¹Patrick H. Donohue, ¹Clive R. Neal
American Mineralogist 103, 284-297 Link to Article [DOI: https://doi.org/10.2138/am-2018-6173]
¹Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, Indiana 46556, U.S.A.
Copyright: The Mineralogical Society of America

Basalt fragment 71597 is the sole high-titanium mare basalt showing evidence for olivine accumulation during formation. The petrogenesis of this unique sample was investigated using quantitative textural analysis and major- and trace-element mineral geochemistry. Crystal size distribution analysis identified two size populations of olivine, which we separate into cumulate and matrix olivine. The spatial distribution of olivine also supports clustering of olivine crystals, likely during accumulation. Observed mineral chemistry was consistent with an origin through olivine accumulation, although where this occurred cannot be discerned (e.g., in ponded melts at the base of or in the lunar crust, or within a thick high-Ti basalt flow). Attempts to place 71597 within a geochemical group were inconclusive both using subtraction of cumulate olivine from bulk composition, and by modal recombination of major phases. However, equilibrium liquid compositions of augite and plagioclase are determined to be consistent with an origin by fractionation from the Type B2 chemical suite of Apollo 17 high-Ti basalts. This method of classification has potential for placing other Type U (“Unclassified”) basalts into chemical suites.

^1,2Fan Wang, ³Brenda B. Bowen, ⁴Ji-Hye Seo, ^2,4Greg Michalski
American Mineralogist 103, 197-206 Link to Article [DOI: https://doi.org/10.2138/am-2018-6141]
¹School of Environment and Energy, Peking University Shenzhen Graduate School, Shenzhen, Guangdong 518055, China
²Department of Earth, Atmospheric and Planetary Sciences, Purdue University, West Lafayette, Indiana 47907, U.S.A.
³Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112, U.S.A.
⁴Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, U.S.A.
Copyright: The Mineralogical Society of America

Large amounts of nitrate salts occur in very specific environments and somewhat rare hyper-arid conditions, which may provide clues to fundamentally different nitrogen cycling and life survival mechanisms. Remote detection of ancient and modern nitrates on Earth and on other planetary bodies where they may occur requires a detailed understanding of their visible to near infrared (VNIR) spectral signatures. This study explores the VNIR spectral characteristics of several synthetic nitrate salts, sulfate minerals, and nitrate-bearing field samples from the Atacama Desert, Chile, to identify diagnostic spectral features of nitrate and possible interferences from other coexisting minerals. Results indicated that most of the nitrate salts have characteristic absorptions around 1.81, 1.94, 2.06, 2.21, and 2.42 μm. A significant positive correlation exists between the continuum-removed band depths of the 2.42 μm absorption and nitrate contents for the Atacama regolith samples, especially for samples with >10 wt% nitrate. The five absorption features of nitrate in the field spectra collected from multiple nitrate-rich regions in the Atacama Desert were then evaluated to determine the variabilities in these features in natural settings, while the band depths of 2.42 μm absorption were further calculated on the continuum-removed field spectra to estimate the nitrate abundances at the study sites. This work will supplement spectral libraries where nitrate spectra are lacking and have implications for future comparisons to planetary spectra to search for potentially life-related nitrate on Mars.

¹James W. Dottin III, ¹James Farquhar, ²Jabrane Labidi
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.01.013]
¹Department of Geology, University of Maryland, College Park, MD 20742, USA
²Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095-1567, USA
Copyright Elsevier

This study reports the quadruple sulfur isotope composition of troilite nodules from Main Group Pallasites. Values range from -0.23‰ to 0.34‰ (average = 0.03±0.17‰ S.D.) in δ34S and 0.008‰ to 0.025‰ (average = 0.018± 0.006‰ S.D.) in Δ33S and -0.38 to -0.01 (average = -0.17±0.11‰ S.D.) in Δ36S. The variance of these analyses is comparable to estimates of analytical uncertainty (±0.3‰, ± 0.008‰, and ±0.3‰, for δ34S, Δ33S, and Δ36S, respectively) and the average of these values is taken as a constraint on the composition of sulfur in the MG Pallasite parent body. The different Δ33S value compared to CDT and IAB iron meteorites at a similar δ34S value is interpreted as a mass-independent signature. This signature is similar in magnitude and direction to previously published values observed in IIIAB iron meteorites, further supporting a genetic relationship between the two groups of meteorites.