¹Christelle Briois et al. (>10)*
Planetary and Space Science (in Press) Link to Article [doi:10.1016/j.pss.2016.06.012]
¹LPC2E, UMR CNRS 7328, Université d’Orléans, Orléans Cedex 2, France
*Find the extensive, full author and affiliation list on the publishers website

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¹Genesis Berlanga,¹Charles A. Hibbitts, ²Driss Takir, ³M. Darby Dyar, ³Elizabeth Sklute
Icarus (in Press) Link to Article [doi:10.1016/j.icarus.2016.06.020]
¹Johns Hopkins Applied Physics Laboratory
²USGS Astrogeology Science Center
³Mount Holyoke College Department of Astronomy
Copyright Elsevier

Previous studies have identified carbon dioxide (CO2) on the surfaces of Jovian and Galilean satellites in regions of non-ice material that are too warm for CO2 ice to exist. CO2 ice would quickly sublimate if not retained by a less-volatile material. To ascertain what non-ice species may be responsible for stabilizing this CO2, we performed CO2 gas adsorption experiments on thirteen powdered CM, CI, and CV carbonaceous chondrite meteorites. Reflectance spectra of the ν3 feature associated with adsorbed CO2 near 4.27 μm were recorded. Results show that many meteorites adsorbed some amount of CO2, as evidenced by an absorption feature that was stable over several hours at ultra-high vacuum (UHV) and high vacuum, (1.0×10−8 and 1.0×10−7 Torr, respectively). Ivuna, the only CI chondrite studied, adsorbed significantly more CO2 than the others. We found that CO2 abundance did not vary with ‘water’ abundance, organics, or carbonates as inferred from the area of the 3-μm band, the 3.2-3.4 μm C-H feature, and the ∼3.8-μm band respectively, but did correlate with hydrous/anhydrous phyllosilicate ratios. Furthermore, we did not observe CO2 ice because the position of the CO2 feature was generally shifted 3-10 nm from that of the 4.27 μm absorption characteristic of ice. The strongest compositional relationship observed was a possible affinity of CO2 for total FeO abundance and complex clay minerals, which make up the bulk of the CI chondrite matrix. This finding implies that the most primitive refractory materials in the Solar System may also act as reservoirs of CO2, and possibly other volatiles, delivering them to parts of the Solar System where their ices would not be stable.

¹Tabb C. Prissel, ¹Stephen W. Parman, ¹James W. Head
American Mineralogist 101, 1624-1635, Link to Article [doi:10.2138/am-2016-5581]
¹Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, Rhode Island 02912, U.S.A.
Copyright: The Mineralogical Society of America

Two competing hypotheses suggest lunar Mg-suite parental melts formed: (1) by shallow-level partial melting of a hybridized source region (containing ultramafic cumulates, plagioclase-bearing rocks, and KREEP), producing a plagioclase-saturated, MgO-rich melt, or (2) when plagioclase-undersaturated, MgO-rich melts were brought to plagioclase saturation during magma-wallrock interactions within the anorthositic crust. To further constrain the existing models, phase equilibria experiments have been performed on a range of Mg-suite parental melt compositions to investigate which composition can best reproduce two distinct spinel populations found within the Mg-suite troctolites—chromite-bearing (FeCr2O4) troctolites and the more rare pink spinel (MgAl2O4 or Mg-spinel) troctolites (PST).

Phase equilibria experiments at 1 atm pressure were conducted under reducing conditions Embedded Image and magmatic temperatures (1225–1400 °C) to explore the spinel compositions produced from melts predicted by the models above. Additionally, the experimental data are used to calculate a Sp-Ol, Fe-Mg equilibrium exchange coe to cient to correct natural spinel for sub-solidus re-equilibration with olivine in planetary samples: Sp-Ol Embedded Image (R2 = 0.956). Melts from each model (≥50% normative anorthite) produce olivine, plagioclase, and Mg-spinel compositionally consistent with PST samples. However, chromite was not produced in any of the experiments testing current Mg-suite parental melt compositions. The lack of chromite in the experiments indicates that current estimates of Mg-suite parental melts can produce Mg-spinel bearing PST, but not chromite-bearing troctolites and dunites. Instead, model calculations using the MAGPOX equilibrium crystallization program predict chromite production from plagioclase-undersaturated melts (<20% normative anorthite). If so, experimental and model results suggest chromite in Mg-suite crystallized from plagioclase-undersaturated parental melts, whereas Mg-spinel in the PST is an indicator of magma-wallrock interactions within the lunar crust (a mechanism that increases the normative anorthite contents of initially plagioclase-undersaturated Mg-suite parental melts, eventually producing Mg-spinel). The constraints for magmatic chromite crystallization suggest Mg-suite parental melts were initially plagioclase-undersaturated. In turn, a plagioclase-undersaturated Mg-suite parent is consistent with mantle overturn models that predict Mg-suite parent magmas resulted from decompression melting of early ultramafic cumulates produced during the differentiation of a global lunar magma ocean.

