High pre eruptive water contents preserved in lunar melt inclusions


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High pre eruptive water contents preserved in lunar melt inclusions

  1. 1. High Pre-Eruptive Water Contents Preserved in Lunar Melt InclusionsErik H. Hauri,1* Thomas Weinreich,2 Alberto E. Saal,2 Malcolm C. Rutherford,2 James A. Van Orman31Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington DC 20015, USA. 2Department ofGeological Sciences, Brown University, Providence, RI 02912, USA. 3Department of Geological Sciences, Case WesternReserve University, Cleveland, OH 44106, USA.*To whom correspondence should be addressed. E-mail: ehauri@ciw.eduThe Moon has long been thought to be highly depleted in within crystals that grow in the magma prior to eruption. Byvolatiles such as water, and indeed published direct virtue of their enclosure within their host crystals, meltmeasurements of water in lunar volcanic glasses have inclusions are protected from loss of volatiles by degassingnever exceeded 50 parts per million (ppm). Here, we during magma eruption. Melt inclusions have been used for Downloaded from www.sciencemag.org on May 29, 2011report in situ measurements of water in lunar melt decades to determine pre-eruptive volatile contents ofinclusions; these samples of primitive lunar magma, by terrestrial magmas from subduction zones (9, 10), hotspotsvirtue of being trapped within olivine crystals prior to (11, 12) and mid-ocean ridges (13, 14), as well as volatilevolcanic eruption, did not experience post-eruptive contents of Martian magmas (15, 16). Using standarddegassing. The lunar melt inclusions contain 615–1410 petrographic methods, we identified nine inclusion-bearingppm water, and high correlated amounts of fluorine (50– olivine crystals (Fig. 1) and analyzed melt inclusions hosted78 ppm), sulfur (612–877 ppm) and chlorine (1.5–3.0 within (17). The measured water contents of the meltppm). These volatile contents are very similar to primitive inclusions range from 615 ppm up to a maximum of 1410terrestrial mid-ocean ridge basalts and indicate that some ppm (Fig. 2); these water contents are up to one hundredparts of the lunar interior contain as much water as times higher than the water content of the matrix glassEarth’s upper mantle. surrounding the olivine crystals (6–30 ppm H2O) and the centers of individual volcanic glass beads from the sameThe Moon is thought to have formed in a giant impact sample (4). The melt inclusions also contain highcollision between a Mars-sized object and an early-formed concentrations of fluorine (50–78 ppm), sulfur (612–877proto-Earth (1). Though all of the inner planets, including ppm) and chlorine (1.5–3.0 ppm) that are two to one hundredEarth, are depleted in water and other volatiles when times higher than the matrix glasses and individual glasscompared with primitive meteorites, the more extreme beads from this sample (Fig. 3). Volatile contents correcteddepletion of volatiles in lunar volcanic rocks has long been for post-entrapment crystallization are on average 21% lowertaken as key evidence for a giant impact that resulted in high- than the measured concentrations (17), and represent the besttemperature catastrophic degassing of the material that estimate of the pre-eruptive concentrations of volatiles in theformed 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 meltwater dissolved in lunar magmas at concentrations up to 46 inclusions contained within olivine from lunar samples, butppm (4), and water contents of lunar apatite grains from mare these existing observations provide important context for thebasalts are consistent with similarly minor amounts of water volatile abundances we have observed. Roedder and Weiblenin primitive lunar magmas (5–7). These results indicate that (18–20) noted the presence of melt silicate inclusions in thethe Moon is not a perfectly anhydrous planetary body, and very first samples returned from the Apollo 11, Apollo 12 andsuggest that some fraction of the Moon’s observed depletion Luna 16 missions, and noted that many primary meltin highly volatile elements may be the result of magmatic inclusions contained a vapor bubble, requiring dissolveddegassing during the eruption of lunar magmas into the near- volatiles to have been present in the melt at the time it wasvacuum 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 thatsample 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 / www.sciencexpress.org / 26 May 2011 / Page 1 / 10.1126/science.1204626
