1. High Pre-Eruptive Water Contents Preserved in Lunar Melt Inclusions
Erik H. Hauri,1* Thomas Weinreich,2 Alberto E. Saal,2 Malcolm C. Rutherford,2 James A. Van Orman3
1
Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington DC 20015, USA. 2Department of
Geological Sciences, Brown University, Providence, RI 02912, USA. 3Department of Geological Sciences, Case Western
Reserve University, Cleveland, OH 44106, USA.
*To whom correspondence should be addressed. E-mail: ehauri@ciw.edu
The Moon has long been thought to be highly depleted in within crystals that grow in the magma prior to eruption. By
volatiles such as water, and indeed published direct virtue of their enclosure within their host crystals, melt
measurements of water in lunar volcanic glasses have inclusions are protected from loss of volatiles by degassing
never exceeded 50 parts per million (ppm). Here, we during magma eruption. Melt inclusions have been used for
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report in situ measurements of water in lunar melt decades to determine pre-eruptive volatile contents of
inclusions; these samples of primitive lunar magma, by terrestrial magmas from subduction zones (9, 10), hotspots
virtue of being trapped within olivine crystals prior to (11, 12) and mid-ocean ridges (13, 14), as well as volatile
volcanic eruption, did not experience post-eruptive contents of Martian magmas (15, 16). Using standard
degassing. The lunar melt inclusions contain 615–1410 petrographic methods, we identified nine inclusion-bearing
ppm water, and high correlated amounts of fluorine (50– olivine crystals (Fig. 1) and analyzed melt inclusions hosted
78 ppm), sulfur (612–877 ppm) and chlorine (1.5–3.0 within (17). The measured water contents of the melt
ppm). These volatile contents are very similar to primitive inclusions range from 615 ppm up to a maximum of 1410
terrestrial mid-ocean ridge basalts and indicate that some ppm (Fig. 2); these water contents are up to one hundred
parts of the lunar interior contain as much water as times higher than the water content of the matrix glass
Earth’s upper mantle. surrounding the olivine crystals (6–30 ppm H2O) and the
centers of individual volcanic glass beads from the same
The Moon is thought to have formed in a giant impact
sample (4). The melt inclusions also contain high
collision between a Mars-sized object and an early-formed
concentrations of fluorine (50–78 ppm), sulfur (612–877
proto-Earth (1). Though all of the inner planets, including
ppm) and chlorine (1.5–3.0 ppm) that are two to one hundred
Earth, are depleted in water and other volatiles when
times higher than the matrix glasses and individual glass
compared with primitive meteorites, the more extreme
beads from this sample (Fig. 3). Volatile contents corrected
depletion of volatiles in lunar volcanic rocks has long been
for post-entrapment crystallization are on average 21% lower
taken as key evidence for a giant impact that resulted in high-
than the measured concentrations (17), and represent the best
temperature catastrophic degassing of the material that
estimate of the pre-eruptive concentrations of volatiles in the
formed the Moon (2, 3). However, recent work on rapidly
74220 magma.
quenched lunar volcanic glasses has detected the presence of
There are few descriptions in the literature of melt
water dissolved in lunar magmas at concentrations up to 46
inclusions contained within olivine from lunar samples, but
ppm (4), and water contents of lunar apatite grains from mare
these existing observations provide important context for the
basalts are consistent with similarly minor amounts of water
volatile abundances we have observed. Roedder and Weiblen
in primitive lunar magmas (5–7). These results indicate that
(18–20) noted the presence of melt silicate inclusions in the
the Moon is not a perfectly anhydrous planetary body, and
very first samples returned from the Apollo 11, Apollo 12 and
suggest that some fraction of the Moon’s observed depletion
Luna 16 missions, and noted that many primary melt
in highly volatile elements may be the result of magmatic
inclusions contained a vapor bubble, requiring dissolved
degassing during the eruption of lunar magmas into the near-
volatiles to have been present in the melt at the time it was
vacuum of the Moon’s surface.
