¹Carles E. Moyano-Cambero,¹Josep M. Trigo-Rodriguez,²Jordi Llorca,³Sonia Fornasier,³Maria A. Barucci,⁴Albert Rimola
Meteoritics & Planetary Science (in Press)  Link to Article [DOI: 10.1111/maps.12703]
¹Institut de Ciències de l’Espai (CSIC-IEEC), Campus UAB, Barcelona, Spain
²Institut de Tècniques Energètiques i Centre de Recerca en Nanoenginyeria, Universitat Politècnica de Catalunya, ETSEIB, Barcelona, Spain
³LESIA, Observatoire de Paris, PSL Research University, CNRS, Univ. Paris Diderot, Sorbonne Paris Cité, UPMC Univ. Paris 06, Sorbonne Universités, Meudon Principal Cedex, France
⁴Departament de Química, Universitat Autònoma de Barcelona, Bellaterra, Spain
Published by arrangement with John Wiley & Sons

A crucial topic in planetology research is establishing links between primitive meteorites and their parent asteroids. In this study, we investigate the feasibility of a connection between asteroids similar to 21 Lutetia, encountered by the Rosetta mission in July 2010, and the CH3 carbonaceous chondrite Pecora Escarpment 91467 (PCA 91467). Several spectra of this meteorite were acquired in the ultraviolet to near-infrared (0.3–2.2 μm) and in the midinfrared to thermal infrared (2.5–30.0 μm or 4000 to ~333 cm−1), and they are compared here to spectra from the asteroid 21 Lutetia. There are several similarities in absorption bands and overall spectral behavior between this CH3 meteorite and 21 Lutetia. Considering also that the bulk density of Lutetia is similar to that of CH chondrites, we suggest that this asteroid could be similar, or related to, the parent body of these meteorites, if not the parent body itself. However, the apparent surface diversity of Lutetia pointed out in previous studies indicates that it could simultaneously be related to other types of chondrites. Future discovery of additional unweathered CH chondrites could provide deeper insight in the possible connection between this family of metal-rich carbonaceous chondrites and 21 Lutetia or other featureless, possibly hydrated high-albedo asteroids.

¹Lingzhi Sun, ^1,2Zongcheng Ling, ¹Jiang Zhang, ¹Bo Li, ¹Jian Chen, ¹Zhongchen Wu, ³Jianzhong Liu
Icarus (in Press) Link to Article [doi:10.1016/j.icarus.2016.07.010]
¹School of Space Science and Physics, Shandong Provincial Key Laboratory of Optical Astronomy & Solar-Terrestrial Environment, Shandong University, Weihai 264209, China
²Key Laboratory of Lunar and Deep Space Exploration, Chinese Academy of Sciences, Beijing 100012, China
³Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550002, China
Copyright Elsevier

Iron and optical maturity (OMAT) are two key geological marks of the Moon that closely related to its geochemical evolution and interactions between surface and space environment. We apply Partial Least Squares (PLS) regression to Chang’E-1 Imaging Interferometer (IIM) (32 bands between 480 and 960 nm) in mapping lunar global FeO and OMAT, and the FeO and OMAT values are derived based on reasonable spectral parameters (absorbance, band ratios, TiO2 and maturity sensitive parameters, etc.). After been calibrated by the FeO map from Lunar Prospector Gamma-Ray Spectrometer (LP-GRS), the global FeO map derived from PLS modeling shows a quantitatively more reasonable result consistent with previous remote sensing results (LP) as well as lunar feldspathic meteorite studies and Chang’E-3 landing site. Based on the new FeO map by Chang’E-1, we discover a compositional inhomogeneity across lunar highland regions, which has not been suggested by previous datasets (e.g., Clementine UVVIS). Furthermore, we suggest that at least part of the FeO enrichments in highlands would be caused by mixing of highland and mare materials. The IIM derived OMAT map does not suggest a dichotomy of the lunar highlands and mare regions, implying the compositional differences between those two terrains have been suppressed. We further check the maturity effect for the young mare basalts (20 wt.%) and ultrahigh-TiO2 (>10 wt.%) tend to have greater OMAT values and vary little with ages; (3) this may be due to the distinct optical maturity effects of ultramafic minerals (i.e., ultrahigh Fe and Ti) and/or the spectral blue shifts of abundant ilmenite.

