¹Kennda L. Lynch, ²Briony H. Horgan, ¹Junko Munakata‐Marr, ³Jennifer Hanley, ⁴Robin J. Schneider, ⁵Kevin A. Rey, ¹John R. Spear, ⁶W. Andrew Jackson, ⁵Scott M. Ritter
¹Department of Civil and Environmental Engineering, Colorado School of Mines, Golden, Colorado, USA
²Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, USA
³Southwest Research Institute, Boulder, Colorado, USA
⁴Department of Chemistry & Geochemistry, Colorado School of Mines, Golden, Colorado, USA
⁵Department of Geological Sciences, Brigham Young University, Provo, Utah, USA
⁶Department of Civil Engineering, Texas Tech University, Lubbock, Texas, USA
Department of Geological Sciences, Brigham Young University, Provo, Utah, USA

The identification and characterization of aqueous minerals within ancient lacustrine environments on Mars is a high priority for determining the past habitability of the red planet. Terrestrial analog studies are useful both for understanding the mineralogy of lacustrine sediments, how the mineralogy varies with location in a lacustrine environment, and for validating the use of certain techniques such as visible-near-infrared spectroscopy (VNIR). In this study, sediments from the Pilot Valley paleolake basin of the Great Salt Lake desert were characterized using visible to near infrared spectroscopy (VNIR) as an analog for Martian paleolake basins. The spectra and subsequent interpretations were then compared to mineralogical characterization by ground truth methods, including X-ray diffraction (XRD), automated scanning electron microscopy (QEMSCAN), and several geochemical analysis techniques. In general, there is good agreement between VNIR and ground truth methods on the major classes of minerals present in the lake sediments and VNIR spectra can also easily discriminate between clay-dominated and salt-dominated lacustrine terrains within the paleolake basin. However, detection of more detailed mineralogy is difficult with VNIR spectra alone as some minerals can dominate the spectra even at very low abundances. At this site, the VNIR spectra are dominated by absorption bands that are most consistent with gypsum and smectites, though the ground truth methods reveal more diverse mineral assemblages that include a variety of sulfates, primary and secondary phyllosilicates, carbonates and chlorides. This study provides insight into the limitations regarding the use of VNIR in characterizing complex mineral assemblages inherent in lacustrine settings.

Reference
Lynch KL, Horgan BH, Munakata‐Marr J, Hanley J, Schneider RJ, Rey KA, Spear JR, Jackson WA, Ritter SM (2015) Near-Infrared Spectroscopy of Lacustrine Sediments in the Great Salt Lake Desert: An Analog Study for Martian Paleolake Basins. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2014JE004707]

Published by arrangement with John Wiley&Sons

¹Amanda Albright Olsen,²Elisabeth Hausrath,³J. Donald Rimstidt
¹School of Earth and Climate Sciences, University of Maine, Orono, ME, USA
²Department of Geoscience, University of Nevada, Las Vegas, Las Vegas, NV, USA
³Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA

High salinity brines, although rare on Earth’s surface, may have been important in the geologic history of Mars. Increasing evidence suggests the importance of liquid brines in multiple locations on Mars. In order to interpret the effect of high ionic strength brines on olivine dissolution, which is widely present on Mars, forty-seven new batch reactor experiments combined with 35 results from a previous study conducted at 25°C from 1 < pH < 4 in magnesium sulfate, sodium sulfate, magnesium nitrate, and potassium nitrate solutions with ionic strengths as high as 12 m show that very high ionic strength brines have an inhibitory effect of forsterite dissolution rates. Multiple linear regression analysis of the data suggests that the inhibition in dissolution rates is due to decreased water activity at high ionic strengths. Regression models also show that mMg up to 4 m, and mSO4 up to 3 m have no effect on forsterite dissolution rates. The effect of decreasing dissolution rates with decreasing aH2O is consistent with the idea that water acts as a ligand that participates in the dissolution process. Less available water to participate in the dissolution reaction results in a slower dissolution rate. Multiple linear regression analysis of the data produces the rate equation inline image. Forsterite in dilute solutions with a water activity of one dissolve twice as fast as those in brines with a water activity of 0.8.

