¹A. Frigeri et al. (>10)*
¹Istituto Nazionale di Astrofisica (INAF), Istituto di Astrofisica e Planetologia Spaziali (IAPS), Via Fosso del Cavaliere 100, Rome, Italy
We currently do not have a copyright agreement with this publisher and cannot display the abstract here

In this manuscript we present the mineralogic mapping of the Av-9 Numisia quadrangle of Vesta using the most up-to-date data from the NASA–Dawn mission.

This quadrangle is located in Vesta’s equatorial zone (22°° south to 22°° north, 218°° to 288°° east, in Claudia coordinate system) and takes its name from the impact crater Numisia. The main feature, which dominates the quadrangle, is the Vestalia Terra plateau, a topographic high about 10 km above the surrounding areas. To the south, this region fades into the Rheasilvia basin, while to the north it is bounded by the steep scarp of Postumia basin.

The Visible and Infrared mapping spectrometer (VIR) onboard NASA/Dawn provided the main data source for this work, at an unprecedented level of spatial and spectral resolution. In particular we are using spectral parameters to synthesize characteristics of the whole spectra into a single value. Pyroxene-related spectral parameters allow for the detection of lower crust or mantle material (diogenites) and upper crust material (eucrites) in the study area.

The combined analysis of albedo from the Framing Camera, the geologic map and the spectroscopic data offer an interesting opportunity to understand better the surface features of this region of Vesta, and their Evolution. Numisia, Cornelia, Fabia, Teia and Drusilla are the main craters in the study area, rich in bright and dark material outcrops, pitted terrains and OH-rich materials.

Using the spectral parameters we demonstrate that the internal composition of Vestalia Terra is mainly diogenite-rich howardite, as shown by materials excavated by Cornelia and Fabia, and the composition of the slope north of Vestalia Terra. This agrees with the strong positive Bouguer Anomaly observed in the area, indicating a higher density of these features in relation to the surrounding Areas. Besides the recently published works based on gravimetric modelling and geologic interpretation, the mineralogic mapping presented herein gives an additional contribution, in order to depict a more complete geologic history of the Numisia quadrangle of Vesta.

Reference
Frigeri A et al. (2015) Mineralogic Mapping of the Av-9 Numisia quadrangle of Vesta. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.07.029]
Copyright Elsevier

^1,2Laura Flagg,²Alycia J. Weinberger,³Keith Matthews
¹Department of Physics and Astronomy, Northern Arizona University, Flagstaff, AZ 86011-6010, USA
²Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington, DC 20015, USA
³Caltech Optical Observatories, California Institute of Technology, MC 301-17, Pasadena, CA 91125, USA

The detectability of planetesimal impacts on imaged exoplanets can be measured using Jupiter during the 1994 comet Shoemaker-Levy 9 events as a proxy. By integrating the whole planet flux with and without impact spots, the effect of the impacts at wavelengths from 2 – 4 μμm is revealed. Jupiter’s reflected light spectrum in the near-infrared is dominated by its methane opacity including a deep band at 2.3 μμm. After the impact, sunlight that would have normally been absorbed by the large amount of methane in Jupiter’s atmosphere was instead reflected by the cometary material from the impacts. As a result, at 2.3 μμm, where the planet would normally have low reflectivity, it brightened substantially and stayed brighter for at least a month.