¹Jibamitra Ganguly, ²Massimiliano Tirone, ³Kenneth Domanik
Geochimica et Cosmochimica Acta (in Press) Link to Article [doi:10.1016/j.gca.2016.07.030]
¹Department of Geosciences, University of Arizona, Tucson, AZ 85721, USA
²Institut für Geologie, Mineralogie, Geophysik, Rühr-Universität, D-44780 Bochum, Germany
³Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA
Copyright Elsevier

We have carried out detailed thermometric and cooling history studies of several LL-, L- and H-chondrites of petrologic types 5 and 6. Among the selected samples, the low-temperature cooling of St. Séverin (LL6) has been constrained in an earlier study by thermochronological data to an average rate of ∼2.6 °C/My below 500 °C. However, numerical simulations of the development of Fe-Mg profiles in Opx-Cpx pairs using this cooling rate grossly misfit the measured compositional profiles. Satisfactory simulation of the latter and low temperature thermochronological constraints requires a two-stage cooling model with a cooling rate of ∼50-200 °C/ky from the peak metamorphic temperature of ∼875 °C down to 450 °C, and then transitioning to very slow cooling with an average rate of ∼2.6 °C/My. Similar rapid high temperature cooling rates (200-600 °C/ky) are also required to successfully model the compositional profiles in the Opx-Cpx pairs in the other samples of L5, L6 chondrites. For the H-chondrite samples, the low temperature cooling rates were determined earlier to be 10-20 °C/My by metallographic method. As in St. Séverin, these cooling rates grossly misfit the compositional profiles in the Opx-Cpx pairs. Modeling of these profiles requires very rapid cooling, ∼200-400 °C/ky, from the peak temperatures (∼810-830 °C), transitioning to the metallographic rates at ∼450 – 500 °C. We interpret the rapid high temperature cooling rates to the exposure of the samples to surface or near surface conditions as a result of fragmentation of the parent body by asteroidal impacts. Using the thermochronological data, the timing of the presumed impact is constrained to be ∼4555 – 4560 My before present for St. Séverin (Fig. 3). We also deduced similar two stage cooling models in earlier studies of H-chondrites and mesosiderites that could be explained, using the available geochronological data, by impact induced fragmentation at around the same time. Diffusion kinetic analysis shows that if a lower petrological type got transformed by the thermal effect of shock impacts to reflect higher metamorphic temperature, as has been suggested as a possibility, then the peak temperatures would have had to be sustained for at least 10 ky and 80 ky, respectively, for transformation to the petrologic types 6 and 4. Finally, we present a model that reconciles textural data supporting an onion-shell parent body of H-chondrites with rapid cooling rate at high temperature caused by impact induced disturbance, and also discuss alternatives to the onion shell parent body model.

^1,2Bruce Fegley Jr., ³Nathan S. Jacobson, ²K. B. Williams, ⁴J. M. C. Plane, ⁵L. Schaefer, ^1,2Katharina Lodders
The Astrophysical Journal 824, 103 Link to Article [http://dx.doi.org/10.3847/0004-637X/824/2/103]
¹Planetary Chemistry Laboratory, McDonnell Center for the Space Sciences, Washington University, St. Louis, MO 63130, USA
²Department of Earth & Planetary Sciences, Washington University, St. Louis, MO 63130, USA
³Materials Division, NASA Glenn Research Center, MS106-1, 21000 Brookpark Road, Cleveland, OH 44135, USA
⁴School of Chemistry, University of Leeds, Leeds LS2 9JT, UK
⁵Harvard—Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

Extensive experimental studies show that all major rock-forming elements (e.g., Si, Mg, Fe, Ca, Al, Na, K) dissolve in steam to a greater or lesser extent. We use these results to compute chemical equilibrium abundances of rocky-element-bearing gases in steam atmospheres equilibrated with silicate magma oceans. Rocky elements partition into steam atmospheres as volatile hydroxide gases (e.g., Si(OH)4, Mg(OH)2, Fe(OH)2, Ni(OH)2, Al(OH)3, Ca(OH)2, NaOH, KOH) and via reaction with HF and HCl as volatile halide gases (e.g., NaCl, KCl, CaFOH, CaClOH, FAl(OH)2) in much larger amounts than expected from their vapor pressures over volatile-free solid or molten rock at high temperatures expected for steam atmospheres on the early Earth and hot rocky exoplanets. We quantitatively compute the extent of fractional vaporization by defining gas/magma distribution coefficients and show that Earth’s subsolar Si/Mg ratio may be due to loss of a primordial steam atmosphere. We conclude that hot rocky exoplanets that are undergoing or have undergone escape of steam-bearing atmospheres may experience fractional vaporization and loss of Si, Mg, Fe, Ni, Al, Ca, Na, and K. This loss can modify their bulk composition, density, heat balance, and interior structure.

