Abstract
and the catalyst tolerates useful substrate functional groups, including aromatic and heteroatom substituents. With the development of improved methods for safe and scalable aerobic oxidation reactions (30), dehydrogenation methods of this type could have an important impact on laboratoryand industrial-scale chemical synthesis.
High Pre-Eruptive Water Contents Preserved in Lunar Melt Inclusions
Erik H. Hauri The Moon has long been thought to be highly depleted in volatiles such as water, and indeed published direct measurements of water in lunar volcanic glasses have never exceeded 50 parts per million (ppm). Here, we report in situ measurements of water in lunar melt inclusions; these samples of primitive lunar magma, by virtue of being trapped within olivine crystals before volcanic eruption, did not experience posteruptive degassing. The lunar melt inclusions contain 615 to 1410 ppm water and high correlated amounts of fluorine (50 to 78 ppm), sulfur (612 to 877 ppm), and chlorine (1.5 to 3.0 ppm). These volatile contents are very similar to primitive terrestrial mid-ocean ridge basalts and indicate that some parts of the lunar interior contain as much water as Earth's upper mantle.
High Pre-Eruptive Water Contents Preserved in Lunar Melt Inclusions
T he Moon is thought to have formed in a giant impact collision between a Marssized object and an early-formed protoEarth (1) . Though all of the inner planets, including Earth, are depleted in water and other volatiles when compared with primitive meteorites, the more extreme depletion of volatiles in lunar volcanic rocks has long been taken as key evidence for a giant impact that resulted in hightemperature catastrophic degassing of the material that formed the Moon (2, 3) . However, recent work on rapidly quenched lunar volcanic glasses has detected the presence of water dissolved in lunar magmas at concentrations up to 46 parts per million (ppm) (4) , and water contents of lunar apatite grains from mare basalts are consistent with similarly minor amounts of water in primitive lunar magmas (5-7). These results indicate that the Moon is not a perfectly anhydrous planetary body and suggest that some fraction of the Moon's observed depletion in highly volatile elements may be the result of magmatic degassing during the eruption of lunar magmas into the nearvacuum of the Moon's surface.
High Pre-Eruptive Water Contents Preserved in Lunar Melt Inclusions
To bypass the process of volcanic degassing, we conducted a search for lunar melt inclusions in Apollo 17 sample 74220, a lunar soil containing~99% high-Ti volcanic glass beads, the socalled orange glass with 9 to 12 weight % (wt %) TiO 2 (8) . Melt inclusions are small samples of magma trapped within crystals that grow in the magma before eruption. By virtue of their enclosure within their host crystals, melt inclusions are protected from loss of volatiles by degassing during magma eruption. Melt inclusions have been used for decades to determine pre-eruptive volatile contents of terrestrial magmas from subduction zones (9, 10) , hotspots (11, 12) , and midocean ridges (13, 14) , as well as volatile contents of martian magmas (15, 16) . Using standard petrographic methods, we identified nine inclusionbearing olivine crystals ( Fig. 1 ) and analyzed melt inclusions hosted within (17) . The measured water contents of the melt inclusions range from 615 ppm to a maximum of 1410 ppm (Fig. 2) ; these water contents are up to 100 times as high as the water content of the matrix glass surrounding the olivine crystals (6 to 30 ppm H 2 O) and the centers of individual volcanic glass beads from the same sample (4). The melt inclusions also contain high concentrations of fluorine (50 to 78 ppm), sulfur (612 to 877 ppm), and chlorine (1.5 to 3.0 ppm) that are 2 to 100 times as high as those of the matrix glasses and individual glass beads from this sample (Fig. 3) . Volatile contents corrected for postentrapment crystallization are on average 21% lower than the measured concentrations (17) and represent the best estimate of the pre-eruptive concentrations of volatiles in the 74220 magma.
