¹M.Telus,¹C.M.O’D.Alexander,¹E.H.Hauri,¹J.Wang
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.06.012]
¹Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, Washington, DC 20015, USA
Copyright Elsevier

To constrain the conditions of aqueous alteration in early planetesimals, we carried out in situ C and O isotope analyses of calcite and dolomite and O isotope analyses of magnetite from the highly altered CM chondrites ALH 83100, ALH 84034, and MET 01070. Petrographic and isotopic analyses of these samples support previous findings of multiple generations of carbonate growth. We observe wide ranges in the C and O isotope compositions of carbonates of up to 80‰ and 30‰, respectively, that span the full range of previously reported bulk carbonate values for CM chondrites. Variations in the Δ17O values indicate that fluid evolution varied for each chondrite. ALH 83100 dolomite-magnetite δ18O fractionation of 23‰ ± 7‰ (2SD) corresponds to dolomite formation temperature of 125°C ± 60°C. δ13C vs δ18O values fall into two groups, one consisting of primary calcite and the other consisting of dolomite and secondary calcite. The positive correlation between δ13C and δ18O for primary calcite is consistent with the precipitation of calcite in equilibrium with a gas mixture of CO (or CH4) and CO2. The isotopic composition of calcite in CM1s and CM2s overlap significantly; however, many CM1 calcite grains are more depleted in δ18O compared to CM2s. Altogether, the data indicate that the fluid composition during calcite formation was initially the same for both CM1s and CM2s. CM1s experienced more episodes of carbonate dissolution and reprecipitation where some fraction of the carbonate grains survive each episode resulting in a highly disequilibrium assemblage of carbonates on the thin-section scale.

^1,2Berengere Mougel,^1,3Frederic Moynier,^4,5Christian Koeberl,⁶Daniel Wielandt,⁶Martin Bizzarro
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13312]
¹Institut de Physique du Globe de Paris, Université Sorbonne Paris Cité, CNRS UMR7154, 1 rue Jussieu, 75238 Paris Cedex 05, France
²Centro de Geociencias, Universidad Nacional Autónoma de México, Blvd. Juriquilla No 3001, Querétaro, 76230 Mexico
³Institut Universitaire de France, 1 rue Descartes, 75231 Paris Cedex 05, France
⁴Department of Lithospheric Research, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria
⁵Natural History Museum, Burgring 7, 1010 Vienna, Austria
⁶Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5‐7 DK‐1350, Copenhagen, Denmark
Published by arrangement with John Wiley & Sons

The existence of mass‐independent chromium isotope variability of nucleosynthetic origin in meteorites and their components provides a means to investigate potential genetic relationship between meteorites and planetary bodies. Moreover, chromium abundances are depleted in most surficial terrestrial rocks relative to chondrites such that Cr isotopes are a powerful tool to detect the contribution of various types of extra‐terrestrial material in terrestrial impactites. This approach can thus be used to constrain the nature of the bolide resulting in breccia and melt rocks in terrestrial impact structures. Here, we report the Cr isotope composition of impact rocks from the ~0.57 Ma Lonar crater (India), which is the best‐preserved impact structure excavated in basaltic target rocks. Results confirm the presence of a chondritic component in several bulk rock samples of up to 3%. The impactor that created the Lonar crater had a composition that was most likely similar to that of carbonaceous chondrites, possibly a CM‐type chondrite.

¹H. Nekvasil,²N.J. DiFrancesco,¹A.D. Rogers,³A.E. Coraor,⁴P.L. King
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005911]
¹Stony Brook University, Department of Geosciences, Stony Brook, NY, USA
²SUNY Oswego, Department of Atmospheric and Geological Sciences, Oswego, NY, USA
³Institute for Molecular Engineering, The University of Chicago, Chicago, IL, USA
⁴Research School of Earth Sciences, The Australian National University, Canberra, ACT, Australia
Published by arrangement with John Wiley & Sons

