¹Doris Breuer, ¹Ana-Catalina Plesa, ^1,2Nicola Tosi, ¹Matthias Grott
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12727]
¹DLR, Institute of Planetary Research, Berlin, Germany
²Department of Astronomy and Astrophysics, Technische Universität Berlin, Berlin, Germany
Published by arrangement with John Wiley & Sons

Petrological analysis of the Martian meteorites suggests that rheologically significant amounts of water are present in the Martian mantle. A bulk mantle water content of at least a few tens of ppm is thus expected to be present despite the potentially efficient degassing during accretion, magma ocean solidification, and subsequent volcanism. We examine the dynamical consequences of different thermochemical evolution scenarios testing whether they can lead to the formation and preservation of mantle reservoirs, and compare model predictions with available data. First, the simplest scenario of a homogenous mantle that emerges when ignoring density changes caused by the extraction of partial melt is found to be inconsistent with the isotopic evidence for distinct reservoirs provided by the analysis of the Martian meteorites. In a second scenario, reservoirs can form as a result of partial melting that induces a density change in the depleted mantle with respect to its primordial composition. However, efficient mantle mixing prevents these reservoirs from being preserved until present unless they are located in the stagnant lid. Finally, reservoirs could be formed during fractional crystallization of a magma ocean. In this case, however, the mantle would likely end up being stably stratified as a result of the global overturn expected to accompany the fractional crystallization. Depending on the assumed density contrast, little secondary crust would be produced and the lithosphere would be extremely cool and dry, in contrast to observations. In summary, it is very challenging to obtain a self-consistent evolution scenario that satisfies all available constraints.

¹William H. Farrand, ²Jeffrey R. Johnson, ³Melissa S. Rice, ⁴Alian Wang, ⁵James F. Bell III
American Mineralogist 101, 2005-2019  Link to Article [DOI: 10.2138/am-2016-5627]
¹Space Science Institute, 4750 Walnut Street, number 205, Boulder, Colorado 80301, U.S.A.
²Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, Maryland 20723, U.S.A.
³Department of Geology, Western Washington University, 516 High Street, Bellingham, Washington 98225, U.S.A.
⁴Department of Earth and Planetary Sciences, Washington University, Campus Box 1169, One Brookings Drive, St. Louis, Missouri 63130, U.S.A.
⁵School of Earth and Space Exploration, Arizona State University, P.O. Box 87104, Tempe, Arizona 85287, U.S.A.
Copyright: The Mineralogical Society of America

Multispectral visible and near infrared (VNIR) observations from the Mars Exploration Rover Pancam multispectral stereo camera systems are consistent with materials having been subjected to various aqueous processes. Ferric oxides in the form of hematite in the Burns and Grasberg formations of Meridiani Planum have been well characterized by Opportunity on the basis of strong 535 and 864 nm absorptions and positive 754–1009 nm and 934–1009 nm slopes. On the rim of Noachian-aged Endeavour crater, Opportunity has observed light-toned veins with high Ca and S, as determined by the rover’s Alpha Particle X-ray Spectrometer (APXS), and a negative 934–1009 nm slope in VNIR spectra extracted from Pancam data, indicative of a 1000 nm H2O overtone absorption. Together these observations indicate that the veins are composed of gypsum. Rocks overturned by Opportunity on the Murray Ridge portion of the Endeavour crater rim display dark- and light-toned coatings. The dark-toned coatings have a red, featureless slope that is consistent with the slope observed in laboratory spectra of high-valence manganese oxide minerals. Potential Mn oxide coatings may also be associated with some exposures of the Grasberg formation. APXS results for high Mg and S in the light-toned coatings of the Murray Ridge overturned rocks and a negative 934–1009 nm slope are consistent with hydrated Mg-sulfates. Opportunity has also observed spectral features in rocks that are consistent with orbital observations of Fe-smectites, as well as Al-smectites and possible hydrated silica in light-toned fracture-fill materials. The Spirit rover observed sulfate-rich light-toned soils exposed by the rover’s wheels. Several of these soil observations contained spectral features, such as a broad absorption centered near 800 nm, consistent with ferric sulfate minerals, a finding confirmed by the rover’s Mössbauer spectrometer. Spirit also excavated light-toned Si-rich soils. These soils have a flat near-infrared spectrum with a drop in reflectance from 934–1009 nm that is consistent with free water contained in voids or adsorbed onto the surface of the silica.