High Pre-Eruptive Water Contents Preserved in Lunar Melt Inclusions
There are few descriptions in the literature of melt inclusions contained within olivine from lunar samples, but these existing observations provide important context for the volatile abundances we have observed. noted the presence of silicate melt inclusions in the first samples returned from the Apollo 11, Apollo 12, and Luna 16 missions and reported that many primary melt inclusions contained a vapor bubble, requiring dissolved volatiles to have been present in the melt at the time it was trapped within the host crystal. Klein and Rutherford (21) and Weitz et al. (22) found sulfur contents of 600 to 800 ppm, similar to our measurements, and Cl contents of <50 ppm that were limited by electron microprobe detection limits. Reheated Apollo 12 melt inclusions, containing medium-Ti magmas (5 to 6 wt % TiO 2 ), show sulfur contents that are 20% higher than our data on average (23) . In our data set, we observe a correlation of all the volatiles with each other (Fig. 3) , pointing toward the degassed compositions of the matrix glass rinds and volcanic glass beads (4) .
High Pre-Eruptive Water Contents Preserved in Lunar Melt Inclusions
The most important aspect of our volatile data on lunar melt inclusions is their similarity to melt inclusions from primitive samples of terrestrial mid-ocean ridge basalts (MORBs), like those recovered from spreading centers located within transform faults (24) ; the melt inclusions from 74220 are markedly similar to melt inclusions from the Siqueiros Fracture Zone on the East Pacific Rise, some of the most primitive midocean ridge magmas that have been measured (Fig. 3) . These similarities suggest that the volatile signature of the lunar mantle source of the high-Ti melt inclusions is very similar to that of the upper mantle source of MORB.
High Pre-Eruptive Water Contents Preserved in Lunar Melt Inclusions
It is important that we have made these measurements on inclusions from olivine crystals contained within primitive lunar volcanic glasses. These inclusions were quenched within minutes after their eruption (4), providing minimal opportunity for posteruptive hydrogen diffusion out of the inclusions and affording a direct H 2 O measurement on primary lunar magma samples that have not experienced posteruptive degassing and associated loss of volatiles. The water concentrations that we measured are 20 to 100 times as high as previous direct measurements of the lunar glass beads from this same sample, which was estimated to have suffered 95 to 98% loss of H 2 O via degassing (4), and they are higher than estimates derived from lunar apatite measurements, which require a 95 to 99% correction for fractional crystallization to estimate primary magma volatile contents (5, 6) . Our results are direct measurements on primary lunar magma compositions that require no such extrapolations.
High Pre-Eruptive Water Contents Preserved in Lunar Melt Inclusions
Our melt inclusion data allow us to place some constraints on the volatile content of the lunar mantle source that generated the high-Ti picritic magmas. Using the most water-rich melt inclusion composition after correction for postentrapment crystallization, and an estimation that the high-Ti magmas originated from 5 to 30% batch partial melting with partitioning similar to that of terrestrial mantle-derived melts (17), we estimate lunar mantle volatile concentrations of 79 to 409 ppm H 2 O, 7 to 26 ppm F, 193 to 352 ppm S, and 0.14 to 0.83 ppm Cl. These estimates overlap most estimates for the volatile content of the terrestrial MORB mantle (24) (25) (26) (27) and are much higher than previous estimates for the lunar mantle based on the volatile content of lunar apatite (5, 6) and the variation of Cl isotopes in lunar rocks (28) , including the sample 74220 that we have studied here. The melt inclusions indicate definitively that some reservoirs within the interiors of Earth and the Moon not only have similar water contents, but also similar contents of fluorine, sulfur, and chlorine associated with this water, a volatile abundance signature shared by both bodies.
High Pre-Eruptive Water Contents Preserved in Lunar Melt Inclusions
These results show that the Moon is the only planetary object in our solar system currently identified to have an internal reservoir with a volatile content similar to that of Earth's upper mantle, and that previous estimates of the lunar inventory for highly volatile elements are biased to low concentrations owing to the degassed nature of lunar samples thus far studied. The Moon has erupted a wide variety of magmas during its history, and it remains to be seen whether other Si indicated by the color scale shown in (A), which ranges from dark regions corresponding to low 16 OH/ 30 Si ratios (e.g., olivine surrounding melt inclusions), to red regions within melt inclusions with 16 OH/ 30 Si ratios approaching 0.25 (corresponding to~1400 ppm H 2 O). The color scale is the same in all images, and all images show a scale bar of 1 mm. Rectangular areas are regions of interest within which each isotope ratio is calculated and converted to a concentration. lunar mantle sources are as volatile rich as the source of Apollo 17 high-Ti magmas. Nevertheless, the hydrated nature of at least part of the Moon's interior is a result that is not consistent with the notion that the Moon lost its entire volatile inventory to the vacuum of space during degassing after a high-energy giant impact, which would be expected to leave a highly desiccated lunar interior.
