¹Matthew Markley, ^1,2,3Gunther Kletetschka
¹Charles University in Prague, Faculty of Science, Albertov 6, 128 00 Prague, Czech Republic
²Academy of Sciences of the Czech Republic, Institute of Geology, Prague, Czech Republic
³Lawrence Berkeley National Laboratory, Berkeley, CA, USA

Airless bodies are constantly exposed to space weathering. The Moon and other similar S-type asteroids physically change through comminution, melting, and agglutinate formation, while spectrally they are darkening, steepening (or reddening) the spectral slope towards longer wavelengths, and reducing silicate mineral absorption bands. In these S-type bodies the production of submicroscopic metallic iron, or nanophase iron (SMFe, npFe0) is a major contributor in these spectral changes. We made a qualitative estimate of both quantity and size distribution of produced metallic iron by space weathered analog, olivine irradiated by laser. Through SEM observation we confirmed that nanoparticles of metallic iron formed in the nm range. Spectroscopic and magnetic susceptibility (MS) through temperature analyses reveal an increasing trend of npFe0 formation, darkening, reddening, and shallowing of the 1 μm olivine absorption band. Olivine that produced the larger end of the size range of npFe0 produced similar effects, except for increased reddening. The magnetic data suggests that with laser irradiation there is both a linear increase of nanoparticles and a logarithmic increase in spectral change with SW time.

Reference
Markley M, Kletetschka G (2015) Nanophase Iron Production through Laser Irradiation and Magnetic Detection of Space Weathering Analogs. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.12.022]
Copyright Elsevier

^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