^1,2Ai-Cheng Zhang, ³Shoichi Itoh, ³Hisayoshi Yurimoto, ⁴Wei-Biao Hsu, ¹Ru-Cheng Wang, ⁵Lawrence A. Taylor
¹State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing, China
²Lunar and Planetary Science Institute, Nanjing University, Nanjing, China
³Department of Natural History Sciences, Hokkaido University, Sapporo, Japan
⁴Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, China
⁵Planetary Geosciences Institute, Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, Tennessee, USA

CM chondrites are a group of primitive meteorites that have recorded the alteration history of the early solar system. We report the occurrence, chemistry, and oxygen isotopic compositions of P-O-rich sulfide phase in two CM chondrites (Grove Mountains [GRV] 021536 and Murchison). This P-O-rich sulfide is a polycrystalline aggregate of nanometer-size grains. It occurs as isolated particles or aggregates in both CM chondrites. These grains, in the matrix and in type-I chondrules from Murchison, were partially altered into tochilinite; however, grains enclosed by Ca-carbonate are much less altered. This P-O-rich sulfide in Murchison is closely associated with magnetite, FeNi phosphide, brezinaite (Cr3S4), and eskolaite (Cr2O3). In addition to sulfur as the major component, this sulfide contains ~6.3 wt% O, ~5.4 wt% P, and minor amounts of hydrogen. Analyses of oxygen isotopes by SIMS resulted in an average δ18O value of −22.5 ‰ and an average Δ17O value of 0.2 ± 9.2 ‰ (2σ). Limited variations in both chemical compositions and electron-diffraction patterns imply that the P-O-rich sulfide may be a single phase rather than a polyphase mixture. Several features indicate that this P-O-rich sulfide phase formed at low temperature on the parent body, most likely through the alteration of FeNi metal (a) close association with other low-temperature alteration products, (b) the presence of hydrogen, (c) high Δ17O values and the presence in altered mesostasis of type-I chondrules and absence in type-II chondrules. The textural relations of the P-O-rich sulfide and other low-temperature minerals reveal at least three episodic-alteration events on the parent body of CM chondrites (1) formation of P-O-rich sulfide during sulfur-rich aqueous alteration of P-rich FeNi metal, (2) formation of Ca-carbonate during local carbonation, and (3) alteration of P-O-rich sulfide and formation of tochilinite during a period of late-stage intensive aqueous alteration

Reference
Zhang A-C, Itoh S, Yurimoto H, Hsu W-B, Wang R-C, Taylor LA (2015)
P-O-rich sulfide phase in CM chondrites: Constraints on its origin on the CM parent body. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12583]
Published by arrangement with John Wiley & Sons

^1,2Xiande Xie, ³Xiangping Gu,²Ming Chen
¹Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China
²Guangdong Key Laboratory of Mineral Physics and Materials, Guangzhou, China
³School of Geosciences and Info-Physics, Central South University, Changsha, Hunan, China

Tuite is a high-pressure γ-form of Ca3(PO4)2. An occurrence of tuite partly transformed from merrillite and chlorapatite was observed in the chondritic area adjacent to the shock veins in the Suizhou meteorite. Tuite grains are found in contact with both merrillite and chlorapatite, indicating two different transformation pathways. Tuite isochemically transformed from merrillite contains much higher contents of Na2O and MgO than those transformed from chlorapatite. Tuite transformed from merrillite does not contain Cl, but tuite transformed from chlorapatite contains 1.90–3.91 wt% of Cl, hence indicating an incomplete phase transformation from chlorapatite to tuite. P-T conditions of above 12 GPa and 1100 °C are probably required for the transformation from merrillite and chlorapatite to tuite. A temperature gradient from the hot vein at 2000 °C to the surrounding chondritic area at 1000 °C corresponds to the partial phase transitions in the Suizhou phosphates. Fast cooling of the thin shock veins plays a key role in the preservation of phosphates that suffered partial high-pressure phase transformation.

