Sabyasachi Sen^a, Scarlett J. Widgeon^a,b, Alexandra Navrotsky^a,b,*, Gabriela Mera^c, Amir Tavakoli^b, Emanuel Ionescu^c, and Ralf Riedel^c

^aDepartment of Chemical Engineering and Materials Science and
^bPeter A. Rock Thermochemistry Laboratory and Nanomaterials in the Environment, Agriculture, and Technology Organized Research Unit, University of California, Davis, CA 95616
^cInstitut für Materialwissenschaft, Technische Universität Darmstadt, D-64287 Darmstadt, Germany

Amorphous silicon oxycarbide polymer-derived ceramics (PDCs), synthesized from organometallic precursors, contain carbon- and silica-rich nanodomains, the latter with extensive substitution of carbon for oxygen, linking Si-centered SiO_xC_4-x tetrahedra. Calorimetric studies demonstrated these PDCs to be thermodynamically more stable than a mixture of SiO₂, C, and silicon carbide. Here, we show by multinuclear NMR spectroscopy that substitution of C for O is also attained in PDCs with depolymerized silica-rich domains containing lithium, associated with SiO_xC_4-x tetrahedra with nonbridging oxygen. We suggest that significant (several percent) substitution of C for O could occur in more complex geological silicate melts/glasses in contact with graphite at moderate pressure and high temperature and may be thermodynamically far more accessible than C for Si substitution. Carbon incorporation will change the local structure and may affect physical properties, such as viscosity. Analogous carbon substitution at grain boundaries, at defect sites, or as equilibrium states in nominally acarbonaceous crystalline silicates, even if present at levels at 10–100 ppm, might form an extensive and hitherto hidden reservoir of carbon in the lower crust and mantle.

Reference
Sen S Widgeon SJ, Navrotsky A, Mera G, Tavakoli A, Ionescu E and Riedel R (in press) Carbon substitution for oxygen in silicates in planetary interiors. PNAS
[doi:10.1016/j.icarus.2013.09.020]

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Marina A. Ivanova^1,*, Cyril A. Lorenz¹, Ian A. Franchi², Andrei Y. Bychkov³, Jeffrey E. Post⁴

¹Vernadsky Institute of Geochemistry of Russian Academy of Sciences, Moscow, Russia
²Planetary and Space Sciences, The Open University, Milton Keynes, UK
³Moscow State University, Moscow, Russia
⁴National Museum of Natural History, Smithsonian Institution, Washington, District of Columbia, USA

We have conducted hydration–dehydration experiments on terrestrial olivine to investigate the behavior of oxygen isotopic fractionation to test the hypothesis that multiple cycles of aqueous and thermal processing on a parent asteroid comprise a genetic relationship between CM2s and metamorphosed carbonaceous chondrites (MCCs). Two experiments were undertaken. In the first experiment, serpentine was obtained by hydrating terrestrial olivine (Fo_90.9) in the laboratory. During this experiment, olivine was reacted with isotopically heavy water (δ¹⁸O 21.5‰) at T = 300 °C, P_H2O = 300 bar, for 100 days. The oxygen isotopic composition of the experimental serpentine was enriched in ¹⁸O (by 10 ‰ in δ¹⁸O) due to exchange of oxygen isotopes between olivine and the ¹⁸O-rich water. Dehydrated serpentine was then produced during laboratory heating experiment in vacuum, at T = 930 °C, for 1 h. The oxygen isotopic composition of the dehydrated serpentine was enriched in ¹⁸O by a further 7 ‰. The net result of the hydration–dehydration process was an enrichment of ¹⁸O in the final material by approximately 17‰. The new experimental results suggest that the oxygen isotopic compositions of MCCs of the Belgica-like group, including Dhofar 225 and Dhofar 725, could be derived from those of typical CM2 chondrites via several cycles of hydration–dehydration caused by aqueous alteration and subsequent thermal metamorphism within their parent asteroids.

Reference
Ivanova MA, Lorenz CA, Franchi IA, Bychkov AY and Post JE (in press) Experimental simulation of oxygen isotopic exchange in olivine and implication for the formation of metamorphosed carbonaceous chondrites. Meteoritics & Planetary Science
[doi:10.1111/maps.12204]
Published by arrangement with John Wiley & Sons

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Mikhail Yu. Zolotov

School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404, USA

Dwarf planet Ceres is the largest body in the main asteroid belt with a rocky surface and uncertain internal structure. Spectra of Ceres in near- and mid-infrared wavelengths are consistent with the occurrence of brucite, Mg-bearing carbonates, and an Fe-rich phyllosilicate cronstedtite. Spectra of 10 Hygiea and 324 Bamberga imply similar compositions. Here, we considered stabilities of these minerals to constrain their origin. Cronstedtite is most stable at the temperature of ~0 °C at moderately oxidizing aqueous conditions, and at high water/rock ratios. Although cronstedtite could form on planetesimals, the apparent lack of serpentine may indicate its formation by Ceres’ temporary surface solutions. Brucite forms at a low activity of dissolved SiO₂, at a low fugacity of CO₂, and at highly alkaline pH. Brucite and cronstedtite do not form together and may not form deep in the Ceres’ interior. The absence of Mg serpentine from Ceres’ surface materials and the unlikely occurrence of very olivine-rich rocks do not indicate a formation of brucite through serpentinization of such rocks. Brucite could form by transient near-surface fluids which do not equilibrate with silicates. Temporary fluids could deposit Mg carbonates before, after, or together with brucite at near-surface conditions that favor CO₂ degassing. Regardless of Ceres’ internal structure, internal thermal and aqueous processes may not affect cold near-surface layers. Percolation of interior fluids is not consistent with the lack of detection of low-solubility salts. However, impacts of ice-rich targets during the Late Heavy Bombardment could account for transient aqueous environments and unusual surface mineralogies of Ceres, Hygiea, and Bamberga. Brucite and Mg carbonates could have formed through hydration and carbonation of MgO evaporated from silicates. Apparently abundant carbonates may indicate an ample impact oxidation of organic matter, and the occurrence of brucite with cronstedtite may reflect turbulent and disequilibrium environments. Clay-like homogeneous surface materials on Ceres could be gravitationally sorted deposits of impact clouds.

