²Annemarie E. Pickersgill, ^1,2Gordon R. Osinski,¹Roberta L. Flemming
¹Department of Earth Sciences and Centre for Planetary Science and Exploration, University of Western Ontario, London, Ontario, Canada
²Department of Physics and Astronomy, The University of Western Ontario, London, Ontario, Canada

Shock metamorphism, caused by hypervelocity impact, is a poorly understood process in feldspar due to the complexity of the crystal structure, the relative ease of weathering, and chemical variations, making optical studies of shocked feldspars challenging. Understanding shock metamorphism in feldspars, and plagioclase in particular, is vital for understanding the history of Earth’s moon, Mars, and many other planetary bodies. We present here a comprehensive study of shock effects in andesine and labradorite from the Mistastin Lake impact structure, Labrador, Canada. Samples from a range of different settings were studied, from in situ central uplift materials to clasts from various breccias and impact melt rocks. Evidence of shock metamorphism includes undulose extinction, offset twins, kinked twins, alternate twin deformation, and partial to complete transformation to diaplectic plagioclase glass. In some cases, isotropization of alternating twin lamellae was observed. Planar deformation features (PDFs) are notably absent in the plagioclase, even when present in neighboring quartz grains. It is notable that various microlites, twin planes, and compositionally different lamellae could easily be mistaken for PDFs and so care must be taken. A pseudomorphous zeolite phase (levyne-Ca) was identified as a replacement mineral of diaplectic feldspar glass in some samples, which could, in some instances, also be potentially mistaken for PDFs. We suggest that the lack of PDFs in plagioclase could be due to a combination of structural controls relating to the crystal structure of different feldspars and/or the presence of existing planes of weakness in the form of twin and cleavage planes.

Reference
Pickersgill AE, Osinski GR, Flemming RL (2015) Shock effects in plagioclase feldspar from the Mistastin Lake impact structure, Canada. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12495]
Published by arrangement with John Wiley&Sons

^1,2Francis M. McCubbin et al. (>10)* 
¹Institute of Meteoritics, University of New Mexico, 200 Yale Boulevard SE, Albuquerque, New Mexico 87131, U.S.A.
²Department of Earth and Planetary Sciences, University of New Mexico, 200 Yale Boulevard SE, Albuquerque, New Mexico 87131, U.S.A.
*Find the extensive, full author and affiliation list on the publishers website

Apatite-melt partitioning experiments were conducted in a piston-cylinder press at 1.0–1.2 GPa and 950–1000 °C using an Fe-rich basaltic starting composition and an oxygen fugacity within the range of ΔIW-1 to ΔIW+2. Each experiment had a unique F:Cl:OH ratio to assess the partitioning as a function of the volatile content of apatite and melt. The quenched melt and apatite were analyzed by electron probe microanalysis and secondary ion mass spectrometry techniques. The mineral-melt partition coefficients (D values) determined in this study are as follows: DFAp-Melt = 4.4–19, DClAp-Melt = 1.1–5, DOHAp-Melt = 0.07–0.24. This large range in values indicates that a linear relationship does not exist between the concentrations of F, Cl, or OH in apatite and F, Cl, or OH in melt, respectively. This non-Nernstian behavior is a direct consequence of F, Cl, and OH being essential structural constituents in apatite and minor to trace components in the melt. Therefore mineral-melt D values for F, Cl, and OH in apatite should not be used to directly determine the volatile abundances of coexisting silicate melts. However, the apatite-melt D values for F, Cl, and OH are necessarily interdependent given that F, Cl, and OH all mix on the same crystallographic site in apatite. Consequently, we examined the ratio of D values (exchange coefficients) for each volatile pair (OH-F, Cl-F, and OH-Cl) and observed that they display much less variability: KdCl-FAp-Melt = 0.21 ± 0.03, KdOH-FAp-Melt= 0.014 ± 0.002, and KdOH-ClAp-Melt= 0.06 ± 0.02. However, variations with apatite composition, specifically when mole fractions of F in the apatite X-site were low (XF < 0.18), were observed and warrant additional study. To implement the exchange coefficient to determine the H2O content of a silicate melt at the time of apatite crystallization (apatite-based melt hygrometry), the H2O abundance of the apatite, an apatite-melt exchange Kd that includes OH (either OH-F or OH-Cl), and the abundance of F or Cl in the apatite and F or Cl in the melt at the time of apatite crystallization are needed (F if using the OH-F Kd and Cl if using the OH-Cl Kd). To determine the H2O content of the parental melt, the F or Cl abundance of the parental melt is needed in place of the F or Cl abundance of the melt at the time of apatite crystallization. Importantly, however, exchange coefficients may vary as a function of temperature, pressure, melt composition, apatite composition, and/or oxygen fugacity, so the combined effects of these parameters must be investigated further before exchange coefficients are applied broadly to determine volatile abundances of coexisting melt from apatite volatile abundances.