  2. 2. magmas (5–6 wt% TiO2), show sulfur contents that are 20% similar contents of fluorine, sulfur and chlorine associatedhigher than our data on average (23). In our data set, we with this water, a volatile abundance signature shared by bothobserve 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 planetaryglass 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 tomelt inclusions is their similarity to melt inclusions from Earth’s upper mantle, and that prior estimates of the lunarprimitive 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 sampleswithin transform faults (24); the melt inclusions from 74220 thus far studied. The Moon has erupted a wide variety ofbear a remarkable resemblance to melt inclusions from the magmas during its history, and it remains to be seen if otherSiqueiros Fracture Zone on the East Pacific Rise, some of the lunar mantle sources are as volatile rich as the source ofmost primitive mid-ocean ridge magmas that have been Apollo 17 high-Ti magmas. Nevertheless, the hydrated naturemeasured (Fig. 3). These similarities suggest that the volatile of at least part of the Moon’s interior is a result that is notsignature of the lunar mantle source of the high-Ti melt consistent with the notion that the Moon lost its entire volatileinclusions is very similar to that of the upper mantle source of inventory to the vacuum of space during degassing followingMORB. a high-energy giant impact, which would be expected to leave Downloaded from www.sciencemag.org on May 29, 2011 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 contentlunar volcanic glasses. These inclusions were quenched similar to our estimate for the high-Ti mantle source, then ourwithin a matter of minutes after their eruption (4), providing results present difficulties for late-accretion models thatminimal opportunity for post-eruptive hydrogen diffusion out require volatile delivery to Earth and the Moon after theirof the inclusions, and it means that we have a direct H2O formation, because these two bodies have very differentmeasurement on primary lunar magma samples that have not accretion cross sections that would predict different internalexperienced post-eruptive degassing and associated loss of volatile contents. An Earth-Moon similarity in volatiles couldvolatiles. The water concentrations that we measure are 20– indicate that chemical exchange of even the most volatile100 times higher than previous direct measurements of the elements between the molten Earth and the proto-lunar disclunar glass beads from this same sample, which was might have been pervasive and extensive, resulting inestimated 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 theapatite measurements, which require a 95–99% correction for presence of a high-temperature convective atmosphericfractional crystallization to estimate primary magma volatile envelope surrounding Earth and the proto-lunar disc as thecontents (5, 6). Our results are direct measurements on Moon solidified (29). Alternatively, it is conceivable that aprimary lunar magma compositions that require no such portion of the lunar interior escaped the widespread meltingextrapolations. 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 ison the volatile content of the lunar mantle source that characteristic of Earth’s upper mantle. Any model for thegenerated the high-Ti picritic magmas. Using the most water- formation of Earth-Moon system must meet the constraintsrich melt inclusion composition after correction for post- imposed by the presence of H2O in the lunar interior, with anentrapment crystallization, and an estimation that the high-Ti abundance similar to Earth’s upper mantle, and with amagmas originated from 5–30% batch partial melting with complement of fluorine, sulfur and chlorine also present atpartitioning similar to terrestrial mantle-derived melts (17), terrestrial levels. To the extent that lunar formation modelswe 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 inclusionsCl. These estimates overlap most estimates for the volatile suggest that we lack understanding on some critical aspects ofcontent of the terrestrial MORB mantle (24–27), and are the physics of planetary moon formation by collisionalmuch 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 waterof Cl isotopes in lunar rocks (28) including the sample 74220 ice in shadowed lunar craters, which has been attributed tothat we have studied here. The melt inclusions indicate cometary and meteoritic impacts (30). It is conceivable thatdefinitively that some reservoirs within the interiors of Earth some of this water could have originated from magmaticand the Moon not only have similar water contents, but also degassing during emplacement and eruption of lunar magmas / www.sciencexpress.org / 26 May 2011 / Page 2 / 10.1126/science.1204626
