¹N.Mangold et al. (>10)*
¹Laboratoire de Planétologie et Géodynamique de Nantes, CNRS, UMR6112, Université de Nantes, Nantes, France
*Find the extensive, full author and affiliation list on the publishers website

The Curiosity rover has analyzed various detrital sedimentary rocks at Gale crater, among which fluvial and lacustrine rocks are predominant [Grotzinger et al., 2014, 2015]. Conglomerates correspond both to the coarsest sediments analyzed and the least modified by chemical alteration, enabling us to link their chemistry to that of source rocks on the Gale crater rims. In this study, we report the results of 6 conglomerate targets analyzed by APXS and 40 analyzed by ChemCam. The bulk chemistry derived by both instruments suggests two distinct end-members for the conglomerate compositions. The first group (Darwin type) is typical of conglomerates analyzed before sol 540; it has a felsic alkali-rich composition, with a Na2O/K2O > 5. The second group (Kimberley type) is typical of conglomerates analyzed between sol 540 and 670 in the vicinity of the Kimberley waypoint; it has an alkali-rich potassic composition with Na2O/K2O < 2. The variety of chemistry and igneous textures (when identifiable) of individual clasts suggest that each conglomerate type is a mixture of multiple source rocks. Conglomerate compositions are in agreement with most of the felsic alkali-rich float rock compositions analyzed in the hummocky plains (as reported in Sautter et al., 2015). The average composition of conglomerates can be taken as a proxy of the average igneous crust composition at Gale crater. Differences between the composition of conglomerates and that of finer-grained detrital sediments analyzed by the rover suggest modifications by diagenetic processes (especially for Mg-enrichments in fine grained rocks), physical sorting and mixing with finer-grained material of different composition.

Reference
Mangold N et al. (2016) Composition of conglomerates analyzed by the Curiosity rover: Implications for Gale crater crust and sediment sources. Journal of Geophysical Research, Planets (in Press)
Link to Article [DOI: 10.1002/2015JE004977]
Published by arrangement with John Wiley & Sons

¹J. Lasue et al. (>10)*
¹IRAP, OMP, CNRS, Toulouse, France
*Find the extensive, full author and affiliation list on the publishers Website

Zinc-enriched targets have been detected at the Kimberley formation, Gale crater, Mars, using the Chemistry Camera (ChemCam) instrument. The Zn content is analyzed with a univariate calibration based on the 481.2 nm emission line. The limit of quantification for ZnO is 3 wt.% (at 95% confidence level) and 1 wt.% (at 68% confidence level). The limit of detection is shown to be around 0.5 wt.%. As of sol 950, 12 targets on Mars present high ZnO content ranging from 1.0 wt.% to 8.4 wt.% (Yarrada, sol 628). Those Zn-enriched targets are almost entirely located at the Dillinger member of the Kimberley formation, where high Mn and alkali contents were also detected, probably in different phases. Zn enrichment does not depend on the textures of the rocks (coarse-grained sandstones, pebbly conglomerates, resistant fins). The lack of sulfur enhancement suggests that Zn is not present in the sphalerite phase. Zn appears somewhat correlated with Na2O and the ChemCam hydration index, suggesting that it could be in an amorphous clay phase (such as sauconite). On Earth, such an enrichment would be consistent with a supergene alteration of a sphalerite gossan cap in a primary siliciclastic bedrock or a possible hypogene non-sulfide zinc deposition where Zn, Fe, Mn, would have been transported in a reduced sulfur-poor fluid and precipitated rapidly in the form of oxides.