High Pre-Eruptive Water Contents Preserved in Lunar Melt Inclusions
If the bulk of the lunar interior has a volatile content similar to our estimate for the high-Ti mantle source, then our results present difficulties for late-accretion models that require volatile delivery to Earth and the Moon after their formation, because these two bodies have very different accretion cross sections that would predict different internal volatile contents. An Earth-Moon similarity in volatiles could indicate that chemical exchange of even the most volatile elements between the molten Earth and the proto-lunar disc might have been pervasive and extensive, resulting in homogenization at the very high temperatures expected after a giant impact; this could have been aided by the presence of a hightemperature convective atmospheric envelope surrounding Earth and the proto-lunar disc as the Moon solidified (29) . Alternatively, it is conceivable that a portion of the lunar interior escaped the widespread melting expected in the aftermath of a giant impact and simply inherited the inventory of water and other volatiles that is characteristic of Earth's upper mantle. Any model for the formation of Earth-Moon system must meet the constraints imposed by the presence of H 2 O in the lunar interior, with an abundance similar to that of Earth's upper mantle and with a complement of fluorine, sulfur, and chlorine also present at terrestrial levels. To the extent that lunar formation models predict very different volatile contents of Earth and the Moon, our results on the volatile content of lunar melt inclusions suggest that we lack understanding on some critical aspects of the physics of planetary moon formation by collisional impact.
High Pre-Eruptive Water Contents Preserved in Lunar Melt Inclusions
Our findings also have implications for the origin of water ice in shadowed lunar craters, which has been attributed to cometary and meteoritic impacts (30) . It is conceivable that some of this water could have originated from magmatic degassing during emplacement and eruption of lunar magmas (31) . These results also underscore the importance of pyroclastic volcanic samples in unraveling the history and composition of the Moon's interior; indeed, such deposits have been identified and mapped on the surfaces of all the terrestrial planets and many satellites. Fig. 3. (A to C) Volatile abundances for lunar melt inclusions (orange circle with black rims) and matrix glasses (orange circles) from Apollo 17 sample 74220. Melt inclusions show the highest concentrations (>600 ppm H 2 O) whereas matrix glasses show the lowest concentrations due to degassing (≤30 ppm H 2 O). The black curves show lunar magma degassing trends, scaled from the volatile-volatile correlations observed in core-rim NanoSIMS data on a lunar glass bead reported by Saal et al. (4) ; the core-rim data were scaled by multiplying the originally reported data for each element, by the ratio of the highest melt inclusion composition to that of the core composition reported in table 2 of (4). The gray field surrounds data for melt inclusions from the Siqueiros Fracture Zone on the East Pacific Rise, as an example of depleted MORB (24) . 
Supporting Online Material Materials & Methods
The samples were examined at high magnification, and optical photographs of each olivine and each melt inclusion were obtained (Fig. 1) . The inclusions are primary and of ovoid shape, with the exception of one inclusion that is triangular and appears to have been trapped between several olivine sub-grains (Fig. 1D) . The inclusions contain variable proportions of glass (~70%), quench-textured olivine (~30%), occasional crystals of an oxide phase that is probably ilmenite, and vapor bubbles in two inclusions. Of the fourteen inclusions, seven were large enough for analysis, six were too small for analysis, and one inclusion consisted mainly of metal and was not analyzed. Seven of the olivine crystals also contained a matrix glass rind that surrounded the exterior of the crystal, and these glasses were analyzed as well.