  3. 3. (31). These results also underscore the importance of 15. H. Y. McSween, R. P. Harvey, Outgased water on Mars:pyroclastic volcanic samples in unraveling the history and Constraints from melt inclusions in SNC meteorites,composition of the Moon’s interior; indeed, such deposits Science 259, 1890 (1993).have been identified and mapped on the surfaces all the 16. L. Leshin-Watson, I. D. Hutcheon, S. Epstein, E. M.terrestrial planets and many satellites. Stolper, Water on Mars: Clues from deuterium/hydrogen and water contents of hydrous phases in SNC meteorites,References and Notes Science 265, 86 (1994).1. R. M. Canup, Dynamics of lunar formation, Ann. Revs. 17. Detailed information on melt inclusion identification and Astron. Astrophy. 42, 441 (2004). analytical methods used in this study, as well as all data,2. S. R. Taylor, in Origin of the Moon, W. K. Hartmann, R. J. are contained in supporting online materials available at Phillips, G. J. Taylor, Eds. (Lunar Planet. Inst., Houston, Science Online. 1986), pp. 125–143. 18. E. Roedder, P. W. Weiblen, Lunar petrology of silicate3. F. Albarede, Volatile accretion history of the terrestrial melt inclusions, Apollo 11 rocks, Proc. Lunar Sci. Conf. 1, planets and dynamic implications, Nature 461, 1227 801 (1970). (2009). 19. E. Roedder, P. W. Weiblen, Petrology of silicate melt4. A. E. Saal et al., Volatile content of the lunar volcanic inclusions, Apollo 11 and Apollo 12 and terrestrial glasses and the presence of water in the Moon’s interior, equivalents, Proc. Lunar Sci. Conf. 2, 507 (1971). Nature 454, 192 (2008). Downloaded from www.sciencemag.org on May 29, 2011 20. E. Roedder, P. W. Weiblen, Silicate melt inclusions and5. F. M. McCubbin et al., Nominally anhydrous magmatism glasses in lunar soil fragments from the Luna 16 core on the Moon, Proc. Natl. Acad. Sci. U.S.A. 107, 11223 sample, Earth Planet. Sci. Lett. 13, 272 (1972). (2010). 21. N. Klein, M. J. Rutherford, Volcanic gas formed during6. J. W. Boyce et al., Lunar apatite with terrestrial volatile eruption of Apollo 17 orange glass magma: Evidence from abundances, Nature 466, 466 (2010). glassy melt inclusions and experiments, Lunar Planet. Sci.7. J. P. Greenwood et al., Hydrogen isotope ratios in lunar 29, 1448 (1998). rocks indicate delivery of cometary water to the Moon, 22. C. M. Weitz, M. J. Rutherford, J. W. Head III, D. S. Nat. Geosci. 4, 79 (2011). McKay, Ascent and eruption of lunar high-titanium8. J. W. Delano, Pristine lunar glasses: Criteria, data and magma as inferred from the petrology of the 74001/2 drill implications, J. Geophys. Res. 91, D201, 1986. core, Met. Planet. Sci. 34, 527 (1999).9. K. A. Kelley et al., Mantle melting as a function of water 23. D. J. Bombardieri, M. D. Norman, V. S. Kamenetsky, L. content beneath back-arc basins, J. Geophys. Res. 111, V. Danyushevsky, Major element and primary sulfur B09208 (2006). concentrations in Apollo 12 mare basalts: The view from10. A. M. Shaw, E. H. 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  4. 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 S. L. Lawson, O. Gasnault, R. C. Wiens, B. L. originally reported data for each element, by the ratio of the Barraclough, R. C. Elphic, T. H. Prettyman, J. T. highest melt inclusion composition to that of the core Steinberg, A. B. Binder, Evidence for water ice near the composition reported in table 2 of (4). The gray field lunar poles, J. Geophys. Res. 106, 23231 (2001). surrounds data for melt inclusions from the Siqueiros Fracture31. A. P. S. Crotts, Lunar outgassing, transient phenomena, Zone on the East Pacific Rise, as an example of depleted mid- and the return to the Moon, I: Existing data, Astrophys. J. ocean ridge basalt (24). 687, 692 (2008).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. Downloaded from www.sciencemag.org on May 29, 2011Supporting Online Materialwww.sciencemag.org/cgi/content/full/science.1204626/DC1Materials and MethodsFigs. S1 and S2Tables S1 and S2References 32 to 3721 February 2011; accepted 10 May 2011Published online 26 May 2011; 10.1126/science.1204626Fig. 1. (A to F) Optical photographs of olivines A1, A2, N3,N6, N8, and N9 from Apollo 17 sample 74220. Inclusionswithin 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 ofolivines A1, A2, N3, N6, N8 and N9 from Apollo 17 sample74220, showing the distribution of water within meltinclusions from the olivine grains shown in Fig. 1. Theimages show the distribution of the isotope ratio 16OH/30Siindicated by the color scale shown in (A), where dark regionscorrespond to low 16OH/30Si ratios (e.g. olivine surroundingmelt inclusions), up to red regions within melt inclusions with16 OH/30Si ratios approaching 0.25 (corresponding to ~1400ppm H2O). The color scale is the same in all images, and allimages show a scale bar of 1 µm. Rectangular areas areregions of interest (ROIs) within which each isotope ratio iscalculated and converted to concentrations.Fig. 3. (A to C) Volatile abundances for lunar melt inclusions(orange circle with black rims) and matrix glasses (orangecircles) from Apollo 17 sample 74220. Melt inclusions showthe highest concentrations (>600 ppm H2O) while matrixglasses show the lowest concentrations due to degassing (≤30ppm H2O). The black curves show lunar magma degassingtrends, scaled from the volatile-volatile correlations observedin core-rim NanoSIMS data on a lunar glass bead reported by / www.sciencexpress.org / 26 May 2011 / Page 4 / 10.1126/science.1204626