¹Lee, M. R., ¹Lindgren, P.
¹School of Geographical and Earth Sciences, University of Glasgow, Glasgow, UK

Forsterite and clinoenstatite in type IAB chondrules from the Murchison CM carbonaceous chondrite have been partially serpentinized, and the mechanisms of their alteration reveal crystallographic and microstructural controls on the reaction of silicate minerals with parent body aqueous solutions. Grains of forsterite were altered in two stages. Narrow veinlets of Fe-rich serpentine formed first and by the filling of sheet pores. Most of these pores were oriented parallel to (010) and (001) and had been produced by earlier fracturing and/or congruent dissolution. In the second stage, the subset of veinlets that were oriented parallel to (001) was widened accompanying the replacement of forsterite by Mg-Fe serpentine. This reaction proceeded most rapidly parallel to [001], and crystallographic controls on the trajectory of retreating vein walls created fine-scale serrations. Murchison clinoenstatite grains have a skeletal appearance due to the presence of abundant veinlets and patches of phyllosilicate. Two alteration stages can again be recognized, with initial water–mineral interaction producing tochilinite-rich veinlets by the filling of (001)-parallel contraction cracks. Pores then formed by congruent dissolution that was guided principally by orthopyroxene lamellae, and they were subsequently filled by submicrometer-sized crystals of polyhedral serpentine. This finding that Murchison forsterite and clinoenstatite grains have been altered demonstrates that aqueous processing of magnesium silicate minerals started much earlier in CM parent body history than previously believed. Our results also show that the occurrence of polyhedral serpentine can be used to locate former pore spaces within the parent body.

Reference
Lee MR, Lindgren P. (2016) Aqueous alteration of chondrules from the Murchison CM carbonaceous chondrite: Replacement, pore filling, and the genesis of polyhedral serpentine. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12644]
Published by arrangement with John Wiley & Sons

¹Elena S. Amador, ²Joshua L. Bandfield
¹Department of Earth and Space Sciences, University of Washington
²Space Science Institute

The Nili Fossae region of Mars contains some of the most mineralogically diverse bedrock on the planet. Previous studies have established three main stratigraphic units in the region: a phyllosilicate-bearing basement rock, a variably altered olivine-rich basalt, and a capping rock. Here, we present evidence for the localized alteration of the northeast Nili Fossae capping unit, previously considered to be unaltered. Both near-infrared and thermal-infrared spectral datasets were analyzed, including the application of a method for determining the relative abundance of bulk-silica (SiO2) over surfaces using Thermal Emission Imaging System (THEMIS) images. Elevated bulk-silica exposures are present on surfaces previously defined as unaltered capping rock. Given the lack of spectral evidence for phyllosilicate, hydrated silica, or quartz phases coincident with the newly detected exposures – the elevated bulk-silica may have formed under a number of aqueous scenarios, including as a product of the carbonation of the underlying olivine-rich basalt under moderate water:rock scenarios and temperatures. Regardless of formation mechanism, the detection of elevated bulk-silica exposures in the Nili Fossae capping unit extends the history of aqueous activity in the region to include all three of the main stratigraphic units.

Reference
Amador ES, Bandfield JL (2016) Elevated bulk-silica exposures and evidence for multiple aqueous alteration episodes in Nili Fossae, Mars. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.04.015]
Copyright Elsevier

^1,2,3Levke Kööp, ^4,5Daisuke Nakashima, ^1,2,3Philipp R. Heck, ⁴Noriko T. Kita, ⁴Travis J. Tenner, ⁶Alexander N. Krot, ⁶Kazuhide Nagashima, ^6,7Changkun Park, ^1,2,3,8Andrew M. Davis
¹Department of the Geophysical Sciences, The University of Chicago, Chicago, IL 60637, USA
²Chicago Center for Cosmochemistry, The University of Chicago, Chicago, IL 60637, USA
³Robert A. Pritzker Center for Meteoritics and Polar Studies, Field Museum of Natural History, Chicago, IL, USA
⁴Department of Geoscience, University of Wisconsin, Madison, WI 53706, USA
⁵Division of Earth and Planetary Material Sciences, Faculty of Science, Tohoku University, Aoba, Sendai, Miyagi 980-8578 Japan
⁶Hawai‘i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, HI
⁷Korea Polar Research Institute, Incheon 406-840, Korea
⁸Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637, USA.