Reference
McCubbin FM et al. (2015) Experimental investigation of F, Cl, and OH partitioning between apatite and Fe-rich basaltic melt at 1.0–1.2 GPa and 950–1000 °C. American Mineralogist 100, 1790-1802
Link to Article [doi:10.2138/am-2015-5233]
Copyright: The Mineralogical Society of America

¹Gokce Ustunisik´, ¹Hanna Nekvasil,¹Donald H. Lindsley,²Francis M. McCubbin
¹Department of Geosciences, Stony Brook University, Stony Brook, New York 11794-2100, U.S.A.
²Institute of Meteoritics, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, U.S.A.

Experimental degassing of H-, F-, Cl-, C-, and S-bearing species from volatile-bearing magma of lunar composition at low pressure and fO2 close to the quartz-iron-fayalite buffer (QIF) indicates that the composition of the fluid/vapor phase that is lost changes over time. A highly H-rich vapor phase is exsolved within the first 10 min of degassing leaving behind a melt that is effectively dehydrated. Some Cl, F, and S is also lost during this time, presumably as HCl, HF, and H2S gaseous species; however much of the original inventory of Cl, F, and S components are retained in the melt. After 10 min, the exsolved vapor is dry and dominated by S- and halogen-bearing phases, presumably consisting of metal halides and sulfides, which evolves over time toward F enrichment. This vapor evolution provides important constraints on the geochemistry of volatile-bearing lunar phases that form subsequent to or during degassing. The rapidity of H loss suggests that little if any OH-bearing apatite will crystallize from surface or near surface (~7m) melts and that degassing of lunar magmas will cause the compositions of apatites to evolve first toward the F-Cl apatite binary and eventually toward end-member fluorapatite during crystallization. During the stage of loss of primarily H component from the melt, Cl would have been lost primarily as HCl, which is reported not to fractionate Cl isotopes at magmatic temperatures (Sharp et al. 2010). After the loss of H-bearing species, continued loss of Cl would result in the degassing of metal chlorides, which have been proposed as a mechanism to fractionate Cl isotopes (Sharp et al. 2010). After the onset of metal chloride degassing, the δ37Cl of the melt would necessarily increase to +6 (82% Cl loss), +8 (85% Cl loss), and +20‰ (95% Cl loss) at 1, 4, and 6 h, respectively, which was approximated using a computed trajectory of δ37Cl values in basalt during degassing of FeCl2. This strong enrichment of 37Cl in the melt after metal chloride volatilization is fully consistent with values measured for the non-leachates of a variety of lunar samples and would be reflected in apatites crystallized from a degassing melt. Our results suggest that a range in δ37Cl from 0 to >20‰ is expected in lunar apatite, with heavy enrichment being the norm. While 95% loss in the initial Cl content of the melt (280 ppm Cl left in the melt) would cause an increase to +20‰ in δ37Cl, the ability to measure this increase in a lunar sample is ultimately dependent upon the starting Cl abundances and whether or not a mechanism exists to concentrate the remaining Cl such that it can be subsequently analyzed with sufficient accuracy. Therefore, the higher the starting Cl abundances in the initial melts, the heavier δ37Cl values that can be measurably preserved. Importantly, such enrichments can occur in spite of high initial hydrogen contents, and therefore, our experiments demonstrate that elevated values of δ37Cl cannot be used as supporting evidence for an anhydrous Moon. Furthermore, if the H-bearing vapor has a significant H2 component, this process should also result in strong enrichment of δD in the residual magmas that reach the lunar surface or near-surface environment. Apatites within some mare basalts exhibit elevated δD of 1000 ‰ depending on the initial value (Tartese and Anand 2013) in addition to the δ37Cl values, but elevated δ37Cl values are accompanied by only modest enrichments in δD in apatites from samples of the highlands crust (McCubbin et al. 2015a).

Reference
Ustunisik G, Nekvasil H, Lindsley DH, McCubbin FM (2015) Degassing pathways of Cl-, F-, H-, and S-bearing magmas near the lunar surface: Implications for the composition and Cl isotopic values of lunar Apatite. American Mineralogist 100, 1717-1727. Link to Article [doi:10.2138/am-2015-4883]

Copyright: The American Mineralogical Society 

¹Sarah T. Crites, ¹Paul G. Lucey, ¹G. Jeffrey Taylor
¹Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Mānoa, 1680 East West Road Post 602, Honolulu, Hawaii 96822, U.S.A.

