as also 70 atmosphere, liquid water is not stable and would evaporate and shown by Wolf and Anders. The high degree of depletion either escape from the lunar surface in a geologically short time compared to other volatile elements may be partially due to or get deposited as ice in the lunar polar regions.175 Watson et their chalcophile nature, leading to them being sequestered in al.175 discussed the possible presence of ice on the Moon and the lunar core. argued that H O ice may well be present in appreciable Depletion of Volatile Elements in the Bulk Silicate Moon 2 quantities in the permanently shadowed depressions in polar Relative to the Bulk Silicate Earth. 176 Summarizing the regions of the Moon. This was supported by later studies assessment above, especially with emphasis on the melt and verified when the LCROSS mission crashed a spent rocket inclusion data, the depletion of volatile elements in the bulk stage into a crater near the South Pole of the Moon, detecting silicate Moon relative to the bulk silicate Earth is summarized both water vapor and ice in the plume.44 Additional as follows: for Zn, Pb, and Cl, the depletion factor is 10−20 on 204 238 spectroscopic mapping and modeling of H2O ice in both the basis of Zn/Fe, Pb/ U, and Cl/Ba; for H2O, F, S, Cu, north and south polar regions of the Moon quantified the ice − − Ga, K, Na, Rb, and Cs, the depletion factor is about 3 6. concentration to be up to 30 wt % in some localities.45 49 These depletion factors are from lunar OHMIs and bulk rocks In addition to H2O ice on the Moon, remote spectroscopic (not from the degassed pyroclastic glass beads) and also 41−43,51,52 studies discovered absorbed H2O and structural OH represent the bulk silicate Moon because the ratios are roughly bands in spectra of the lunar surface, with estimated constant during igneous evolution (except for degassing). The concentrations of 10−1000 ppm.41 The spectroscopic data are plotted in Figure 12 as a function of Tc. The data show measurements were ground-truthed by measurements on lunar soil samples:50 Liu et al.50 made both FTIR and SIMS measurements of lunar soil samples and showed that H2Oin bulk regolith samples is about 70 ppm and such H2O is largely in agglutinate glasses. The agreement between FTIR and SIMS measurements50 indicate H measured by SIMS is indeed in the form of structural OH. In addition, on the basis of 2H/1H ratio 50 measurements, Liu et al. concluded that lunar surface H2O originated mostly from solar wind implantation, meaning that other airless bodies such as Mercury and Vesta are also expected to contain such surface H2O. Some surface H2Oas well as other volatiles may also originate from condensates of erupted volatiles.177 Liu et al.178,179 continued the studies on 51 H2O in lunar regolith samples. Li and Milliken reanalyzed near-infrared reflectance spectroscopic data by the Moon Mineralogy Mapper and found that lunar surface H2O (present as OH) abundance increases with latitude. Figure 12. Inferred ratio of concentrations of volatile elements in the bulk silicate Moon (BSM) over the bulk silicate Earth (BSE) as a ■ SIGNIFICANCE ON THE ORIGIN OF THE MOON: function of 50% condensation temperature, Tc. Tc values are from refs EARLY VENEER AND LATE VENEER 60, except for that of H O, which is from ref 59. The C /C ratios 2 − BSM BSE are largely based on melt inclusion work,33 37 plus literature data for The paradigm shift from a dry to a wet Moon has already had a Li, Na, K, Rb, Cs, and Ga. significant impact on the Giant Impact Hypothesis for the origin of the Moon. The early thinking that the Moon was 13 essentially devoid of H2O (at less than ppb level ) was that the depletion factor for the bulk silicate Moon relative to thought to be consistent with the Giant Impact Hypothesis in − the bulk silicate Earth is not log linearly dependent on the Tc which the Moon formed from ejected high-temperature pieces (or bond energy53). That is, the data do not support the log− that lost H O. However, the measurement of significant H O 2 − 2 linear trend drawn by Albarede et al.53 Furthermore, some in lunar volcanic products14,33 35 required rethinking about elements in Figure 12 are both volatile and chalcophile (such the origin of H2O in the Moon. Before 2013, only relatively as Pb, Zn, and Cu) and hence may go into the lunar core, young (≤3.9 Ga) mare basalts were found to contain high leading to an anomalous estimate of lunar depletion. For all H2O concentrations, which permitted a bone-dry Moon at the assessed volatiles except for Cl, Zn, and Pb, the depletion time of Moon formation from the Giant Impact (4.4 to 4.5 Ga) ffi factor is nearly constant, ranging from 3 to 6, independent of because there was su cient time for delivery of H2O to the fi 180,181 31 Tc (either Tc of ref60 or Tc of ref 59). The signi cance of this Moon after the Giant Impact. At the time Hui et al. near-constancy in the depletion factor of many volatile published results that the lunar magma ocean contained ≥100

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14 31−40,53,77 ppm H2O, it was thought then that the Giant Impact of Saal et al., and with numerous works since then, Hypothesis for Moon formation would be in trouble.180 the paradigm gradually shifted to a fairly wet Moon. However, it turned out that the Giant Impact Hypothesis is Nonetheless, there is still a debate on, how wet is the Moon fl resilient and exible enough to accommodate the new and does the bulk silicate Moon contain about 100 ppm H2O discoveries. For example, one suggested solution is that right or about 1 ppm H2O? In addition, the abundance of other after the Giant Impact, a gas disk enveloped the newly formed volatile elements has also been more reliably estimated. In proto-Moon and dissolution of H species (mostly OH) from retrospect, the new concentration data for many volatile the gas disk into the lunar magma ocean is enough to establish elements based on microbeam analyses of lunar melt