Reference
Flagg L, Weinberger AJ, Matthews K (2015) Detectability of Planetesimal Impacts on Giant Exoplanets. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.08.024]
Copyright Elsevier

^1,2Marina A. Ivanova, ¹Cyril A. Lorenz, ³Alexander N. Krot,²Glenn J. MacPherson
¹Vernadsky Institute of Geochemistry and Analytical Chemistry of Russian Academy of Sciences, Moscow, Russia
²National Museum of Natural History, Smithsonian Institution, Washington, District of Columbia, USA
³Hawaiʻi Institute of Geophysics and Planetology, University of Hawaiʻi at Mānoa, Honolulu, Hawaiʻi, USA

A calcium-aluminum-rich inclusion 3N from the Northwest Africa (NWA) 3118 CV3 carbonaceous chondrite is a unique cm-sized compound object, primarily a forsterite-bearing type B (FoB) CAI, that encloses at least 26 smaller CAIs of different types, including compact type A (CTA), B, C, and an ultra-refractory inclusion. Relative to typical type A and B CAIs found elsewhere, the bulk compositions of the types A and B CAIs within 3N more closely match the bulk compositions predicted by equilibrium condensation of a gas of solar composition. Being trapped within the FoB melt may have protected them from melt evaporation that affected most “stand-alone” CAIs. 3N originated either as an aggregate of many smaller (mostly types A, B, C) CAIs plus accreted Fo-bearing material (like an amoeboid olivine aggregate) which experienced partial melting of the whole, or else as a FoB melt droplet that collided with and trapped many smaller solid CAIs. In the former case, 3N recorded the earliest accretion of pebble-sized bodies known. In the latter case, the presence of a large number of individual refractory inclusions within 3N suggests a very high local density of refractory solids in the immediate region of the host CAI during the brief time while it was melted. Collisions would have occurred on time scales of hours at most, assuming a melt solidification interval for the host CAI of 300–400 °C (maximum) and a cooling rate of ~10 °C/h.

Reference
Ivanov MA, Lorenz CA, Krot AN, MacPherson GJ (2015) A compound Ca-, Al-rich inclusion from CV3 chondrite Northwest Africa 3118: Implications for understanding processes during CAI Formation. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12489]
Published by Arrangement with John Wiley&Sons

¹A. D. Beard, ^1,2H. Downes,³M. Chaussidon
¹Department of Earth and Planetary Sciences, UCL/Birkbeck Centre for Planetary Sciences, Birkbeck, London, UK
²Department of Earth Sciences, Natural History Museum, London, UK
³Institute of Physics of the Globe, Paris, France

EET 87720 is a polymict ureilite breccia known to contain numerous nonindigenous fragments. We have discovered a microgranitic clast in an interior chip of Elephant Moraine (EET) 87720. The clast consists of a granophyre-like intergrowth of a pure SiO2 phase (tridymite) and albite, mantling a zoned oligoclase phenocryst. In the intergrowth, the tridymite occurs as thin elongate vermicular blebs within larger albite crystals. The granophyre-like intergrowth and the oligoclase phenocryst share a common margin, suggesting that the clast was originally part of a larger fragment. An estimate of its bulk composition is equivalent to that of granite (77 wt% SiO2). Patches of high-Si K-bearing glass occur interstitially within the clast; they have high concentrations of SO3 (11–12 wt%) and contain Cl (0.6 wt%), suggesting that the clast formed on a volatile-rich parent body perhaps resembling early Mars. The mean oxygen isotope composition of the feldspar and tridymite in the clast is very different from the oxygen isotope compositions of ureilites, and is similar to those of silicate inclusions in IIE and IVA irons. Thus, the clast is not indigenous to the ureilite parent body, but it provides evidence for the formation of evolved melts on an unknown parent body in the early solar system.

Reference
Beard AD, Downes, H, Chaussidon M (2015) Petrology of a nonindigenous microgranitic clast in polymict ureilite EET 87720: Evidence for formation of evolved melt on an unknown parent Body. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12484]

Published by arrangement with John Wiley&Sons

¹Lydia Bonal et al. (>10)*
¹Institut de Planétologie et d’Astrophysique de Grenoble, CNRS/UJF Grenoble 1, Grenoble, France
*Find the extensive, full author and affiliation list on the publishers website

