¹Carl Alwmark, ²Jens Ormö, ³Arne T. Nielsen
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13230]
¹Department of Geology, Lund University,22362 Lund, Sweden
²Centro de Astrobiologia (INTA‐CSIC),28850 Torrejon de Ardoz, Spain
³Department of Geosciences & Natural Resource Management, University of Copenhagen, , 1350 Copenhagen, Denmark
Published by arrangement with John Wiley & Sons

Here we present a study of the abundance and orientation of planar deformation features (PDFs) in the Vakkejokk Breccia, a proposed lower Cambrian impact ejecta layer in the North‐Swedish Caledonides. The presence of PDFs is widely accepted as evidence for shock metamorphism associated with cosmic impact events and their presence confirms that the Vakkejokk Breccia is indeed the result of an impact. The breccia has previously been divided into four lithological subunits (from bottom to top), viz. lower polymict breccia (LPB), graded polymict breccia (GPB), top sandstone (TS), and top conglomerate (TC). Here we show that the LPB contains no shock metamorphic features, indicating that the material derives from just outside of the crater and represents low‐shock semi‐autochthonous bombarded strata. In the overlying, more fine‐grained GPB and TS, quartz grains with PDFs are relatively abundant (2–5% of the grain population), and with higher shock levels in the upper parts, suggesting that they have formed by reworking of more distal ejecta by resurge of water toward the crater in a marine setting. The absence of shocked quartz grains in the TC indicates that this unit represents later slumps associated with weathering and erosion of the protruding crater rim. Sparse shocked quartz grains (<0.2%) were also found in sandstone beds occurring at the same stratigraphic level as the Vakkejokk Breccia 15–20 km from the inferred crater site. It is currently unresolved whether the sandstone at these distal sites is related to the impact or just contains rare reworked quartz grains with PDFs.

¹Rudolf Välja, ¹Kalle Kirsimäe, ^2,3Christian Köeberl, ⁴Daniel Boamah, ¹Juho Kirs
Meteoritics & Plantary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13225]
¹Department of Geology, University of Tartu, , 50411 Tartu, Estonia
²Department of Lithospheric Research, University of Vienna, , 1090 Vienna, Austria
³Natural History Museum, , 1010 Vienna, Austria
⁴Ghana Geological Survey Department, , Accra, Ghana
Published by arrangement with John Wiley & Sons

The petrographic, mineralogical, and geochemical compositions of the incipient devitrification products in impact melt fragments found in outer suevites at the Bosumtwi impact crater were studied to reconstruct the postimpact environmental constraints on the suevite formation and to refine its cooling history. Our study shows that devitrified melt/particles contain numerous microlitic crystals and crystal aggregates of different shapes derived from rapid cooling. The matrix of melt/particles in Bosumtwi suevites contains abundant Mg‐hercynite (pleonaste)‐type spinels with sizes rarely exceeding a few micrometers. High nucleation density of microlites suggests rapid crystallization under strong undercooling in the presence of abundant volatiles. Although the Bosumtwi impact event took place in a continental environment, the possible sources for elevated fluid/volatile content could have been the groundwater in the deeply weathered and fractured‐jointed Birimian basement, dewatering of abundant hydrous phases in weathered crust or hydrothermally altered basement, and the shale/phyllite–greywacke lithologies in the target rocks. Our results show that enough volatiles were present in the target rocks at the time of impact for the effective impact melt dispersion observed in Bosumtwi impactites.

¹Bruce M. Simonson, ²Nicolas J. Beukes, ³Sandra Biller
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13228]
¹Geology Department, Oberlin College, , Oberlin, Ohio, 44074 USA
²DST‐NRF Centre of Excellence for Integrated Mineral and Energy Resource Analysis, Department of Geology, University of Johannesburg, , Auckland Park, 2006 South Africa
³SNAP‐Ed Program Manager, University of Wyoming Extension, , Laramie, Wyoming, 82071 USA
Published by arrangement with John Wiley & Sons