Reference
Xie X, Gu X, Chen M (2015) An occurrence of tuite, γ-Ca3(PO4)2, partly transformed from Ca-phosphates in the Suizhou meteorite. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12577]
Published by arrangement with John Wiley & Sons

^1,2Nicole G. Lunning, ³Kees C. Welten, ²Harry Y. McSween Jr, ⁴Marc W. Caffee,⁵Andrew W. Beck
¹Department of Mineral Sciences, Smithsonian Institution, National Museum of Natural History, Washington, District of Columbia, USA
²Department of Earth and Planetary Sciences and Planetary Geosciences Institute, University of Tennessee, Knoxville, Tennessee, USA
³Space Science Laboratory, University of California, Berkeley, California, USA
⁴Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana, USA
⁵The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA

Regolithic howardites are analogs for the surface materials of asteroid 4 Vesta, recently mapped by the Dawn spacecraft. Rigorously evaluating pairing of howardites recovered in 1995 in the Grosvenor Mountains (GRO 95), Antarctica, enables an examination of a larger, more representative regolith sample. Previous work on two of the howardites studied here concluded that GRO 95602 and GRO 95535 are solar wind-rich surface regolith samples and that they are not paired with each other, leading to uncertainty regarding pairing relationships between the other GRO 95 howardites. Based on petrology, cosmic-ray exposure history, and terrestrial age, four GRO 95 howardites are paired. The paired howardites (GRO 95534, 95535, 95574, 95581) were from a meteoroid with radius of 10–15 cm, a preatmospheric size comparable to that of Kapoeta, the largest known regolithic howardite. The paired GRO 95 howardites contain clasts of at least 18 separate HED lithologies, providing evidence they were assembled from diverse source materials. The total eucrite:diogenite mixing ratio (ratio of all eucrite lithologies to all diogenite lithologies) in the paired GRO 95 howardites is ~2:1. Petrographically determined basaltic eucrite:cumulate eucrite ratios in regolithic howardites, studied here and previously, vary more widely than total eucrite:diogenite ratios. Relative to eucritic pyroxene, plagioclase is depleted in these howardites, which provides evidence that plagioclase is preferentially comminuted in the vestan regolith. The extent of plagioclase depletion could be an indicator of regolith maturity.

Reference
Lunning NG, Welten KC, McSween Jr HY, Caffee MC, Beck AW (2015)
Grosvenor Mountains 95 howardite pairing group: Insights into the surface regolith of asteroid 4 Vesta. Meteoritics & Planetary Sciences (in Press)
Link to Article [DOI: 10.1111/maps.12580]
Published by arrangement with John Wiley & Sons

¹I. Weber, ¹A. Morlok, ¹A. Bischoff,¹H. Hiesinger1 ¹D. Ward, ²K. H. Joy, ²S. A. Crowther, ²N. D. Jastrzebski, ²J. D. Gilmour, ²P. L. Clay, ²R. A. Wogelius, ³R. C. Greenwood, ³I. A. Franchi,⁴C. Münker
¹Institut für Planetologie, Münster, Germany
²School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Manchester, UK
³Planetary and Space Sciences, The Open University, Milton Keynes, UK
⁴Institut für Geologie und Mineralogie, Universität zu Köln, Köln, Germany

This work is part of a project to build an infrared database in order to link IR data of planetary materials (and therefore possible Mercury material) with remote sensing observations of Mercury, which will probably be obtained by the MERTIS instrument on the forthcoming BepiColombo mission.
The unique achondrite Northwest Africa (NWA) 7325, which has previously been suggested to represent the first sample from Mercury, was investigated by optical and electron microscopy, and infrared and Raman spectroscopy. In addition, the oxygen, strontium, xenon, and argon isotopes were measured and the abundance of selected trace elements determined. The meteorite is a cumulate rock with subchondritic abundances of HFSE and REE and elevated Sr contents, which underwent a second heating and partial remelting process. Oxygen isotope measurements show that NWA 7325 plots in the ureilite field, close to the ALM-A trachyandesitic fragment found in the unique Almahata Sitta meteorite breccia. On the other hand, mineralogical investigations of the pyroxenes in NWA 7325 provide evidence for similarities to the lodranites and acapulcoites. Furthermore, the rock is weakly shocked and argon isotope data record ancient (~4.5 Ga) plateau ages that have not been reset. The sample records a cosmogenic exposure age of ~19 Ma. Systematics of Rb-Sr indicate an extreme early volatile depletion of the precursor material, similar to many other achondrite groups. However, despite its compositional similarities to other meteorite groups, our results suggest that this meteorite is unique and unrelated to any other known achondrite group. An origin for NWA 7325 as a sample from the planet Mercury is not supported by the results of our investigation. In particular, the evidence from infrared spectroscopy indicates that a direct relationship between NWA 7325 and the planet Mercury can be ruled out: no acceptable spectral match between laboratory analyses and remote sensing observations from Mercury has been obtained. However, we demonstrate that infrared spectroscopy is a rapid and nondestructive method to characterize mineral phases and thus an excellent tool for planetary surface characterization in space missions.

