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

^1,2Justin Filiberto et al. (>10)*
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12680]
¹Department of Geology, Southern Illinois University, Carbondale, Illinois, USA
²School of Environment, Earth, and Ecosystem Sciences, The Open University, Walton Hall, Milton Keynes, UK
Published by arrangement with John Wiley & Sons
*Find the extensive, full author and affiliation list on the publishers website

Multiple observations from missions to Mars have revealed compelling evidence for a volatile-rich Martian crust. A leading theory contends that eruption of basaltic magmas was the ultimate mechanism of transfer of volatiles from the mantle toward the surface after an initial outgassing related to the crystallization of a magma ocean. However, the concentrations of volatile species in ascending magmas and in their mantle source regions are highly uncertain. This work and this special issue of Meteoritics & Planetary Science summarize the key findings of the workshop on Volatiles in the Martian Interior (Nov. 3–4, 2014), the primary open questions related to volatiles in Martian magmas and their source regions, and the suggestions of the community at the workshop to address these open questions.

^1,2Gordon R. Osinski,¹Richard A. F. Grieve,¹Anna Chanou,¹Haley M. Sapers
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12728]
¹Department of Earth Sciences/Centre for Planetary Science and Exploration, University of Western Ontario, London, Ontario, Canada
²Department of Physics and Astronomy, University of Western Ontario, London, Ontario, Canada
Published by arrangement with John Wiley & Sons

The term “suevite” has been applied to various impact melt-bearing breccias found in different stratigraphic settings within terrestrial impact craters. Suevite was coined initially for impact glass-bearing breccias from the Ries impact structure, Germany, which is the type locality. Various working hypotheses have been proposed to account for the formation of the Ries suevite deposits over the past several decades, with the most recent being molten-fuel-coolant interaction (MFCI) between an impact melt pool and water. This mechanism is also the working hypothesis for the origin of the bulk of the Onaping Formation at the Sudbury impact structure, Canada. In this study, the key characteristics of the Ries suevite, the Onaping Formation and MFCI deposits from phreatomagmatic volcanic eruptions are compared. The conclusion is that there are clear and significant lithological, stratigraphic, and petrographic observational differences between the Onaping Formation and the Ries suevite. The Onaping Formation, however, shares many key similarities with MFCI deposits, including the presence of layering, their well-sorted and fine-grained nature, and the predominance of vitric particles with similar shapes and lacking included mineral and lithic clasts. These differences argue against the viability of MFCI as a working hypothesis for genesis of the Ries suevite and for a required alternative mechanism for its formation.

^1,2Yang Liu,^2,3Ioannis P. Baziotis,³Paul D. Asimow,⁴Robert J. Bodnar,²Lawrence A. Taylor
Meteoritcs & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12726]
¹Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
²Planetary Geosciences Institute, Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, Tennessee, USA
³Department of Natural Resources Management and Agricultural Engineering, Laboratory of Mineralogy and Geology, Agricultural University of Athens, Athens, Greece
³Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
⁴Department of Geosciences, Virginia Tech, Blacksburg, Virginia, USA
Published by arrangement with John Wiley & Sons

The Tissint meteorite is a geochemically depleted, olivine-phyric shergottite. Olivine megacrysts contain 300–600 μm cores with uniform Mg# (~80 ± 1) followed by concentric zones of Fe-enrichment toward the rims. We applied a number of tests to distinguish the relationship of these megacrysts to the host rock. Major and trace element compositions of the Mg-rich core in olivine are in equilibrium with the bulk rock, within uncertainty, and rare earth element abundances of melt inclusions in Mg-rich olivines reported in the literature are similar to those of the bulk rock. Moreover, the P Kα intensity maps of two large olivine grains show no resorption between the uniform core and the rim. Taken together, these lines of evidence suggest the olivine megacrysts are phenocrysts. Among depleted olivine-phyric shergottites, Tissint is the first one that acts mostly as a closed system with olivine megacrysts being the phenocrysts. The texture and mineral chemistry of Tissint indicate a crystallization sequence of: olivine (Mg# 80 ± 1) → olivine (Mg# 76) + chromite → olivine (Mg# 74) + Ti-chromite → olivine (Mg# 74–63) + pyroxene (Mg# 76–65) + Cr-ulvöspinel → olivine (Mg# 63–35) + pyroxene (Mg# 65–60) + plagioclase, followed by late-stage ilmenite and phosphate. The crystallization of the Tissint meteorite likely occurred in two stages: uniform olivine cores likely crystallized under equilibrium conditions; and a fractional crystallization sequence that formed the rest of the rock. The two-stage crystallization without crystal settling is simulated using MELTS and the Tissint bulk composition, and can broadly reproduce the crystallization sequence and mineral chemistry measured in the Tissint samples. The transition between equilibrium and fractional crystallization is associated with a dramatic increase in cooling rate and might have been driven by an acceleration in the ascent rate or by encounter with a steep thermal gradient in the Martian crust.