¹Nicholas Castle, ¹Christopher D. K. Herd
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12739]
¹Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada
Published by arrangement with John Wiley & Sons

Tissint is an olivine-phyric shergottite from an incompatible element depleted Martian mantle source. Oxythermobarometry applied to Tissint mineral phases demonstrates that the Tissint magma underwent an increase in oxygen fugacity, from ~3.5 log units below the quarz-fayalite-magnetite (QFM) buffer during the early stages of crystallization, to QFM−1.4 during the latter stages. This is the first time that such an oxidation event has been observed in a depleted shergottite. The reason for the oxidation event is unclear; however, calculations using the MELTS thermodynamic model suggest that auto-oxidation is insufficient to cause more than ~1 log unit of oxidation, and therefore an external oxidation mechanism—such as oxidation by degassing—is required. If volatiles are responsible for the oxidation, then it indicates that volatiles are not exclusively tied to the enriched Martian mantle reservoir. A series of experiments using the Tissint parental magma were carried out under fixed (isothermal) or variable (cooling rate) temperature control, and at either reducing (QFM−3.2) or oxidizing (QFM−1) redox conditions. The observed liquid line of descent supports a potential genetic relationship between basaltic shergottites and olivine-phyric shergottites. A peritectic relation where olivine is resorbed to form pyroxene is favored by increased oxygen fugacity; if oxidation during crystallization is more common than presently believed, it may explain why olivine is typically anhedral in olivine-phyric shergottites. Results from a cooling-rate experiment in which the oxygen fugacity was changed during the latter stages of crystallization resulted in olivine with a Cr compositional profile consistent with oxidized isothermal experiments, despite forming primarily under reducing conditions. A similar profile is observed in Tissint olivines, consistent with its redox history. Our results provide insights into the potential influence of oxidation events on the compositional zoning of minor or trace elements in olivine in olivine-phyric basalts.

¹Dwijesh Ray,¹S. Ghosh,¹S.V.S. Murty
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12742]
¹Planetary Sciences Division, Physical Research Laboratory, Ahmedabad, India
Published by arrangement with John Wiley & Sons

Microtextural study of a single troilite-metal nodule (TMN) from the Katol L6-7 chondrite, a recent fall (May, 2012) in India suggests that the TMN is primarily an aggregate of submicron-scale intergrowth of troilite and kamacite (mean Ni: 6.18 wt%) juxtaposed with intensely fractured silicates, mainly olivine (Fa: 25 mole%), low-Ca pyroxene (Fs: 21.2 mole%), and a large volume of maskelynite. Evidence of shock textures in the TMN indicates a high degree of shock metamorphism that involves plagioclase-maskelynite and olivine-wadsleyite/ringwoodite transformations and formation of quenched metal-sulfide melt textures due to localized shear-induced frictional melting. It is inferred that the TMN formation is an independent, localized event by a high energy impact and its subsequent incorporation in the ejected chondritic fragment of the parent body. Katol chondrite has been calibrated with a peak shock pressure of S5 (~45 GPa) after Stöffler et al. (1991), whereas peak shock pressure within the TMN exceeds the shock facies S6 (>45 GPa) following Bennett and McSween (1996) and Stöffler et al. (1991). Overall, the shock-thermal history of the Katol TMN is dissimilar as compared to the host chondrite.

^1,2A. Calzada-Diaz,³K. H. Joy,^1,2I. A. Crawford,⁴S. Strekopytov
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12737]
¹Department of Earth and Planetary Sciences, Birkbeck College, London WC1E 7HX, UK
²Centre for Planetary Sciences UCL/Birkbeck, London WC1E 7HX, UK
³School of Earth and Environmental Sciences, University of Manchester, Manchester M13 9PL, UK
⁴Imaging and Analysis Centre, Natural History Museum, London SW7 5BD, UK
Published by arrangement with John Wiley & Sons

Meteorites ejected from the surface of the Moon as a result of impact events are an important source of lunar material in addition to Apollo and Luna samples. Here, we report bulk element composition, mineral chemistry, age, and petrography of Miller Range (MIL) 090036 and 090070 lunar meteorites. MIL 090036 and 090070 are both anorthositic regolith breccias consisting of mineral fragments and lithic clasts in a glassy matrix. They are not paired and represent sampling of two distinct regions of the lunar crust that have protoliths similar to ferroan anorthosites. 40Ar-39Ar chronology performed on two subsplits of MIL 090070,33 (a pale clast impact melt and a dark glassy melt component) shows that the sample underwent two main degassing events, one at ~3.88 Ga and another at ~3.65 Ga. The cosmic ray exposure data obtained from MIL 090070 are consistent with a short (~8–9 Ma) exposure close to the lunar surface. Bulk-rock FeO, TiO2, and Th concentrations in both samples were compared with 2-degree Lunar Prospector Gamma Ray Spectrometer (LP-GRS) data sets to determine areas of the lunar surface where the regolith matches the abundances observed on the sample. We find that MIL 090036 bulk rock is compositionally most similar to regolith surrounding the Procellarum KREEP Terrane, whereas MIL 090070 best matches regolith in the feldspathic highlands terrane on the lunar farside. Our results suggest that some areas of the lunar farside crust are composed of ferroan anorthosite, and that the samples shed light on the evolution and impact bombardment history of the ancient lunar highlands.