Hayabusa-returned samples offer a unique perspective for understanding the link between asteroids and cosmomaterials available in the laboratory, and provide insights on the early stages of surface space weathering. This study characterizes the mineralogy and the extent of space weathering of the three Itokawa particles RA-QD02-0163, RA-QD02-0174, and RA-QD02-0213 provided by JAXA to our consortium. We report here a series of results based on nondestructive analyses through visible-near-infrared reflectance and Raman spectroscopy. Results were obtained on the raw particles, both in their original containers and deposited on diamond windows. Identification of the minerals, characterization of their elemental compositions, and measurements of their relative abundances were led through Raman spectroscopy in punctual and automatic mode. Reflectance spectra in the visible and near-IR wavelengths constrain the mineralogy of the grains and allow direct comparison with the surface of Itokawa. The spectra reflect the extent of space weathering experienced by the three particles. Particle RA-QD02-0163 consists of a heterogeneous mixture of minerals: olivine (Fo76) dominates an assemblage with both Ca-rich (En50, Wo50) and Ca-poor (En85) pyroxenes. The elemental compositions of the silicates are consistent with those previously reported for distinct Hayabusa particles. Particles RA-QD-0174 and RA-QD02-0213 are solely composed of olivine, whose chemical composition is similar to that observed in RA-QD02-0163. It has been previously shown that the S-type asteroid 25143 Itokawa is a breccia of poorly equilibrated LL4 and highly equilibrated LL5 and LL6 materials. The three particles studied here can be related to the least metamorphosed lithology (LL4) based on the high forsterite content of the olivine. Neither carbonaceous matter nor hydrated minerals were detected through Raman on the three allocated particles. The NIR-VIS reflectance (incidence = 45°, light collection at e = 0°) spectra of the three particles, in particular the 1 μm band, are consistent with the presence of both olivine and pyroxene detected via Raman. The spectra of particles RA-QD02-0163 and RA-QD02-0213 are also fully compatible with the ground-based observations of asteroid (25143) Itokawa in terms of both spectral features and slope. By contrast, particle RA-QD02-0174 has a similar 1 μm band depth but higher (redder) spectral slope than the surface of Itokawa. This probably reveals a variable extent of space weathering among the regolith particles. RA-QD02-0174 may contain a higher amount of nanophase metallic iron and nanophase FeS. Such phases are products by space weathering induced by solar wind, previously detected on other Itokawa particles

Reference
Bonal L. et al. (2015) Visible-IR and Raman microspectroscopic investigation of three Itokawa particles collected by Hayabusa: Mineralogy and degree of space weathering based on nondestructive analyses. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12496]
Published by arrangement with John Wiley&Sons

¹Catherine M. Corrigan, ^1,2Michael A. Velbel, ³Edward P. Vicenzi
¹Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, District of Columbia, USA
²Department of Geological Sciences, Michigan State University, East Lansing, Michigan, USA
³Museum Conservation Institute, Smithsonian Institution, Suitland, Maryland, USA

Nakhlites, clinopyroxenite meteorites from Mars, share common crystallization and ejection ages, suggesting that they might have been ejected from the same place on Mars by the same ejection event (impact) and are different samples of the same thick volcanic flow unit or shallow sill. Mean modal abundances and abundance ranges of pyroxene, olivine, and mesostasis vary widely among different thin-sections of an individual nakhlite. Lithologic heterogeneity is the main factor contributing to the observed modal-abundance variations measured in thin-sections prepared from different fragments of the same stone. Two groups of nakhlites are distinguished from one another by which major constituent varies the least and the abundance of that constituent. The group consisting of Nakhla, Lafayette, Governador Valadares, and the Yamato nakhlite pairing group is characterized by low modal mesostasis and pyroxene-olivine covariance, whereas the group consisting of the Miller Range nakhlite pairing group and Northwest Africa 5790 is characterized by low modal olivine and pyroxene-mesostasis covariance. These two groups sample the slowest-cooled interior portion and the chilled margin, respectively, of the nakhlite emplacement body as presently understood, and appear to be also related to recently proposed nakhlite groups independently established using compositional rather than petrographic observations. Phenocryst modal abundances vary with inferred depth in the nakhlite igneous body in a manner consistent with solidification of the nakhlite stack from dynamically sorted phenocryst-rich magmatic crystal-liquid mush.

