¹F.Zambon et al. (>10)*
¹INAF-IAPS Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere, 100, 00133 Rome, Italy
*Find the extensive, full author and affiliation list on the publishers website

Vesta’s surface is mostly composed of pyroxene-rich lithologies compatible with howardite, eucrite and diogenite (HED) meteorites (e.g., Feierberg, Drake, 1980 and McCord, Adams, Johnson, 1970). Data provided by the Visible and Infrared (VIR) spectrometer, onboard the NASA Dawn spacecraft, revealed that all Vesta reflectance spectra show absorption bands at ∼ 0.9 μm and ∼ 1.9 μm, which are typical of iron-bearing pyroxenes ( De Sanctis et al., 2012a). Other minerals may be present in spectrally significant concentrations; these include olivine and opaque phases like those found in carbonaceous chondrites. These additional components modify the dominant pyroxene absorptions. We apply linear spectral unmixing on bright material (BM) units of Vesta to identify HEDs and non-HED phases. We explore the limits of applicability of linear spectral unmixing, testing it on laboratory mixtures. We find that the linear method is applicable at the VIR pixel resolution and it is useful when the surface is composed of pyroxene-rich lithologies containing moderate quantities of carbonaceous chondrite, olivine, and plagioclase. We found three main groups of BM units: eucrite-rich, diogenite-rich, and olivine-rich. For the non-HED spectral endmember, we choose either olivine or a featureless component. Our work confirms that Vesta’s surface contains a high content of pyroxenes mixed with a lower concentration of other phases. In many cases, the non-HED endmember that gives the best fit is the featureless phase, which causes a reduction in the strength of both bands. The anticorrelation between albedo and featureless endmember indicates that this phase is associated with low-albedo, CC-like opaque material. Large amounts of olivine have been detected in Bellicia, Arruntia and BU14 BM units. Other sites present low olivine content ( < 30%) mostly with a high concentration of diogenite.

Reference
Zambon F et al. (2016) Lithologic variation within bright material on Vesta revealed by linear spectral unmixing. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.01.009]
Copyright Elsevier

^1,3Anna Neubeck, ²Marek Tulej, ³Magnus Ivarsson, ¹Curt Bromana, ²Andreas Riedo, ⁴Sean McMahon, ²Peter Wurz, ³Stefan Bengtson
¹Department of Geological Sciences, Stockholm University, Svante Arrhenius väg 8, 106 91 Stockholm, Sweden
²Space Research and Planetary Sciences, Physics Institute, University of Bern, CH-3012 Bern, Switzerland
³Department of Palaeobiology and Nordic Center for Earth Evolution (NordCEE), Swedish Museum of Natural History, Stockholm, Sweden
⁴Department of Geology & Geophysics, Yale University, Connecticut, USA

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

Reference
Neubeck A, Tulej M, Ivarsson M, Broman C, Riedo A, McMahon S, Wurz P, Bengtson S (2015) Mineralogical determination in situ of a highly heterogeneous material using a miniaturized laser ablation mass spectrometer with high spatial resolution. International Journal of Astrobiology (in Press)
Link to Article [DOI: http://dx.doi.org/10.1017/S1473550415000269]

¹Alian Wang,¹Bradley L. Jolliff,²Yang Liu,¹Kathryn Connor
¹Dept. Earth and Planetary Sciences and McDonnell Center for Space Sciences, Washington University in St. Louis, USA
²Southwest Research Institute, San Antonio, Texas, USA

Monohydrated Mg sulfate (MgSO4·H2O) and polyhydrated sulfate are the most common and abundant hydrous sulfates observed thus far on Mars. They are widely distributed and coexist in many locations. On the basis of results from two new sets of experiments, in combination with past experimental studies and the subsurface salt mineralogy observed at a saline playa (Dalangtan, DLT) in a terrestrial analogue hyperarid region on the Tibet Plateau, we can now set new constraints on the nature and origin of these two major martian sulfates. Starkeyite (MgSO4·4H2O) is the best candidate for polyhydrated sulfate. MgSO4·H2O in the form of “LH-1w” [Wang et al., 2009], generated from dehydration of Mg-sulfates with high degrees of hydration, is the most likely mineral form for the majority of martian monohydrated Mg-sulfate. Two critical properties of Mg-sulfates are responsible for the coexistence of these two phases that have very different degrees of hydration: (1) the metastability of a sub-structural unit in starkeyite at relatively low temperatures; and (2) catalytic effects attributed to co-precipitated species (sulfates, chlorides, oxides, and hydroxides) from chemically complex brines that help overcome the metastability of starkeyite. The combination of these two properties controls the coexistence of the LH-1w layer and starkeyite layers at many locations on Mars, which sometimes occur in an interbedded stratigraphy. The structural H2O held by these two broadly distributed sulfates represents a large H2O reservoir at the surface and in the shallow subsurface on current Mars.