¹Allan H. Treiman, ^2,3Jeremy W. Boyce, ⁴James P. Greenwood, ²John M. Eiler, ⁵Juliane Gross, ²Yunbin Guan, ²Chi Ma, ²Edward M. Stolper
American Mineralogist 101, 1596-1603    Link to Article [doi:10.2138/am-2016-5582]
¹Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, Texas 77058, U.S.A.
²Division of Geological & Planetary Sciences, Caltech, 1200 East California Boulevard, Pasadena, California 91125, U.S.A.
³Department of Earth, Planetary, and Space Sciences, UCLA, California 90095, U.S.A.
⁴Department of Earth & Environmental Sciences, Wesleyan University, Middletown, Connecticut 06459, U.S.A.
⁵Department of Earth and Planetary Sciences, Rutgers University, 610 Taylor Road, Piscataway, New Jersey 08854, U.S.A.
Copyright: The Mineralogical Society of America

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^1,2Bethany L. Ehlmann et al. (>10)*
American Mineralogist 101, 1527-1542 Link to Article [DOI: 10.2138/am-2016-5574]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A.
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, U.S.A.
*Find the extensive, full author and affiliation list on the publishers website
Copyright: The Mineralogical Society of America

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¹Z. W. Hu, ²R. P. Winarski
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12674]
¹XNano Sciences Inc., Huntsville, Alabama, USA
²Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, USA
Published by arrangement with John Wiley & Sons

Unlocking the 3-D structure and properties of intact chondritic porous interplanetary dust particles (IDPs) in nanoscale detail is challenging, which is also complicated by atmospheric entry heating, but is important for advancing our understanding of the formation and origins of IDPs and planetary bodies as well as dust and ice agglomeration in the outer protoplanetary disk. Here, we show that indigenous pores, pristine grains, and thermal alteration products throughout intact particles can be noninvasively visualized and distinguished morphologically and microstructurally in 3-D detail down to ~10 nm by exploiting phase contrast X-ray nanotomography. We have uncovered the surprisingly intricate, submicron, and nanoscale pore structures of a ~10-μm-long porous IDP, consisting of two types of voids that are interconnected in 3-D space. One is morphologically primitive and mostly submicron-sized intergranular voids that are ubiquitous; the other is morphologically advanced and well-defined intragranular nanoholes that run through the approximate centers of ~0.3 μm or lower submicron hollow grains. The distinct hollow grains exhibit complex 3-D morphologies but in 2-D projections resemble typical organic hollow globules observed by transmission electron microscopy. The particle, with its outer region characterized by rough vesicular structures due to thermal alteration, has turned out to be an inherently fragile and intricately submicron- and nanoporous aggregate of the sub-μm grains or grain clumps that are delicately bound together frequently with little grain-to-grain contact in 3-D space.

¹Benton C. Clark et al. (>10)*
American Mineralogist 101 (7) 1515-1526   Link to Article [DOI: 10.2138/am-2016-5575]
¹Space Science Institute, 4750 Walnut, Boulder, Colorado 80301, U.S.A.
*Find the extensive, full author and affiliation list on the publishers website
Copyright: The Mineralogical Society of America

In the search for evidence of past aqueous activity by the Mars Exploration Rover Opportunity, fracture-filling veins and rock coatings are prime candidates for exploration. At one location within a segment of remaining rim material surrounding Endeavour Crater, a set of “boxwork” fractures in an outcrop called Esperance are filled by a bright, hydrated, and highly siliceous (SiO2 ~ 66 wt%) material, which has overall a montmorillonite-like chemical composition. This material is partially covered by patches of a thin, dark coating that is sulfate-rich (SO3 ~ 21 wt%) but also contains significant levels of Si, Fe, Ca, and Mg. The simultaneous presence of abundant S, Si, and Fe indicates significant mineralogical complexity within the coating. This combination of vein and coating compositions is unlike previous analyses on Mars. Both materials are heterogeneously eroded, presumably by eolian abrasion. The evidence indicates at least two separate episodes of solute precipitation from aqueous fluids at this location, possibly widely separated in time. In addition to the implications for multiple episodes of alteration at the surface of the planet, aqueous chemical environments such as these would have been habitable at the time of their formation and are also favorable for preservation of organic material.