We report oxygen, calcium, titanium and 26Al-26Mg isotope systematics for spinel-hibonite inclusions (SHIBs), a class of calcium-aluminum-rich inclusions (CAI) common in CM chondrites. In contrast to previous studies, our analyses of 33 SHIBs and four SHIB-related objects obtained with high spatial resolution demonstrate that these CAIs have a uniform Δ17O value of approximately –23‰, similar to many other mineralogically pristine CAIs from unmetamorphosed chondrites (e.g., CR, CV, and Acfer 094). Five SHIBs studied for calcium and titanium isotopes have no resolvable anomalies beyond 3σ uncertainties. This suggests that nucleosynthetic anomalies in the refractory elements had been significantly diluted in the environment where SHIBs with uniform Δ17O formed. We established internal 26Al-26Mg isochrons for eight SHIBs and found that seven of these formed with uniformly high levels of 26Al (a multi-CAI mineral isochron yields an initial 26Al/27Al ratio of ∼4.8×10–5), but one SHIB has a smaller initial 26Al/27Al of ∼2.5×10–5, indicating variation in 26Al/27Al ratios when SHIBs formed. The uniform calcium, titanium and oxygen isotopic characteristics found in SHIBs with both high and low initial 26Al/27Al ratios allow for two interpretations. (1) If subcanonical initial 26Al/27Al ratios in SHIBs are due to early formation, as suggested by Liu et al. (2012), our data would indicate that the CAI formation region had achieved a high degree of isotopic homogeneity in oxygen and refractory elements before a homogeneous distribution of 26Al was achieved. (2) Alternatively, if subcanonical ratios were the result of 26Al-26Mg system resetting, the clustering of SHIBs at a Δ17O value of ∼ –23‰ would imply that a 16O-rich gaseous reservoir existed in the nebula until at least ∼0.7 Ma after the formation of the majority of CAIs.

Reference
Kööp L, Nakashima D, Heck PR, Kita NT, Tenner TJ, Krot AN, Nagashima K, Park C, Davis AM (2016) New constraints on the relationship between 26Al and oxygen, calcium, and titanium isotopic variation in the early Solar System from a multielement isotopic study of spinel-hibonite inclusions. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.04.018]
Copyright Elsevier

¹Altobelli N. et al. (>10)*
¹European Space Agency, European Space Astronomy Centre, Madrid, Spain.
*Find the extensive, full author and affiliation list on the publishers website

Interstellar dust (ISD) is the condensed phase of the interstellar medium. In situ data from the Cosmic Dust Analyzer on board the Cassini spacecraft reveal that the Saturnian system is passed by ISD grains from our immediate interstellar neighborhood, the local interstellar cloud. We determine the mass distribution of 36 interstellar grains, their elemental composition, and a lower limit for the ISD flux at Saturn. Mass spectra and grain dynamics suggest the presence of magnesium-rich grains of silicate and oxide composition, partly with iron inclusions. Major rock-forming elements (magnesium, silicon, iron, and calcium) are present in cosmic abundances, with only small grain-to-grain variations, but sulfur and carbon are depleted. The ISD grains in the solar neighborhood appear to be homogenized, likely by repeated processing in the interstellar medium.

Reference
Altobelli N et al. (2016) Flux and composition of interstellar dust at Saturn from Cassini’s Cosmic Dust Analyzer. Science 352, 312-318
Link to Article [DOI: 10.1126/science.aac6397]
Reprinted with permission from AAAS

¹L. Fimiani et al. (>10)*
¹Physik Department, Technische Universitat Munchen, D-85748 Garching, Germany
*Find the extensive, full author and affiliation list on the publishers website

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

Reference
Fimani F et al. (2016) Interstellar Fe60 on the Surface of the Moon
Physical Review Letters 116, 151104
Link to Article [DOI:http://dx.doi.org/10.1103/PhysRevLett.116.151104]

¹Hannah H. Kaplan, ¹Ralph E. Milliken, ²David Fernández-Remolar, ³Ricardo Amils, ¹Kevin Robertson, ⁴Andrew H. Knoll
¹Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI, 02912 USA
²British Geological Survey, Nicker Hill, Keyworth, NG12 5GG, UK
³Centro de Astrobiologia (INTA-CSIC), Ctra Ajalvir km 4, Torrejon de Ardoz, 28850, Spain
⁴Department of Organismic and Evolutionary Biology, Harvard University, Çambridge, MA, USA