Reference
Corrigan CM, Velbel MA, Vicenzi EP (2015) Modal abundances of pyroxene, olivine, and mesostasis in nakhlites: Heterogeneity, variation, and implications for nakhlite Emplacement. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12492]
Published by arrangement with John Wiley&Sons

²Annemarie E. Pickersgill, ^1,2Gordon R. Osinski,¹Roberta L. Flemming
¹Department of Earth Sciences and Centre for Planetary Science and Exploration, University of Western Ontario, London, Ontario, Canada
²Department of Physics and Astronomy, The University of Western Ontario, London, Ontario, Canada

Shock metamorphism, caused by hypervelocity impact, is a poorly understood process in feldspar due to the complexity of the crystal structure, the relative ease of weathering, and chemical variations, making optical studies of shocked feldspars challenging. Understanding shock metamorphism in feldspars, and plagioclase in particular, is vital for understanding the history of Earth’s moon, Mars, and many other planetary bodies. We present here a comprehensive study of shock effects in andesine and labradorite from the Mistastin Lake impact structure, Labrador, Canada. Samples from a range of different settings were studied, from in situ central uplift materials to clasts from various breccias and impact melt rocks. Evidence of shock metamorphism includes undulose extinction, offset twins, kinked twins, alternate twin deformation, and partial to complete transformation to diaplectic plagioclase glass. In some cases, isotropization of alternating twin lamellae was observed. Planar deformation features (PDFs) are notably absent in the plagioclase, even when present in neighboring quartz grains. It is notable that various microlites, twin planes, and compositionally different lamellae could easily be mistaken for PDFs and so care must be taken. A pseudomorphous zeolite phase (levyne-Ca) was identified as a replacement mineral of diaplectic feldspar glass in some samples, which could, in some instances, also be potentially mistaken for PDFs. We suggest that the lack of PDFs in plagioclase could be due to a combination of structural controls relating to the crystal structure of different feldspars and/or the presence of existing planes of weakness in the form of twin and cleavage planes.

Reference
Pickersgill AE, Osinski GR, Flemming RL (2015) Shock effects in plagioclase feldspar from the Mistastin Lake impact structure, Canada. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12495]
Published by arrangement with John Wiley&Sons

^1,2Francis M. McCubbin et al. (>10)* 
¹Institute of Meteoritics, University of New Mexico, 200 Yale Boulevard SE, Albuquerque, New Mexico 87131, U.S.A.
²Department of Earth and Planetary Sciences, University of New Mexico, 200 Yale Boulevard SE, Albuquerque, New Mexico 87131, U.S.A.
*Find the extensive, full author and affiliation list on the publishers website