^1,2P. Mane, ¹R. Hervig, ^1,2M. Wadhwa, ^1,2L. A. J. Garvie, ^3,4J. B. Balta, ³H. Y. McSween Jr
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12717]
¹School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, USA
²Center for Meteorite Studies, Arizona State University, Tempe, Arizona, USA
³Department of Earth and Planetary Sciences and Planetary Geosciences Institute, University of Tennessee, Knoxville, Tennessee, USA
⁴Department of Geology and Planetary Science, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
Published by arrangement with John Wiley & Sons

The hydrogen isotopic composition of planetary reservoirs can provide key constraints on the origin and history of water on planets. The sources of water and the hydrological evolution of Mars may be inferred from the hydrogen isotopic compositions of mineral phases in Martian meteorites, which are currently the only samples of Mars available for Earth-based laboratory investigations. Previous studies have shown that δD values in minerals in the Martian meteorites span a large range of −250 to +6000‰. The highest hydrogen isotope ratios likely represent a Martian atmospheric component: either interaction with a reservoir in equilibrium with the Martian atmosphere (such as crustal water), or direct incorporation of the Martian atmosphere due to shock processes. The lowest δD values may represent those of the Martian mantle, but it has also been suggested that these values may represent terrestrial contamination in Martian meteorites. Here we report the hydrogen isotopic compositions and water contents of a variety of phases (merrillites, maskelynites, olivines, and an olivine-hosted melt inclusion) in Tissint, the latest Martian meteorite fall that was minimally exposed to the terrestrial environment. We compared traditional sample preparation techniques with anhydrous sample preparation methods, to evaluate their effects on hydrogen isotopes, and find that for severely shocked meteorites like Tissint, the traditional sample preparation techniques increase water content and alter the D/H ratios toward more terrestrial-like values. In the anhydrously prepared Tissint sample, we see a large range of δD values, most likely resulting from a combination of processes including magmatic degassing, secondary alteration by crustal fluids, shock-related fractionation, and implantation of Martian atmosphere. Based on these data, our best estimate of the δD value for the Martian depleted mantle is −116 ± 94‰, which is the lowest value measured in a phase in the anhydrously prepared section of Tissint. This value is similar to that of the terrestrial upper mantle, suggesting that water on Mars and Earth was derived from similar sources. The water contents of phases in Tissint are highly variable, and have been affected by secondary processes. Considering the H2O abundances reported here in the driest phases (most likely representing primary igneous compositions) and appropriate partition coefficients, we estimate the H2O content of the Tissint parent magma to be ≤0.2 wt%.

¹Walter S. Kiefer, ^1,2Qingsong Li
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12720]
¹Lunar and Planetary Institute, Houston, Texas, USA
²BP, Houston, Texas, USA
Published by arrangement with John Wiley & Sons

Based on meteorite evidence, the present-day Martian mantle has a combined abundance of up to a few hundred ppm of H2O, Cl, and F, which lowers the solidus and enhances the magma production rate. Adiabatic decompression melting in upwelling mantle plumes is the best explanation for young (last 200 Myr) volcanism on Mars. We explore water undersaturated mantle plume volcanism using a finite element mantle convection model coupled to a model of hydrous peridotite melting. Relative to a dry mantle, the reduction in solidus temperature due to water increases the magma production rate by a factor of 1.3–1.7 at 50 ppm water and by a factor of 1.9–3.2 at 200 ppm water. Mantle water also decreases the viscosity and increases the vigor of convection, which indirectly increases the magma production rate by thinning the thermal boundary layer and increasing the flow velocity. At conditions relevant to Mars, these indirect effects can cause an order of magnitude increase in the magma production rate. Using geologic and geophysical observations of the Late Amazonian magma production rate and geochemical observations of melt fractions in shergottite meteorites, present-day Mars is constrained to have a core–mantle boundary temperature of ~1750 to 1800 °C and a volume-averaged thermal Rayleigh number of 2 × 106 to 107, indicating that moderately vigorous mantle convection has persisted to the present day. Melting occurs at depths of 2.5–6 GPa and is controlled by the Rayleigh number at the low pressure end and by the mantle water concentration at high pressure.