The Monteville spherule layer (MSL) was deposited in the Griqualand West Basin (GWB) on the Kaapvaal Craton approximately 2.63 Ga. The spherules were generated by a large impact and reworked by impact‐generated waves and/or currents. The MSL has been intersected in three previously undescribed cores. Two of the cores, GKF‐1 and GKP‐1, were drilled ~30 km west of the southernmost outcrop of the MSL. The third core, BH‐47, was drilled ~250 km south and east of the GWB. The MSL contains medium to coarse sand‐size spherules like those described previously in all three cores but each one was emplaced in a different way. In GKF‐1, the MSL is 90 cm thick and contains large rip‐up clasts of basinal carbonate and early diagenetic pyrite. In GKP‐1, the MSL is only 1.5 cm thick and consists largely of fine carbonate sand, yet it contains pyrite intraclasts up to ~1 cm long. In BH‐47, the MSL consists of a lower coarse sandy zone ~37 cm thick rich in spherules, carbonate peloids/ooids, pyrite intraclasts, and quartzose sand and an upper, finer sandy zone ~46 cm thick; neither zone contains any large intraclasts. The new occurrences triple the known extent of the MSL from ~15,000 to ~46,000 km2, support the oceanic impact model for the formation of the MSL, demonstrate that it is a persistent regional time‐stratigraphic marker, place new constraints on the Kaapvaal paleoshoreline at the time of impact, and support the existence of Vaalbara.

¹Michelle K.Jordan, ¹Hao Lan Tang, ¹Issaku E.Kohl, ¹Edward D.Young
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.12.005]
¹Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, USA
Copyright Elsevier

We determined the Fe isotope fractionation between the metal and silicate phases of two aubrite meteorites, Norton County and Mount Egerton. We find that the metallic phase is high in 57Fe/54Fe with respect to the silicate phase, with Δ57Femetal-silicate = 0.08‰ ± 0.04 for Mount Egerton and 0.09 ± 0.02 ‰ for Norton County. These data, combined with new measurements of 57Fe/54Fe of IIIAB iron meteorites, are used to constrain the origins of the high 57Fe/54Fe exhibited by all classes of iron meteorites. We find that if the parent bodies of the iron meteorites had chondritic bulk 57Fe/54Fe values, their cores must have been unusually small (≤ 8% by mass). Relaxing the constraint that the bodies were chondritic in their bulk iron isotope ratios allows for larger core mass fractions commensurate with usual expectations. In this case, the elevated 57Fe/54Fe values of iron meteorites are due in part to evaporation of melt during the accretion stages of the parent bodies and not solely the result of metal-silicate differentiation.

¹Lyubov P. Ogorodova, ^1,2Yuliya D. Gritsenko, ¹Marina F. Vigasina, ¹Andrey Y. Bychkov, ¹Dmitry A. Ksenofontov, ¹Lyubov V. Melchakova
American Mineralogist 103, 1945-1952 Link to Article [https://doi.org/10.2138/am-2018-6475]
¹Geological Faculty, M.V. Lomonosov Moscow State University, Leninskie Gory, Moscow, 119234, Russia
²Fersman Mineralogical Museum RAS, Leninskiy prospect 18-2, Moscow, 117071, Russia
Copyright: The American Mineralogical Society

In the present study, four samples of natural melilites were characterized using electron microprobe analysis, powder X-ray diffraction, FTIR, and Raman spectroscopy, and their thermodynamic properties were measured with a high-temperature heat-flux Tian-Calvet microcalorimeter. The enthalpies of formation from the elements were determined to be: –3796.3 ± 4.1 kJ/mol for Ca_1.8Na_0.2(Mg_0.7Al_0.2Fe2+0.1Fe0.12+⁠)Si₂O₇, –3753.6 ± 5.2 kJ/mol for Ca_1.6Na_0.4(Mg_0.5Al_0.4Fe2+0.1Fe0.12+⁠)Si₂O₇, –3736.4 ± 3.7 kJ/mol for Ca_1.6Na_0.4(Mg_0.4Al_0.4Fe2+0.2Fe0.22+⁠)Si₂O₇, and –3929.2 ± 3.8 kJ/mol for Ca₂(Mg_0.4Al_0.6)[Si_1.4Al_0.6O₇]. Using the obtained formation enthalpies and estimated entropies, the standard Gibbs free energies of formation of these melilites were calculated. Finally, the enthalpies of the formation of the end-members of the isomorphic åkermanite-gehlenite and åkermanite-alumoåkermanite series were derived. The obtained thermodynamic properties of melilites of different compositions can be used for quantitative modeling of formation conditions of these minerals in related geological and industrial processes.

