Louise Alexander^1,2, Joshua F. Snape^2,3,4, Ian A. Crawford^1,2, Katherine H. Joy^3,5 and Hilary Downes^1,2

¹Department of Earth and Planetary Science, Birkbeck College, University of London, London, UK
²The Centre for Planetary Sciences at UCL-Birkbeck, London, UK
³Department of Earth Sciences, University College London, London, UK
⁴Department of Physical Sciences, Open University, Milton Keynes, UK
⁵School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, UK

New data from a petrological and geochemical examination of 12 coarse basaltic fines from the Apollo 12 soil sample 12023,155 provide evidence of additional geochemical diversity at the landing site. In addition to the bulk chemical composition, major, minor, and trace element analyses of mineral phases are employed to ascertain how these samples relate to the Apollo 12 lithological basalt groups, thereby overcoming the problems of representativeness of small samples. All of the samples studied are low-Ti basalts (0.9–5.7 wt% TiO₂), and many fall into the established olivine, pigeonite, and ilmenite classification of Apollo 12 basaltic suites. There are five exceptions: sample 12023,155_1A is mineralogically and compositionally distinct from other Apollo 12 basalt types, with low pigeonite REE concentrations and low Ni (41–55 ppm) and Mn (2400–2556 ppm) concentrations in olivine. Sample 12023,155_11A is also unique, with Fe-rich mineral compositions and low bulk Mg# (=100 × atomic Mg/[Mg+Fe]) of 21.6. Sample 12023,155_7A has different plagioclase chemistry and crystallization trends as well as a wider range of olivine Mg# (34–55) compared with other Apollo 12 basalts, and shows greater similarities to Apollo 14 high-Al basalts. Two other samples (12023,155_4A, and _5A) are similar to the Apollo 12 feldspathic basalt 12038, providing additional evidence that feldspathic basalts represent a lava flow proximal to the Apollo 12 site rather than material introduced by impacts. We suggest that at least one parent magma, and possibly as many as four separate parent magmas, are required in addition to the previously identified olivine, pigeonite, and ilmenite basaltic suites to account for the observed chemical diversity of basalts found in this study.

Reference
Alexander L, Snape JF, Crawford IA, Joy KH and Downes H (in press) Searching for nonlocal lithologies in the Apollo 12 regolith: A geochemical and petrological study of basaltic coarse fines from the Apollo lunar soil sample 12023,155. Meteoritics & Planetary Science
[doi:10.1111/maps.12319]
Published by arrangement with John Wiley & Sons

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Brendt C. Hyde¹, James M. D. Day², Kimberly T. Tait¹, Richard D. Ash³, David W. Holdsworth⁴ and Desmond E. Moser⁵

¹Department of Natural History, Mineralogy, Royal Ontario Museum, Toronto, Ontario, Canada
²Geosciences Research Division, Scripps Institution of Oceanography, La Jolla, California, USA
³Department of Geology, University of Maryland, College Park, Maryland, USA
⁴Robarts Research Institute, Imaging Research Laboratories, London, Ontario, Canada
⁵Department of Earth Sciences, Western University, London, Ontario, Canada

Terrestrial weathering of hot desert achondrite meteorite finds and heterogeneous phase distributions in meteorites can complicate interpretation of petrological and geochemical information regarding parent-body processes. For example, understanding the effects of weathering is important for establishing chalcophile and siderophile element distributions within sulfide and metal phases in meteorites. Heterogeneous mineral phase distribution in relatively coarsely grained meteorites can also lead to uncertainties relating to compositional representativeness. Here, we investigate the weathering and high-density (e.g., sulfide, spinel, Fe-oxide) phase distribution in sections of ultramafic achondrite meteorite Northwest Africa (NWA) 4872. NWA 4872 is an olivine-rich brachinite (Fo_{63.6 ± 0.5}) with subsidiary pyroxene (Fs_9.7 ± 0.1Wo_{46.3 ± 0.2}), Cr-spinel (Cr# = 70.3 ± 1.1), and weathered sulfide and metal. Raman mapping confirms that weathering has redistributed sulfur from primary troilite, resulting in the formation of Fe-oxide (-hydroxide) and marcasite (FeS₂). From Raman mapping, NWA 4872 is composed of olivine (89%), Ca-rich pyroxene (0.4%), and Cr-spinel (1.1%), with approximately 7% oxidized metal and sulfide and 2.3% marcasite-dominated sulfide. Microcomputed tomography (micro-CT) observations reveal high-density regions, demonstrating heterogeneities in mineral distribution. Precision cutting of the largest high-density region revealed a single 2 mm Cr-spinel grain. Despite the weathering in NWA 4872, rare earth element (REE) abundances of pyroxene determined by laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) indicate negligible modification of these elements in this mineral phase. The REE abundances of mineral grains in NWA 4872 are consistent with formation of the meteorite as the residuum of the partial melting process that occurred on its parent body. LA-ICP-MS analyses of sulfide and alteration products demonstrate the mobility of Re and/or Os; however, highly siderophile element (HSE) abundance patterns remain faithful recorders of processes acting on the brachinite parent body(ies). Detailed study of weathering and phase distribution offers a powerful tool for assessing the effects of low-temperature alteration and for identifying robust evidence for parent-body processes.