^1,2,3Eve L. Berger, ³Dante S. Lauretta, ^3,4Thomas J. Zega, ⁵Lindsay P. Keller
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12721]
¹GeoControl Systems, Inc.—Jacobs JETS contract—NASA Johnson Space Center, Houston, Texas, USA
²NASA Postdoctoral Program, Oak Ridge, Tennessee, USA
³Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA
⁴Naval Research Laboratory, Washington, District of Columbia, USA
⁵NASA Johnson Space Center, Houston, Texas, USA
Published by arrangement with John Wiley & Sons

¹P.G.Conrad et al. (>10*)
Earth and Planetary Science Letters 454, 1-9 Link to Article [http://dx.doi.org/10.1016/j.epsl.2016.08.028]
¹Goddard Space Flight Center, Greenbelt, MD 20771, USA
Copyright Elsevier
*Find the extensive, full author and affiliation list on the publishers website

Mars Science Laboratory’s Sample Analysis at Mars (SAM) investigation has measured all of the stable isotopes of the heavy noble gases krypton and xenon in the martian atmosphere, in situ, from the Curiosity Rover at Gale Crater, Mars. Previous knowledge of martian atmospheric krypton and xenon isotope ratios has been based upon a combination of the Viking mission’s krypton and xenon detections and measurements of noble gas isotope ratios in martian meteorites. However, the meteorite measurements reveal an impure mixture of atmospheric, mantle, and spallation contributions. The xenon and krypton isotopic measurements reported here include the complete set of stable isotopes, unmeasured by Viking. The new results generally agree with Mars meteorite measurements but also provide a unique opportunity to identify various non-atmospheric heavy noble gas components in the meteorites. Kr isotopic measurements define a solar-like atmospheric composition, but deviating from the solar wind pattern at 80Kr and 82Kr in a manner consistent with contributions originating from neutron capture in Br. The Xe measurements suggest an intriguing possibility that isotopes lighter than 132Xe have been enriched to varying degrees by spallation and neutron capture products degassed to the atmosphere from the regolith, and a model is constructed to explore this possibility. Such a spallation component, however, is not apparent in atmospheric Xe trapped in the glassy phases of martian meteorites.

¹David C. Rubie, ¹Vera Laurenz, ^1,2Seth A. Jacobson, ²Alessandro Morbidelli, ³Herbert Palme, ¹Antje K. Vogel, ¹Daniel J. Frost
Science 353, 6304, 1141-1144 Link to Article [DOI: 10.1126/science.aaf6919]
¹Bayerisches Geoinstitut, Bayreuth, Germany.
²Observatoire de la Cote d’Azur, Nice, France.
³Forschungsinstitut und Naturmuseum Senckenberg, Frankfurt, Germany
Reprinted with permission from AAAS

Highly siderophile elements (HSEs) are strongly depleted in the bulk silicate Earth (BSE) but are present in near-chondritic relative abundances. The conventional explanation is that the HSEs were stripped from the mantle by the segregation of metal during core formation but were added back in near-chondritic proportions by late accretion, after core formation had ceased. Here we show that metal-silicate equilibration and segregation during Earth’s core formation actually increased HSE mantle concentrations because HSE partition coefficients are relatively low at the high pressures of core formation within Earth. The pervasive exsolution and segregation of iron sulfide liquid from silicate liquid (the “Hadean matte”) stripped magma oceans of HSEs during cooling and crystallization, before late accretion, and resulted in slightly suprachondritic palladium/iridium and ruthenium/iridium ratios.

^1,2J.H. Hooijschuur, ¹M.F.C. Verkaaik, ²G.R. Davies, ¹F. Ariese
Netherlands Journal of Geosciences – Geologie en Mijnbouw 95, 141-151 Link to Article [DOI: http://dx.doi.org/10.1017/njg.2015.3]
¹LaserLaB, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, the Netherlands
²Deep Earth and Planetary Science, Faculty of Earth and Life Sciences, VU University Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, the Netherlands

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^1,2Iuliia Myrgorodska, ¹Thomas Javelle, ¹Cornelia Meinert, ¹Uwe J. Meierhenrich
Israel Journal of Chemistry (in Press) Link to Article [DOI: 10.1002/ijch.201600067]
¹Institut de Chimie de Nice ICN, UMR CNRS 7272, Université Nice Sophia Antipolis, Faculté des Sciences, Nice, France
²Synchrotron SOLEIL, L’Orme des Merisiers, Gif-sur-Yvette, France

