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

¹Connor Brolly, ¹John Parnell, ¹Stephen Bowden
¹Department of Geology & Petroleum Geology, University of Aberdeen, Aberdeen, UK

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Reference
Brolly C, Parnell J, Bowden S (2016) Raman spectroscopy: Caution when interpreting organic carbon from oxidising Environments. Planetary and Space Science 121, 53–59
Link to Article [doi:10.1016/j.pss.2015.12.008]

¹Karel Žák, ¹Roman Skála, ²Zdeněk Řanda, ²Jiří Mizera, ³Kurt Heissig,, ¹Lukáš Ackerman, ¹Jana Ďurišová, ¹Šárka Jonášová, ²Jan Kameník, ⁴Tomáš Magna
¹Institute of Geology, The Czech Academy of Sciences, Rozvojová 269, CZ-165 00 Prague 6, Czech Republic
²Nuclear Physics Institute, The Czech Academy of Sciences, Hlavní 130, CZ-250 68 Husinec-Řež, Czech Republic
³Bayerische Staatssammlungen für Paläontologie und Geologie, Paläontolgisches Museum, Richard-Wagner-Straße 10, D-80333 München, Germany
⁴Czech Geological Survey, Klárov 3, CZ-118 21 Prague 1, Czech Republic

Moldavites, tektites of the Central European strewn field, have been traditionally linked with the Ries impact structure in Germany. They are supposed to be derived mainly from the near-surface sediments of the Upper Freshwater Molasse of Miocene age that probably covered the target area before the impact. Comparison of the chemical composition of moldavites with that of inferred source materials requires recalculation of the composition of sediments to their water-, organic carbon- and carbon dioxide-free residuum. This recalculation reflects the fact that these compounds were lost almost completely from the target materials during their transformation to moldavites. Strong depletions in concentrations of many elements in moldavites relative to the source sediments (e.g., Mo, Cu, Ag, Sb, As, Fe) are contrasted with enrichments of several elements in moldavites (e.g., Cs, Ba, K, Rb). These discrepancies can be generally solved using two different approaches, either by involvement of a component of specific chemical composition, or by considering elemental fractionation during tektite formation. The proposed conceptual model of moldavite formation combines both approaches and is based on several steps: (i) the parent mixture (Upper Freshwater Molasse sediments as the dominant source) contained also a minor admixture of organic matter and soils; (ii) the most energetic part of the ejected matter was converted to vapor (plasma) and another part produced melt directly upon decompression; (iii) following further adiabatic decompression, the expanding vapor phase disintegrated the melt into small melt droplets and some elements were partially lost from the melt because of their volatility, or because of the volatility of their compounds, such as carbonyls of Fe and other transition metals (e.g., Ni, Co, Mo, Cr, and Cu); (iv) large positively charged ions such as Cs+, Ba2+, K+, Rb+ from the plasma portion were enriched in the late-stage condensation spherules or condensed directly onto negatively charged melt droplets; (v) simultaneously, the melt droplets coalesced into larger tektite bodies. Steps (iii) to (v) may have overlapped in time. The still melted moldavite bodies reaching their final size were reshaped by further melt flow. This melt flow was related to moldavite rotation and escape (bubbling off) of the last portion of gaseous volatiles during their flight in a low-pressure region above the dense layer of the atmosphere.

Reference
Žák K, Skála R, Řanda Z, Mizera J, Heissig K, Ackerman L, Ďurišová J, Jonášová Š, Kameník J,  Magna T (2016) Chemistry of Tertiary sediments in the surroundings of the Ries impact structure and moldavite formation revisited. Geochmica et Cosmochimcia Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.01.025]
Copyright Elsevier

¹Samuel Ebert, ¹Addi Bischoff
¹Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany

Al-rich objects (Ca,Al-rich inclusions (CAIs), Al-rich chondrules, Al-rich fragments) occur in all chondrite classes. These objects can be centimeter-sized in CV3 carbonaceous chondrites, but they are generally much smaller in other chondrite groups and classes. Within the ordinary chondrites, most Al-rich objects are chondrules that vary from Ca- to Na-rich. Here, we have investigated the mineralogy and major element chemistry of 32 Na-rich chondrules and 3 Na-rich fragments from 15 different chondrites. Most objects (chondrules and chondrule fragments) are from ordinary chondrites (petrologic types 3.2-3.8), but two of the chondrules are from two CO3 chondrites, and three of the chondrules are from one Rumuruti (R)-chondrite. We found that these Na-rich objects have bulk Na2O-concentrations between 4.3 and 15.2 wt%. Texturally, they typically consist of euhedral to subhedral (often skeletal) mafic minerals (olivine and pyroxenes) embedded within a nepheline-normative, glassy mesostasis, which is brownish in transmitted light. In addition, some chondrules contain euhedral to subhedral spinel. Bulk chondrule compositions show group II, group III, and ultrarefractory rare earth element (REE) patterns similar to those found in CAIs. These results clearly demonstrate that the Na-rich chondrules must have been formed by melting of precursors containing an (ultra)-refractory element-rich component and Na-rich constituents. The Na-rich chondrules showed Sm and Eu anomalies, indicating that they must have formed at low oxygen fugacities. Based on the chemical composition of the Na-rich objects, we can rule out that they were formed as a result of planetary formation due to metasomatic processes or processes related to collisions between molten planetesimals.

Reference
Ebert S, Bischoff A (2016) Genetic relationship between Na-rich chondrules and Ca,Al-rich inclusions? – Formation of Na-rich chondrules by melting of refractory and volatile precursors in the Solar Nebula. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.01.014]
Copyright Elsevier