Most models of early lunar evolution predict that the anorthositic highlands crust is the result of plagioclase flotation on a magma ocean. However, the lunar highlands crust typically contains 4 wt% FeO and so is more mafic than the strict definition of the anorthosites thought to comprise it. We used new Clementine-based mineral maps of the Moon as inputs to a series of mixing models that calculate the abundance and distribution of major highland rock types and shed light on three possible sources of excess mafic material in the lunar highlands: mafic (15 vol% mafic minerals) anorthosites, post-magma ocean igneous activity, and mafic basin ejecta. Mixing models that feature pure anorthosites like the purest anorthosite (PAN) described by Ohtake et al. (2009) and Pieters et al. (2009) are most compatible with the data. They allow us to place an upper limit of 10–20 vol% mantle material that could be mixed with the primary highlands crust. The upper limit on mantle material indicated by the mixing models is significantly lower than the 30–40 vol% mantle material expected from simple geometric calculations of the major lunar basins’ excavation cavities based on an excavation cavity depth/diameter ratio of 1/10; this discrepancy allows us to conclude that the excavation cavities of the three largest lunar basins may have been significantly shallower than those of the smaller basins. Our results are consistent with excavation cavity depth/diameter ratios for these largest basins in the range of 0.035 to 0.06, which agrees with previous gravity measurements by Wieczorek and Phillips (1999).

Reference
Crites ST, Lucey PG, Taylor GJ (2015) The mafic component of the lunar crust: Constraints on the crustal abundance of mantle and intrusive rock, and the mineralogy of lunar anorthosites. American Mineralogist 100, 1708-1716
Link to Article [doi: 10.2138/am-2015-4872]

Copyright: The Mineralogical Society of America

^1,2Francis M. McCubbin et al. (>10)*
¹Institute of Meteoritics, University of New Mexico, 200 Yale Blvd SE, Albuquerque, New Mexico 87131, U.S.A.
²Department of Earth and Planetary Sciences, University of New Mexico, 200 Yale Blvd SE, Albuquerque, New Mexico 87131, U.S.A.
*Find the extensive, full author and affiliation list on the publishers website

Many studies exist on magmatic volatiles (H, C, N, F, S, Cl) in and on the Moon, within the last several years, that have cast into question the post-Apollo view of lunar formation, the distribution and sources of volatiles in the Earth-Moon system, and the thermal and magmatic evolution of the Moon. However, these recent observations are not the first data on lunar volatiles. When Apollo samples were first returned, substantial efforts were made to understand volatile elements, and a wealth of data regarding volatile elements exists in this older literature. In this review paper, we approach volatiles in and on the Moon using new and old data derived from lunar samples and remote sensing. From combining these data sets, we identified many points of convergence, although numerous questions remain unanswered.

The abundances of volatiles in the bulk silicate Moon (BSM), lunar mantle, and urKREEP [last ~1% of the lunar magma ocean (LMO)] were estimated and placed within the context of the LMO model. The lunar mantle is likely heterogeneous with respect to volatiles, and the relative abundances of F, Cl, and H2O in the lunar mantle (H2O > F >> Cl) do not directly reflect those of BSM or urKREEP (Cl > H2O ≈ F). In fact, the abundances of volatiles in the cumulate lunar mantle were likely controlled by partitioning of volatiles between LMO liquid and nominally anhydrous minerals instead of residual liquid trapped in the cumulate pile. An internally consistent model for lunar volatiles in BSM should reproduce the absolute and relative abundances of volatiles in urKREEP, the anorthositic primary crust, and the lunar mantle within the context of processes that occurred during the thermal and magmatic evolution of the Moon. Using this mass-balance constraint, we conducted LMO crystallization calculations with a specific focus on the distributions and abundances of F, Cl, and H2O to determine whether or not estimates of F, Cl, and H2O in urKREEP are consistent with those of the lunar mantle, estimated independently from the analysis of volatiles in mare volcanic materials. Our estimate of volatiles in the bulk lunar mantle are 0.54–4.5 ppm F, 0.15–5.3 ppm H2O, 0.26–2.9 ppm Cl, 0.014–0.57 ppm C, and 78.9 ppm S. Our estimates of H2O are depleted compared to independent estimates of H2O in the lunar mantle, which are largely biased toward the “wettest” samples. Although the lunar mantle is depleted in volatiles relative to Earth, unlike the Earth, the mantle is not the primary host for volatiles. The primary host of the Moon’s incompatible lithophile volatiles (F, Cl, H2O) is urKREEP, which we estimate to have 660 ppm F, 300–1250 ppm H2O, and 1100–1350 ppm Cl. This urKREEP composition implies a BSM with 7.1 ppm F, 3–13 ppm H2O, and 11–14 ppm Cl. An upper bound on the abundances of F, Cl, and H2O in urKREEP and the BSM, based on F abundances in CI carbonaceous chondrites, are reported to be 5500 ppm F, 0.26–1.09 wt% H2O, and 0.98–1.2 wt% Cl and 60 ppm F, 27–114 ppm H2O, and 100–123 ppm Cl, respectively.