Reference
Weber I, Morlok A, Bischoff A, Hiesinger H, Ward D, Joy KH, Crowther SA, Jastrzebski ND, Gilmour JD, Clay PL, Wogelius RA, Greenwood RC, Franchi IA, Münker C (2015) Cosmochemical and spectroscopic properties of Northwest Africa 7325—A consortium study. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12586]
Published by arrangement with John Wiley & Sons

¹Ashley J. King,¹Jake R. Solomon, ¹Paul F. Schofield, ¹Sara S. Russell
¹Department of Earth Sciences, Natural History Museum

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Reference
King AJ, Solomon JR, Schofield PF, Russell SS (2015) Characterising the CI and CI-like carbonaceous chondrites using thermogravimetric analysis and infrared spectroscopy. Earth, Planets and Space 67, 198
Link to Article [DOI: 10.1186/s40623-015-0370-4]

^1,2Arya Udry, ¹Harry Y. McSween Jr., ³Richard L. Hervig,¹Lawrence A. Taylor
¹Department of Earth and Planetary Sciences, Planetary Geosciences Institute, University of Tennessee, Knoxville, Tennessee, USA
²Department of Geoscience, University of Nevada, Las Vegas, Nevada, USA
³School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, USA

Degassed magmatic water was potentially the major source of surficial water on Mars. We measured Li, B, and Be abundances and Li isotope profiles in pyroxenes, olivines, and maskelynite from four compositionally different shergottites—Shergotty, QUE 94201, LAR 06319, and Tissint—using secondary ion mass spectrometry (SIMS). All three light lithophile elements (LLE) are incompatible: Li and B are soluble in H2O-rich fluids, whereas Be is insoluble. In the analyzed shergottites, Li concentration decreases and Be concentration increases from cores to rims in pyroxenes. However, B concentrations do not vary consistently with Li and Be abundances, except in QUE 94201 pyroxenes. Additionally, abundances of these three elements in olivines show a normal igneous-fractionation trend consistent with the crystallization of olivine before magma ascent and degassing. We expect that kinetic effects would lead to fractionation of 6Li in the vapor phase compared to 7Li during degassing. The Li isotope profiles, with increasing δ7Li from cores to rims, as well as Li and B profiles indicate possible degassing of hydrous fluids only for the depleted shergottite QUE 94201, as also supported by degassing models. Conversely, Shergotty, LAR 06319, and Tissint appear to have been affected by postcrystallization diffusion, based on their LLE and Li isotope profiles, accompanied by diffusion models. This process may represent an overlay on a degassing pattern. The LLE profiles and isotope profiles in QUE 94201 support the hypothesis that degassing of some basaltic shergottite magmas provided water to the Martian surface, although evidence may be obscured by subsolidus diffusion processes.