Outcrops of hydrated minerals are widespread across the surface of Mars, with clay minerals and sulfates being commonly identified phases. Orbitally-based reflectance spectra are often used to classify these hydrated components in terms of a single mineralogy, although most surfaces likely contain multiple minerals that have the potential to record local geochemical conditions and processes. Reflectance spectra for previously identified deposits in Ius and Melas Chasma within the Valles Marineris, Mars, exhibit an enigmatic feature with two distinct absorptions between 2.2 – 2.3 µm. This spectral ‘doublet’ feature is proposed to result from a mixture of hydrated minerals, although the identity of the minerals has remained ambiguous. Here we demonstrate that similar spectral doublet features are observed in airborne, field, and laboratory reflectance spectra of rock and sediment samples from Rio Tinto, Spain. Combined visible-near infrared reflectance spectra and X-ray diffraction measurements of these samples reveals that the doublet feature arises from a mixture of Al-phyllosilicate (illite or muscovite) and jarosite. Analyses of orbital data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) shows that the martian spectral equivalents are also consistent with mixtures of Al-phyllosilicates and jarosite, where the Al-phyllosilicate may also include kaolinite and/or halloysite. A case study for a region within Ius Chasma demonstrates that the relative proportions of the Al-phyllosilicate(s) and jarosite vary within one stratigraphic unit as well as between stratigraphic units. The former observation suggests that the jarosite may be a diagenetic (authigenic) product and thus indicative of local pH and redox conditions, whereas the latter observation may be consistent with variations in sediment flux and/or fluid chemistry during sediment deposition.

Reference
Kaplan HH, Milliken RE, Fernández-Remolar D, Amils R, Robertson K, Knoll AH (2016)
Orbital Evidence for Clay and Acidic Sulfate Assemblages on Mars Based on Mineralogical Analogs from Rio Tinto, Spain. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.03.019]
Copyright Elsevier

¹Hannah H. Kaplan, ¹Ralph E. Milliken, ²David Fernández-Remolar, ³Ricardo Amils, ¹Kevin Robertson, ⁴Andrew H. Knoll
¹Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI, 02912 USA
²British Geological Survey, Nicker Hill, Keyworth, NG12 5GG, UK
³Centro de Astrobiologia (INTA-CSIC), Ctra Ajalvir km 4, Torrejon de Ardoz, 28850, Spain
⁴Department of Organismic and Evolutionary Biology, Harvard University, Çambridge, MA, USA

Outcrops of hydrated minerals are widespread across the surface of Mars, with clay minerals and sulfates being commonly identified phases. Orbitally-based reflectance spectra are often used to classify these hydrated components in terms of a single mineralogy, although most surfaces likely contain multiple minerals that have the potential to record local geochemical conditions and processes. Reflectance spectra for previously identified deposits in Ius and Melas Chasma within the Valles Marineris, Mars, exhibit an enigmatic feature with two distinct absorptions between 2.2 – 2.3 µm. This spectral ‘doublet’ feature is proposed to result from a mixture of hydrated minerals, although the identity of the minerals has remained ambiguous. Here we demonstrate that similar spectral doublet features are observed in airborne, field, and laboratory reflectance spectra of rock and sediment samples from Rio Tinto, Spain. Combined visible-near infrared reflectance spectra and X-ray diffraction measurements of these samples reveals that the doublet feature arises from a mixture of Al-phyllosilicate (illite or muscovite) and jarosite. Analyses of orbital data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) shows that the martian spectral equivalents are also consistent with mixtures of Al-phyllosilicates and jarosite, where the Al-phyllosilicate may also include kaolinite and/or halloysite. A case study for a region within Ius Chasma demonstrates that the relative proportions of the Al-phyllosilicate(s) and jarosite vary within one stratigraphic unit as well as between stratigraphic units. The former observation suggests that the jarosite may be a diagenetic (authigenic) product and thus indicative of local pH and redox conditions, whereas the latter observation may be consistent with variations in sediment flux and/or fluid chemistry during sediment deposition.

Reference
Kaplan HH, Milliken RE, Fernández-Remolar D, Amils R, Robertson K, Knoll AH (2016)
Orbital Evidence for Clay and Acidic Sulfate Assemblages on Mars Based on Mineralogical Analogs from Rio Tinto, Spain. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.03.019]
Copyright Elsevier

¹Catherine M. Weitz,²Janice L. Bishop
¹Planetary Science Institute, Tucson, AZ
²SETI Institute, Mountain View, CA

We investigate the morphology, mineralogy, and stratigraphy of light-toned layered deposits within a trough of Coprates Catena, centered at -15°N, 300°E. One of the deposits in the eastern portion of the trough contains numerous hydrated minerals, including: Al-phyllosilicates, Fe/Mg-phyllosilicates, hydrated silica, hydrated sulfates, jarosite and acid alteration products characterized by a spectral doublet between 2.2-2.3 µm, and weakly hydrated materials. The Al-phyllosilicates are observed both stratigraphically above and below the Fe/Mg-phyllosilicate unit, which is a rare and perhaps unique association on Mars. Most of the western light-toned layered deposit underlies a terraced fan. This deposit contains hydrated materials, including Al-phyllosilicates and Fe/Mg-phyllosilicates. Dip measurements indicate both the eastern and western deposits dip towards the center of the trough, indicating they post-date formation of the trough and are consequently Late Hesperian or younger in age. Volcanic ash, most likely erupted during formation of the pit crater in the eastern portion of the trough, seems to best explain our observations for several of the units. Valleys sourced from water along the plateau may have flowed into the trough and altered the sediments, with changing aqueous chemistries over time resulting in the diverse range of mineralogies now observed in the eastern light-toned deposit. Our results reveal a complex sedimentary and aqueous history within the Coprates Catena trough, indicating that localized habitable conditions were possible relatively late in martian history at a time when colder, drier conditions likely dominated the majority of the planet.