The role of volatiles in many lunar geologic processes was also determined and discussed. Specifically, analyses of volatiles from lunar glass beads as well as the phase assemblages present in coatings on those beads were used to infer that H2 is likely the primary vapor component responsible for propelling the fire-fountain eruptions that produced the pyroclastic glass beads (as opposed to CO). The textural occurrences of some volatile-bearing minerals are used to identify hydrothermal alteration, which is manifested by sulfide veining and sulfide-replacement textures in silicates. Metasomatic alteration in lunar systems differs substantially from terrestrial alteration due to differences in oxygen fugacity between the two bodies that result in H2O as the primary solvent for alteration fluids on Earth and H2 as the primary solvent for alteration fluids on the Moon (and other reduced planetary bodies). Additionally, volatile abundances in volatile-bearing materials are combined with isotopic data to determine possible secondary processes that have affected the primary magmatic volatile signatures of lunar rocks including degassing, assimilation, and terrestrial contamination; however, these processes prove difficult to untangle within individual data sets. Data from remote sensing and lunar soils are combined to understand the distribution, origin, and abundances of volatiles on the lunar surface, which can be explained largely by solar wind implantation and spallogenic processes, although some of the volatiles in the soils may also be either indigenous to the Moon or terrestrial contamination. We have also provided a complete inventory of volatile-bearing mineral phases indigenous to lunar samples and discuss some of the “unconfirmed” volatile-bearing minerals that have been reported. Finally, a compilation of unanswered questions and future avenues of research on the topic of lunar volatiles are presented, along with a critical analysis of approaches for answering these questions.

Reference
McCubbin FM et al. (2015) Magmatic volatiles (H, C, N, F, S, Cl) in the lunar mantle, crust, and regolith: Abundances, distributions, processes, and Reservoirs. American Mineralogist 100, 1668-1707
Link to Article [doi: 10.2138/am-2015-4934CCBYNCND]

Copyright: The Mineralogical Society of America

¹Yoshihiro Furukawa, ¹Hiromoto Nakazawa, ²Toshimori Sekine, ³Takamichi Kobayashi, ¹Takeshi Kakegawa
¹Department of Earth Science, Tohoku University, 6-3 Aramaki Aza Aoba, Aoba-ku, Sendai 980-8578, Japan
²Department of Earth and Planetary Systems Science, Hiroshima University, 1-3-1 Kagami-yama, Higashi-Hiroshima 739-8526, Japan
³National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan

The emergence of life’s building blocks on the prebiotic Earth was the first crucial step for the origins of life. Extraterrestrial delivery of intact amino acids and nucleobases is the prevailing hypothesis for their availability on prebiotic Earth because of the difficulties associated with the production of these organics from terrestrial carbon and nitrogen sources under plausible prebiotic conditions. However, the variety and amounts of these intact organics delivered by meteorites would have been limited. Previous shock–recovery experiments have demonstrated that meteorite impact reactions could have generated organics on the prebiotic Earth. Here, we report on the simultaneous formation of nucleobases (cytosine and uracil) found in DNA and/or RNA, various proteinogenic amino acids (glycine, alanine, serine, aspartic acid, glutamic acid, valine, leucine, isoleucine, and proline), non-proteinogenic amino acids, and aliphatic amines in experiments simulating reactions induced by extraterrestrial objects impacting on the early oceans. To the best of our knowledge, this is the first report of the formation of nucleobases from inorganic materials by shock conditions. In these experiments, bicarbonate was used as the carbon source. Bicarbonate, which is a common dissolved carbon species in CO2-rich atmospheric conditions, was presumably the most abundant carbon species in the early oceans and in post-impact plumes. Thus, the present results expand the possibility that impact-induced reactions generated various building blocks for life on prebiotic Earth in large quantities through the use of terrestrial carbon reservoirs.