Reference
Olsen AA, Hausrath E, Rimstidt JD (2015) Forsterite dissolution rates in Mg-sulfate-rich Mars-analog brines, and implications the aqueous history of Mars. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2014JE004664]

Published by arrangement with John Wiley&Sons

¹Kevin M. Cannon, ¹John F. Mustard, ^2,3Carl B. Agee
¹Department of Earth, Environmental and Planetary Sciences, Brown University, Box 1846, RI 02903, United States
²Institute of Meteoritics, University of New Mexico, Albuquerque, NM 87131, United States
³Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, United States

Northwest Africa (NWA) 7034 is the first breccia meteorite from Mars, and unlike the shergottite, nakhlite, and chassignite (SNC) martian meteorites, it matches the estimated chemical composition of martian crust. Here we show that the visible-infrared reflectance spectrum of NWA 7034 is unique compared to other SNCs and is more similar than them to remotely sensed data from Mars, suggesting the martian regolith may contain significant brecciated material produced during heavy bombardment of the crust.

Reference
Cannon KM, Mustard JF, Agee CB (2015) Evidence for a Widespread Basaltic Breccia Component in the Martian Low-Albedo Regions from the Reflectance Spectrum of Northwest Africa 7034. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.01.016]

Copyright Elsevier

¹M.R. Lee, ^1,2T. Tomkinson, ¹L.J. Hallis, ²D.F. Mark
¹School of Geographical and Earth Sciences, University of Glasgow, Gregory Building, Lilybank Gardens, Glasgow G12 8QQ, U.K.
²Scottish Universitites Environmental Research Centre, Rankine Avenue, Scottish Enterprise Technology Park, East Kilbride, G75 0QF, U.K.

The Lafayette meteorite is an olivine clinopyroxenite that crystallized on Mars ∼1300 million years ago within a lava flow or shallow sill. Liquid water entered this igneous rock ∼700 million years later to produce a suite of secondary minerals, collectively called ‘iddingsite’, that occur as veins within grains of augite and olivine. The deuterium/hydrogen ratio of water within these secondary minerals shows that the aqueous solutions were sourced from one or more near-surface reservoirs. Several petrographically distinct types of veins can be recognised by differences in their width, shape, and crystallographic orientation. Augite and olivine both contain veins of a very fine grained hydrous Fe- and Mg-rich silicate that are ∼1-2 micrometres in width and lack any preferred crystallographic orientation. These narrow veins formed by cementation of pore spaces that had been opened by fracturing and probably in response to shock. The subset of olivine-hosted veins whose axes lie parallel to (001) have serrated walls, and formed by widening of the narrow veins by interface coupled dissolution-precipitation. Widening started by replacement of the walls of the narrow precursor veins by Fe-Mg silicate, and a crystallographic control on the trajectory of the dissolution-precipitation front created micrometre-scale {111} serrations. The walls of many of the finely serrated veins were subsequently replaced by siderite, and the solutions responsible for carbonation of olivine also partially recrystallized the Fe-Mg silicate. Smectite was the last mineral to form and grew by replacement of siderite. This mineralization sequence shows that Lafayette was exposed to two discrete pulses of aqueous solutions, the first of which formed the Fe-Mg silicate, and the second mediated replacement of vein walls by siderite and smectite. The similarity in size, shape and crystallographic orientation of iddingsite veins in the Lafayette meteorite and in terrestrial basalts demonstrates a common microstructural control on water-mineral interaction between Mars and Earth, and indicates that prior shock deformation was not a prerequisite for aqueous alteration of the martian crust.

Reference
Lee MR, Tomkinson T, Hallis LJ, Mark DF (2015) Formation of iddingsite veins in the martian crust by centripetal replacement of olivine: Evidence from the nakhlite meteorite Lafayette. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.01.022]

Copyright Elsevier