Reference
Wang A, Jolliff BL, Liu Y, Connor K (2016) Setting Constraints on the Nature and Origin of the two Major Hydrous Sulfates on Mars — Monohydrated and Polyhydrated Sulfates. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2015JE004889]
Published by arrangement with John Wiley&Sons

¹Erwin Dehouck, ²Anne Gaudin, ³Vincent Chevrier, ²Nicolas Mangold
¹Department of Geosciences, State University of New York at Stony Brook, Stony Brook, NY 11794-2100, USA
²Laboratoire de Planétologie et Géodynamique de Nantes (LPGN), CNRS/Université de Nantes, 44322 Nantes, France
³Arkansas Center for Space and Planetary Sciences, University of Arkansas, Fayetteville, AR 72701, USA

Sulfates and Fe-oxides identified on the Martian surface by orbital and in situ missions indicate that oxidizing conditions have existed on early Mars, at least locally and/or episodically. In the context of rock alteration and weathering, redox conditions are especially critical for the behavior of iron, which is soluble in its divalent state but insoluble in its trivalent state. Here, we combine results from a series of laboratory experiments conducted under Mars-like conditions to address the influence of highly-oxidizing compounds such as hydrogen peroxide (H2O2) on the alteration pathways of primary materials. We show that, if early Mars had a dense CO2 atmosphere allowing for relatively “warm and wet” conditions and surface weathering, highly-oxidizing conditions would have strongly inhibited the formation of Fe/Mg-smectite clays from alteration of igneous ferromagnesian minerals, and possibly enhanced the formation of carbonates. But a decade of mineral mapping of the Martian surface show abundant, widespread Fe/Mg-clays and rare carbonates, which we interpret here as a mineralogical record of poorly-oxidizing (or even reducing) conditions during most of the Noachian era. Oxidizing conditions would have occurred later in Martian history as a consequence of a higher rate of H2 escape or of a lower rate of volcanic outgassing, or both.

References
Dehouck E, Gaudin A, Chevrier V, Mangold N (2016) Mineralogical record of the redox conditions on early Mars. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.01.030]
Copyright Icarus

¹Marie Protin, ¹Pierre-Henri Blard, ¹Yves Marrocchi, ¹François Mathon
¹CRPG, UMR 7358, CNRS-Université de Lorraine, 54500 Vandoeuvre-lès-Nancy, France

This study reports new experimental results that demonstrate that large amounts of atmospheric helium may be adsorbed onto the surfaces of olivine grains. This behavior is surface-area-related in that this contamination preferentially affects grains that are smaller than 125 μm in size. One of the most striking results of our study is that in vacuo heating at 900°C for 15 minutes is not sufficient to completely remove the atmospheric contamination. This suggests that the adsorption of helium may involve high-energy trapping of helium through irreversible anomalous adsorption. This trapping process of helium can thus be compared to a “lobster pot” adsorption: atmospheric helium easily gets in, but hardly gets out. While this type of behavior has previously been reported for heavy noble gases (Ar, Kr, Xe), this is the first time that it has been observed for helium. Adsorption of helium has, until now, generally been considered to be negligible on silicate surfaces. Our findings have significant implications for helium and noble gas analysis of natural silicate samples, such as for cosmic-ray exposure dating or noble gas characterization of extraterrestrial material. Analytical procedures in future studies should be adapted in order to avoid this contamination. The results of this study also allow us to propose an alternative explanation for previously described matrix loss of cosmogenic 3He.