Martian magmas were likely enriched in S and Cl with respect to H₂O. Exsolution of a vapor phase from these magmas and ascent of the gas bubbles through the magma plumbing system would have given rise to shallow magmas that were gas‐charged. Release and cooling of this gas from lava flows during eruption may have resulted in the addition of a significant amount of vapor‐deposited phases to the fines of the surface. Experiments were conducted to simulate degassing of gas‐charged lava flows and shallow intrusions in order to determine the nature of vapor‐deposited phases that may form through this process. The results indicate that magmatic gas may have contributed a large amount of Fe, S, and Cl to the martian surface through the deposition of iron oxides (magnetite, maghemite, hematite), chlorides (molysite, halite, sylvite), sulfur and sulfides (pyrrhotite, pyrite). Primary magmatic vapor‐deposited minerals may react during cooling to form a variety of secondary products, including iron oxychloride (FeOCl), akaganéite (Fe³⁺O (OH,Cl)), and jarosite (KFe³⁺₃(OH)₆(SO₄)₂). Vapor‐deposition does not transport significant amounts of Ca, Al, or Mg from the magma and hence, this process does not directly deposit Ca‐ or Mg‐sulfates.

¹D.P. Quinn,²B.L. Ehlmann
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005706]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
Published by arrangement with John Wiley & Sons

Ancient stratigraphy on Isidis Basin’s western margin records the history of water on early Mars. Noachian units are overlain by layered, basaltic‐composition sedimentary rocks that are enriched in polyhydrated sulfates and capped by more resistant units. The layered sulfates –uniquely exposed at northeast Syrtis Major – comprise a sedimentary sequence up to 600‐m thick that has undergone a multi‐stage history of deposition, alteration, and erosion. Siliciclastic sediments enriched in polyhydrated sulfates are bedded at m‐scale and were deposited on slopes up to 10°, embaying and thinning against pre‐existing Noachian highlands around the Isidis basin rim. The layered sulfates were modified by volume‐loss fracturing during diagenesis. Resultant fractures hosted channelized flow and jarosite mineral precipitation to form resistant ridges upon erosion. The structural form of the layered sulfates is consistent with packages of sediment fallen from either atmospheric or aqueous suspension; coupling with substantial diagenetic volume‐loss may favor deepwater basin sedimentation. After formation, the layered sulfates were capped by a “smooth capping unit” and then eroded to form paleovalleys. Hesperian Syrtis Major lavas were channelized by this paleotopography, capping it in some places and filling it in others. Later fluvial features and phyllosilicate‐bearing lacustrine deposits, sharing a regional base level of ~‐2300m, were superimposed on the sulfate‐lava stratigraphy. The layered sulfates suggest surface bodies of water and active groundwater upwelling during the Noachian–Hesperian transition. The northeast Syrtis Major stratigraphy records at least four distinct phases of surface and subsurface aqueous activity spanning from late Noachian to early Amazonian time.

¹Lowery, C.M. et al. (>10)
Oceanography 32, 120-134 Link to Article [DOI: 10.5670/oceanog.2019.133]
¹University of Texas Institute for Geophysics, Jackson School of Geosciences, Austin, TX, United States

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¹Stennikov, A.V.,¹Voropaev, S.A.,¹Fedulov, V.S.,¹Dushenko, N.V.,¹Naimushin, S.G.
Solar System Research 53, 199-207 Link to Article [DOI: 10.1134/S0038094619030055]
¹Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, 119991, Russian Federation

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¹K.M.Primm,¹D.E.Stillman,²T.I.Michaels
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.06.003]
¹Dept. of Space Studies, Southwest Research Institute, 1050 Walnut St. #300, Boulder, CO 80302, USA
²SETI Institute, 189 Bernardo Ave Suite 200, Mountain View, CA 94043, USA
Copyright Elsevier