¹Chi Ma, ¹John R. Beckett
American Mineralogist 103, 1918-1924 Link to Article [https://doi.org/10.2138/am-2018-6599]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A.
Copyright: The Mineralogical Society of America

Nuwaite (Ni6GeS2, IMA 2013-018) and butianite (Ni6SnS2, IMA 2016-028) are two new chalcogenide minerals, occurring as micrometer-sized crystals with grossular, Na-bearing melilite, heazlewoodite, and Ge-bearing Ni-Fe alloys in veins and as mono-mineralic crack-filling material in igneous diopside in the Type B1 Ca-Al-rich inclusion (CAI) ACM-2 from the Allende CV3 carbonaceous chondrite. The chemical composition of type nuwaite is (wt%) Ni 65.3, S 10.3, Ge 8.2, Te 7.9, Sn 5.1, and Fe 1.7, with a sum of 98.5 and an empirical formula of (Ni5.95Fe0.16)(Ge0.60Sn0.23)(S1.72Te0.33). The simplified formula is Ni6(Ge,Sn)(S,Te)2, leading to an end-member of Ni6GeS2. The chemical composition of type butianite is (wt%) Ni 62.1, Sn 8.9, Te 10.3, S 8.9, Ge 5.3, Fe 1.3, sum 99.1, giving rise to an empirical formula of (Ni5.93Fe0.13)(Sn0.52Ge0.41)(S1.56Te0.45). Butianite’s simplified formula is Ni6(Sn,Ge) (S,Te)2 and the end-member formula is Ni6SnS2. Both nuwaite and butianite have an I4/mmm inter-growth structure with a = 3.65 Å, c = 18.14 Å, V = 241.7 Å3, and Z = 2. Their calculated densities are 7.24 and 7.62 g/cm3, respectively. Nuwaite and butianite are the first known meteoritic minerals with high Ge and Sn concentrations.
Nuwaite and butianite are very late-stage, vapor-deposited, alteration products, filling in pores within preexisting grossular-rich alteration veins and cracks in igneous Al,Ti-diopside. These phases and associated heazlewoodite and Ge-bearing alloys are observed only within the Ca-,Al-rich inclusion (CAI) and not outside it or at the inclusion-matrix interface. As only sections in one half of ACM-2 contain nuwaite/butianite, they were probably derived through a relatively low fO2-fS2 sulfidation process, in which a highly localized, low-temperature Ge-, Sn-bearing fluid interacted with a portion of the host CAI. It is likely that the fluid became relatively more Sn- and Te-enriched with time and that crack fillings post-date vein fillings, possibly due to a late remobilization of vein sulfides.

¹Christian Mavris, ¹Javier Cuadros, ²José Miguel Nieto, ³Janice L. Bishop, ⁴Joseph R. Michalski
American Mineralogist 103, 1877-1890 Link to Article [https://doi.org/10.2138/am-2018-6330]
¹Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, U.K.
²Department of Earth Sciences, University of Huelva, 21071 Huelva, Spain
³SETI Institute, Mountain View, California 94043, U.S.A.
⁴Department of Earth Sciences and Laboratory for Space Research, University of Hong-Kong, Pokfulam Road, Hong-Kong, China
Copyright: The Mineralogical Society of America

Earth analogs are indispensable to investigate mineral assemblages on Mars because they enable detailed analysis of spectroscopic data from Mars and aid environmental interpretation. Samples from four sites in the Iberian Pyrite Belt (El Villar, Calañas, Quebrantahuesos, and Tharsis) were investigated using mineralogical, chemical, and spectroscopic techniques, with a focus on clay minerals and alteration environments. They represent Earth analogs of areas on Mars that underwent acidic alteration. X-ray diffraction and transmittance mid-infrared data indicate that the rocks were subjected to several degrees of acid alteration corresponding to assemblages characterized by the following mixtures: (1) illite, chlorite, interstratified chlorite-vermiculite, kaolinite-smectite, and kaolinite; (2) illite, kaolinite, and alunite; and (3) jarosite and goethite. According to mineral stability data, these three assemblages correspond to pH values 7–5, 5–3, and <3, respectively. The lack of goethite in the illite-kaolinitealunite assemblage suggests an alteration in reducing conditions. Illite was progressively dissolved by acidic alteration but is sufficiently resilient not to be diagnostic of the intensity of the alteration. Illite and kaolinite were the two most abundant phyllosilicate minerals observed, and the main reaction involving phyllosilicates was the alteration of illite to kaolinite. Mixed-layer phases appeared mainly in the mildest degree of acid alteration, with few exceptions. This suggests a transition from a mechanism dominated by transformation to a mechanism dominated by dissolution-precipitation as the intensity of the acid alteration increases. Our results highlight the sparse kaolinite-alunite occur-rences on Mars as worthy of specific investigation. Acid alteration on Mars is expected to be patchy and/or consisting of fine alteration rims. Alunite occurrences on Mars in the absence of goethite may indicate an acid alteration in reducing conditions. Kaolinite produced through acid alteration on Mars is expected to exist mainly as an end-member phase of low crystallinity, which would enhance IR absorption and increase its visibility.