Reference
Lasue J et al. (2016) Observation of >5 wt % zinc at the Kimberley outcrop, Gale crater, Mars. Journal of Geophysical Research, Planets (in Press)
Link to Article [DOI: 10.1002/2015JE004946]
Published by arrangement with John Wiley & Sons

^1,2Erin L. Walton, ³Thomas G. Sharp, ³Jinping Hu
¹MacEwan University, Department of Physical Sciences, Edmonton, AB, T5J 4S2, Canada
²University of Alberta, Department of Earth & Atmospheric Sciences, Edmonton, AB, T6G 2E3, Canada
³Arizona State University, School of Earth & Space Exploration, Tempe, AZ, 85287-1404, USA

Shock-produced melt within crystalline basement rocks of the Steen River impact structure (SRIS) are observed as thin (1 – 510 μm wide), interlocking networks of dark veins which cut across and displace host rock minerals. Solid-state phase transformations, such as ferro-pargasite to an almandine-andradite-majorite garnet and amorphization of quartz and feldspar, are observed in zones adjacent to comparatively wider (50─500 μm) sections of the shock veins. Shock pressure estimates based on the coupled substitution of Na+, Ti4+ and Si4+ for divalent cations, Al3+ and Cr3+ in garnet (14─19 GPa) and the pressure required for plagioclase (Ab62-83) amorphization at elevated temperature (14−20 GPa) are not appreciably different from those recorded by deformation effects observed in non-veined regions of the bulk rock (14─20 GPa). This spatial distribution is the result of an elevated temperature gradient experienced by host rock minerals in contact with larger volumes of impact-generated melt and large deviatoric stresses experienced by minerals along vein margins.
Micrometer-size equant crystals of almandine-pyrope-majorite garnet define the shock vein matrix, consistent with rapid quench (100─200 ms) at 7.5─10 GPa. Crystallization of the vein occurred during a 0.1─0.15 s shock pressure pulse. Majoritic garnet, formed during shock compression by solid state transformation of pargasite along shock vein margins, is observed in TEM bright field images as nanometer-size gouge particles produced at strain rates in the supersonic field (106─108). These crystals are embedded in vesiculated glass, and this texture is interpreted as continued movement and heating along slip planes during pressure release. The deformation of high-pressure minerals formed during shock compression may be the first evidence of oscillatory slip in natural shock veins, which accounts for the production of friction melt via shear when little or no appreciable displacement is observed. Our observations of the mineralogy, chemistry and microtextures of shock veins within crystalline rocks of the SRIS allow us to propose a model for shock vein formation by shear-induced friction melting during shock compression.

Reference
Walton EL, Sharp TG, Hu J (2016) Frictional melting processes and the generation of shock veins in terrestrial impact structures: evidence from the Steen River impact structure, Alberta, Canada. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.02.024]
Copyright Elsevier

¹Timothy D. Glotch, ²Joshua L. Bandfield, ¹Michael J. Wolff, ³Jessica A. Arnold, ¹Congcong Che
¹Department of Geological Sciences, Stony Brook University, Stony Brook, NY
²Space Science Institute
³University of Oxford, Oxford, UK

Chloride salt-bearing deposits on Mars were discovered using the Mars Odyssey Thermal Emission Imaging System (THEMIS) and have been characterized by both mid-infrared (MIR) and visible-to-near-infrared (VNIR) remote sensing instruments. The chloride salt-bearing deposits exhibit a blue slope at MIR wavelengths and a featureless red slope at VNIR wavelengths. These deposits also lack strong 3 µm bands in VNIR spectra, indicating that they are desiccated compared to the surrounding regolith. The lack of VNIR spectral features suggest that an anhydrous chloride salt, the most likely of which is halite, is responsible for the observed spectral slope.
In this work, we use laboratory spectra and a hybrid T-matrix/Hapke light scattering model to constrain the particle sizes and salt abundances of the Martian chloride salt-bearing deposits. Our work shows that the two broad spectral classes of these deposits observed by THEMIS can be explained by a difference in the particle size of the admixed silicate regolith. In all cases, chloride salt abundances of 10-25% are required to match the THEMIS data. The chloride salt abundances determined in this work suggest deposition in a lacustrine/playa setting or in association with late-stage groundwater upwelling.