¹Wencke Wegner, ²Christian Koeberl
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12731]
¹Department of Lithospheric Research, University of Vienna, Vienna, Austria
²Natural History Museum, Vienna, Austria
Published by arrangement with John Wiley & Sons

The 3.6 Ma El’gygytgyn structure, located in northeastern Russia on the Chukotka Peninsula, is an 18 km diameter complex impact structure. The bedrock is formed by mostly high-silica volcanic rocks of the ~87 Ma old Okhotsk-Chukotka Volcanic Belt (OCVB). Volcanic target rocks and impact glasses collected on the surface, as well as drill core samples of bedrock and impact breccias have been investigated by thermal ionization mass spectrometry (TIMS) to obtain new insights into the relationships between these lithologies in terms of Nd and Sr isotope systematics. Major and trace element data for impact glasses are added to compare with the composition of target rocks and drill core samples. Sr isotope data are useful tracers of alteration processes and Nd isotopes reveal characteristics of the magmatic sources of the target rocks, impact breccias, and impact glasses. There are three types of target rocks mapped on the surface: mafic volcanics, dacitic tuff and lava of the Koekvun’ Formation, and dacitic to rhyolitic ignimbrite of the Pykarvaam Formation. The latter represents the main contributor to the impact rocks. The drill core is divided into a suevite and a bedrock section by the Sr isotope data, for which different postimpact alteration regimes have been detected. Impact glasses from the present-day surface did not suffer postimpact hydrothermal alteration and their data indicate a coherent alteration trend in terms of Sr isotopes with the target rocks from the surface. Surprisingly, the target rocks do not show isotopic coherence with the Central Chukotka segment of the OCVB or with the Berlozhya magmatic assemblage (BMA), a late Jurassic felsic volcanic suite that crops out in the eastern part of the central Chukotka segment of the OCVB. However, concordance for these rocks exists with the Okhotsk segment of the OCVB. This finding argues for variable source magmas having contributed to the build-up of the OCVB.

¹M.R. Sexton, ¹M.E. Elwood Madden, ²A.L. Swindle, ³V.E. Hamilton, ⁴B.R. Bickmore, ¹A.S. Elwood Madden
Icarus (in Press) Link to Article [http://dx.doi.org/10.1016/j.icarus.2016.10.014]
¹School of Geology and Geophysics, University of Oklahoma, 100 E. Boyd, Norman, OK 73019
²Wichita State University, Wichita KS 67260
³Southwest Research Institute, Boulder CO 80302
⁴Department of Geological Sciences, Brigham Young University, Provo UT 84602
Copyright Elsevier

The enigmatic and unexpected occurrence of coarse crystalline (gray) hematite spherules at Terra Meridiani on Mars in association with deposits of jarosite-rich sediments fueled a variety of hypotheses to explain their origin. In this study, we tested the hypothesis that freezing of aqueous hematite nanoparticle suspensions, possibly produced from low-temperature weathering of jarosite-bearing deposits, could produce coarse-grained hematite aggregate spherules. We synthesized five hematite nanoparticle suspensions with a range of sizes and morphologies and performed freezing experiments. All sizes of hematite nanoparticles rapidly aggregate during freezing. Regardless of the size or shape of the initial starting material, they rapidly collect into aggregates that are then too big to push in front of a stable advancing ice front, leading to incohesive masses of particles, rather than solid spherules. We also explored the effects of “seed” silicates, a matrix of sand grains, various concentrations of NaCl and CaCl2, and varying the freezing temperature on hematite nanoparticle aggregation. However, none of these factors resulted in mm-scale spherical aggregates. By comparing our measured freezing rates with empirical and theoretical values from the literature, we conclude that the spherules on Mars could not have been produced through the freezing of aqueous hematite nanoparticle suspensions; ice crystallization front instability disrupts the aggregation process and prevents the formation of mm-scale continuous aggregates.

¹J. Flahaut, ^1,2M. Martinot, ³J.L. Bishop, ¹G.R. Davies, ^1,4N.J. Potts
Icarus (in Press) Link to Article [http://dx.doi.org/10.1016/j.icarus.2016.09.041]
¹Faculty of Earth and Life Sciences, Vrije University Amsterdam, The Netherlands
²Univ Lyon, Université Lyon 1, ENS-Lyon, CNRS, UMR 5276 LGL-TPE, F-69622, Villeurbanne, France
³Carl Sagan Center, The SETI Institute, Mountain View, CA 94043, USA
⁴School of GeoSciences, University of Edinburgh, King’s Buildings, Edinburgh, EH9 3FE, UK
Copyright Elsevier