¹V. Clesi, ¹M.A. Bouhifd, ¹N. Bolfan-Casanova, ¹G. Manthilake, ¹A. Fabbrizio, ¹D. Andrault
Geochimica et Cosmochmica Acta (in Press) Link to Article [doi:10.1016/j.gca.2016.07.029]
¹Laboratoire Magmas et Volcans, Université Blaise Pascal, CNRS UMR 6524, OPGC-IRD, Campus Universitaire des Cézeaux, 6 Avenue Blaise Pascal, 63178 Aubie‘re Cedex, France
Copyright Elsevier

This study investigates the metal-silicate partitioning of Ni, Co, V, Cr, Mn and Fe during core mantle differentiation of terrestrial planets under hydrous conditions. For this, we equilibrated a molten hydrous CI chondrite model composition with various Fe-rich alloys in the system Fe-C-Ni-Co-Si-S in a multi-anvil over a range of P, T, fO2fO2 and water content (5 – 20 GPa, 2073 – 2500 K, from 1 to 5 log units below the iron-wüstite (IW) buffer and for XH2OXH2O varying from 500 ppm to 1.5 wt%). By comparing the present experiments with the available data sets on dry systems, we observes that the effect of water on the partition coefficients of moderately siderophile elements is only moderate. For example, for iron we observed a decrease in the partition coefficient of Fe (View the MathML sourceDmet/silFe) from 9.5 to 4.3, with increasing water content of the silicate melt, from 0 to 1.44 wt%, respectively. The evolution of metal-silicate partition coefficients of Ni, Co, V, Cr, Mn and Fe are modelled based on sets of empirical parameters. These empirical models are then used to refine the process of core segregation during accretion of Mars and the Earth. It appears that the likely presence of 3.5 wt% water on Mars during the core-mantle segregation could account for ∼∼ 74% of the FeO content of the Martian mantle. In contrast, water does not play such an important role for the Earth; only 4 to 6% of the FeO content of its mantle could be due to the water-induced Fe-oxidation, for a likely initial water concentration of 1.8 wt%. Thus, in order to reproduce the present-day FeO content of 8 wt% in the mantle, the Earth could initially have been accreted from a large fraction (between 85 to 90%) of reducing bodies (similar to EH chondrites), with 10 to 15% of the Earth’s mass likely made of more oxidized components that introduced the major part of water and FeO to the Earth. This high proportion of enstatite chondrites in the original constitution of the Earth is consistent with the 17O17O, 48Ca48Ca, 50Ti50Ti, 62Ni62Ni and 90Mo90Mo isotopic study by Dauphas2014. If we assume that the CI-chondrite was oxidized during accretion, its intrinsically high water content suggests a maximum initial water concentration in the range of 1.2 to 1.8 wt% for the Earth, and 2.5 to 3.5 wt% on Mars.

¹Tasha L. Dunn,^2,3Juliane Gross,⁴Marina A. Ivanova,⁵Simone E. Runyon,⁶Andrea M. BruckMeteoritics & Planetary Sciences (in Press) Link to Article [DOI: 10.1111/maps.12691]
¹Department of Geology, Colby College, Waterville, Maine, USA
²Department of Earth and Planetary Sciences, Rutgers University, Piscataway, New Jersey, USA
³Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, USA
⁴Vernadsky Institute of Geochemistry, Moscow, Russia
⁵Department of Geosciences, University of Arizona, Tucson, Arizona, USA
⁶Department of Chemistry, SUNY Stony Brook, Stony Brook, New York, USA
Published by arrangement with John Wiley & Sons

Bulk isotopic and elemental compositions of CV and CK chondrites have led to the suggestion that both originate from the same asteroid. It has been argued that magnetite compositions also support this model; however, magnetite has been studied almost exclusively in the equilibrated (type 4-6) CKs. Magnetite in seven unequilibrated CKs analyzed here is enriched in MgO, TiO2, and Al2O3 relative to the equilibrated CKs, suggesting that magnetite compositions are affected by metamorphism. Magnetite in CKs is compositionally distinct from CVs, particularly in abundances of Cr2O3, NiO, and TiO2. Although there are minor similarities between CV and equilibrated CK chondrite magnetite, this is contrary to what we would expect if the CVs and CKs represent a single metamorphic sequence. CV magnetite should resemble CK3 magnetite, as both were metamorphosed to type 3 conditions. Oxygen fugacities and temperatures of CVox and CK chondrites are also difficult to reconcile using existing CV-CK parent body models. Mineral chemistries, which eliminate issues of bulk sample heterogeneity, provide a reliable alternative to techniques that involve a small amount of sample material. CV and CK chondrite magnetite has distinct compositional differences that cannot be explained by metamorphism.