inclusions 5,6 ff lunar H2O abundance. Another suggested solution is that the are not too di erent from pre-2008 literature data using bulk Moon-forming disk was dominated by an atmosphere of heavy rock analyses even though the latter may show more scatter to atoms or molecules, leading to diffusion-limited H loss, which both higher and lower concentrations. So far, only about 10 ffi 7 is ine cient, meaning that the Moon was able to retain H2O. lunar igneous rocks have been investigated for H2O and other These developments do highlight the importance of establish- volatiles using microbeam methods. In order to further ing the abundances of not only H2O but also other volatiles in constrain H2O and other volatile element concentration in the Moon in setting stringent constraints on the origin of the the bulk silicate Moon, it is necessary to use microbeam Moon. analyses to study more lunar volcanic rocks to evaluate post- As shown in Figure 12, rather than a trend of increasing eruptive loss of volatiles and to examine the effect of cooling degree of depletion for more volatile elements (lower Tc), rates. New key measurements to better constrain H2O and currently available data indicate that the degree of depletion for other volatiles in the Moon include the following: (i) volatile/ many volatile elements in the Moon relative to the Earth lies in refractory elemental ratios in minerals and melt inclusions in − a narrow range, by a factor of 3 6, regardless of the lunar mare basalts, (ii) examination of H2O concentration in condensation temperature. One possible explanation of the plagioclase in highland anorthosites and troctolites as a data in Figure 12 is as follows. After the giant impact origin of function of their crystallization age, and (iii) experimental − ffi the Earth Moon system, both the Earth and the Moon were determination of H2O partition coe cient between minerals fairly depleted in the volatile elements. An early veneer (likely and lunar melts. It is also hoped that future lunar missions will before the solidification of the lunar magma ocean, e.g., prior bring back lunar mantle samples, allowing direct evaluation of to 4.45 Ga) delivered volatile elements to the Moon and the volatile element concentrations in them. Accurate knowledge Earth. However, the Moon received proportionally less early of the abundances of H2O and other volatiles will have veneer materials compared to the Earth so that the important implications for our understanding of the origin of concentration of the volatiles in the Moon is lower by a factor the Moon and the evolution of the Moon. of 3−6 compared to the Earth. This early veneer must be early because the LMO at the time of plagioclase crystallization ■ AUTHOR INFORMATION fi ∼ already contained signi cant ( 100 ppm) H2O. The early Corresponding Author veneer is expected to also bring siderophile and chalcophile Youxue Zhang − Department of Earth and Environmental elements to the Moon, which would sink through the LMO to fi Sciences, The University of Michigan, Ann Arbor, Michigan form the lunar core. After near solidi cation of the LMO, 48109, United States; orcid.org/0000-0002-7439-0086; continued delivery of planetesimals would constitute a late Email: [email protected] veneer, which would have brought siderophile elements to the − lunar mantle.182 187 However, this explanation of an early Complete contact information is available at: veneer delivery of volatile elements to the Moon before LMO https://pubs.acs.org/10.1021/acsearthspacechem.9b00305 crystallization needs to be reconciled with high similarity of − isotope ratios between the Moon and the Earth188 190 as well Notes as the slight enrichment of heavy isotopes in lunar basalts than The author declares no competing financial interest. − in terrestrial basalts.145,191 194 ■ ACKNOWLEDGMENTS ■ SUMMARY I thank H. Palme, Malcolm Rutherford, Peng Ni, and two One of the legacies of the Apollo mission is the lunar samples anonymous reviewers for careful reviews and insightful collected by astronauts and returned to the Earth. These comments. This work is supported by NASA Grants returned samples have allowed humankind to learn a great deal NNX15AH37G and 80NSSC19K0782. about the origin of the Moon and the Earth, the composition and evolution of the Moon, as well as various lunar processes. ■ REFERENCES fi Since the rst return of the Apollo samples in 1969, H2O (1) Hartmann, W. K.; Davis, D. R. Satellite-sized planetesimals and concentrations in lunar basalts, breccia, and soil were analyzed lunar origin. Icarus 1975, 24, 504−515. by heating and release of H2O from bulk rock samples. Even (2) Cameron, A. G. W.; Ward, W. R. The origin of the moon. Lunar Planet. Sci. Conf. 7th 1976, 120−122. though H2O concentrations were measured to be tens to hundreds of ppm, terrestrial contamination could not be ruled (3) Cameron, A. G. W.; Benz, W. The origin of the Moon and the − − out,66 68 and the scientific community initially thought that single impact hypothesis IV. Icarus 1991, 92, 204 216. (4) Canup, R. M. Forming a moon with an earth-like composition the lunar interior was completely dry, with H2O content below 13 via a giant impact. Science 2012, 338, 1052−1055. 1 ppb. Technological advancement gradually allowed the (5) Pahlevan, K.; Karato, S.; Fegley, B. Speciation and dissolution of interior spots of glass, minerals, and melt inclusions to be hydrogen in the proto-lunar disk. Earth Planet. Sci. Lett. 2016, 445, measured by microbeam FTIR and SIMS methods, which 104−113. demonstrated the presence of innate H2O in lunar volcanic (6) Sharp, Z. D. Nebular ingassing as a source of volatiles to the materials. Starting from 2008 after the landmark contribution terrestrial planets. Chem. Geol. 2017, 448, 137−150.