Reference
Glotch TD, Bandfield JL, Wolff MJ, Arnold JA, Che C (2016) Constraints on the composition and particle size of chloride salt‐bearing deposits on Mars. Journal of Geophysical Research, Planets (in Press)
Link to Article [DOI: 10.1002/2015JE004921]
Published by arrangement with John Wiley & Sons

¹Mehmet Yesiltas, ²Yoko Kebukawa
¹Department of Geosciences, Stony Brook University, Stony Brook, New York, USA
²Faculty of Engineering, Yokohama National University, Yokohama, Japan

We have investigated spatial and spectral associations between mineral species and organic matter in the Tagish Lake meteorite. Synchrotron-based infrared microspectroscopy allowed us to spatially locate specific organic and inorganic compounds within multiple Tagish Lake grains with high spatial resolution. Generated two-dimensional infrared maps present strong spatial association between aliphatic C-H and OH in phyllosilicates in Tagish Lake grains. These observations indicate possible roles of phyllosilicates for the formation, evolution, and preservation of organic matter. Infared spectra of all studied Tagish Lake grains show a strong carbonate band, which also shows a weak but positive correlation with organic matter in some grains. However, intergrain correlation was not observed between carbonates and organics, which is likely due to the difference of carbonate occurrence, e.g., presence of larger grains or intergrowth of carbonates on phyllosilicates. Possible scenarios further explaining the observed associations of organics with phyllosilicates and carbonates are presented.

Reference
Yesiltas M, Kebukawa Y (2016) Associations of organic matter with minerals in Tagish Lake meteorite via high spatial resolution synchrotron-based FTIR microspectroscopy. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12609]
Published by arrangement with John Wiley & Sons

¹Estelle Déau, ¹Linda J. Spilker, ²Alberto Flandes
¹NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena 91109 CA United States
²Ciencias Espaciales, Instituto de Geofísica, Universidad Nacional Autónoma de México, México, D.F., C.P. 04510, México

We investigate connections between the opposition phase curves and the spectra from ultraviolet to near infrared wavelengths of stony meteorites. We use two datasets: the reflectance dataset of Capaccioni et al., 1990 (Icarus, 83, 325), which consists of optical phase curves (from 2 to 45°) of 17 stony meteorites (3 carbonaceous chondrites, 11 ordinary chondrites, and 3 achondrites), and the spectral dataset from the RELAB database consisting of near-ultraviolet to near-infrared spectra of the same meteorites. We re-analyzed the first dataset and fit it with two morphological models to derive the amplitude A, the angular width HWHM of the surge and the slope S of the linear part. Our re-analysis confirms that stony meteorites have a non-monotonic behavior of the surge amplitude with albedo, which is also observed in planetary surfaces (Déau et al. 2013, Icarus, 226, 1465), laboratory samples (Nelson et al., 2004, Proc. Lunar Sci. Conf. 35, p. 1089) and asteroids (Belskaya and Shevchenko, 2000, Icarus, 147, 94). We find a very strong correlation between the opposition effect morphological parameters and the slope of the spectra between 0.75 μm and 0.95 μm. In particular, we found that meteorites with a positive amplitude-albedo correlation have a positive spectral slope between 0.75 μm and 0.95 μm, while meteorites with a negative amplitude-albedo correlation have a negative spectral slope between 0.75 μm and 0.95 μm. We have ruled out the role of the meteorite samples’ macro-properties (grain size, porosity and macroscopic roughness) in the correlations found because these properties were constant during the preparation of the samples. If this hypothesis is correct, this implies that other properties like the composition or the micro-properties (grain inclusions, grain shape or microscopic roughness) could have a preponderant role in the non-monotonic behavior of the surge morphology with albedo at small and moderate phase angles. Further accurate characterization of carbonaceous chrondrites samples are necessary to draw conclusions about the role of the micro-properties.