Apatite-melt partitioning experiments were conducted in a piston-cylinder press at 1.0–1.2 GPa and 950–1000 °C using an Fe-rich basaltic starting composition and an oxygen fugacity within the range of ΔIW-1 to ΔIW+2. Each experiment had a unique F:Cl:OH ratio to assess the partitioning as a function of the volatile content of apatite and melt. The quenched melt and apatite were analyzed by electron probe microanalysis and secondary ion mass spectrometry techniques. The mineral-melt partition coefficients (D values) determined in this study are as follows: DFAp-Melt = 4.4–19, DClAp-Melt = 1.1–5, DOHAp-Melt = 0.07–0.24. This large range in values indicates that a linear relationship does not exist between the concentrations of F, Cl, or OH in apatite and F, Cl, or OH in melt, respectively. This non-Nernstian behavior is a direct consequence of F, Cl, and OH being essential structural constituents in apatite and minor to trace components in the melt. Therefore mineral-melt D values for F, Cl, and OH in apatite should not be used to directly determine the volatile abundances of coexisting silicate melts. However, the apatite-melt D values for F, Cl, and OH are necessarily interdependent given that F, Cl, and OH all mix on the same crystallographic site in apatite. Consequently, we examined the ratio of D values (exchange coefficients) for each volatile pair (OH-F, Cl-F, and OH-Cl) and observed that they display much less variability: KdCl-FAp-Melt = 0.21 ± 0.03, KdOH-FAp-Melt= 0.014 ± 0.002, and KdOH-ClAp-Melt= 0.06 ± 0.02. However, variations with apatite composition, specifically when mole fractions of F in the apatite X-site were low (XF < 0.18), were observed and warrant additional study. To implement the exchange coefficient to determine the H2O content of a silicate melt at the time of apatite crystallization (apatite-based melt hygrometry), the H2O abundance of the apatite, an apatite-melt exchange Kd that includes OH (either OH-F or OH-Cl), and the abundance of F or Cl in the apatite and F or Cl in the melt at the time of apatite crystallization are needed (F if using the OH-F Kd and Cl if using the OH-Cl Kd). To determine the H2O content of the parental melt, the F or Cl abundance of the parental melt is needed in place of the F or Cl abundance of the melt at the time of apatite crystallization. Importantly, however, exchange coefficients may vary as a function of temperature, pressure, melt composition, apatite composition, and/or oxygen fugacity, so the combined effects of these parameters must be investigated further before exchange coefficients are applied broadly to determine volatile abundances of coexisting melt from apatite volatile abundances.

Reference
McCubbin FM et al. (2015) Experimental investigation of F, Cl, and OH partitioning between apatite and Fe-rich basaltic melt at 1.0–1.2 GPa and 950–1000 °C. American Mineralogist 100, 1790-1802
Link to Article [doi:10.2138/am-2015-5233]
Copyright: The Mineralogical Society of America

¹Gokce Ustunisik´, ¹Hanna Nekvasil,¹Donald H. Lindsley,²Francis M. McCubbin
¹Department of Geosciences, Stony Brook University, Stony Brook, New York 11794-2100, U.S.A.
²Institute of Meteoritics, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, U.S.A.

Experimental degassing of H-, F-, Cl-, C-, and S-bearing species from volatile-bearing magma of lunar composition at low pressure and fO2 close to the quartz-iron-fayalite buffer (QIF) indicates that the composition of the fluid/vapor phase that is lost changes over time. A highly H-rich vapor phase is exsolved within the first 10 min of degassing leaving behind a melt that is effectively dehydrated. Some Cl, F, and S is also lost during this time, presumably as HCl, HF, and H2S gaseous species; however much of the original inventory of Cl, F, and S components are retained in the melt. After 10 min, the exsolved vapor is dry and dominated by S- and halogen-bearing phases, presumably consisting of metal halides and sulfides, which evolves over time toward F enrichment. This vapor evolution provides important constraints on the geochemistry of volatile-bearing lunar phases that form subsequent to or during degassing. The rapidity of H loss suggests that little if any OH-bearing apatite will crystallize from surface or near surface (~7m) melts and that degassing of lunar magmas will cause the compositions of apatites to evolve first toward the F-Cl apatite binary and eventually toward end-member fluorapatite during crystallization. During the stage of loss of primarily H component from the melt, Cl would have been lost primarily as HCl, which is reported not to fractionate Cl isotopes at magmatic temperatures (Sharp et al. 2010). After the loss of H-bearing species, continued loss of Cl would result in the degassing of metal chlorides, which have been proposed as a mechanism to fractionate Cl isotopes (Sharp et al. 2010). After the onset of metal chloride degassing, the δ37Cl of the melt would necessarily increase to +6 (82% Cl loss), +8 (85% Cl loss), and +20‰ (95% Cl loss) at 1, 4, and 6 h, respectively, which was approximated using a computed trajectory of δ37Cl values in basalt during degassing of FeCl2. This strong enrichment of 37Cl in the melt after metal chloride volatilization is fully consistent with values measured for the non-leachates of a variety of lunar samples and would be reflected in apatites crystallized from a degassing melt. Our results suggest that a range in δ37Cl from 0 to >20‰ is expected in lunar apatite, with heavy enrichment being the norm. While 95% loss in the initial Cl content of the melt (280 ppm Cl left in the melt) would cause an increase to +20‰ in δ37Cl, the ability to measure this increase in a lunar sample is ultimately dependent upon the starting Cl abundances and whether or not a mechanism exists to concentrate the remaining Cl such that it can be subsequently analyzed with sufficient accuracy. Therefore, the higher the starting Cl abundances in the initial melts, the heavier δ37Cl values that can be measurably preserved. Importantly, such enrichments can occur in spite of high initial hydrogen contents, and therefore, our experiments demonstrate that elevated values of δ37Cl cannot be used as supporting evidence for an anhydrous Moon. Furthermore, if the H-bearing vapor has a significant H2 component, this process should also result in strong enrichment of δD in the residual magmas that reach the lunar surface or near-surface environment. Apatites within some mare basalts exhibit elevated δD of 1000 ‰ depending on the initial value (Tartese and Anand 2013) in addition to the δ37Cl values, but elevated δ37Cl values are accompanied by only modest enrichments in δD in apatites from samples of the highlands crust (McCubbin et al. 2015a).