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(7) Nakajima, M.; Stevenson, D. J. Inefficient volatile loss from the (27) Tartese, R.; Anand, M.; McCubbin, F. M.; Elardo, S. M.; Moon-forming disk: reconciling the giant impact hypothesis and a wet Shearer, C. K.; Franchi, I. A. Apatite in lunar KREEP basalts: the Moon. Earth Planet. Sci. Lett. 2018, 487, 117−126. missing link to understanding the H isotope systematics of the Moon. (8) Elkins-Tanton, L. T.; Grove, T. L. Water (hydrogen) in the lunar Geology 2014, 42, 363−366. mantle: results from petrology and magma ocean modeling. Earth (28) Pernet-Fisher, J. F.; Howarth, G. H.; Liu, Y.; Chen, Y.; Taylor, Planet. Sci. Lett. 2011, 307, 173−179. L. A. Estimating the lunar mantle water budget from phosphates: (9) Lin, Y.; Tronche, E. J.; Steenstra, E. S.; van Westrenen, W. complications associated with silicate-liquid-immiscibility. Geochim. Evidence for an early wet Moon from experimental crystallization of Cosmochim. Acta 2014, 144, 326−341. the lunar magma ocean. Nat. Geosci. 2017, 10,14−18. (29) Robinson, K. L.; Barnes, J. J.; Nagashima, K.; Thomen, A.; (10) Lin, Y.; Tronche, E. J.; Steenstra, E. S.; van Westrenen, W. Franchi, I. A.; Huss, G. R.; Anand, M.; Taylor, G. J. Water in evolved Experimental constraints on the solidification of a nominally dry lunar lunar rocks: evidence for multiple reservoirs. Geochim. Cosmochim. magma ocean. Earth Planet. Sci. Lett. 2017, 471, 104−116. Acta 2016, 188, 244−260. (11) Crawford, I. A. Lunar resources: a review. Prog. Phys. Geogr. (30) Konecke, B. A.; Fiege, A.; Simon, A. C.; Holtz, F. Cryptic 2015, 39, 137−167. metasomatism during late-stage lunar magmatism implicated by sulfur (12) The Lunar Sample Preliminary Examinations Team. Prelimi- in apatite. Geology 2017, 45, 739−742. nary examination of lunar samples from Apollo 11: A physical, (31) Hui, H.; Peslier, A. H.; Zhang, Y.; Neal, C. R. Water in lunar chemical, mineralogical, and biological analysis of 22 kilograms of anorthosites and evidence for a wet early Moon. Nat. Geosci. 2013, 6, − lunar rocks and fines. Science 1969, 165, 1211−1227. . 177 180. (13) Taylor, S. R.; Pieters, C. M.; MacPherson, G. J. Earth-Moon (32) Hui, H.; Guan, Y.; Chen, Y.; Peslier, A. H.; Zhang, Y.; Liu, Y.; system, planetary science, and lessons learned. Rev. Mineral. Geochem. Flemming, R. L.; Rossman, G. R.; Eiler, J. M.; Neal, C. R.; Osinski, G. 2006, 60, 657−704. R. A heterogeneous lunar interior for hydrogen isotopes as revealed − (14) Saal, A. E.; Hauri, E. H.; Cascio, M. L.; Van Orman, J. A.; by the lunar highlands samples. Earth Planet. Sci. Lett. 2017, 473,14 Rutherford, M. J.; Cooper, R. F. Volatile content of lunar volcanic 23. glasses and the presence of water in the Moon’s interior. Nature 2008, (33) Hauri, E. H.; Weinreich, T.; Saal, A. E.; Rutherford, M. J.; Van − Orman, J. A. High pre-eruptive water contents preserved in lunar melt 454, 192 196. − (15) Boyce, J. W.; Liu, Y.; Rossman, G. R.; Guan, Y.; Eiler, J. M.; inclusions. Science 2011, 333, 213 215. Stolper, E. M.; Taylor, L. A. Lunar apatite with terrestrial volatile (34) Hauri, E. H.; Saal, A. E.; Rutherford, M. J.; Van Orman, J. A. − Water in the moon’s interior: truth and consequences. Earth Planet. abundances. Nature 2010, 466, 466 469. − (16) Boyce, J. W.; Tomlinson, S. M.; McCubbin, F. M.; Greenwood, Sci. Lett. 2015, 409, 252 264. J. P.; Treiman, A. H. The lunar apatite paradox. Science 2014, 344, (35) Chen, Y.; Zhang, Y.; Liu, Y.; Guan, Y.; Eiler, J. M.; Stolper, E. − M. Water, fluorine, and sulfur concentrations in the lunar mantle. 400 402. − (17) Boyce, J. W.; Treiman, A. H.; Guan, Y.; Ma, C.; Eiler, J. M.; Earth Planet. Sci. Lett. 2015, 427,37 46. (36) Ni, P.; Zhang, Y.; Guan, Y. Volatile loss during homogenization Gross, J.; Greenwood, J. P.; Stolper, E. M. The chlorine isotope of lunar melt inclusions. Earth Planet. Sci. Lett. 2017, 478, 214−224. fingerprint of the lunar magma ocean. Sci. Adv. 2015, 1, e1500380. (37) Ni, P.; Zhang, Y.; Chen, S.; Gagnon, J. A melt inclusion study (18) Boyce, J. W.; Kanee, S. A.; McCubbin, F. M.; Barnes, J. J.; on volatile abundances in the lunar mantle. Geochim. Cosmochim. Acta Bricker,H.;Treiman,A.H.Earlyloss,fractionation,and 2019, 249,17−41. redistribution of chlorine in the Moon as revealed by the low-Ti (38) Saal, A. E.; Hauri, E.; Van Orman, J. A.; Rutherford, M. lunar mare basalt suite. Earth Planet. Sci. Lett. 2018, 500, 205−214. Hydrogen isotopes in lunar volcanic glasses and melt inclusions reveal (19) McCubbin, F. M.; Steele, A.; Hauri, E. H.; Nekvasil, H.; a carbonaceous chondritic heritage. Science 2013, 340, 1317−1320. Yamashita, S.; Hemley, R. J. Nominally hydrous magmatism on the − (39) Mills, R. D.; Simon, J. I.; Alexander, C. M. O. D.; Wang, J.; Moon. Proc. Natl. Acad. Sci. U. S. A. 2010, 107, 11223 11228. Hauri, E. H. Water in alkali feldspar: the effect of rhyolite generation (20) Greenwood, J. P.; Itoh, S.; Sakamoto, N.; Warren, P. H.; on the lunar hydrogen budget. Geochem. Perspectives Lett. 2017, 3, Taylor, L. A.; Yurimoto, H. Hydrogen isotope ratios in lunar rocks 115−123. indicate delivery of cometary water to the Moon. Nat. Geosci. 2011, 4, − (40) Simon, J. I.; Christoffersen, R.; Wang, J.; Mouser, M. D.; Mills, 79 82. R. D.; Ross, D. K.; Rahman, Z.; Alexander, C. M. O. D. Volatiles in (21) Barnes, J. J.; Franchi, I. A.; Anand, M.; Tartese, R.; Starkey, N. lunar felsite clasts: impact-related delivery of hydrous material to an A.; Koike, M.; Sano, Y.; Russell, S. S. Accurate and precise ancient dry lunar crust. Geochim. Cosmochim. Acta 2020, 276, 299− measurements of the D/H ratio and hydroxyl content in lunar 326. − − apatites using nanoSIMS. Chem. Geol. 2013, 337 338,48 55. (41) Clark, R. N. Detection of adsorbed water and hydroxyl on the (22) Barnes, J. J.; Tartese, R.; Anand, M.; McCubbin, F. M.; Franchi, Moon. Science 2009, 326, 562−564. I. A.; Starkey, N. A.; Russell, S. S. The origin of water in the primitive (42) Pieters, C. M.; Goswami, J. N.; Clark, R. N.; et al. Character moon as revealed by the lunar highland samples. Earth Planet. Sci. and spatial distribution of OH/H2O on the surface of the Moon seen − Lett. 2014, 390, 244 252. by M3 on Chandrayaan-1. Science 2009, 326, 568−572. (23) Barnes, J. J.; Kring, D. A.; Tartese, R.; Franchi, I. A.; Anand, M.; (43) Sunshine, J. M.; Farnham, T. L.; Feaga, L. M.; Groussin, O.; Russell, S. S. An asteroidal origin for water in the moon. Nat. Merlin, F.; Milliken, R. E.; A’Hearn, M. F. Temporal and spatial Commun. 