Liquid solution stability has been a highly studied topic in the Martian community since the detection of perchlorate (ClO4−) at the Phoenix landing site and the global detection of chloride (Cl−) by THEMIS (Thermal Emission Imagining System, onboard Mars Odyssey). Understanding how brines form and react to changing environmental conditions helps identify potentially habitable environments on Mars, both at present and in the past. Here we measure the extent of metastability of magnesium chloride (MgCl2) and sodium chloride (NaCl) brines when freezing. We find that the metastable eutectic temperature of MgCl2 depends on the maximum temperature (Tmax) reached before freezing. If Tmax < −15 °C, the metastable eutectic temperature (mTeu) is only 3 °C below the stable eutectic temperature, and if Tmax > −15 °C, mTeu is 15 °C below the stable eutectic temperature (Teu). We speculate that this metastable behavior follows the phase diagram for the transition into the 8 hydrate for MgCl2, thus, yielding a different freezing temperature, the peritectic for MgCl2·8H2O. However, mTeu for NaCl is independent of Tmax and was constantly at 3 °C below Teu with no peritectic (consistent with the phase diagram). We also found that MgCl2 brine can exist for at least 60 h at 5 °C below its Teu. Applying our findings, we determined the potential time evolution of brines at Palikir crater, using a time-series of modeled temperature profiles. Surficial layers melt more frequently, but layers at 2–3 cm depth are able to warm above Tmax > −15 °C and maintain brine for longer than surficial layers. The evaporation rate of brine buried by 2–3 cm of regolith is greatly reduced due to the generally cold temperatures, solute concentration, and by the regolith overburden. We also found that at Palikir crater, only the deep subsurface (~9.5 cm depth) has water activities (~0.75) high enough to support life. Overall, the metastable properties of brines can drastically affect their formation and longevity on Mars, and should be considered in future models.

¹I.Varatharajan,¹A.Maturilli,¹J.Helbert,²G.Alemanno,³H.Hiesinger
Earth and Planetary Science Letters (in Press) Link to Article [https://doi.org/10.1016/j.epsl.2019.05.020]
¹Deutsches Zentrum für Luft- Und Raumfahrt
²Universita del Salento
³Westfälische Wilhelms-Universität Münster
Copyright Elsevier

To detect the mineral diversity of a planet’s surface, it is essential to study the spectral variations over a broad wavelength range at relevant simulated laboratory conditions. The MESSENGER (Mercury Surface, Space Environment, Geochemistry, and Ranging) mission to Mercury discovered that irrespective of its formation closest to the Sun, Mercury is richer in volatiles than previously expected. This is especially true for sulfur (S), with an average abundance of 4 wt%. It has been proposed that sulfur in the interior of Mercury can be brought to the surface through volcanic activity in the form of sulfides as slag deposits in Mercury hollows and pyroclastic deposits. However, comprehensive spectral library of sulfide minerals measured under vacuum conditions in a wide spectral range (0.2–100 μm) was lacking. This affects the detectability and understanding of the distribution, abundance, and type of sulfides on Mercury using remote-sensing spectral observations. In the case of Mercury, the effect of thermal weathering affecting the spectral behavior of these sulfides must be studied carefully for their effective detection. In this study, we present a spectral library of synthetic sulfides including MgS, FeS, CaS, CrS, TiS, NaS, and MnS. For each sample, we performed emissivity measurements in the thermal infrared range (TIR: ∼7–14 μm) for sample temperatures from 100 °C–500 °C, covering the daytime temperature cycle on Mercury’s surface. In addition, for each sample we measured the spectral reflectance of fresh and thermally processed sulfides over a wide spectral range (0.2–100 μm) and at four different phase angles, 26°, 40°, 60°, 80°. This spectral library facilitates the detection of sulfides by past and future missions to Mercury by any optical spectrometer of any spectral range. Specifically, the emissivity measurements in this study will support the Mercury Radiometer and Thermal Imaging Spectrometer (MERTIS) instrument on the ESA/JAXA BepiColombo mission, which will study the surface mineralogy over a wavelength range of 7–14 μm at a spatial resolution of 500 m/pixel. The measured reflectance of these sulfides in 0.2–100 μm at various phase angles will support the interpretation of measurements from past (MDIS, MASCS on MESSENGER) and future missions (SIMBIO-SYS on BepiColombo).

¹Sedykh, E.M.,¹Gromyak, I.N.,¹Lorents, K.A.,¹Skripnik, A.Y.,¹Kolotov, V.P.
Journal of Analytical Chemistry 74, 393-400 Link to Article [DOI: 10.1134/S1061934819040129]
¹Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, 119991, Russian Federation

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¹Maksimova, A.A.,²Unsalan, O.,¹Chukin, A.V.,¹Oshtrakh, M.I.
Hyperfine Interactions 240, 47 Link to Article [DOI: 10.1007/s10751-019-1593-8]
¹Institute of Physics and Technology, Ural Federal University, Ekaterinburg, 620002, Russian Federation
²Department of Physics, Faculty of Science, Ege University, Izmir, Bornova 35100, Turkey

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