Reference
Weitz CM, Bishop JL (2016) Stratigraphy and Formation of Clays, Sulfates, and Hydrated Silica within a Depression in Coprates Catena, Mars. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2015JE004954]
Published by arrangement with John Wiley & Sons

¹James J. Wray et al. (>10)*
¹School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
*Find the extensive, full author and affiliation list on the publishers website

Carbonates are key minerals for understanding ancient Martian environments because they are indicators of potentially habitable, neutral-to-alkaline water and may be an important reservoir for paleo-atmospheric CO₂. Previous remote sensing studies have identified mostly Mg-rich carbonates, both in Martian dust and in a Late Noachian rock unit circumferential to the Isidis basin. Here we report evidence for older Fe- and/or Ca-rich carbonates exposed from the subsurface by impact craters and troughs. These carbonates are found in and around the Huygens basin northwest of Hellas, in western Noachis Terra between Argyre basin and Valles Marineris, and in other isolated locations spread widely across the planet. In all cases they co-occur with or near phyllosilicates, and in Huygens basin specifically they occupy layered rocks exhumed from ~5 km depth. We discuss factors that might explain their observed regional distribution, arguments for why carbonates may be even more widespread in Noachian materials than presently appreciated, and what could be gained by targeting these carbonates for further study with future orbital or landed missions to Mars.

Reference
Wray JJ et al. (2016) Orbital evidence for more widespread carbonate-bearing rocks on Mars. Journal of Geophysical Research, Planets (in Press)
Link to Article [DOI: 10.1002/2015JE004972]
Published by arrangement with John Wiley & Sons

¹Danilo Di Genova, ¹Kai-Uwe Hess, ²Magdgdalena Oryaëlle Chevrel, ¹Donald B. Dingwell
¹Department Earth and Environmental Sciences, Ludwig-Maximilians-Universität, Theresienstrasse 41/III, 80333 München, Germany
²Departamento de Vulcanología, Instituto de Geofísica, Universidad Nacional Autónoma de México, 04510, México D.F., Mexico

To develop Raman spectroscopy as a quantitative tool in both geosciences and planetary sciences the effect of iron oxidation state (Fe3+/Fetot) on the Raman spectra of basaltic and pantelleritic glasses has been investigated. We have used remelted pantellerite from Pantelleria Island and synthetic iron-rich basaltic glasses [from Chevrel et al. (2014)].
The Raman spectra of pantelleritic glasses reveal dramatic changes in the high wavelength region of the spectrum (800–1200 cm–1) as iron oxidation state changes. In particular the 970 cm–1 band intensity increases with increasing oxidation state of the glass (Fe3+/Fetot ratio from 0.24 to 0.83). In contrast, Raman spectra of the basaltic glasses do not show the same oxidation state sensitivity (Fe3+/Fetot ratio from 0.15 to 0.79). A shift, however, of the 950 cm–1 band to high wavenumber with decreasing iron oxidation state can be observed.
We present here two empirical parameterizations (for silica- and alkali-rich pantelleritic glasses and for iron-rich basaltic glasses) to enable estimation of the iron oxidation state of both anhydrous and hydrous silicate glasses (up to 2.4 wt% H2O). The validation of the models derived from these parameterizations have been obtained using the independent characterization of these melt samples plus a series of external samples via wet chemistry.
The “pantelleritic” model can be applied within SiO2, FeO, and alkali content ranges of ~69–75, ~7–9, and ~8–11 wt%, respectively. The “basaltic” model is valid within SiO2, FeO, and alkali content ranges of ~42–54, ~10–22, and ~3–6 wt%, respectively.
The results of this study contribute to the expansion of the compositionally dependent database previously presented by Di Genova et al. (2015) for Raman spectra of complex silicate glasses. The applications of these models range from microanalysis of silicate glasses (e.g., melt inclusions) to handheld in situ terrestrial field investigations and studies under extreme conditions such as extraterrestrial (i.e., Mars), volcanic, and submarine environments.

Reference
Di Genova D, Hess K-U, Chevrel MO, Dingwell DB (2016) Models for the estimation of Fe3+/Fetot ratio in terrestrial and extraterrestrial alkali- and iron-rich silicate glasses using Raman spectroscopy. American Mineralogist 101, 943–952
Link to Article [DOI: http://dx.doi.org/10.2138/am-2016-5534CCBYNCND]
Copyright: The Mineralogical Society of America