¹Alessondra Springmann, ¹Dante S.Lauretta, ²Bjoern Klaue, ³Yulia S.Goreva, ⁴Joel D.Blum, ⁵Alexandre Andronikov, ^6,7Jordan K.Steckloff
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.12.022]
¹Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, 85721, United States
²TSI GMBH, Neuköllner Strasse 4, Aachen, 52068, Germany
³NASA Jet Propulsion Laboratory, Pasadena, CA, 91109, United States
⁴Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI, 48109, United States
⁵Czech Geological Survey, Geologicka 6, Prague, 152 00, Czech Republic
⁶Department of Aerospace Engineering and Engineering Mechanics, University of Texas at Austin, Austin, TX, 78712, United States
⁷Planetary Science Institute, Tucson, AZ, 85719, United States
Copyright Elsevier

Carbonaceous chondrite meteorites are some of the oldest Solar System planetary materials available for study. The CI group has bulk abundances of elements similar to those of the solar photosphere. Of particular interest in carbonaceous chondrite compositions are labile elements, which vaporize and mobilize efficiently during post-accretionary parent-body heating events. Thus, they can record low-temperature alteration events throughout asteroid evolution. However, the precise nature of labile-element mobilization in planetary materials is unknown. Here we characterize the thermally induced movements of the labile elements S, As, Se, Te, Cd, Sb, and Hg in carbonaceous chondrites by conducting experimental simulations of volatile-element mobilization during thermal metamorphism. This process results in appreciable loss of some elements at temperatures as low as 500 K. This work builds on previous laboratory heating experiments on primitive meteorites and shows the sensitivity of chondrite compositions to excursions in temperature. Elements such as S and Hg have the most active response to temperature across different meteorite groups. Labile element mobilization in primitive meteorites is essential for quantifying elemental fractionation that occurred on asteroids early in Solar System history. This work is relevant to maintaining a pristine sample from asteroid (101955) Bennu from the OSIRIS-REx mission and constraining the past orbital history of Bennu. Additionally, we discuss thermal effects on surface processes of near-Earth asteroids, including the thermal history of “rock comets” such as (3200) Phaethon. This work is also critical for constraining the concentrations of contaminants in vaporized water extracted from asteroid regolith as part of future in situ resource utilization for sustained robotic and human space exploration.

¹Michael P.Lucas, ¹Joshua P.Emery, ¹Eric M.MacLennan, ²Noemi Pinilla-Alonso,³Richard J.Cartwright, ⁴Sean S.Lindsay, ⁵Vishnu Reddy, ⁶Juan A.Sanchez, ⁷Cristina A.Thomas, ^8,9VaniaLorenzi
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.12.010]
¹Department of Earth & Planetary Sciences, University of Tennessee, 1621 Cumberland Ave., 602 Strong Hall, Knoxville, TN 37996
²Florida Space Institute, University of Central Florida, Orlando, FL 32816
³SETI Institute, 189 N Bernardo Ave. #200, Mountain View, CA 94043
⁴Department of Physics & Astronomy, University of Tennessee, 1408 Circle Drive, Knoxville, TN 37996
⁵Lunar and Planetary Laboratory, 1629 E University Blvd., Tucson, AZ 85721
⁶Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719
⁷Department of Physics and Astronomy, Northern Arizona University, PO Box 6010, Flagstaff, AZ 86011
⁸Fundación Galileo Galilei – Istituto Nazionale di Astrofisica, Rambla José Ana Fernández Pérez n°7, E-38712 Breña Baja, Spain
⁹Instituto de Astrofísica de Canarias – IAC, C/ Vía Láctea, s/n, E-38205 – La Laguna (Tenerife), Spain
Copyright Elsevier