The identification and characterization of hydrated minerals within ancient aqueous environments on Mars are high priorities for determining the past habitability of the planet. Few studies, however, have focused on characterizing the entire mineral assemblage, even though it could aide our understanding of past environments. In this study we use both spaceborne and field (VNIR spectroscopy) analyses to study the mineralogy of various salt flats (salars) of the northern region of Chile as an analog for Martian evaporites. These data are then compared to laboratory based Raman and XRD analyses for a complete overview on mineral assemblages. Central (core) and marginal zones within the salars are easily distinguished on the Landsat 8 band color composites. These areas host different mineral assemblages that often result in different landscapes. The lower elevation Salar de Atacama, located in the Andean pre-depression, is characterized by a unique thick halite crust at its center, whereas various assemblages of calcium sulfates (gypsum, bassanite, anhydrite) and sodium sulfates (mirabilite, thenardite, blodite, glauberite), borates (ulexite, pinnoite), Al/Fe- clays and carbonates (calcite, aragonite) were found at its margin. Sulfates form the main crust of the Andean salars to the east, although various compositions are observed. These compositions appear controlled by the type of feeder brine (Ca, SO4 or mixed), a result of the local geology among other factors. Sulfate crusts were found to be generally thin (<5 cm) with a sharp transition to the underlying clay, silt, or sand-rich alluvial deposits. Coupled with morphologic analyses, VNIR spectroscopy provides a powerful tool to distinguish different salt crusts. XRD analysis allowed us to quantify the mineral assemblages and assess the limitations of VNIR techniques in the presence of hydrated sulfates, which tend to mask the signatures of other minerals such as clays, chlorides, and carbonates. We found that the Atacama’s unique arid and volcanic environment, coupled with the transition recorded in some of the salars has a strong Mars analog potential. Characterizing the outcrop mineralogy at a variety of environments from alkaline, lake waters to more acidic salar brines may help in constraining geochemical environments on Mars.

^1,2,3Juliane Gross, ¹Allan H. Treiman, ³George E. Harlow
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12741]
¹Department of Earth and Planetary Sciences, Rutgers University, Piscataway, New Jersey, USA
²Lunar and Planetary Institute, Houston, Texas, USA
³Department of Earth and Planetary Sciences, The American Museum of Natural History, New York, New York, USA
Published by arrangement with John Wiley & Sons

A grain of light-blue sulfate material was reported in the lunar highlands regolith meteorite PCA 02007 (Satterwhite and Righter 2013). Allocated grains of that material are, in fact, aluminosilicate glass with a chemical composition like that of the bulk meteorite and other lunar highlands regoliths. The calcium sulfate detected in PCA 02007 was likely a surface coating, and reasonably of Antarctic (not lunar) origin.

¹Morgan F. Schaller, ¹Megan K. Fung, ²James D. Wright, ¹Miriam E. Katz, ^2,3Dennis V. Kent
Science 354, 225-229 Link to Article [DOI: 10.1126/science.aaf5466]
¹Earth and Environmental Sciences, Rensselaer Polytechnic Institute (RPI), Troy, NY 12180, USA.
²Earth and Planetary Sciences, Rutgers University, Piscataway, NJ 08854, USA.
³Lamont-Doherty Earth Observatory (LDEO), Columbia University, Palisades, NY 10964, USA.
Reprinted with permission from AAAS

Extraterrestrial impacts have left a substantial imprint on the climate and evolutionary history of Earth. A rapid carbon cycle perturbation and global warming event about 56 million years ago at the Paleocene-Eocene (P-E) boundary (the Paleocene-Eocene Thermal Maximum) was accompanied by rapid expansions of mammals and terrestrial plants and extinctions of deep-sea benthic organisms. Here, we report the discovery of silicate glass spherules in a discrete stratigraphic layer from three marine P-E boundary sections on the Atlantic margin. Distinct characteristics identify the spherules as microtektites and microkrystites, indicating that an extraterrestrial impact occurred during the carbon isotope excursion at the P-E boundary.

^1,2Ai-Cheng Zhang, ¹Qiu-Li Li, ^2,3Hisayoshi Yurimoto, ³Naoya Sakamoto, ¹Xian-Hua Li, ⁴Sen Hu, ⁴Yang-Ting Lin, ¹Ru-Cheng Wang
Nature Communications 7, 12844 Link to Article [doi:10.1038/ncomms12844]
¹State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210046, China
²Department of Natural History Sciences, Hokkaido University, Sapporo 060-0810, Japan
³Isotope Imaging Laboratory, Creative Research Institution Sousei, Hokkaido University, Sapporo 001-0021, Japan
⁴Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China

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^1,2Yuan Li, ¹Rajdeep Dasgupta, ¹Kyusei Tsuno, ³Brian Monteleone, ³Nobumichi Shimizu
Nature Geoscience 9, 781–785 Link to Article [doi:10.1038/ngeo2801]
¹Department of Earth Science, Rice University, 6100 Main Street, MS 126, Houston, Texas 77005, USA
²Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
³Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA

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