¹Blanca Rincón-Tomás, ¹Bahar Khonsari, ¹Dominik Mühlen, ¹Christian Wickbold, ²Nadine Schäfer, ²Dorothea Hause-Reitner, ^1,3Michael Hoppert, ^2,3Joachim Reitner
International Journal of Astrobiology 15, 219-229 Link to Article [DOI: http://dx.doi.org/10.1017/S1473550416000264]
¹Georg-August-University Göttingen, Institute of Microbiology and Genetics, Grisebachstraße 8, 37077 Göttingen, Germany
²Georg-August-University Göttingen, Göttingen Centre of Geosciences, Goldschmidtstraße 3, 37077 Göttingen, Germany
³Göttingen Academy of Sciences and Humanities, Theaterstraße 7, 37073 Göttingen, Germany

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^1,2,3Nicola J. Potts,^1,4,5Romain Tartèse,^1,6Mahesh Anand,²Wim van Westrenen,^1,7Alexandra A. Griffiths,¹Thomas J. Barrett,¹Ian A. Franchi
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12681]
¹Planetary and Space Sciences, The Open University, Milton Keynes, UK
²Faculty of Earth and Life Sciences, VU University Amsterdam, 1081 HV Amsterdam, the Netherlands
³School of GeoSciences, University of Edinburgh, Edinburgh, UK
⁴Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, ⁵Muséum National d’Histoire Naturelle, Sorbonne Universités, CNRS, UPMC & IRD, Paris, France
⁶Department of Earth Sciences, The Natural History Museum, London, SW7 5BD, UK
⁷School of Earth, Atmospheric and Environmental Sciences, University of Manchester, UK
Published by arrangement with John Wiley & Sons

Recent studies geared toward understanding the volatile abundances of the lunar interior have focused on the volatile-bearing accessory mineral apatite. Translating measurements of volatile abundances in lunar apatite into the volatile inventory of the silicate melts from which they crystallized, and ultimately of the mantle source regions of lunar magmas, however, has proved more difficult than initially thought. In this contribution, we report a detailed characterization of mesostasis regions in four Apollo mare basalts (10044, 12064, 15058, and 70035) in order to ascertain the compositions of the melts from which apatite crystallized. The texture, modal mineralogy, and reconstructed bulk composition of these mesostasis regions vary greatly within and between samples. There is no clear relationship between bulk-rock basaltic composition and that of bulk-mesostasis regions, indicating that bulk-rock composition may have little influence on mesostasis compositions. The development of individual melt pockets, combined with the occurrence of silicate liquid immiscibility, exerts greater control on the composition and texture of mesostasis regions. In general, the reconstructed late-stage lunar melts have roughly andesitic to dacitic compositions with low alkali contents, displaying much higher SiO2 abundances than the bulk compositions of their host magmatic rocks. Relevant partition coefficients for apatite-melt volatile partitioning under lunar conditions should, therefore, be derived from experiments conducted using intermediate compositions instead of compositions representing mare basalts.

¹Paul A. Giesting,²Justin Filiberto
Meteoritics&Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12675]
¹Department of Earth and Planetary Science, University of Tennessee, Knoxville, Tennessee, USA
²Department of Geology, Southern Illinois University, Carbondale, Illinois, USA
Published by arrangement with John Wiley & Sons

Potassic-chloro-hastingsite has been found in melt inclusions in MIL 03346, its paired stones, and NWA 5790. It is some of the most chlorine-rich amphibole ever analyzed. In this article, we evaluate what crystal chemistry, terrestrial analogs, and experiments have shown about how chlorine-dominant amphibole (chloro-amphibole) forms and apply these insights to the nakhlites. Chloro-amphibole is rare, with about a dozen identified localities on Earth. It is always rich in potassium and iron and poor in titanium. In terrestrial settings, its presence has been interpreted to result from medium to high-grade alteration (>400 °C) of a protolith by an alkali and/or iron chloride-rich aqueous fluid. Ferrous chloride fluids exsolved from mafic magmas can cause such alteration, as can crustal fluids that have reacted with rock and lost H2O in preference to chloride, resulting in concentrated alkali chloride fluids. In the case of the nakhlites, an aqueous alkali-ferrous chloride fluid was exsolved from the parental melt as it crystallized. This aqueous chloride fluid itself likely unmixed into chloride-dominant and water-dominant fluids. Chloride-dominant fluid was trapped in some melt inclusions and reacted with the silicate contents of the inclusion to form potassic-chloro-hastingsite.