^1,2Emilie T. Dunham,^3,4,5J. Brian Balta,^1,2 Meenakshi Wadhwa,² Thomas G. Sharp,⁵ Harry Y. McSween Jr.
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13262]
¹Center for Meteorite Studies, Arizona State University, Tempe, Arizona, 8528 USA
²School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, 8528 USA
³Department of Geology & Geophysics, Texas A&M University, College Station, Texas, 77843 USA
⁴ Department of Earth and Environmental Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania, 15260 USA
⁵Department of Earth and Planetary Sciences, Planetary Geosciences Institute, University of Tennessee Knoxville, Knoxville, Tennessee, 37996 USA
Published by arrangement with John Wiley & Sons

Larkman Nunatak (LAR) 12095 and LAR 12240 are recent olivine‐phyric shergottite finds. We report the results of petrographic and chemical analyses of these two samples to understand their petrogenesis on Mars. Based on our analyses, we suggest that these samples are likely paired and are most similar to other depleted olivine‐phyric shergottites, particularly Dar al Gani (DaG) 476 and Sayh al Uhaymir (SaU) 005 (and samples paired with those). The olivine megacryst cores in LAR 12095 and LAR 12240 are not in equilibrium with the groundmass olivines. We infer that these megacrysts are phenocrysts and their major element compositions have been homogenized by diffusion (the cores of the olivine megacrysts have Mg# ~70, whereas megacryst rims and groundmass olivines typically have Mg# ~58–60). The rare earth element (REE) microdistributions in the various phases (olivine, low‐ and high‐Ca pyroxene, maskelynite, and merrillite) in both samples are similar and support the likelihood that these two shergottites are indeed paired. The calculated parent melt (i.e., in equilibrium with the low‐Ca pyroxene, which is one of the earliest formed REE‐bearing minerals) has an REE pattern parallel to that of melt in equilibrium with merrillite (i.e., one of the last‐formed minerals). This suggests that the LAR 12095/12240 paired shergottites represent the product of closed‐system fractional crystallization following magma emplacement and crystal accumulation. Utilizing the europium oxybarometer, we estimate that the magmatic oxygen fugacity early in the crystallization sequence was ~IW. Finally, petrographic evidence indicates that LAR 12095/12240 experienced extensive shock prior to being ejected from Mars.

¹J. Semprich,²S. P. Schwenzer,¹ A. H. Treiman,¹ J. Filiberto
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005869]
¹Lunar and Planetary Institute, USRA, Houston, TX, USA
²School of Environment, Technology, Engineering and Mathematics, The Open University, Milton Keynes, UK
Published by arrangement with John Wiley & Sons

Hydrous phases have been identified to be a significant component of martian mineralogy. Particularly prehnite, zeolites, and serpentine are evidence for low‐grade metamorphic reactions at elevated temperatures in mafic and ultramafic protoliths. Their presence suggests that at least part of the martian crust is sufficiently hydrated for low‐grade metamorphic reactions to occur. A detailed analysis of changes in mineralogy with variations in fluid content and composition along possible martian geotherms can contribute to determine the conditions required for subsurface hydrous alteration, fluid availability and rock properties in the martian crust. In this study, we use phase equilibria models to explore low‐grade metamorphic reactions covering a pressure‐temperature range of 0‐0.5 GPa and 150‐450 °C for several martian protolith compositions and varying fluid content. Our models replicate the detected low‐grade metamorphic/hydrothermal mineral phases like prehnite, chlorite, analcime, unspecified zeolites, and serpentine. Our results also suggest that actinolite should be a part of lower‐grade metamorphic assemblages, but actinolite may not be detected in reflectance spectra for several reasons. By gradually increasing the water content in the modeled whole rock composition, we can estimate the amount of water required to precipitate low‐grade metamorphic phases. Mineralogical constraints do not necessarily require an elevated geothermal gradient for the formation of prehnite. However, restricted crater excavation depths even for large impact craters are not likely sampling prehnite along colder gradients, either suggesting a geotherm of ~ 20 °C/km in the Noachian or an additional heat source such as hydrothermal or magmatic activity.