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¹M.H. Steiner, ¹E.M. Hausrath, ²M.E. Elwood Madden, ¹O. Tschauner, ³B.L. Ehlmann, ⁴A.A. Olsen, ¹S.R. Gainey, ⁵J.S. Smith
Geochimica et Cosmochmica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2016.08.035]
¹Department of Geoscience, University of Nevada, Las Vegas 4505 S. Maryland Parkway, Las Vegas, NV 89154-4010
²School of Geology and Geophysics, University of Oklahoma, 100 E Boyd, Suite 710, Norman, OK 73019
³Division of Planetary Science, California Institute of Technology, 1200 East California Boulevard Pasadena, CA 91125
⁴Department of Earth Sciences, University of Maine, 5790 Bryand Global Sciences Center, Orono, ME 04469
⁵HPCAT, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, IL 60439
Copyright Elsevier

Increasing evidence suggests the presence of recent liquid water, including brines, on Mars. Brines have therefore likely impacted clay minerals such as the Fe-rich mineral nontronite found in martian ancient terrains. To interpret these interactions, we conducted batch experiments to measure the apparent dissolution rate constant of nontronite at 25.0 °C at activities of water (aH2O) of 1.00 (0.01 M CaCl2 or NaCl), 0.75 (saturated NaCl or 3.00 mol kg-1 CaCl2), and 0.50 (5.00 mol kg-1 CaCl2). Experiments at aH2O = 1 (0.01 M CaCl2) were also conducted at 4.0 °C, 25.0 °C, and 45.0 °C to measure an apparent activation energy for the dissolution of nontronite.

Apparent dissolution rate constants at 25.0 °C in CaCl2-containing solutions decrease with decreasing activity of water as follows: 1.18×10-12 ± 9 x 10-14 moles mineral m-2 s-1(aH2O = 1)> 2.36 x 10-13 ± 3.1 x 10-14 moles mineral m-2 s-1(aH2O = 0.75)> 2.05 x 10-14 ± 2.9 x 10-15 moles mineral m-2 s-1 (aH2O = 0.50). Similar results were observed at 25.0 °C in NaCl-containing solutions : 1.89 x 10-12 ± 1 x 10-13 moles mineral m-2 s-1 (aH2O = 1)> 1.98 x 10-13 ± 2.3 x 10-14 moles mineral m-2 s-1(aH2O = 0.75). This decrease in apparent dissolution rate constants with decreasing activity of water follows a relationship of the form: log kdiss = 3.70 ± 0.20 x aH2O – 15.49, where kdiss is the apparent dissolution rate constant, and aH2O is the activity of water. The slope of this relationship (3.70 ± 0.20) is within uncertainty of that of other minerals where the relationship between dissolution rates and activity of water has been tested, including forsteritic olivine (log R = 3.27 ± 0.91 x aH2O – 11.00) ( Olsen et al., 2015)and jarosite (log R = 3.85 ± 0.43 x aH2O – 12.84) ( Dixon et al., 2015), where R is the mineral dissolution rate. This result allows prediction of mineral dissolution as a function of activity of water and suggests that with decreasing activity of water, mineral dissolution will decrease due to the role of water as a ligand in the reaction.

Apparent dissolution rate constants in the dilute NaCl solution (1.89 x 10-12 ± 1 x 10-13 moles mineral m-2 s-1) are slightly greater than those in the dilute CaCl2 solutions (1.18 x 10-12 ± 9 x 10-14 moles mineral m-2 s-1). We attribute this effect to the exchange of Na with Ca in the nontronite interlayer. An apparent activation energy of 54.6 ± 1.0 kJ/mol was calculated from apparent dissolution rate constants in dilute CaCl2- containing solutions at temperatures of 4.0 °C, 25.0 °C, and 45.0 °C: 2.33×10-13 ± 1.3 x 10-14 moles mineral m-2 s-1(4.0 °C), 1.18 x 10-12 ± 9 x 10-14 moles mineral m-2 s-1(25.0 °C), and 4.98 x 10-12 ± 3.8 x 10-13 moles mineral m-2 s-1(45.0 °C).

The greatly decreased dissolution of nontronite in brines and at low temperatures suggests that any martian nontronite found to be perceptibly weathered may have experienced very long periods of water-rock interaction with brines at the low temperatures prevalent on Mars, with important implications for the paleoclimate and long-term potential habitability of Mars.