Spectral observations of asteroid family members provide valuable information regarding parent body interiors, the origin and source regions of near-Earth asteroids, and the link between meteorites and their parent bodies. Asteroids of the Hungaria family represent some of the closest samples to the Earth from a collisional family (∼1.94 AU), permitting observations of smaller family fragments than accessible for Main Belt families. We have carried out a ground-based observational campaign entitled Hungaria Asteroid Region Telescopic Spectral Survey (HARTSS) to record reflectance spectra of these preserved samples from the inner-most regions of the primordial asteroid belt. During HARTSS phase one (Lucas et al. [2017]. Icarus 291, 268-287) we found that ∼80% of the background population is comprised of stony S-complex asteroids that exhibit considerable spectral and mineralogical diversity. In HARTSS phase two, we turn our attention to family members to determine if the Hungaria collisional family is compositionally homogeneous or heterogeneous. We use taxonomic classification, geometric albedo (p_v) estimates, and near-infrared (NIR) spectral properties to infer the composition of the family.

During phase two of HARTSS we acquired NIR spectra of 50 new Hungarias (19 family; 31 background) with the SpeX spectrograph at NASA’s Infrared Telescope Facility (IRTF) and with the NICS spectrograph at the Telescopio Nazionale Galileo (TNG). We analyzed X-type spectra for NIR color indices (0.85-J; J–K), and a subtle ∼0.9 µm absorption feature that may be attributed to Fe-poor orthopyroxene ± the sulfide mineral oldhamite. Surviving fragments of an asteroid collisional family typically exhibit similar taxonomies, albedos, and spectral properties. Spectral analysis of Hungaria family X-types and independently calculated WISE albedos for family members (average p_v=0.403; n=192) is consistent with this scenario. Furthermore, about one-fourth of the background population exhibit similar spectral properties and albedos to family X-types.

Spectral observations of 92 Hungaria region asteroids acquired during both phases of HARTSS uncover a compositionally-heterogeneous background population—including two rare olivine-dominated A-types and one apparent D-type interloper—and spectral homogeneity down to ∼2 km for collisional family members. Taxonomy, albedos, and spectral properties indicate that the Hungaria family progenitor was an igneous body that formed under reduced conditions, and was likely consistent in composition with the enstatite achondrite (i.e., aubrite) meteorite group.

¹M.Ferrari, ¹S.De Angelis, ¹M.C.De Sanctis, ²E.Ammannito, ¹S.Stefani, ¹G.Piccioni
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.11.031]
¹IAPS-INAF, Via fosso del Cavaliere, 100, 00133, Rome, Italy
²Agenzia Spaziale Italiana, Via del Politecnico, 00133, Rome, Italy
Copyright Elsevier

The identification of NH4-bearing phyllosilicates on Ceres poses the question on the NH4-carrier phase(s) and in this study we describe the laboratory production and IR spectroscopic measurements of a suite of ten NH4-phyllosilicates, starting from the corresponding NH4-free minerals. For each mineral, we prepared three types of powder samples: raw (R), ammoniated (A), and leached (L). All samples have been spectrally characterized by means of visible/infrared spectroscopy in the INAF-IAPS laboratories with the FieldSpec Pro in the 0.35-2.5 μm range, and with the FT-IR, using a Vertex 80 spectrometer operating in the range of 2 to 14 µm. The samples were also measured with the SPectral IMager, an imaging spectrometer operating in the spectral range 0.2 – 5.1 µm, which is a replica of the VIR spectrometer on-board Dawn spacecraft. Reflectance spectra of the ammoniated clays show bands near 1.56 μm, 2.05 μm, 2.12 μm, 3.06 μm, 3.25 μm, 3.55 μm, 4.2 μm, 5.7 μm and 7.0 μm that are related to the presence of nitrogen complexes. Treatment of phyllosilicates with ammonia shows that different minerals behave in different ways: NH4+ ions are easily accepted by the smectites, while other non-expandable structures do not accept these ions. The obtained results can be used to better constrain the NH4-bearing species present on Ceres and, possibly, other bodies of the solar system.