Supporting Online Material Materials & Methods
In order to eliminate the possibility of volatile element diffusion during the interaction of an electron beam with the samples, we performed all of the SIMS volatile analyses prior to analyzing the samples for major elements. Major element analyses were performed using a JEOL Superprobe at the Carnegie Institution of Washington's Geophysical Laboratory. We used a 30nA beam focused to 1-2 µm for olivine analyses, and defocussed to 10µm for glass analyses; standardization was checked by reproducing the major element compositions of 74220 glass beads reported previously (4) . Melt inclusions and matrix glass rinds consisted of ~70% glass and ~30% quench crystals of olivine, and their bulk compositions were measured by averaging a number of analyses distributed around the full exposure of the inclusion. We also conducted traverses of olivine adjacent to melt inclusions, and found no evidence for Fe-rich rims that exceeded 1 µm in width; even these are subject to possible phase boundary excitation, which can occur over 2-3 µm length scales. Average 2σ reproducibility of melt inclusion and matrix glass major elements is Si (1.4%), Ti (9.6%), Al (9.6%), Fe (2%), Mn (6%), Mg (13%), Ca (18%), Na (14%), K (17%) and P (17%). Average 2σ reproducibility of olivine analyses is 3-6% for all elements reported.
Supporting Online Material Materials & Methods
Major element compositions are reported in Table S1 . The melt inclusions are contained in olivine with forsterite contents that range from Fo 80.5 to Fo 82.2 . Melt inclusion MgO contents range from 3.3% to 13.4% and overlap the range of compositions displayed by matrix glass rinds on the outside of the host olivines, and volcanic glass beads from this same sample (Fig. S1 ). The melt inclusions exhibit postentrapment olivine crystallization that ranged from 5.4% to 36%, averaging 21%; matrix glass rinds exhibit a similar average amount of post-entrapment crystallization (19%). After correction for this crystallization, the MgO contents of the 74220 melt inclusions (11.8% to 15.3%) are at the high end of the range of MgO observed in 74220 glass beads (max. 15.4% MgO), demonstrating their primitive compositions.
Supporting Online Material Materials & Methods
Analyses for volatile abundances were performed using the Cameca NanoSIMS 50L scanning ion microprobe at the Carnegie Institution of Washington's Department of Terrestrial Magnetism. A primary ion beam of Cs was used as the probe, rastering over an area of 30x30µm or 10x10µm, and negatively charged ions of the isotopes 16 OH, 19 F, 30 Si, 32 S and 35 Cl were measured simultaneously on six electron multipliers using ion counting. For every analysis location, we first performed a pre-sputtering step on a 30x30µm area for 2 minutes with a 10nA primary beam, then switched to a primary beam of 1nA on a 30x30µm or 10x10µm area for data acquisition. We used basaltic glass ALV519-4-1 as a standard to determine relative sensitivity factors for H 2 O, F, S and Cl, and we used synthetic forsterite to monitor the detection limits of these elements, as described previously (32, 33) . Mass resolving power of the instrument was set to ~6000 in order to resolve 16 OH from 17 O as well as other isobaric interferences; average 30 Si count rates were on the order of 200,000 cps. For standardization and detection limit determinations, we obtained data in two different modes of operation: standard Dynamic SIMS, and Scanning Ion Imaging SIMS. For the measurements of lunar melt inclusions and matrix glasses, only Scanning Ion Imaging SIMS was used and it is this data that is reported in Table S2 .
Dynamic SIMS
In this mode of operation, only ion counts are recorded as data with no associated imaging. We divided the rastered area into 64x64 pixels and utilized a 245µm dwell time on each pixel (equivalent to 1 second per frame); we collected 50 cycles of data at 1 second per cycle, and corrected the data for system deadtime (electronically set to 44 ns). To eliminate stray ions from the edge of the crater that contribute to high background counts, we enabled electronic beam blanking to record data only from the innermost pixels from within the central of 3.7x3.7µm of the 10x10µm sputter crater, or within the central 11x11µm of a 30x30µm crater.
Scanning Ion Imaging SIMS
In this mode of operation, the instrument was used in an identical fashion as with Dynamic SIMS, except that the sputter crater was divided into 256x256 pixels and beam blanking was not used. Data were recorded as scanning ion images obtained simultaneously on each mass ( 16 OH, 19 F, 30 Si, 32 S and 35 C); in this mode, acquisition of a single frame takes ~16 seconds, and 10 frames were acquired at each analysis location, resulting in a total acquisition time of ~3 minutes.