^1,2Mingming Zhang,^1,2Yangting Lin,³Ingo Leya,⁴ Guoqiang Tang,⁴Yu Liu
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13260]
¹Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
²University of Chinese Academy of Sciences, Beijing, 100049 China
³Physical Institute, Space Sciences and Planetology, University of Bern, 3012 Bern, Switzerland
⁴State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
Published by arrangement with John Wiley & Sons

Palisade bodies, mineral assemblages with spinel shells, in coarse‐grained Ca‐, Al‐rich inclusions (CAIs) have been considered either as exotic “mini‐CAIs” captured by their host inclusions (Wark and Lovering 1982) or as in situ crystallization products of a bubble‐rich melt (Simon and Grossman 1997). In order to clarify their origins, we conducted a comprehensive study of palisade bodies in an Allende Type B CAI (BBA‐7), using electron backscatter diffraction (EBSD), micro‐computed tomography (Micro‐CT), electron probe microanalysis (EPMA), and secondary ion mass spectrometry (SIMS). New observations support the in situ crystallization mechanism: early/residual melt infiltrated into spinel‐shelled bubbles and crystallized inside. Evidence includes (1) continuous crystallography of anorthite from the interior of the palisade body to the surrounding host; (2) partial consolidation of two individual palisade bodies revealed by micro‐CT; (3) a palisade body was entirely enclosed in a large anorthite crystal, and the anorthite within the palisade body shows the same crystallographic orientation as the anorthite host; and (4) identical chemical and oxygen isotopic compositions of the constituent minerals between the palisade bodies and the surrounding host. Oxygen isotopic compositions of the major minerals in BBA‐7 are bimodal‐distributed. Spinel and fassaite are uniformly 16O‐rich with ∆17O = −23.3 ± 1.5‰ (2SD), and melilite and anorthite are homogeneously 16O‐poor with ∆17O = −3.2 ± 0.7‰ (2SD). The latter ∆17O value overlaps with that of the Allende matrix (∆17O ~ −2.87‰) (Clayton and Mayeda 1999), which could be explained by secondary alteration with a 16O‐poor fluid in the parent body. The mobility of fluid could be facilitated by the high porosity (1.56–2.56 vol%) and connectivity (~0.17–0.55 vol%) of this inclusion.

^1,2Gregory J. Archer,¹ Richard J. Walker,¹Anthony J. Irving
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13261]
¹Department of Geology, University of Maryland, College Park, Maryland, 20742 USA
²Institut für Planetologie, University of Münster, Münster, 48149 Germany
³Department of Earth and Space Sciences, University of Washington, Seattle, Washington, 98195 USA
Published by arrangement with John Wiley & Sons

The abundances of highly siderophile elements (HSE; including Re, Os, Ir, Ru, Pt, and Pd) and ¹⁸⁷Re‐¹⁸⁷Os isotopic systematics were determined for two fragments from ungrouped achondrite NWA 7325. Rhenium‐Os systematics are consistent with closed‐system behavior since formation or soon after. The abundances of the HSE were therefore largely unaffected by late‐stage secondary processes such as shock or terrestrial weathering. As an olivine gabbro cumulate, this meteorite has a bulk composition consistent with derivation from a body that produced a core, mantle, and crust. Also consistent with derivation from a body that produced a core, both fragments of NWA 7325 have HSE abundances that are highly depleted compared to bulk chondrites. One fragment has ~0.002× CI chondrite Ir and relative HSE abundances similar to bulk chondrites. The other fragment has ~0.0002× CI chondrite Ir and relative HSE abundances that are fractionated compared to bulk chondrites. The chondritic relative HSE abundances of the fragment characterized by higher HSE abundances most likely reflect the addition of exogenous chondritic material during or after crystallization by surface impacts. The HSE in the other fragment is likely more representative of the parent body crust. One formation model that can broadly account for the HSE abundances in this fragment is multiple episodes of low‐pressure metal‐silicate equilibration, followed by limited late accretion and mantle homogenization. Given the different HSE compositions of the two adjoining fragments, this meteorite provides an example of the overprint of global processes (differentiation and late accretion) by localized impact contamination.

¹D. S. Burnett,^2,3A. J. G. Jurewicz, ⁴D. S. Woolum
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13266]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, 91125 USA
²Center for Meteorite Studies/School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, 85287–1404 USA
³Department of Earth Sciences, Dartmouth College, Hanover, New Hampshire, 03755, USA
⁴Department of Physics, California State University, Fullerton, California, 92831 USA
Published by arrangement with John Wiley & Sons

Solar abundances are important to planetary science since the prevalent model assumes that the composition of the solar photosphere is that of the solar nebula from which planetary materials formed. Thus, solar abundances are a baseline for planetary science. Previously, solar abundances have only been available through spectroscopy or by proxy (CI). The Genesis spacecraft collected and returned samples of the solar wind for laboratory analyses. Elemental and isotopic abundances in solar wind from Genesis samples have been successfully measured despite the crash of the re‐entry capsule. Here we present science rationales for a set of 12 important (and feasible postcrash) Science and Measurement Objectives as goals for the future (Table 1). We also review progress in Genesis sample analyses since the last major review (Burnett 2013). Considerable progress has been made toward understanding elemental fractionation during the extraction of the solar wind from the photosphere, a necessary step in determining true solar abundances from solar wind composition. The suitability of Genesis collectors for specific analyses is also assessed. Thus far, the prevalent model remains viable despite large isotopic variations in a number of volatile elements, but its validity and limitations can be further checked by several Objectives.