¹Jeffrey R. Johnson et al. (>10)*
American Mineralogist 101, 1501-1514 Link to Article [doi:10.2138/am-2016-5553]
¹Applied Physics Laboratory, Johns Hopkins University, 11101 Johns Hopkins Road 200-W230 Laurel, Maryland 20723-6005, U.S.A.
*Find the extensive, full author and affiliation list on the publishers website
Copyright: The Mineralogical Society of America

Relative reflectace point spectra (400–840 nm) were acquired by the Chemistry and Camera (ChemCam) instrument on the Mars Science Laboratory (MSL) rover Curiosity in passive mode (no laser) of drill tailings and broken rock fragments near the rover as it entered the lower reaches of Mt. Sharp and of landforms at distances of 2–8 km. Freshly disturbed surfaces are less subject to the spectral masking effects of dust, and revealed spectral features consistent with the presence of iron oxides and ferric sulfates. We present the first detection on Mars of a ~433 nm absorption band consistent with small abundances of ferric sulfates, corroborated by jarosite detections by the Chemistry and Mineralogy (CheMin) X-ray diffraction instrument in the Mojave, Telegraph Peak, and Confidence Hills drilled samples. Disturbed materials near the Bonanza King region also exhibited strong 433 nm bands and negative near-infrared spectral slopes consistent with jarosite. ChemCam passive spectra of the Confidence Hills and Mojave drill tailings showed features suggestive of the crystalline hematite identified by CheMin analyses. The Windjana drill sample tailings exhibited flat, low relative reflectance spectra, explained by the occurrence of magnetite detected by CheMin. Passive spectra of Bonanza King were similar, suggesting the presence of spectrally dark and neutral minerals such as magnetite. Long-distance spectra of the “Hematite Ridge” feature (3–5 km from the rover) exhibited features consistent with crystalline hematite. The Bagnold dune field north of the Hematite Ridge area exhibited low relative reflectance and near-infrared features indicative of basaltic materials (olivine, pyroxene). Light-toned layers south of Hematite Ridge lacked distinct spectral features in the 400–840 nm region, and may represent portions of nearby clay minerals and sulfates mapped with orbital near-infrared observations. The presence of ferric sulfates such as jarosite in the drill tailings suggests a relatively acidic environment, likely associated with flow of iron-bearing fluids, associated oxidation, and/or hydrothermal leaching of sedimentary rocks. Combined with other remote sensing data sets, mineralogical constraints from ChemCam passive spectra will continue to play an important role in interpreting the mineralogy and composition of materials encountered as Curiosity traverses further south within the basal layers of the Mt. Sharp complex.

¹Kathleen C. Benison
American Mineralogist 101, 1499-1500 Link to Article [DOI: 10.2138/am-2016-5802]
¹Department of Geology and Geography, West Virginia University, Morgantown, West Virginia 26506, U.S.A.
Copyright: The Mineralogical Society of America

Identification of minerals on the surface of Mars is critical to understanding the geological history of our neighbor planet. In this issue of American Mineralogist, Ehlmann et al. report their discovery of alunite [KAl3(SO4)2(OH)6] in Cross Crater on Mars. Because terrestrial alunite forms from Al-rich acid sulfate waters, these results strongly suggest the past presence of Al-rich acid saline martian waters.

¹John F. Pernet-Fisher
American Mineralogist 101, 1497-1498 Link to Article [DOI: 10.2138/am-2016-5790]
¹School of Earth, Atmospheric, and Environmental Sciences, University of Manchester, Manchester M13 2PL, U.K.
Copyright: The Mineralogical Society of America

Earth-like δD values reported from lunar mare-basalt apatites have typically been interpreted to reflect the intrinsic isotopic composition of lunar-mantle water. New data indicates that some of these basalts are also characterized by having experienced a slow cooling history after their emplacement onto the lunar surface. This suggests that these basalts may have experienced metasomatism by fluxes generated during the degassing of the lunar regolith induced by the long-duration, high-temperature residence times of overlying basalts.