2016, 7, 11684. variability of lunar hydration as observed by Deep Impact Spacecraft. (24) Barnes, J. J.; Tartese, R.; Anand, M.; McCubbin, F. M.; Neal, C. Science 2009, 326, 565−568. R.; Franchi, I. A. Early degassing of lunar urKREEP by crust-breaching (44) Colaprete, A.; Schultz, P.; Heldmann, J.; Wooden, D.; Shirley, impact(s). Earth Planet. Sci. Lett. 2016, 447,84−94. M.; Ennico, K.; Hermalyn, B.; Marshall, W.; Ricco, A.; Elphic, R. C.; (25) Tartese, R.; Anand, M.; Barnes, J. J.; Starkey, N. A.; Franchi, I. Goldstein, D.; Summy, D.; Bart, G. D.; Asphaug, E.; Korycansky, D.; A.; Sano, Y. The abundance, distribution, and isotopic composition of Landis, D.; Sollitt, L. Detection of water in the LCROSS ejecta plume. hydrogen in the moon as revealed by basaltic lunar samples: Science 2010, 330, 463−468. implications for the volatile inventory of the moon. Geochim. (45) Mitrofanov, I. G.; Sanin, A. B.; Boynton, W. V.; Chin, G.; Cosmochim. Acta 2013, 122,58−74. Garvin, J. B.; Golovin, D.; Evans, L. G.; Harshman, K.; Kozyrev, A. S.; (26) Tartese, R.; Anand, M.; Joy, K. H.; Franchi, I. A. H and Cl Litvak, M. L.; Malakhov, A.; Mazarico, E.; McClanahan, T.; Milikh, isotope systematics of apatite in brecciated lunar meteorites G.; Mokrousov, M.; Nandikotkur, G.; Neumann, G. A.; Nuzhdin, I.; Northwest Africa 4472, Northwest Africa 773, Sayh al Uhaymia Sagdeev, R.; Shevchenko, V.; Shvetsov, V.; Smith, D. E.; Starr, R.; 169, and Kalahari 009. Meteor. Planet. Sci. 2014, 49, 2266−2289. Tretyakov, V. I.; Trombka, J.; Usikov, D.; Varenikov, A.; Vostrukhin,

1495 https://dx.doi.org/10.1021/acsearthspacechem.9b00305 ACS Earth Space Chem. 2020, 4, 1480−1499 ACS Earth and Space Chemistry http://pubs.acs.org/journal/aesccq Review

A.; Zuber, M. T. Hydrogen mapping of the lunar South Pole using (65) Ganapathy, R.; Keays, R. R.; Laul, J. C.; Anders, E. Trace LRO Neutron Detector Experiment LEND. Science 2010, 330, 483− elements in Apollo 11 lunar rocks: implications for meteorite influx 486. and origin of moon. Proc. Apollo 11 Lunar Sci. Conf. 1970, 2, 1117− (46) Mitrofanov, I. G.; Sanin, A. B.; Litvak, M. L. Water in the 1142. moon’s polar areas: results of LEND neutron telescope mapping. (66) Epstein, S.; Taylor, H. P., Jr. 18O/16O, 30Si/28Si, D/H, and Dokl. Phys. 2016, 61,98−101. 13C/12C studies of lunar rocks and minerals. Science 1970, 167, (47) Hayne, P. O.; Hendrix, A.; Sefton-Nash, E.; Siegler, M. A.; 533−535. Lucey, P. G.; Retherford, K. D.; Williams, J. P.; Greenhagen, B. T.; (67) Epstein, S.; Taylor, H. P., Jr. D/H and 18O/16O ratios of H2O Paige, D. A. Evidence for exposed water ice in the Moon’s south polar in the ″rusty″ brecia 66095 and the origin of ″lunar water″. Proc. 5th regions from Lunar Reconnanssance Orbiter ultraviolet albedo and Lunar Conf. 1974, 2, 1839−1854. temperature measurements. Icarus 2015, 255,58−69. (68) Beckinsale, R. D. Hydrogen, oxygem, and silicon isotope (48) Fisher, E. A.; Lucey, P. G.; Lemelin, M.; Greenhagen, B. T.; systematics in lunar material. Phyil. Trans. R Soc. London A 1977, 285, Siegler, M. A.; Mazarico, E.; Aharonson, O.; Williams, J. P.; Hayne, P. 417−426. O.; Neumann, G. A.; Paige, D. A.; Smith, D. E.; Zuber, M. T. (69) Fogel, R. A.; Rutherford, M. J. Magmatic volatiles in primitive Evidence for surface water ice in the lunar polar regions using lunar glasses: I. FTIR and EMPA analyses of Apollo 15 green and reflectance measurements from the Lunar Orbiter Laser Altimeter and yellow glasses and revision of the volatile-assisted fire-fountain theory. temperature measurements from the Divine Lunar Radiometer Geochim. Cosmochim. Acta 1995, 59, 201−215. − Experiment. Icarus 2017, 292,74 85. (70) Wolf, R.; Anders, E. Moon and Earth: compositional (49) Li, S.; Lucey, P. G.; Milliken, R. E.; Hayne, P. O.; Fisher, E.; differences inferred from siderophiles, volatiles, and alkalis in basalts. Williams, J. P.; Hurley, D. M.; Elphic, R. C. Direct evidence of surface Geochim. Cosmochim. Acta 1980, 44, 2111−2124. exposed water ice in the lunar polar regions. Proc. Natl. Acad. Sci. U. S. (71) O’Neill, H. S. C. The origin of the moon and the early history − A. 2018, 115, 8907 8912. of the earth - a chemical model. Part 1. the moon. Geochim. (50) Liu, Y.; Guan, Y.; Zhang, Y.; Rossman, G. R.; Eiler, J. M.; Cosmochim. Acta 1991, 55, 1135−1157. Taylor, L. A. Direct measurement of hydroxyl in the lunar regolith and (72) Newcombe, M. E.; Beckett, J. R.; Baker, M. B.; Newman, S.; − the origin of lunar surface water. Nat. Geosci. 2012, 5, 779 782. Guan, Y.; Eiler, J. M.; Stolper, E. M. Effects of pH2O, pH2, and fO2 (51) Li, S.; Milliken, R. E. Water on the surface of the Moon as seen on the diffusion of H-bearing species in lunar basaltic liquid and an by the Moon Mineralogy Mapper: distribution, abundance, and iron-free basaltic analog at 1 atm. Geochim. Cosmochim. Acta 2019, origins. Sci. Adv. 2017, 3, e1701471. 259, 316−343. (52) Milliken, R. E.; Li, S. Remote detection of widespread (73) Zhang, L.; Guo, X.; Li, W.-C.; Ding, J.; Zhou, D.; Zhang, L.; Ni, indigenous water in lunar pyroclastic deposits. Nat. Geosci. 2017, 10, − H. Reassessment of pre-eruptive water content of lunar volcanic glass 561 565. based on new data of water diffusivity. Earth Planet. Sci. Lett. 2019, (53) Albarede, F.; Albalat, E.; Lee, C. T. A. An intrinsic volatility 522,40−47. scale relevant to the Earth and Moon and the status of water in the (74) McCubbin, F. M.; Nekvasil, H.; Jolliff, B. L.; Carpenter, P. K.; moon. Meteor. Planet. Sci. 2015, 50, 568−577. Zeigler, R. A. A survey of lunar apatite volatile contents for (54) Wetzel, D. T.; Hauri, E. H.; Saal, A. E.; Rutherford, M. J. determining bulk lunar waterL how dry is ″bone dry″? Lunar Planet. Carbon content and degassing history of the lunar volcanic glasses. Sci. Conf. Abstr. 