Reference
Protin M, Blard P-H, Marrocchi Y, Mathon F (2016) Irreversible Adsorption of Atmospheric Helium on Olivine: A Lobster Pot Analogy. Geochmica et Cosmochmica (in Press)
Link to Article [doi:10.1016/j.gca.2016.01.032]
Copyright Elsevier

^1,2,3Zongcheng Lin et al. (>10)*
¹Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai 264209, China
²Department of Earth & Planetary Sciences and McDonnell Center for the Space Sciences, Washington University, St Louis, Missouri 63130, USA
³Key Laboratory of Lunar and Deep Space Exploration, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China
*Find the extensive, full author and affiliation list on the publishers website

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

Reference
Lin Z et al. (2015) Correlated compositional and mineralogical investigations at the Chang′e-3 landing site. Nature Communications 6,8880
Link to Article [doi:10.1038/ncomms9880]

^1,2Zongcheng Ling, ¹Fengke Cao, ¹Yuheng Ni, ¹Zhongchen Wu, ¹Jiang Zhang, ¹Bo Li
¹Shandong Provincial Key Laboratory of Optical Astronomy & Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai 264209, China
²Key Laboratory of Lunar and Deep Space Exploration, Chinese Academy of Sciences, Beijing 100012, China

Detailed chemical, structural and spectroscopic properties of jarosite solid solution minerals are key information for their potential discoveries by future remote sensing and in-situ detections on Mars. We successfully synthesized seven homogeneous K-Na jarosite solid solutions under hydrothermal conditions at 140°C, whose phase identifications and chemical compositions are confirmed by X-ray diffraction (XRD) and inductively coupled plasma mass spectrometry (ICP-MS). The chemical ratios of K/(K+Na) in jarosite solid solutions lead to systematic shifts of their characteristic Raman peaks ν1 (SO4)2− (from 1006 to 1011.3 cm−1), ν3 (SO4)2− (from 1100.6 to 1111.2 cm−1), ν2 (SO4)2− (from 434.2 to 444.8 cm−1) with the increase of Na content. While the OH stretching mode decreases with even larger peak position variations (e.g., ∼3410 cm−1 peak shifts from 3410.5 to 3385.7 cm−1) as the K-Na jarosite solid solutions are enriched in Na content. Raman spectroscopic measurements of the seven K-Na jarosite solid solutions enabled us to build a calibration that uses Raman peak positions to estimate K-Na variation in jarosite, which is the key step for their possible applications in the future Raman applications on Mars’ missions (e.g., ExoMars and Mars 2020 missions). The band assignments and compositional related variations of their XRD, near-infrared (NIR) and mid-infrared (MIR) spectra also provide informative clues for identifying the jarosite minerals and inferring their composition during Martian in-situ and remote sensing measurements.

Reference
Ling Z,Cao F,Ni Y,Wu Z,Jiang Zhanga,Li B (2016) Correlated analysis of chemical variations with spectroscopic features of the K-Na jarosite solid solutions relevant to Mars. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.01.028]
Copyright Elsevier

¹Christine E. Jilly-Rehak, ²Gary R. Huss, ³Lydie Bonal, ⁴Eric Twelker
¹Department of Geology and Geophysics, University of Hawai‘i at Mānoa, 1680 East-West Road, POST 517A, Honolulu, HI 96822, USA
²Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, HI, USA
³Institut de Planétologie et d’Astrophysique de Grenoble, Grenoble, France
⁴The Meteorite Market, Port Townsend, WA, USA

We classify a new chondritic find Northwest Africa (NWA) 7402. This meteorite is highly unequilibrated, and is therefore potentially significant for the study of primitive Solar System materials. Mineralogy, mineral chemistry, and modal abundances of minerals indicate that NWA 7402 is most likely an L chondrite. However, the specimen contains a higher abundance of sulfide than commonly seen in ordinary chondrites. The structural order of organic matter in the matrix and the chromium content of Fe-rich olivine grains indicate a petrologic type of 3.1. NWA 7402 largely escaped thermal metamorphism, and secondary phases formed by aqueous alteration are rare to absent. Minor planar fractures and undulatory extinction of olivine grains suggest that NWA 7402 experienced shock up to stage 2 or 3. Terrestrial weathering is heterogeneous in the specimen; much of the stone’s exterior shows substantial Fe oxidation (weathering grade 2), while some parts of the interior remain relatively fresh (weathering grade 1). NWA 7402 has some unusual features that should be investigated further. The sulfide abundance is higher than reported sulfide contents for other L chondrites, and the chromium content of the olivines does not fall on the trend established for unequilibrated ordinary chondrites by Grossman and Brearley (2005).