Reference
Déau E, Spilker LJ, Flandes A (2016) Re-analysis of previous laboratory phase curves: 2. Connections between opposition effect morphology and spectral features of stony meteorites. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.01.035]
Copyright Elsevier

¹Jaesub Hong, ²Suzanne Romaine and The MiXO team
¹Harvard University, 60 Garden Street, Cambridge 02138, MA, USA
²Smithsonian Astrophysics Observatory, 60 Garden Street, Cambridge 02138, MA, USA

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

Reference
HongJ, Romaine S and The MiXO team (2016) Miniature lightweight X-ray optics (MiXO) for surface elemental composition mapping of asteroids and comets. Earth, Planets and Space 68:35
Link to Article [doi:10.1186/s40623-016-0409-1]

¹Serventi Giovanna, ²Carli Cristian, ¹Sgavetti Mariaamaria
¹Department of Physics and Earth Sciences, University of Parma, Italy
²IAPS-Inaf, Tor Vergata, Roma, Italy

Anorthositic rocks are widespread on the lunar surface and have probably been formed by flotation of PL over a magma ocean. A large portion of pristine rocks are characterized by a low Mg/(Mg+Fe) ratio, and have been classified as ferroan anorthosite, and recently, after observation from SELENE Spectral Profiler,pure anorthosites regions with more than 98% PL have been recognized.
In this paper we analyze a set of mixtures with PL content similar to the ferroan anorthosites and to the pure anorthosite regions, using the Origin Software and the Modified Gaussian Model.We consider three plagioclases with varying FeOwt% contents (PL1, PL2 and PL3)andthree mafic end-members (1)100% orthopyroxene, (2) 56% orthopyroxene and 44% clinopyroxene, and (3) 100% olivine (OL). The spectral parameters considered here are: band depth, band center, band width, c0 (the continuum intercept) and c1 (the continuum offset).
Here we have shown that in pyroxene (PX)-bearing mixtures, the PX is distinguishable even in mixtures with only 1% PX and that PX band at ca. 900 nm is always deeper than PL1 band while PL2 and PL3are deeperthan OPX 900 nm band from95, 96% PL. In OL-bearing mixtures, OL detection limit is 2% when mixed with PL1, and 3% and 4% if mixed with PL2 and PL3.
We also demonstrated how spectral parameters vary with PL%, and, generally, increasing the PL content: (1) 1250 nm band depth decreases when mixed with OL, while it deepens in mixtures with PX; (2) 1250 nm band centers generally move towards longer wavelength for PL1-bearing mixtures, while do not show significant variationsconsidering PL2/PL3-mixtures; (3)1250 nm band width of PL1 in E1 and E5-mixtures substantially widens while in other mixtures itonly slightly varies.
Here we also proposed an application to a real case, from Proclus crater, revealing how studying terrestrial analogues is fundamental to infer hypothesis on the mineralogical composition of a planetary surface, but also how the spectral convergence of spectra characterized by different compositions can led to misleading interpretations.

Reference
Giovanna S, Cristian C, Mariaamaria S (2016) Deconvolution of mixtures with high plagioclase content for the remote interpretation of lunar plagioclase-rich regions. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.01.020]
Copyright Elsevier

¹Jérôme Aléon
¹Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), UMR 7590, Sorbonne Universités, Museum National d’Histoire Naturelle, CNRS, UPMC, IRD, 61 rue Buffon, 75005 Paris, France

A major unanswered question in solar system formation is the origin of the oxygen isotopic dichotomy between the Sun and the planets. Individual Calcium–Aluminum-rich inclusions (CAIs) from CV chondrites exhibit almost the full isotopic range, but how their composition evolved is still unclear, which prevents robust astrochemical conclusions. A key issue is notably the yet unsolved origin of the 16O-rich isotopic composition of pyroxene in type B CAIs. Here, I report an in-situ oxygen isotope study of the archetypal type B CAI USNM-3529-Z from Allende with emphasis on the isotopic composition of pyroxene and its isotopic and petrographic relationships with other major minerals. The O isotopic composition of pyroxene is correlated with indicators of magmatic growth, indicating that the pyroxene evolved from a 16O-poor composition and became progressively enriched in 16O during its crystallization, contrary to the long held assumption that pyroxene was initially 16O-rich. This variation is well explained by isotopic exchange between a 16O-poor partial melt having the isotopic composition of melilite and a 16O-rich gas having the isotopic composition of spinel, during pyroxene crystallization.