2008, 39, 1788. Nat. Geosci. 2015, 8, 755−758. (75) Potts, N. J.; Barnes, J. J.; Tartese, R.; Franchi, I. A.; Anand, M. (55) Hauri, E. H.; Saal, A. E.; Nakajima, M.; Anand, M.; Rutherford, M. J.; Van Orman, J. A.; Le Voyer, M. Origin and evolution of water Chlorine isotopic compositions of apatite in Apollo 14 rocks: in the moon’s interior. Annu. Rev. Earth Planet. Sci. 2017, 45,89−111. evidence for widespread vapor-phase metasomatism on the lunar nearside ∼ 4 billion years ago. Geochim. Cosmochim. Acta 2018, 230, (56) McCubbin, F. M.; Vander Kaaden, K. E.; Tartese, R.; Klima, R.; − Liu, Y.; Mortimer, J.; Barnes, J. J.; Shearer, C. K.; Treiman, A. H.; 46 59. Lawrence, D. J.; Elardo, S. M.; Hurley, D. M.; Boyce, J. W.; Anand, M. (76) Wang, Y.; Hsu, W.; Guan, Y. An extremely heavy chlorine Magmatic volatiles (H, C, N, F, S, Cl) in the lunar mantle, crust, and reservoit in the Moon: Insights from the apatite in lunar meteorites. regolith: abundances, distributions, processes, and reservoirs. Am. Sci. Rep. 2019, 9, 5727. Mineral. 2015, 100, 1668−1707. (77) Sharp, Z. D.; Shearer, C. K.; McKeegan, K. D.; Barnes, J. D.; (57) Greenwood, J. P.; Karato, S.; Vander Kaaden, K. E.; Pahlevan, Wang, Y. Q. , The chlorine isotope composition of the moon and − K.; Usui, T. Water and volatile inventories of Mercury, Venus, the implicaitons for an anhydrous mantle. Science 2010, 329, 1050 1053. Moon, and Mars. Space Sci. Rev. 2018, 214, 92. (78) Sharp, Z. D.; Barnes, J. D.; Brearley, A. J.; Chaussidon, M.; (58) Wulf, A. V.; Palme, H.; Jochum, K. P. Fractionation of volatile Fischer, T. P.; Kamenetsky, V. S. Chlorine isotope homogeneity of the − elements in the early solar system: evidence from heating experiments mantle crust and carbonaceous chondrites. Nature 2007, 446, 1062 on primitive meteorites. Planet. Space Sci. 1995, 43, 451−468. 1065. (59) Lodders, K. Solar system abundances and condensation (79) Sharp, Z. D.; Barnes, J. D.; Fischer, T. P.; Halick, M. An temperatures of the elements. Astrophys. J. 2003, 591, 1220−1247. experimental determination of chlorine isotope fractionation in acid (60) Wood, B. J.; Smythe, D. J.; Harrison, T. The condensation systems and applications to volcanic fumaroles. Geochim. Cosmochim. temperatures of the elements: a reappraisal. Am. Mineral. 2019, 104, Acta 2010, 74, 264−273. 844−856. (80) Delano, J. W. Pristine lunar glasses: criteria, data, and (61) Taylor, G. J.; Warren, P.; Ryder, G.; Delano, J.; Pieters, C.; implications. J. Geophys. Res. 1986, 91 (B4), 201−213. Lofgren, G., Lunar rocks. In Lunar Sourcebook: A User’s Guide to the (81) Ma, C.; Liu, Y. Discovery of a zinc-rich mineral on the surface Moon; Heiken, G. H., Vaniman, D. T., French, B. M., Eds.; Cambridge of lunar orange pyroclastic beads. Am. Mineral. 2019, 104, 447−452. University Press, 1991; pp 183−284. (82) Meyer, C., Jr.; McKay, D. S.; Anderson, D. H.; Butler, P., Jr. (62) Neal, C. R.; Taylor, L. A. Petrogenesis of mare basalts: a record The source of sublimates on the Apollo 15 green and Apollo 17 of lunar volcanism. Geochim. Cosmochim. Acta 1992, 56, 2177−2211. orange glass samples. Proc. Lunar Planet. Conf. 1975, 6, 1673−1699. (63) Giguere, T. A.; Taylor, G. J.; Hawke, B. R.; Lucey, P. G. The (83) Anderson, A. T., Jr.; Newman, S.; Williams, S. N.; Druitt, T. H.; titanium contents of lunar mare basalts. Meteorit. Planet. Sci. 2000, 35, Skirius, C.; Stolper, E. H2O, CO2, Cl and gas in Plinian and ash-flow 193−200. Bishop rhyolite. Geology 1989, 17, 221−225. (64) Gast, P. W.; Hubbard, N. J. Abundance of alkali metals, alkaline (84) Anderson, A. T.; Brown, G. G. CO2 content and formation and rare earths, and srtontium-87/strontium-86 ratios in lunar pressures of some Kilauean melt inclusions. Am. Mineral. 1993, 78, samples. Science 1970, 167, 485−487. 794−803.

1496 https://dx.doi.org/10.1021/acsearthspacechem.9b00305 ACS Earth Space Chem. 2020, 4, 1480−1499 ACS Earth and Space Chemistry http://pubs.acs.org/journal/aesccq Review

(85) Wallace, P. J. Volatiles in subduction zone magmas: evidence for H2O and F open system behavior in melt inclusions. concentrations and fluxes based on melt inclusion and volcanic gas Earth Planet. Sci. Lett. 2009, 287, 442−452. data. J. Volcanol. Geotherm. Res. 2005, 140, 217−240. (107) Taylor, L. A.; McCallister, R. H.; Sardi, O. Cooling histories of (86) Lu, F.; Anderson, A. T.; Davis, A. M. Diffusional gradients at lunar rocks based on opaque mineral geothermometers. Proc. 4th the crystal/melt interface and their effect on the composition of melt Lunar Sci. Conf. (Suppl. 4, Geochim. Cosmochim. Acta) 1973, 1, 819− inclusions. J. Geol. 1995, 103, 591−597. 828. (87) Zhang, Y.; Ni, H.; Chen, Y. Diffusion data in silicate melts. Rev. (108) Taylor, L. A.; Uhlmann, D. R.; Hopper, R. W.; Misra, K. C. Mineral. Geochem. 2010, 72, 311−408. Absolute cooling rates of lunar rocks: theory and application. Proc. (88) Kress, V. C.; Ghiorso, M. S. Thermodynamic modeling of post- Lunar Sci. Conf. 6th 1975, 181−191. entrapment crystallization in igneous phases. J. Volcanol. Geotherm. (109) Taylor, L. A.; Onorato, P. I.; Uhlmann, D. R. Cooling rate Res. 2004, 137, 247−260. estimations based on kinetic modelling of Fe-Mg diffusion in olivine. (89) Newcombe, M. E.; Fabbrizio, A.; Zhang, Y.; Ma, C.; Le Voyer, Proc. Lunar Sci. Conf. 8th 1977, 1581−1592. M.; Guan, Y.; Eiler, J. M.; Saal, A. E.; Stolper, E. M. Chemical (110) Lofgren, G.; Donaldson, C. H.; Williams, R. J.; Mullins, O.; zonation in olivine-hosted melt inclusions. Contrib. Mineral. Petrol. Usselman, T. M. Experimentally reproduced textures and mineral 2014, 168, 1030. chemistry of Apollo 15 quartz normative basalts. Proc. Fifth Lunar (90) Wallace, P. J.; Kamenetsky, V. S.; Cervantes, P. Melt inclusion Conf. (Suppl. 5, Geochim. Cosmochim. Acta) 1974, 549−567. CO2 contents, pressures of olivine crystallization, and the problem of (111) Lofgren, G. E.; Donaldson, C. H.; Usselman, T. M. Geology, shrinkage bubbles. Am. Mineral. 