Iron Isotope Constraints on Planetesimal Core Formation in the Early Solar System

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.

Thermodynamic properties of natural melilites

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 Ca1.8Na0.2(Mg0.7Al0.2Fe2+0.1Fe0.12+)Si2O7, –3753.6 ± 5.2 kJ/mol for Ca1.6Na0.4(Mg0.5Al0.4Fe2+0.1Fe0.12+)Si2O7, –3736.4 ± 3.7 kJ/mol for Ca1.6Na0.4(Mg0.4Al0.4Fe2+0.2Fe0.22+)Si2O7, and –3929.2 ± 3.8 kJ/mol for Ca2(Mg0.4Al0.6)[Si1.4Al0.6O7]. 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.

Nuwaite (Ni6GeS2) and butianite (Ni6SnS2), two new minerals from the Allende meteorite: Alteration products in the early solar system

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.

Diverse mineral assemblages of acidic alteration in the Rio Tinto area (southwest Spain): Implications for Mars

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.

Thermal Alteration of Labile Elements in Carbonaceous Chondrites

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.

Hungaria Asteroid Region Telescopic Spectral Survey (HARTSS) II: Spectral Homogeneity Among Hungaria Family Asteroids

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 (pv) 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; JK), 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 pv=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.

Reflectance spectroscopy of ammonium-bearing phyllosilicates

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.