The isotopic evolution of 3529-Z is consistent with formation in an initially 16O-rich environment where spinel and gehlenitic melilite crystallized, followed by a 16O-depletion associated with melilite partial melting and recrystallization and finally a return to the initial 16O-rich environment before pyroxene crystallization. This strongly suggests that the environment of CAI formation was globally 16O-rich, with local 16O-depletions systematically associated with high temperature events. The Al/Mg isotopic systematics of 3529-Z further indicates that this suite of isotopic changes occurred in the first 150 000 yr of the solar system, during the main CAI formation period. A new astrophysical setting is proposed, where the 16O-depletion occurs in an optically thin surface layer of the disk and may have originated by evaporation of 16O-poor interstellar dust or non-mass-dependant isotopic fractionation.

Reference
Aléon J (2016) Oxygen isotopes in the early protoplanetary disk inferred from pyroxene in a classical type B CAI. Earth and Planetary Science Letters 440, 62–70.
Link to Article [doi:10.1016/j.epsl.2016.02.007]
Copyright Elsevier

¹Frank Richter, ²Marc Chaussidon, ¹Ruslan Mendybaev, ¹Edwin Kite
¹The University of Chicago, 5734 South Ellis Avenue, Chicago, IL, 60637, U.S.A.
²Institute de Physique du Globe Paris, Sorbonne Paris Cite, UMR CNRS 7154, 1 rue Jussieu, 75005 Paris, France

Lithium concentration and isotopic fractionation profiles across augite grains from two Martian meteorites – MIL 03346 and NWA 817 – were used to determine their thermal history and implications for their geologic setting. The iron-magnesium zoning and associated magnesium isotopic fractionation of olivine grains from NWA 817 were also measured and provide a separate estimate of the cooling rate. The observed correlation of concentration with isotopic fractionation provides the essential evidence that the zoning of these grains was in fact due to diffusion and thus can be used as a measure of their cooling rate. The diffusion rate of lithium in augite depends on the oxygen fugacity, which has to be taken into account when determining a cooling rate based on the lithium zoning. The Fe-Mg exchange in olivine is much less sensitive to oxygen fugacity, but it is significantly anisotropic and for this reason we determined the direction relative to crystallographic axes of the line along which the Fe-Mg zoning was measured. We found that the cooling rate of NWA 817 determined from the lithium zoning in augite grains and that based on the Fe-Mg zoning of olivines are in good agreement at an oxygen fugacity close to that of quartz-fayalite-magnetite oxygen buffer. The cooling rate of MIL 03346 was found to be resolvably faster than that of NWA 817 – of the order of 1°C/hr for the former and of the order of 0.2°C/hr for the latter. An important observation regarding the history of MIL 03346 and NWA 817 is that the lithium and Fe-Mg zoning are only observed where the augite or olivine is in contact with the mesostasis, which implies that they were already about 80% crystallized at the time diffusion began. The augite and olivine core compositions while very homogeneous are not in equilibrium with each other, which we interpret to imply that prior to the rapid cooling there must have been a protracted period of the order of years above the solidus, during which the much faster Fe-Mg exchange in olivine compared to that in augite allowed the olivine to maintain equilibrium with a changing melt composition while the augite was not significantly affected. We suggest two possible geological settings for the origin and evolution of MIL 03346 and NWA 817: (1) A slow cooling stage in a crystallization front in a crustal magma chamber, followed by eruption of melt plus portions of the crystallization front onto the surface where the final fast cooling took place at the bottom of a lava flow or melt pond, and (2) Eruption of a crystal laden melt as a thick long-lived lava flow where the crystals continued to grow as a cumulate and were rapidly cooled when the overlying lava layer was suddenly drained.

Reference
Richter F, Chaussidon M, Mendybaev R, Kite E (2016) Reassessing the Cooling Rate and Geologic Setting of Martian Meteorites MIL 03346 and NWA 817. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.02.020]
Copyright Elsevier