Reference
Ustunisik G, Nekvasil H, Lindsley DH, McCubbin FM (2015) Degassing pathways of Cl-, F-, H-, and S-bearing magmas near the lunar surface: Implications for the composition and Cl isotopic values of lunar Apatite. American Mineralogist 100, 1717-1727. Link to Article [doi:10.2138/am-2015-4883]

Copyright: The American Mineralogical Society 

¹Sarah T. Crites, ¹Paul G. Lucey, ¹G. Jeffrey Taylor
¹Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Mānoa, 1680 East West Road Post 602, Honolulu, Hawaii 96822, U.S.A.

Most models of early lunar evolution predict that the anorthositic highlands crust is the result of plagioclase flotation on a magma ocean. However, the lunar highlands crust typically contains 4 wt% FeO and so is more mafic than the strict definition of the anorthosites thought to comprise it. We used new Clementine-based mineral maps of the Moon as inputs to a series of mixing models that calculate the abundance and distribution of major highland rock types and shed light on three possible sources of excess mafic material in the lunar highlands: mafic (15 vol% mafic minerals) anorthosites, post-magma ocean igneous activity, and mafic basin ejecta. Mixing models that feature pure anorthosites like the purest anorthosite (PAN) described by Ohtake et al. (2009) and Pieters et al. (2009) are most compatible with the data. They allow us to place an upper limit of 10–20 vol% mantle material that could be mixed with the primary highlands crust. The upper limit on mantle material indicated by the mixing models is significantly lower than the 30–40 vol% mantle material expected from simple geometric calculations of the major lunar basins’ excavation cavities based on an excavation cavity depth/diameter ratio of 1/10; this discrepancy allows us to conclude that the excavation cavities of the three largest lunar basins may have been significantly shallower than those of the smaller basins. Our results are consistent with excavation cavity depth/diameter ratios for these largest basins in the range of 0.035 to 0.06, which agrees with previous gravity measurements by Wieczorek and Phillips (1999).

Reference
Crites ST, Lucey PG, Taylor GJ (2015) The mafic component of the lunar crust: Constraints on the crustal abundance of mantle and intrusive rock, and the mineralogy of lunar anorthosites. American Mineralogist 100, 1708-1716
Link to Article [doi: 10.2138/am-2015-4872]

Copyright: The Mineralogical Society of America