2015, 100, 787−794. petrology, and crystallization of Apollo 15 quartz-normative basalts. (91) Gaetani, G. A.; Watson, E. B. Open system behavior of olivine- Proc. Lunar Sci. Conf. 6th 1975,79−99. hosted inclusions. Earth Planet. Sci. Lett. 2000, 183,27−41. (112) Uhlmann, D. R.; Yinnon, H.; Fang, C.-Y. Simplified model (92) Chen, Y.; Provost, A.; Schiano, P.; Cluzel, N. The rate of water evaluation of cooling rates for glass-containing lunar compositions. loss from olivine-hosted melt inclusions. Contrib. Mineral. Petrol. Proc. Lunar Planet. Sci. 1981, 12B, 281−288. 2011, 162, 625−636. (113) Donaldson, C. H.; Usselman, T. M.; Williams, R. J.; Lofgren, (93) Gaetani, G. A.; O’Leary, J. A.; Shimizu, N.; Bucholz, C. E.; G. E. Experimental modeling of the cooling history of Apollo 12 Newville, M. Rapid reequilibration of H2O and oxygen fugacity in olivine basalts. Proc. Lunar Sci. Conf. 6th 1975, 843−869. olivine-hosted melt inclusions. Geology 2012, 40, 915−918. (114) Takeda, H.; Miyamoto, M.; Ishii, T.; Lofgren, G. E. Relative (94) Chen, Y.; Provost, A.; Schiano, P.; Cluzel, N. Magma ascent cooling rates of mare basalts at the Apollo 12 and 15 sites as estimated rate and initial water concentration inferred from diffusive water loss from pyroxene exsolution data. Proc. Lunar Sci. Conf. 6th 1975, 987− from olivine-hosted melt inclusions. Contrib. Mineral. Petrol. 2013, 996. 165, 525−541. (115) Usselman, T. M.; Lofgren, G. E.; Donaldson, C. H.; Williams, (95) Bucholz, C. E.; Gaetani, G. A.; Behn, M. D.; Shimizu, N. Post- R. J. Experimentally reproduced textures and mineral chemistries of entrapment modification of volatiles and oxygen fugacity in olivine- high-titanium mare basalts. Proc. Lunar Sci. Conf. 6th 1975, 997− hosted melt inclusions. Earth Planet. Sci. Lett. 2013, 374, 145−155. 1020. (96) Singer, J. A.; Greenwood, J. P.; Itoh, S.; Sakamoto, N.; (116) Arndt, J.; Rombach, N. Derivation of the thermal history of Yurimoto, H. Evidence for the solar wind in lunar magmas: a study of tektites and lunar glasses from their thermal expansion characteristics. slowly cooled samples of the Apollo 12 olivine basalt suite. Geochem. J. Proc. Lunar Sci. Conf. 7th 1976, 1123−1141. 2017, 51,95−104. (117) Walker, D.; Longhi, J.; Kirkpatrick, R. J.; Hays, J. F. (97) Uhlmann, D. R.; Klein, L.; Kritchevsky, G.; Hopper, R. W. The Differentiation of an Apollo 12 picrite magma. Proc. Lunar Sci. formation of lunar glasses. Proc. 5th Lunar Conf. (Suppl. 5, Geochim. Conf. 7th 1976, 1365−1389. Cosmochim. Acta) 1974, 3, 2317−2331. (118) Walker, D.; Longhi, J.; Lasaga, A. C.; Stolper, E. M.; Grove, T. (98) Hui, H.; Hess, K. U.; Zhang, Y.; Nichols, A. L.; Peslier, A. H.; L.; Hays, J. F. Slowly cooled microgabbros 15555 and 15065. Proc. Lange, R. A.; Dingwell, D. B.; Neal, C. R. Cooling rates of lunar Lunar Sci. Conf. 8th 1977, 1521−1547. orange glass beads. Earth Planet. Sci. Lett. 2018, 503,88−94. (119) Bianco, A. S.; Taylor, L. A. Applications of dynamic (99) Salters, V. J.; Stracke, A. Composition of the depleted mantle. crystallization studies: Lunar olivine-normative basalts. Proc. Lunar Geochem., Geophys., Geosyst. 2004, 5, Q05B07. Sci. Conf. 8th 1977, 1593−1610. (100) Sun, S.; McDonough, W. F. Chemical and isotopic systematics (120) Grove, T. L.; Walker, D. Cooling histories of Apollo 15 of oceanic basalts: implications for mantle composition and processes. quartz-normative basalts. Proc. Lunar Sci. Conf. 8th 1977, 1501−1520. In Magmatism in the Ocean Basins; Sauders, A. D., Norry, M. J., Eds.; (121) Grove, T. L. Use of exsolution lamellae in lunar Geological Society Special Publications, Vol. 42; The Geological clinopyroxenes as cooling rate speedometers: An experimental Society, Blackwell: Oxford, U.K., 1989; pp 313−345. calibration. Am. Mineral. 1982, 67, 251−268. (101) Michael, P. J. The concentration, behavior and storage of H2O (122) Zhang, Y.; Xu, Z.; Zhu, M.; Wang, H. Silicate melt properties in the suboceanic upper mantle: implications for mantle metasoma- and volcanic eruptions. Rev. Geophys. 2007, 45, RG4004. tism. Geochim. Cosmochim. Acta 1988, 52, 555−566. (123) McDonough, W. F.; Sun, S.-S. The composition of the Earth. (102) Michael, P. J. Regionally distinctive sources of depleted Chem. Geol. 1995, 120, 223−253. MORB: evidence from trace elements and H2O. Earth Planet. Sci. (124) Carlson, R. W.; Lugmair, G. W. The age of ferroan anorthosite Lett. 1995, 131, 301−320. 60025: oldest crust on a young Moon? Earth Planet. Sci. Lett. 1988, (103) Dixon, J. E.; Leist, L.; Langmuir, C.; Schilling, J. G. Recycled 90, 119−130. dehydrated lithosphere observed in plume-influenced mid-ocean-ridge (125) Nemchin, A.; Timms, N.; Pidgeon, R.; Geisler, T.; Reddy, S.; basalt. Nature 2002, 420, 385−389. Meyer, C. Timing of crystallization of the lunar magma ocean (104) Saal, A. E.; Hauri, E. H.; Langmuir, C. H.; Perfit, M. R. Vapor constrained by the oldest zircon. Nat. Geosci. 2009, 2, 133−136. undersaturation in primitive mid-ocean-ridge basalt and the volatile (126) Borg, L. E.; Connelly, J. N.; Boyet, M.; Carlson, R. W. content of Earth’s upper mantle. Nature 2002, 419, 451−455. Chronological evidence that the Moon is either young or did not have (105) Workman, R. K.; Hauri, E. H.; Hart, S. R.; Wang, J.; Blusztajn, a global magma ocean. Nature 2011, 477,70−72. J. Volatile and trace elements in basaltic glass from Samoa: (127) Borg, L. E.; Gaffney, A. M.; Shearer, C. K. A review of lunar implications for water distribution in the mantle. Earth Planet. Sci. chronology revealing a preponderance of 4.34−4.37 Ga ages. Meteor. Lett. 2006, 241, 932−951. Planet. Sci. 2015, 50, 715−732. (106) Koleszar, A. M.; Saal, A. E.; Hauri, E. H.; Nagle, A. N.; Liang, (128) Gaffney, A. M.; Borg, L. E. A young solidification age for the Y.; Kurz, M. D. The volatile contents of the Galapagos plume; lunar magma ocean. Geochim. Cosmochim. Acta 2014, 140, 227−240.