Reference
Hyde BC, Day JMD, Tait KT, Ash RD, Holdsworth DW and Moser DE (in press) Characterization of weathering and heterogeneous mineral phase distribution in brachinite Northwest Africa 4872. Meteoritics & Planetary Science
[doi:10.1111/maps.12320]
Published by arrangement with John Wiley & Sons

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T. Öhman^1,2,3, G. Y. Kramer^1,2 and D. A. Kring^1,2

¹Lunar and Planetary Institute, Universities Space Research Association, Houston, Texas, USA
²Center for Lunar Science and Exploration, NASA Lunar Science Institute
³Now at Arctic Planetary Science Institute, Rovaniemi, Finland

We used Moon Mineralogy Mapper (M³), Arecibo and Mini-RF radar, and Diviner radiometer data with Lunar Reconnaissance Orbiter (LRO) Camera and Kaguya Terrain Camera images to characterize the target, ejecta, and impact melt-rich lithologies in and around lunar central peak crater Kepler. M³ data indicate the impact melt rocks of crater floor to be high-Ca pyroxene dominated, distinct from the low-Ca pyroxene-dominated crater wall. The central uplift is high-Ca pyroxene dominated, and has higher albedo. These observations are consistent with thin mare basalts underlain by noritic Imbrium ejecta, underlain by gabbroic crustal material. M³ data reveal an enigmatic, splash-like feature of melt-rich material on the southeastern (uprange) crater wall and flank. M³ data also highlight halos around Kepler. In detail the halos are slightly variable, but in broad terms they define a consistent feature, offset to the inferred downrange direction, and interpreted to reflect the distribution of glass-bearing impact breccia. The radar data sets show most of the proximal ejecta to be radar-bright. However, Diviner rock abundance data do not indicate the presence of blocks on the surface nor can they be seen using LRO Narrow Angle Camera images. Thus, the blocks giving rise to the enhanced radar signal are buried. Beyond the radar-bright zone, a subtle radar-dark halo emerges, coincident with a region of very low rock abundance in Diviner data. This multidisciplinary approach provides a robust analysis of the main characteristics of a lunar complex crater and reveals previously unidentified features related to the distribution of impact melt.

Reference
Öhman T, Kramer GY and Kring DA (in press) Characterization of melt and ejecta deposits of Kepler crater from remote sensing data. Journal of Geophysical Research: Planets
[doi:10.1002/2013JE004501]
Published by arrangement with John Wiley & Sons

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C.D. Neish^a, J. Madden^b, L.M. Carter^c, B.R. Hawke^d, T. Giguere^d,e, V.J. Bray^f, G.R. Osinski^g, J.T.S. Cahill^h

^aDepartment of Physics and Space Sciences, Florida Institute of Technology, Melbourne, FL, 32901
^bFranklin and Marshall College, Lancaster, PA, 17603
^cNASA Goddard Space Flight Center, Greenbelt, MD, 20771
^dUniversity of Hawai’i at Manoa, Honolulu, HI, 96822
^eIntergraph Corporation, Box 75330, Kapolei, HI, 96707
^fLunar and Planetary Laboratory, University of Arizona, Tucson, AZ, 85721
^gCentre for Planetary Science and Exploration, Departments of Earth Sciences and Physics and Astronomy, University of Western Ontario, London, Ontario, N6A 3K7
^hThe Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723

In this study, we analyzed the distribution and properties of 146 craters with impact melt deposits exterior to their rims. Many of these craters were only recently discovered due to their unusual radar properties in the near-global Mini-RF data set. We find that most craters with exterior deposits of impact melt are small, ⩽ 20 km, and that the smallest craters have the longest melt flows relative to their size. In addition, exterior deposits of impact melt are more common in the highlands than the mare. This may be the result of differing target properties in the highlands and mare, the difference in titanium content, or the greater variation of topography in the highlands. We find that 80% of complex craters and 60% of simple craters have melt directions that are coincident or nearly coincident with the lowest point in their rim, implying that pre-existing topography plays a dominant role in melt emplacement. This is likely due to movement during crater modification (complex craters) or breached crater rims (simple craters). We also find that impact melt flows have very high circular polarization ratios compared to other features on the Moon. This suggests that their surfaces are some of the roughest material on the Moon at the centimeter to decimeter scale, even though they appear smooth at the meter scale.

Reference
Neish CD, Madden J, Carter LM, Hawke BR, Giguere T, Bray VJ, Osinski GR and Cahill JTS (in press) Global distribution of lunar impact melt flows. Icarus
[doi:10.1016/j.icarus.2014.05.049]
Copyright Elsevier

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