Reference
Furukawa Y, Nakazawa H, Sekine T, Kobayashi T, Kakegawa T (2015) Nucleobase and amino acid formation through impacts of meteorites on the early ocean. Earth and Planetary Science Letters (in Press)
Link to Article [doi:10.1016/j.epsl.2015.07.049]
Copyright Elsevier

^1,2C. Lantz, ³R. Brunetto, ¹M. A. Barucci, ³E. Dartois, ⁴J. Duprat, ⁴C. Engrand, ⁴M. Godard, ⁴D. Ledu, ⁵E. Quirico 
¹Laboratoire d’Études Spatiales et d’Instrumentation en Astrophysique (LESIA) – Observatoire de Paris, CNRS (UMR 8109)/UPMC (Paris 6) / Univ. Paris Diderot (Paris 7), 92195 Meudon Cedex, France
²Université Paris Diderot, Sorbonne Paris Cité, 75205 Paris Cedex 13, France
³Institut d’Astrophysique Spatiale (IAS), CNRS (UMR 8617)/Université Paris-Sud (Paris 11), 91405 Orsay Cedex, France
⁴Centre de Sciences Nucléaires et de Sciences de la Matière (CSNSM), IN2P3 – CNRS (UMR 8609)/Université Paris-Sud (Paris 11), 91405 Orsay Cedex, France
⁵Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), Université J. Fournier – Grenoble 1/CNRS-INSU (UMR 5274), 38041 Grenoble Cedex 9, France

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Reference
Lantz C, Brunetto R, Barucci MA, Dartois E, Duprat J, Engrand C, Godard M, Ledu D, Quirico E (2015) Ion irradiation of the Murchison meteorite: Visible to mid-infrared spectroscopic results. Astronomy & Astrophysics 577, A41
Link to Article [dx.doi.org/10.1051/0004-6361/201425398 ]

^1,2Amaury Thiabaud, ^1,2Ulysse Marboeuf, ^1,2,4Yann Alibert, ^1,2Ingo Leya, ^1,3Klaus Mezger
¹Center for Space and Habitability, Universität Bern, 3012 Bern, Switzerland
e-mail: amaury.thiabaud@csh.unibe.ch
²Physikalisches Institut, Universität Bern, 3012 Bern, Switzerland
³Institut für Geologie, Universität Bern, 3012 Bern, Switzerland
⁴On leave from CNRS, Observatoire de Besançon, 25000 Besançon, France

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

Reference
Thiabaud A, Marboeuf U, Alibert Y, Leya I, Mezger K (2015) Elemental ratios in stars vs planets. Astronomy & Astrophysics 580, A30
Link to Article [dx.doi.org/10.1051/0004-6361/201525963]

¹Daniel Carrera, ¹Anders Johansen, ¹Melvyn B. Davies
¹Lund ObservatoryDepartment of Astronomy and Theoretical Physics, Lund University, Box 43, 22100 Lund, Sweden

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Reference
Carrera D, Johansen A, Davies MB (2015) How to form planetesimals from mm-sized chondrules and chondrule aggregates. Astronomy & Astrophysics 579, A43
Link to Article [dx.doi.org/10.1051/0004-6361/201425120]

¹Peter Hoppe, ¹Jan Leitner, ¹János Kodolányi
¹Max Planck Institute for Chemistry, Hahn-Meitner-Weg 1, D-55128 Mainz, Germany

We studied about 5000 μm2 of fine-grained matrix material in the Acfer 094 meteorite by high-resolution (nominal 50 nm) NanoSIMS ion imaging for the presence of O-rich presolar (stardust) grains. This approach permits identifying presolar grains down to 150 nm in lower-resolution (nominal 100 nm) ion imaging surveys. The number density of identified presolar grains is a about a factor of two to three higher than what was found by lower-resolution ion imaging studies. The abundances of grains of O isotope Group 3 and 4 are higher than previously found. None of the presolar grains shows the strong enrichments in 16O expected from model predictions for the majority of supernova (SN) grains. Other potential O-rich SN grains, the Group 4 and some of the Group 3 grains, make up 33% by number and 19% by mass. This is clearly higher than the ~10% (by number) inferred before and the 5% (by mass) estimated by a model for stellar dust in the interstellar medium. Our work shows that O-rich SN grains might be more abundant among the population of presolar grains in primitive solar system materials than currently thought, even without the 16O-rich grains as predominantly expected from SN models.

Reference
Hoppe P, Leitner J, Kodolányi J (2015) New Constraints on the Abundances of Silicate and Oxide Stardust from Supernovae in the Acfer 094 Meteorite. Astrophysical Journal 808 L9.
Link to Article [doi:10.1088/2041-8205/808/1/L9]