1497 https://dx.doi.org/10.1021/acsearthspacechem.9b00305 ACS Earth Space Chem. 2020, 4, 1480−1499 ACS Earth and Space Chemistry http://pubs.acs.org/journal/aesccq Review

(129) Solomon, S. C.; Longhi, J. Magma oceanography: 1. thermal Proc. 4th Lunar Sci. Conf. (Suppl. 4 Geochim. Cosmochim. Acta) 1973, evolution. Proc. Lunar Sci. Conf. 8th 1977, 583−599. 2, 1461−1481. (130) Longhi, J. Magma oceanography 2: chemical evolution and (150) Wanke, H.; Palme, H.; Baddenhausen, H.; Dreibus, G.; crustal formation. Proc. Lunar Sci. Conf. 8th 1977, 601−621. Jagoutz, E.; Kruse, H.; Palme, C.; Spettel, B.; Teschke, F.; Thacker, R. (131) Longhi, J. Petrogenesis of picritic mare magmas: constraints New data on the chemistry of lunar samples: primary matter in the on the extent of early lunar differentiation. Geochim. Cosmochim. Acta lunar highlands and the bulk composition of the Moon. Proc. Lunar 2006, 70, 5919−5934. Sci. Conf. 6th 1975, 1313−1340. (132) Warren, P. H. The magma ocean concept and lunar evolution. (151) Wanke, H.; Palme, H.; Kruse, H.; Baddenhausen, H.; Annu. Rev. Earth Planet. Sci. 1985, 13, 201−240. Cendales, G.; Dreibus, G.; Hofmeister, H.; Jagoutz, E.; Palme, C.; (133) Shearer, C. K.; Hess, P. C.; Wieczorek, M. A.; Pritchard, M. Spettel, B.; Thacker, R. Chemistry of lunar highland rocks: a refined E.; Parmentier, E. M.; Borg, L.; Longhi, J.; Elkins-Tanton, L.; Neal, C. evaluation of the composition of the primary matter. Proc. Lunar Sci. R.; Antonenko, I.; Canup, R. M.; Halliday, A. N.; Grove, T. L.; Hager, Conf. 7th 1976, 3479−3499. B. H.; Lee, D.-C.; Wiechert, U. Thermal and magmatic evolution of (152) Xirouchakis, D.; Hirschmann, M. M.; Simpson, J. A. The effect the Moon. Rev. Mineral. Geochem. 2006, 60, 365−518. of titanium on the silica content and on mineral-liquid partitioning of (134) Snyder, G. A.; Taylor, L. A.; Neal, C. R. A chemical model for mantle-equilibrated melts. Geochim. Cosmochim. Acta 2001, 65, generating the sources of mare basalts: combined equilibrium and 2201−2217. fractional crystallization of the lunar magmasphere. Geochim. (153) Rosenthal, A.; Hauri, E. H.; Hirschmann, M. M. Experimental Cosmochim. Acta 1992, 56, 3809−3823. determination of C, F, and H partitioning between mantle minerals (135) Elardo, S. M.; Draper, D. S.; Shearer, C. K., Jr. Lunar magma and carbonated basalt, CO2/Ba, CO2/Nb systematics of partial ocean crystallization revisited: bulk composition, early cumulate melting and the CO2 contents of basaltic source regions. Earth Planet. mineralogy, and the source regions of the highlands Mg-suite. Sci. Lett. 2015, 412,77−87. Geochim. Cosmochim. Acta 2011, 75, 3024−3045. (154) Hirschmann, M. M. Constraints on the early delivery and (136) Johnson, E. A.; Rossman, G. R. The concentration and fractionation of Earth’s major volatiles from C/H, C/N, and C/S speciation of hydrogen in feldspars using FTIR and 1H MSA NMR ratios. Am. Mineral. 2016, 101, 540−552. spectroscopy. Am. Mineral. 2003, 88, 901−911. (155) Le Roux, V.; Lee, C. T. A.; Turner, S. J. Zn/Fe systematics in (137) Johnson, E. A. Water in nominally anhydrous crustal minerals: mafic and ultramafic systems: implications for detecting major speciation, concentration, and geologic significance. Rev. Mineral. element heterogeneities in the Earth’s mantle. Geochim. Cosmochim. Geochem. 2006, 62, 117−154. Acta 2010, 74, 2779−2796. (138) Hamada, M.; Ushioda, M.; Fujii, T.; Takahashi, E. Hydrogen (156) Lee, C. T. A.; Luffi, P.; Le Roux, V.; Dasgupta, R.; Albarede, concentration in plagioclase as a hygrometer of arc basaltic melts: F.; Leeman, W. P. The redox state of arc mantle using Zn/Fe approaches from melt inclusion analyses and hydrous melting systematics. Nature 2010, 468, 681−685. experiments. Earth Planet. Sci. Lett. 2013, 365, 253−262. (157) Zhang, Y. Quantification of the elemental incompatibility (139) Mosenfelder, J. L.; Rossman, G. R.; Johnson, E. A. Hydrous sequence, and composition of the ″superchondritic″ mantle. Chem. species in feldspars: a reassessment based on FTIR and SIMS. Am. Geol. 2014, 369,12−21. Mineral. 2015, 100, 1209−1221. (158) Zhang, Y.; Gan, T. Depletion ages and factors of MORB (140) Caseres, J. R.; Mosenfelder, J. L.; Hirschmann, M. M. mantle sources. Earth Planet. Sci. Lett. 2020, 530, 115926. Partitioning of hydrogen and fluorine between feldspar and melt (159) Gale, A.; Dalton, C. A.; Langmuir, C. H.; Su, Y.; Schilling, J. under the conditions of lunar crust formation. Lunar Planet. Sci. Conf. G. The mean composition of ocean ridge basalts. Geochem., Geophys., Abstr. 2017, No. 2303. Geosyst. 2013, 14, 489−518. (141) Lin, Y. H.; Hui, H.; Li, Y.; Xu, Y.; van Westrenen, W. A lunar (160) Norris, C. A.; Wood, B. J. Earth’s volatile contents established hygrometer based on plagioclase-melt partitioning of water. Geochem. by melting and vaporization. Nature 2017, 549, 507−510. Persp. Lett. 2019, 10,14−19. (161) Sossi, P. A.; Nebel, O.; O’Neill, H. S. C.; Moynier, F. Zinc (142) Ihinger, P. D.; Zhang, Y.; Stolper, E. M. The speciation of isotope composition of the Earth and its behavior during planetary dissolved water in rhyolitic melt. Geochim. Cosmochim. Acta 1999, 63, accretion. Chem. Geol. 2018, 477,73−84. 3567−3578. (162) Wimpenny, J.; Marks, N.; Knight, K.; Rolison, J. M.; Borg, L.; (143) Herzog, G. F.; Moynier, F.; Albarede, F.; Berezhnoy, A. A. Eppich, G.; Badro, J.; Ryerson, F. J.; Sanborn, M.; Huyskens, M. H.; Isotopic and elemental abundances of copper and zinc in lunar Yin, Q. Experimental determination of Zn isotope fractionation samples, Zagami, Pele’s hairs, and a terrestrial basalt. Geochim. during evaporative loss at extreme temperatures. Geochim. Cosmochim. Cosmochim. Acta 2009, 73, 5884−5904. Acta 2019, 259, 391−411. (144) Lindsay, F. N.; Herzog, G. F.; Albarede, F.; Korotev, R. L. (163) Rutherford, M. J.; Head, J. W.; Saal, A. E.; Hauri, E.; WIlson, Elemental and isotopic abundances of Fe, Cu, and Zn in low-Ti lunar L. Model for the origin, ascent, and eruption of lunar picritic magmas. basalts. Lunar Planet. Sci. Conf. Abstr. 2011, 1907. Am. Mineral. 2017, 102, 2045−2053. (145) Day, J. M. D.; van Kooten, E. M. M. E.; Hofmann, B. A.; (164) Pineau, F.; Javoy, M. Strong degassing at ridge crests: the Moynier, F. Mare basalt meteorites, magnesian-suite rocks and behavior of dissolved carbon and water in basalt glasses at 14°N, Mid- KREEP reveal loss of zinc during and after lunar formation. Earth Atlantic Ridge. Earth Planet. Sci. Lett. 1994, 123, 179−198. Planet. Sci. Lett. 2020, 531, 115998. (165) Greenwood, J. P.; Itoh, S.; Kawasaki, N.; Sakamoto, N.; (146) Johnson, E. A.; Rossman, G. R. A survey of hydrous species Yurimoto, H. Hydrogen isotopes, volatile an refrectory trace element and concentrations in igneous feldspars. Am. Mineral. 2004, 89, 586− composition of melt inclusions and apatite in a consanguineous suite 600. of Apollo 12 olivine basalts. Lunar Planet. Sci. Conf. Abstr. 2019, (147) Wieczorek, M. A.; Neumann, G. A.; Nimmo, F.; Kiefer, W. S.; No. 2371. et al. The crust of the Moon as seen by GRAIL. Science 2013, 339, (166) Michael, P. J.; Schilling, J. G. Chlorine in mid-ocean ridge 671−675. magmas: evidence for assimilation of seawater-incfluenced compo- (148) Lin, Y.; Hui, H.; Xia, X.; Shang, S.; van Westrenen, W. nents. Geochim. Cosmochim. Acta 1989, 53, 3131−3143. Experimental constraints on the solidification of a hydrous lunar (167) Le Roux, P. J.; Shirey, S. B.; Hauri, E. H.; Perfit, M. R.; magma ocean. Meteorit. Planet. Sci. 2020, 55, 207−230. Bender,J.F.Theeffectsofvariablesources,processesand (149) Wanke, H.; baddenhausen, H.; Dreibus, G.; Jagoutz, E.; Kruse, contaminants on the composition of northern EPR MORB (8− H.; Palme, H.; Spettel, B.; Teschke, F. Multielement analysis of 10°N and 12−14°N): evidence from volatiles (H2O, CO2, S) Apollo 15, 16, and 17 samples and the bulk composition of the moon. andhalogens (F,Cl). Earth Planet. Sci. Lett. 2006, 251, 209−231.