trapped within the host crystal. Klein & Rutherford (21) and
In order to bypass the process of volcanic degassing, we
Weitz et al. (22) found sulfur contents of 600–800 ppm,
conducted a search for lunar melt inclusions in Apollo 17
similar to our measurements, and Cl contents of <50 ppm that
sample 74220, a lunar soil containing ~99% high-Ti volcanic
were limited by electron microprobe detection limits.
glass beads, the so-called “orange glass” with 9–12 wt% TiO2
Reheated Apollo 12 melt inclusions, containing medium-Ti
(8). Melt inclusions are small samples of magma trapped
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2. magmas (5–6 wt% TiO2), show sulfur contents that are 20% similar contents of fluorine, sulfur and chlorine associated
higher than our data on average (23). In our data set, we with this water, a volatile abundance signature shared by both
observe a correlation of all the volatiles with each other (Fig. bodies.
3) pointing toward the degassed compositions of the matrix These results show that the Moon is the only planetary
glass rinds and volcanic glass beads (4). object in our solar system currently identified to have an
The most important aspect of our volatile data on lunar internal reservoir with a volatile content that is similar to
melt inclusions is their similarity to melt inclusions from Earth’s upper mantle, and that prior estimates of the lunar
primitive samples of terrestrial mid-ocean ridge basalts inventory for highly volatile elements are biased to low
(MORB), like those recovered from spreading centers located concentrations owing to the degassed nature of lunar samples
within transform faults (24); the melt inclusions from 74220 thus far studied. The Moon has erupted a wide variety of
bear a remarkable resemblance to melt inclusions from the magmas during its history, and it remains to be seen if other
Siqueiros Fracture Zone on the East Pacific Rise, some of the lunar mantle sources are as volatile rich as the source of
most primitive mid-ocean ridge magmas that have been Apollo 17 high-Ti magmas. Nevertheless, the hydrated nature
measured (Fig. 3). These similarities suggest that the volatile of at least part of the Moon’s interior is a result that is not
signature of the lunar mantle source of the high-Ti melt consistent with the notion that the Moon lost its entire volatile
inclusions is very similar to that of the upper mantle source of inventory to the vacuum of space during degassing following
MORB. a high-energy giant impact, which would be expected to leave
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It is important that we have made these measurements on a highly desiccated lunar interior.
inclusions from olivine crystals contained within primitive If the bulk of the lunar interior has a volatile content
lunar volcanic glasses. These inclusions were quenched similar to our estimate for the high-Ti mantle source, then our
within a matter of minutes after their eruption (4), providing results present difficulties for late-accretion models that
minimal opportunity for post-eruptive hydrogen diffusion out require volatile delivery to Earth and the Moon after their
of the inclusions, and it means that we have a direct H2O formation, because these two bodies have very different
measurement on primary lunar magma samples that have not accretion cross sections that would predict different internal
experienced post-eruptive degassing and associated loss of volatile contents. An Earth-Moon similarity in volatiles could
volatiles. The water concentrations that we measure are 20– indicate that chemical exchange of even the most volatile
100 times higher than previous direct measurements of the elements between the molten Earth and the proto-lunar disc
lunar glass beads from this same sample, which was might have been pervasive and extensive, resulting in
estimated to have suffered 95–98% loss of H2O via degassing homogenization at the very high temperatures expected
(4), and they are higher than estimates derived from lunar following a giant impact; this could have been aided by the
apatite measurements, which require a 95–99% correction for presence of a high-temperature convective atmospheric
fractional crystallization to estimate primary magma volatile envelope surrounding Earth and the proto-lunar disc as the
contents (5, 6). Our results are direct measurements on Moon solidified (29). Alternatively, it is conceivable that a
primary lunar magma compositions that require no such portion of the lunar interior escaped the widespread melting
extrapolations. expected in the aftermath of a giant impact, and simply
Our melt inclusion data allow us to place some constraints inherited the inventory of water and other volatiles that is
on the volatile content of the lunar mantle source that characteristic of Earth’s upper mantle. Any model for the
generated the high-Ti picritic magmas. Using the most water- formation of Earth-Moon system must meet the constraints
rich melt inclusion composition after correction for post- imposed by the presence of H2O in the lunar interior, with an
entrapment crystallization, and an estimation that the high-Ti abundance similar to Earth’s upper mantle, and with a
magmas originated from 5–30% batch partial melting with complement of fluorine, sulfur and chlorine also present at
partitioning similar to terrestrial mantle-derived melts (17), terrestrial levels. To the extent that lunar formation models
we estimate lunar mantle volatile concentrations of 79–409 predict very different volatile contents of Earth and the Moon,
ppm H2O, 7–26 ppm F, 193–352 ppm S, and 0.14–0.83 ppm our results on the volatile content of lunar melt inclusions
Cl. These estimates overlap most estimates for the volatile suggest that we lack understanding on some critical aspects of
content of the terrestrial MORB mantle (24–27), and are the physics of planetary moon formation by collisional
much higher than prior estimates for the lunar mantle based impact.