Reference
Udry A, McSween Jr. HY, Hervig RL, Taylor LA (2015) Lithium isotopes and light lithophile element abundances in shergottites: Evidence for both magmatic degassing and subsolidus diffusion. Meteoritics & Planetary Sciences (in Press)
Link to Article [DOI: 10.1111/maps.12582]

Published by arrangement with John Wiley & Sons

¹Ohgo S, ¹Nishido H, ¹Ningawa K
¹Department of Biosphere–Geosphere Science, Okayama University of Science 2) Department of Applied Physics, Okayama University of Science

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Reference
Ohgo S, Nishido H, Ningawa K (2015) Cathodoluminescence characterization of enstatite. Journal of Mineralogical and Petrological Sciences 110, 241-246
Link to Article [http://doi.org/10.2465/jmps.150713b]

¹Robin M. Canup,^1,2Channon Visscher,¹Julien Salmon,³Bruce Fegley Jr
¹Planetary Sciences Directorate, Southwest Research Institute, Boulder, Colorado 80302, USA
²Chemistry and Planetary Sciences, Dordt College, Sioux Center, Iowa 51250, USA
³Department of Earth and Planetary Sciences and McDonnell Center for Space Sciences, Washington University, St Louis, Missouri 63130, USA

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Reference
Canup RM, Visscher C, Salmon J, Fegley Jr B (2015) Lunar volatile depletion due to incomplete accretion within an impact-generated disk. Nature Geoscience 8, 918 – 921
Link to Article [doi:10.1038/ngeo2574]

¹P. Bonnand, ²H.M. Williams, ^3,4I.J. Parkinson, ¹B.J. Wood, ¹A.N. Halliday
¹Department of Earth Sciences, University of Oxford, South Parks Road, Oxford, OX1 3AN, United Kingdom
²Department of Earth Sciences, Durham University, Sciences Labs, Durham, DH1 3LE, United Kingdom
³School of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, United Kingdom
⁴Department of Environment, Earth and Ecosystems, CEPSAR, The Open University, Walton Hall, Milton Keynes, MK7 6AA, United Kingdom

We present new mass independent and mass dependent Cr isotope compositions for meteorites measured by double spike thermal ionisation mass spectrometry. Small differences in both mass independent 53Cr and 54Cr relative to the Bulk Silicate Earth are reported and are very similar to previously published values. Carbonaceous chondrites are characterised by an excess in 54Cr compared to ordinary and enstatite chondrites which make mass independent Cr isotopes a useful tool for distinguishing between meteoritic groups. Mass dependent stable Cr isotope compositions for the same samples are also reported. Carbonaceous and ordinary chondrites are identical within uncertainty with average δ53Crδ53Cr values of −0.118±0.040‰−0.118±0.040‰ and −0.143±0.074‰−0.143±0.074‰ respectively. The heaviest isotope compositions are recorded by an enstatite chondrite and a CO carbonaceous chondrite, both of which have relatively reduced chemical compositions implying some stable Cr isotope fractionation related to redox processes in the circumstellar disk. The average δ53Crδ53Cr values for chondrites are within error of the estimate for the Bulk Silicate Earth (BSE) also determined by double spiking. The lack of isotopic difference between chondritic material and the BSE provides evidence that Cr isotopes were not fractionated during core formation on Earth. A series of high-pressure experiments was also carried out to investigate stable Cr isotope fractionation between metal and silicate and no demonstrable fractionation was observed, consistent with our meteorites data. Mass dependent Cr isotope data for achondrites suggest that Cr isotopes are fractionated during magmatic differentiation and therefore further work is required to constrain the Cr isotopic compositions of the mantles of Vesta and Mars.

Reference
Bonnand P,Williams HM, Parkinson IJ,Wood BJ,Halliday AN (2016) Stable chromium isotopic composition of meteorites and metal–silicate experiments: Implications for fractionation during core formation. Earth and Planetary Science Letters 435, 14–21
Link to Article [doi:10.1016/j.epsl.2015.11.026]
Copyright Elsevier

¹M. C. De Sanctis et al. (>10)*
¹Istituto di Astrofisica e Planetologia Spaziali, INAF, Via del Fosso del Cavaliere 100, 00133 Roma, Italy
*Find the extensive, full author and affiliation list on the publishers website

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Reference
De Sanctis MC et al. (2015) Ammoniated phyllosilicates with a likely outer Solar System origin on (1) Ceres. Nature 528, 241–244
Link to Article [doi:10.1038/nature16172]