1498 https://dx.doi.org/10.1021/acsearthspacechem.9b00305 ACS Earth Space Chem. 2020, 4, 1480−1499 ACS Earth and Space Chemistry http://pubs.acs.org/journal/aesccq Review

(168) Greenwood, J. P.; Sakamoto, N.; Itoh, S.; Warren, P. H.; (191) Wang, K.; Jacobsen, S. B. Potassium isotopic evidence for a Singer, J. A.; Yanai, K.; Yurimoto, H. The lunar magma ocean volatile high-energy giant impact origin of the moon. Nature 2016, 538, 487− signature recorded in chlorine-rich glasses in KREEP basalts 15382 490. and 15386. Geochem. J. 2017, 51, 105−114. (192) Kato, C.; Moynier, F. Gallium isotopic evidence for extensive (169) Kato, C.; Moynier, F.; Valdes, M. C.; Dhaliwal, J. K.; Day, J. volatile loss from the Moon during its formation. Sci. Adv. 2017, 3, M. D. Extensive volatile loss during formation and differentiation of e1700571. the moon. Nat. Commun. 2015, 6, 7617. (193) Pringle, E. A.; Moynier, F. Rubidium isotopic composition of (170) Ni, P.; Zhang, Y. Cu diffusion in a basaltic melt. Am. Mineral. the Earth, meteorites, and the Moon: evidence for the origin of 2016, 101, 1474−1482. volatile loss during planetary accretion. Earth Planet. Sci. Lett. 2017, (171) McDonough, W. F.; Sun, S.-S.; Ringwood, A. E.; Jagoutz, E.; 473,62−70. Hofmann, A. W. Potassium, rubidium, and cesium in the Earth and (194) Dhaliwal, J. K.; Day, J. M. D.; Moynier, F. Volatile element Moon and the evolution of the mantle of the Earth. Geochim. loss during planetary magma ocean phases. Icarus 2018, 300, 249− Cosmochim. Acta 1992, 56, 1001−1012. 260. (172) Righter, K. Volatile element depletion of the Moon - The roles of precursors, post-impact disk dynamics, and core formation. Sci. Adv. 2019, 5, eaau7658. (173) Neal, C. Mare Basalt Database, 2008; http://www3.nd.edu/ ~cneal/Lunar-L/Mare-Basalt-Database.xls (accessed May 11, 2016). (174) Nemchin, A. A.; Whitehouse, M. J.; Grange, M. L.; Muhling, J. R. On the elusive isotopic composition of lunar Pb. Geochim. Cosmochim. Acta 2011, 75, 2940−2964. (175) Watson, K.; Murray, B.; Brown, H. On the possible presence of ice on the moon. J. Geophys. Res. 1961, 66, 1598−1600. (176) Feldman, W. C.; Maurice, S.; Binder, A. B.; Barraclough, B. L.; Elphic, R. C.; Lawrence, D. J. Fluxes of fast and epithermal neutrons from Lunar Prospector: evidence for water ice at the lunar poles. Science 1998, 281, 1496−1500. (177) Zhu, C.; Crandall, P. B.; Gillis-Davis, J. J.; Ishii, H. A.; Bradley, J. P.; Corley, L. M.; Kaiser, R. I. Untangling the formation and liberation of water in the lunar regolith. Proc. Natl. Acad. Sci. U. S. A. 2019, 116, 11165−11170. (178) Liu, Y.; Guan, Y.; Barrat, J. A.; Taylor, L. A. Contrasting water chemistry in howardites and lunar regolith breccias. Lunar Planet. Sci. Conf. Abstr. 2017, No. 1543. (179) Liu, Y.; Guan, Y.; Chen, Y.; Taylor, L. A. Impact melt (agglutinitic glass) of lunar regolith: a volatile recorder of the lunar surface. New View Moon Workshop Abstr. 2016, No. 6010. (180) Hauri, E. H. Traces of ancient lunar water. Nat. Geosci. 2013, 6, 159−160. (181) Tartese, R.; Anand, M. Late delivery of chondritic hydrogen into the lunar mantle: insights from mare basalts. Earth Planet. Sci. Lett. 2013, 361, 480−486. (182) Walker, R. J.; Horan, M. F.; Shearer, C. K.; Papike, J. J. Low abundances of highly siderophile elements in the lunar mantle: evidence for prolonged late accretion. Earth Planet. Sci. Lett. 2004, 224, 399−413. (183) Day, J. M. D.; Pearson, D. G.; Taylor, L. A. Highly siderophile element constraints on accretion and differentiation of the Earth- Moon system. Science 2007, 315, 217−219. (184) Bottke, W. F.; Walker, R. J.; Day, J. M. D.; Nesvorny, D.; Elkins-Tanton, L. Stochastic late accretion to Earth, the Moon and Mars. Science 2010, 330, 1527−1530. (185) Schlichting, H. E.; Warren, P. H.; Yin, Q. Z. The last stages of terrestrial planet formation: dynamical friction and the late veneer. Astrophys. J. 2012, 752,8. (186) Day, J. M. D.; Walker, R. J. Highly siderophile element depletion in the moon. Earth Planet. Sci. Lett. 2015, 423, 114−124. (187) Zhu, M. H.; Artemieva, N.; Morbidelli, A.; Yin, Q. Z.; Becker, H.; Wunnemann, K. Reconstructing the late-accretion history of the Moon. Nature 2019, 571, 226−229. (188) Clayton, R. N.; Mayeda, T. K. Genetic relations between the moon and meteorites. Proc. Lunar Sci. Conf. 6th 1975, 1761−1769. (189) Millet, M. A.; Dauphas, N.; Greber, N. D.; Burton, K. W.; Dale, C. W.; Debret, B.; MacPherson, C. G.; Nowell, G. M.; Williams, H. M. Titanium stable isotope investigation of magmatic processes on the Earth and Moon. Earth Planet. Sci. Lett. 2016, 449, 197−205. (190) Cano, E. J.; Sharp, Z. D.; Shearer, C. K. Distinct oxygen isotope compositions of the Earth and Moon. Nat. Geosci. 2020, 13, 270−274.

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