on the volatile content of lunar apatite (5, 6) and the variation Our findings also have implications for the origin of water
of Cl isotopes in lunar rocks (28) including the sample 74220 ice in shadowed lunar craters, which has been attributed to
that we have studied here. The melt inclusions indicate cometary and meteoritic impacts (30). It is conceivable that
definitively that some reservoirs within the interiors of Earth some of this water could have originated from magmatic
and the Moon not only have similar water contents, but also degassing during emplacement and eruption of lunar magmas
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4. 30. W. C. Feldman, S. Maurice, D. J.. Lawrence, R. C. Little, Saal et al. (4); the core-rim data was scaled by multiplying the
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Acknowledgments: This work was supported by the
Carnegie Institution of Washington, the NASA LASER
and Cosmochemistry programs, the NASA Lunar Science
Institute, and the NASA Astrobiology Institute. We thank
J. Wang for NanoSIMS assistance, and L. Nittler and Z.
Peeters for help with image processing software. All data
can be found in supporting online materials available at
Science Online.
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Supporting Online Material
www.sciencemag.org/cgi/content/full/science.1204626/DC1
Materials and Methods
Figs. S1 and S2
Tables S1 and S2
References 32 to 37
21 February 2011; accepted 10 May 2011
Published online 26 May 2011; 10.1126/science.1204626
Fig. 1. (A to F) Optical photographs of olivines A1, A2, N3,
N6, N8, and N9 from Apollo 17 sample 74220. Inclusions
within circles indicate the inclusions that were imaged in Fig.
2. Scale bars are 10 µm in all photos.
Fig. 2. (A to F) NanoSIMS scanning isotope images of
olivines A1, A2, N3, N6, N8 and N9 from Apollo 17 sample
74220, showing the distribution of water within melt
inclusions from the olivine grains shown in Fig. 1. The
images show the distribution of the isotope ratio 16OH/30Si
indicated by the color scale shown in (A), where dark regions
correspond to low 16OH/30Si ratios (e.g. olivine surrounding
melt inclusions), up to red regions within melt inclusions with
16
OH/30Si ratios approaching 0.25 (corresponding to ~1400
ppm H2O). The color scale is the same in all images, and all
images show a scale bar of 1 µm. Rectangular areas are
regions of interest (ROIs) within which each isotope ratio is
calculated and converted to concentrations.
Fig. 3. (A to C) Volatile abundances for lunar melt inclusions
(orange circle with black rims) and matrix glasses (orange
circles) from Apollo 17 sample 74220. Melt inclusions show
the highest concentrations (>600 ppm H2O) while matrix
glasses show the lowest concentrations due to degassing (≤30
ppm H2O). The black curves show lunar magma degassing
trends, scaled from the volatile-volatile correlations observed
in core-rim NanoSIMS data on a lunar glass bead reported by
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