Scanning Ion Imaging SIMS
Data were extracted and processed from the ion images using the L'Image software package for PV Wave written by Larry Nittler (DTM-CIW). Data were first corrected for system deadtime, and the last nine images were summed (first image used as a presputter); images were ratioed to produce scanning isotope ratio images ( 16 Si) , and data were extracted from specific userdefined regions of interest (ROIs) located within the isotope ratio images. Each ROI consisted of a unique 25x25 or 75x75 pixel area of the image (equivalent to 0.8x0.8µm similar to the beam diameter for a 10x10µm image, or ~3 beam diameters for a 30x30µm image) and a number of ROIs were specified for each isotope ratio image so that they did not overlap, were contained within the inclusion without overlapping host olivine, and did not overlap areas of containing surface contamination of volatiles (vapor bubble in Fig. 2A , crater edges in Fig. 2B,D,E) . The isotope ratio images for standards and synthetic forsterite are essentially homogeneous (to within a few percent) except at the crater edges; for isotope ratio images of melt inclusions, the NanoSIMS sample stage was adjusted so that the inclusion was centered in the sputter crater prior to presputtering and image acquisition. For images of standards and synthetic forsterite, 30 ROIs were located in the center of the image; for images of melt inclusions, the number of ROIs varied from 6 (for small inclusions) to 36 (for large melt inclusions, see Figure 2 ); ROIs were located in the most homogeneous areas of the isotope ratio images, and verified to avoid overlap with host olivines and/or vapor bubbles guided by photographs of each melt inclusion taken prior to the NanoSIMS measurements, scaled to the size of the imaged area on the sample.
Scanning Ion Imaging SIMS
Within each ROI, the total number of 30 Si ion counts averaged around 200,000; for synthetic forsterite, average counts per ROI were 314 for 16 35 Cl (42 ppm Cl). The size of the ROIs and the number of images acquired were chosen so that, in general, the ROI was similar to the primary beam diameter, and the theoretical precision of each isotope ratio in each ROI was on the order of a few percent. For ALV519-4-1 standard, the 2-sigma reproducibility of all the ROIs was 5% or better for all elements. For synthetic forsterite used to measure detection limits, the 2-sigma reproducibility of the ROIs was 20% for H 2 O, 34% for fluorine, 43% for sulfur, and 98% for chlorine -these were directly related to the total number of counts per ROI.
Comparison of Scanning Ion Imaging SIMS with Dynamic SIMS
An important part of the methods development for this study involved verification that the same isotope ratios could be obtained from Dynamic SIMS and processing of data from images obtained by Scanning Ion Imaging SIMS, in effect providing a groundtruthing of both scanning ion imaging and data processing methods. This was demonstrated on the ALV519-4-1 basaltic glass standard (for calibration purposes) and the synthetic forsterite (for detection limit purposes). For this comparison, we made five different measurements of each, in which each measurement was subjected to presputtering (as described above), followed by a Dynamic SIMS measurement (lasting 1 minute), followed lastly by a Scanning Ion Image acquisition (lasting 3 minutes). The data show that the isotope ratios obtained from both methods agree to within 3% on average, over a dynamic range of almost 5 orders of magnitude (isotope ratio values from ~5e-4 to 1.3, see Figure S2 ). From these measurements, the data for ALV519-4-1 were used to calculate the relative sensitivity calibrations for H 2 O, F, S and Cl (using count rates normalized to 30 Si) while the data from synthetic forsterite were used to measure the detection limits of the same elements (7ppm H 2 O, 0.06 ppm F, 0.07 ppm S and 0.02 ppm Cl).