Reference
Jilly-Rehak CE, Huss GR, Bonal L, Twelker E (2016) Petrography and classification of NWA 7402: A new sulfide-rich unequilibrated ordinary chondrite. Chemie der Erde (in Press)
Link to Article [doi:10.1016/j.chemer.2016.01.001]
Copyright Elsevier

¹Dailto Silva, ²Cristiano Lana,¹Carlos Roberto de Souza Filho
¹Department of Geology and Natural Resources, University of Campinas, Sao Paulo, Brazil
²Department of Geology (DEGEO), Federal University of Ouro Preto (UFOP), Minas Gerais, Brazil

Petrographic and geochemical data obtained on the Araguainha impact crater (Goiás/Mato Grosso States, Brazil) indicate the existence of several molten products that originated during impact-induced congruent melting of an alkali-granite exposed in the inner part of the central uplift of the structure. Although previous studies have described these melts to some extent, there is no detailed discussion on the petrographic and geochemical variability in the granite and its impactogenic derivatives, and therefore, little is known about the geochemical behavior and mobility of trace elements during its fusion in the central part of the Araguainha crater. This paper demonstrates that the preserved granitoid exposed in the core of the structure is a magnesium-rich granite, similar to postcollisional, A-type granites, also found in terrains outside the Araguainha crater, in the Brasília orogenic belt. The molten products are texturally distinct and different from the original rock, but have very similar geochemical composition, making it difficult to separate these lithotypes based on concentrations of major and minor elements. This also applies for trace and rare earth elements (REE), thus indicating a high degree of homogenization during impact-induced congruent melting under high pressure and postshock temperature conditions. Petrographic observations, along with geochemical data, indicate that melting occurs selectively, where some of the elements are transported with the melt. Simultaneously, there is an effective dissolution of the rock (granite), which leads to entrainment of the most resistant solid phases (intact or partially molten minerals) into the melt. Minerals more resistant to melting, such as quartz and oxides, contribute substantially to a chemical balance between the preserved granite and the fusion products generated during the meteoritic impact.

Reference
Silva D, Lana C, de Souza Filho CB (2016) Petrographic and geochemical characterization of the granitic rocks of the Araguainha impact crater, Brazil. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12601]
Published by arrangement with John Wiley & Sons

^1,2Winfried H. Schwarz, ^1,2Mario Trieloff, ¹Klemens Bollinger, ¹Niklas Gantert, ^1,3Vera A. Fernandes, ¹Hans-Peter Meyer, ⁴Hal Povenmire,⁵Elmar K. Jessberger, ^1,2Massimo Guglielmino, ^6,7Christian Koeberl
¹Institut für Geowissenschaften, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 234-236, 69120 Heidelberg, Germany
²Klaus-Tschira-Labor für Kosmochemie, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 234-236, 69120 Heidelberg, Germany
³Museum für Naturkunde – Berlin, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Invalidenstrasse 43, D-10115 Berlin, Germany
⁴7560 Greenboro Drive, #4, West Melbourne, FL 32904
⁵Institut für Planetologie, Universität Münster, Wilhelm Klemm Straße 10, 48419 Münster,Germany
⁶Department of Lithospheric Research, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria
⁷Natural History Museum, Burgring 7, 1010 Vienna, Austria

High resolution 40Ar-39Ar step heating dating of australites and indochinites, representing a large area of the Australasian strewn field, and more recently discovered tektite like glasses from Central America (Belize) and Western Canada, were analysed. Precise plateau ages were obtained in all cases, yielding indistinguishable ages of 789 ± 9 ka for four australites, 783 ± 5 ka for four indochinites, 783 ± 17 ka for one Western Canadian and 769 ± 16 ka for one Belize impact melt glass. Concerning major elements and REEs, australites and the Western Canadian impact melt glass are indistinguishable. If the Western Canadian sample was transported by impact ejection and belongs to the Australasian strewn field, this implies extremely far ballistic transport of 9000 km distance assuming a source crater in southern Asia. The distinct major element and REE composition of the Belize impact melt glass suggests formation in another separate impact event. We conclude that the Australasian/Western Canadian impact melt glasses formed 785 ± 7 ka ago and Belize impact melt glass 769 ± 16 ka ago. The two impact events forming these two strewn fields occurred remarkably closely related in time, i.e., separated by <30 ka.

Reference
Schwarz WH, Trieloff M, Bollinger K, Gantert N, Fernandes VA, Meyer H-P, Povenmire H, Jessberger EK, Guglielmino M, Koeberl (2016) Coeval ages of Australasian, Central American and Western Canadian tektites reveal multiple impacts 790 ka ago. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.12.037]
Copyright Elsevier