¹A.Pantazidi,¹I.Baziotis,^2,3A.Solomonidou,⁴E.Manoutsoglou,⁵D.Palles,⁵ E.Kamitsos,⁶A.Karageorgis,⁷G.Profitiliotis,¹M.Kondoyanni,⁸S.Klemme,⁸J.Berndt,⁹D.Ming,¹⁰P.Asimow
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.02.026]
¹Agricultural University of Athens, Mineral Resources and Agricultural Engineering, Iera Odos str. 75, 11855 Athens, Greece
²European Space Agency (ESA), European Space Astronomy Centre (ESAC), Madrid, Spain
³LESIA-Observatoire de Paris, Paris Sciences and Letters Research University, CNRS, Sorbonne Université, Université Paris-Diderot, Meudon, France
⁴Technical University of Crete, Greece
⁵National Hellenic Research Foundation, Athens, Greece
⁶Hellenic Centre for Marine Research (HCMR), Institute of Oceanography, Athens, Greece
⁷National Technical University of Athens, Greece
⁸Westfälische Wilhelms-Univ. Münster, Institut für Mineralogie, Correnstrasse 24, Münster, Germany
⁹NASA Johnson Space Center, Houston, TX 77058, USA
¹⁰California Institute of Technology, Geological and Planetary Sciences, Pasadena, CA, USA
Copyright Elsevier

The interpretation of geologic processes on Mars from sparse meteorite, remote sensing and rover data is influenced by knowledge gained from well-characterized terrestrial analogues. This calls for detailed study of candidate terrestrial analogues and comparison of their observable features to those encountered on the surface of Mars. We evaluated the mineralogical, geochemical, and physical properties of the Balos cove basalts (BCB) from the island of Santorini and compared them to Martian meteorites, Mars rover surface measurements, and other verified Martian analogues obtained from the International Space Analogue Rockstore (ISAR). Twenty rock samples were collected from the Balos cove area based on their freshness, integrity, and basaltic appearance in the field. Optical microscopy of BCB revealed a pilotaxitic to trachytic texture, with olivine and clinopyroxene phenocrysts in a fine groundmass of olivine, clinopyroxene, plagioclase, magnetite, and devitrified glass. All major minerals show normal zoning, including calcic plagioclase (An_78–85 at the core and An_60–76 at the rim), augite (En_36-48Wo_41-44Fs_11–21), and olivine (Fo_74–88). The dominant bands in the infrared-attenuated total reflectance (IR-ATR) spectra from BCB can be assigned to olivine (~875 cm⁻¹), calcic plagioclase (~1130 cm⁻¹), and augite (~970 cm⁻¹). The whole-rock chemical compositions and mineralogy of the BCB are similar to published analyses of typical olivine-phyric shergottites and basalts and basaltic materials analyzed in Gusev and Gale craters on Mars. BCB porosity is in the range of 7–15% and is similar to the porosities of the ISAR samples. Although no terrestrial rock is ever a perfect match to Martian compositions, the differences in mineralogy and geochemistry between BCB and some classes of Martian samples are relatively subtle and the basalts of Santorini are as close a match as other accepted Mars basalt analogues. The Santorini site offers excellent field logistics that, together with the petrology of the outcrop, makes it a valuable locality for testing and calibration deployments, field training, and other activities related to current and future Mars exploration.

¹Connor D.Hilton,¹Katherine R.Bermingham,¹Richard J.Walker,²J.McCoy
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.02.035]
¹Department of Geology, University of Maryland, College Park, Maryland, 20742, USA
²Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, DC, 20560-0119, USA
Copyright Elsevier

The nucleosynthetic Mo, Ru, and W isotopic compositions of the South Byron Trio iron meteorite grouplet (SBT) are consistent with all three meteorites originating on a single parent body that formed in the carbonaceous chondrite (CC) isotopic domain within the Solar nebula. Consistent with a common origin, the highly siderophile element (HSE) concentrations of the SBT can be related to one another by moderate degrees of fractional crystallization of a parental melt with initially chondritic relative abundances of HSE, and with initial S and P contents of ∼7 and ∼1 wt. %, respectively. Tungsten-182 isotopic data for the SBT indicate the parent body underwent metal-silicate differentiation 2.1 ± 0.8 Myr after calcium aluminum rich inclusion formation, and thermal modeling suggests the parent body formed 1.1 ± 0.5 Myr after CAI formation. This accretion age is not resolved from the accretion ages of other CC and most noncarbonaceous (NC) type iron meteorite parent bodies. Comparison of the projected parental melt composition of the SBT to those projected for the IVA and IVB iron meteorite groups suggests that at least some portions of the CC nebular domain were more oxidized compared to the NC domain. In addition, comparison of the SBT parental melt S content to estimates for parent bodies of the IIAB, IIIAB, IVA, IID, and IVB “magmatic” iron meteorite groups suggests that CC type iron meteorite parental melts were characterized by a general depletion in S, in addition to depletions in some other moderately volatile elements.