Data for Lunar Melt Inclusions
Using standard petrographic methods, we identified fourteen inclusions in nine olivine crystals; seven of the inclusions were large enough for accurate analysis, seven were too small, and one was an inclusion of metal. Only Scanning Ion Imaging SIMS was used to obtain data on the lunar melt inclusions so as to preserve the material for future measurements; nevertheless, one of the viable melt inclusions (74220-N9#1) was sufficiently thin that it sputtered away during an attempted repeat analysis. The isotope ratio data were extracted from a number of ROIs located within each inclusion, the data from individual ROIs was corrected for detection limits, and an average concentration and 2-standard error uncertainty for each image acquisition was obtained by averaging the ROI data for each analysis. The "repeat" analyses in Table S1 indicate separate repeat image acquisitions obtained on the same melt inclusion (for olivines N3, N6 and N8); two melt inclusions were located in olivine N9 and a single image acquisition was obtained for each.
Data for Lunar Melt Inclusions
Errors reported in Table S2 are the average 2-sigma standard errors for the melt inclusion and matrix glass volatile data; these errors include the propagated uncertainties (as 2 standard deviations) of the detection limits, and are a measure of the precision of each image acquisition. Repeat image acquisitions of the same melt inclusions agree at a level that is similar to the calculated precision. Accuracy of the data is on the order of 5-10% (2-sigma) as indicated by the calibration discussion in Hauri et al. (34) .
Data for Lunar Melt Inclusions
The major element data indicate that some degree of post-entrapment crystallization of olivine has occurred on the inside walls of these melt inclusions; there are no discernable compositional rims at the inclusion-olivine boundaries that exceed 1 µm in width, and even these are subject to possible phase boundary excitiation which can occur over length scales of 2-3 µm. As anticipated, the measured melt inclusion compositions fall within the range of compositions displayed by 74220 glass beads; this is also true for the matrix glass at the edges of olivine crystals. The olivines range from Fo 80.5 to Fo 82.2 . The Fe-Mg Kd values for inclusion-olivine pairs range from 0.060 to 0.245; these values are lower than expected and are consistent with post-entrapment crystallization (PEC).
Data for Lunar Melt Inclusions
The amount of PEC determined from the major element data has a correspondingly minor effect on the volatile contents of the melt inclusions. We calculated melt inclusion compositions corrected for PEC of olivine in the standard fashion, by adding back equilibrium olivine in 0.1% increments, recalculating the melt composition at each step, until the melt inclusions arrived at Fe-Mg equilibrium with their host olivine crystals, indicated by an olivine-melt Kd value of 0.250 to 0.280. It is important to note that, at the high TiO 2 contents of our melts, olivine-melt Kd values are inversely correlated with melt TiO 2 contents, as demonstrated previously in several experimental studies (35) (36) (37) , and this effect is included in our correction for postentrapment crystallization.
Data for Lunar Melt Inclusions
The corrected melt inclusion compositions overlap completely with the highest MgO glass beads from 74220, and indicate that the inclusions experienced PEC of olivine varying from 5.4% up to 33% (average 21%, Table S1 ); these amounts of PEC are essentially identical for melt inclusions and associated matrix glasses.
Data for Lunar Melt Inclusions
The corrected volatile contents in Table S2 have been reduced by the amount of post-entrapment crystallization determined for each inclusion or matrix glass; for inclusion N9 #2, we corrected the volatile contents by the same amount as inclusion N9 #1 in the same crystal (27%); for inclusion N3, we corrected the volatile contents by the average amount of inclusion PEC (21%). These corrections (5.4% to 33%) are minor compared with the 20-100X difference between the melt inclusions and glass beads from this sample. Figure S1 . Major elements of melt inclusions from Apollo 17 sample 74220, showing compositions measured for melt inclusions and matrix glasses, and inclusions corrected for post-entrapment crystallization (PEC), compared with compositions for glass beads (4) . The slightly lower FeO* contents for PEC-corrected melt inclusions may be the result of fractionation of small amounts of iron metal prior to inclusion entrapment, which we have not accounted for. *Correction for post-entrapment crystallization using percentage PEC from Table S1 . D range is the range of mantle-melt partition coefficients used to model lunar mantle concentrations. "Lunar Mantle" is the lunar mantle source concentration, assuming a range from 5% to 30% batch melting, the range of partition coefficients, and the most enriched corrected melt inclusion composition.
Data for Lunar Melt Inclusions
17. Detailed information on melt inclusion identification and analytical methods used in this study, as well as all data, are contained in supporting online materials available at Science Online.

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