Based on chemical and O isotope similarities, prior studies have suggested the possibility of a common parent body for the SBT and the Milton pallasite. Molybdenum and Ru isotopic compositions of Milton also provide permissive evidence for this. The HSE concentrations in the Milton metal, however, cannot be related to the SBT by any known crystal-liquid fractionation or mixing path. Thus, Milton more likely formed on a different, chemically distinct, but genetically identical parent body present in the CC nebular domain.

^1,2James M.D.Day,²Paolo A.Sossi,³Charles K.Shearer,^2,4Frederic Moynier
Geochimica et Cosmochimcia Acta(in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.02.036]
¹Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0244, USA
²Institut de Physique du Globe de Paris, Université Paris Diderot, Sorbonne Paris Cité, 1 rue Jussieu, 75005, Paris, France
³Institute of Meteoritics, University of New Mexico, Albuquerque, NM 87131, USA
⁴Institut Universitaire de France, 75005, Paris
Copyright Elsevier

The Apollo 16 ‘Rusty Rock’ impact melt breccia 66095 is a volatile-rich sample, with the volatiles inherited through vapor condensation from an internal lunar source formed during thermo-magmatic evolution of the Moon. We report Cu and Fe isotope data for 66095 and find that bulk-rocks, residues and acid leaches span a relatively limited range of compositions (3.0 ±1.3 wt.% FeO [range = 2.0-4.8 wt.%], 5.4 ±3.1 ppm Cu [range = 3-12 ppm], average δ⁵⁶Fe of 0.15 ± 0.05‰ [weighted mean = 0.16‰] and δ⁶⁵Cu of 0.72 ± 0.14‰ [weighted mean = 0.78‰]). In contrast to the extreme enrichment of light isotopes of Zn and heavy isotopes of Cl in 66095, δ⁶⁵Cu and δ⁵⁶Fe in the sample lie within the previously reported range for lunar mare basalts (0.92 ± 0.16‰ and 0.12 ± 0.02‰, respectively). The lack of extreme isotopic fractionation for Cu and Fe isotopes reflects compositions inherent to 66095, with condensation of a cooling gas from impact-generated fumarolic activity at temperatures too low to lead to the condensation of Cu and Fe, but higher than required to condense Zn. Together with thermodynamic models, these constraints suggest that the gas condensed within 66095 between 700 and 900 °C (assuming a pressure of 10^-6 and an fO₂ of IW-2). That the Cu and Fe isotopic compositions of sample 66095 are within the range of mare basalts removes the need for an exotic, volatile-enriched source. The enrichment in Tl, Br, Cd, Sn, Zn, Pb, Rb, Cs, Ga, B, Cl, Li relative to Bi, Se, Te, Ge, Cu, Ag, Sb, Mn, P, Cr and Fe in the ‘Rusty Rock’ is consistent with volcanic outgassing models and indicates that 66095 likely formed distal from the original source of the gas. The volatile-rich character of 66095 is consistent with impact-generated fumarolic activity in the region of the Cayley Plains, demonstrating that volatile-rich rocks can occur on the lunar surface from outgassing of a volatile-poor lunar interior. The ‘Rusty Rock’ indicates that the lunar interior is significantly depleted in volatile elements and compounds and that volatile-rich lunar surface rocks likely formed through vapor condensation. Remote sensing studies have detected volatiles on the lunar surface, attributing them dominantly to solar wind. Based on the ‘Rusty Rock’, some of these surface volatiles may also originate from the Moon’s interior.

^1,2Chuantong Zhangab,^1,2Bingkui Miao,³Huaiyu He
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2019.02.007]
¹Institution of Meteorites and Planetary Materials Research, Guilin University of Technology, Guilin, 541006, China
²Key Laboratory of Planetary Geological Evolution, Guilin University of Technology, Guilin, 541006, China
³Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China

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¹Katarzyna Łuszczek,¹Tadeusz A.Przylibski
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2019.02.005]
¹Wrocław University of Science and Technology, Faculty of Geoengineering, Mining and Geology, Wybrzeże S. Wyspiańskiego 27, 50-370, Wrocław, Poland

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