Reference
Zolotov MY (in press) Formation of brucite and cronstedtite-bearing mineral assemblages on Ceres. Icarus
[doi:10.1016/j.icarus.2013.09.020]
Copyright Elsevier

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Jennifer F. Rapp^1,2,*, David S. Draper¹, Cameron M. Mercer³

¹Astromaterials Research Office, Astromaterials Research and Exploration Science Directorate, NASA Johnson Space Center, Houston, Texas, USA
²Lunar and Planetary Institute, Houston, Texas, USA
³School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, USA

We report the results of nominally anhydrous equilibrium and fractional crystallization experiments on a synthetic Yamato-980459 (Y98) bulk composition at 0.5 GPa. These experiments allow us to test a suggested fractional crystallization model, calculated using MELTS by Symes et al. (), in which a Y98-like initial liquid yielded a magma closely resembling the bulk composition of QUE 94201. Although the two meteorites cannot be cogenetic owing to their age difference, they are thought to represent bona fide magmatic liquids rather than products of crystal accumulation, as are most Martian basaltic meteorites. Hence, understanding possible petrogenetic links between these types of liquids could be revealing about processes of melting and crystallization that formed the range of Martian basalts. We find that Y98 can, in fact, generate a residual liquid closely resembling QUE, but only after a very different crystallization process, and different degree of crystallization, than that modeled using MELTS. In addition, both the identity and sequence of crystallizing phases are very different between model and experiments. Our fractional crystallization experiments do not produce a QUE-like liquid, and the crystallizing phases are an even poorer match to the MELTS-calculated compositions than in the equilibrium runs. However, residual liquids from our experiments define a liquid line of descent that encompasses bulk compositions of parental melts calculated for several Martian basaltic meteorites, suggesting that the known Martian basaltic meteorites had their ultimate origin from the same or very similar source lithologies. These are, in turn, similar to source rocks modeled by previous studies as products of extensive crystallization of an initial Martian magma ocean.

Reference
Rapp JF, Draper DS and Mercer CM (in press) Anhydrous liquid line of descent of Yamato-980459 and evolution of Martian parental magmas. Meteoritics & Planetary Science
[doi:10.1111/maps.12197]
Published by arrangement with John Wiley & Sons

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Junko Isa^a,b,*, Alan E. Rubin^a,b and John T. Wasson^a,b,c

^aInstitute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095–1567, USA
^bDepartment of Earth and Space Sciences, University of California, Los Angeles, CA 90095–1567, USA
^cDepartment of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095–1567, USA

Reference
Isa J, Rubin AE and Wassona JT (in press) R-chondrite bulk-chemical compositions and diverse oxides: Implications for parent-body processes. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2013.09.018]
Copyright Elsevier

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F Zhang^a,b,*, Y L Zou^a, Zheng^a,c, X H Fu^a and Y C Zhu^a,b

^aNational Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China
^bUniversity of Chinese Academy of Sciences, Beijing 100049, China
^cCenter for Space Science Research, The Hong Kong University of Science and Technology, Hong Kong, China

Reference
Zhang F, Zou YL, Zheng YC, Fu XH and Zhu YC (in press) Lunar Mare Basalts in the Aristarchus Region: Implications for the Stratigraphic Sequence from Clementine UVVIS data. Icarus
[doi:10.1016/j.icarus.2013.09.011]
Copyright Elsevier

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U. Munari¹, R. L. M. Corradi^2,3, A. Siviero⁴, L. Baldinelli⁵ and A. Maitan⁵

¹INAF Osservatorio Astronomico di Padova, 36012 Asiago ( VI), Italy
²Instituto de Astrofisica de Canarias, 38200, La Laguna, Tenerife, Spain
³Departamento de Astrofísica, Universidad de La Laguna, 38206, La Laguna, Tenerife, Spain
⁴Department of Physics and Astronomy, University of Padova, 36012 Asiago ( VI), Italy
⁵ANS Collaboration, c/o Astronomical Observatory, 36012 Asiago ( VI), Italy

Reference
Munari U, Corradi RLM, Siviero A, Baldinelli L and Maitan A (in press) Discovery of a planetary nebula surrounding the symbiotic star DT Serpentis. Astronomy & Astrophysics
[doi:10.1051/0004-6361/201321883]
Reproduced with permission © ESO

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J. E. Chappelow

Meteoritics Inc., 1148 Sundance Loop, Fairbanks, Alaska 99709, USA

Reference
Chappelow JE (in press) Simple impact crater shape determination from shadows. Meteoritics & Planetary Science
[doi:10.1111/maps.12201]
Published by arrangement with John Wiley & Sons

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Thomas J. Zega^a,d,*, Larry R. Nittler^b, Frank Gyngard^b,c, Conel M.O’D. Alexander^b, Rhonda M. Stroud^d, Ernst K. Zinner^c

^aDepartment of Planetary Sciences, Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd, Tucson AZ 85721-0092
^bDepartment of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Rd NW, Washington D.C. 20015
^cLaboratory for Space Sciences and Physics Department, Washington University, One Brookings Drive, Physics Department, Campus Box 1105, St. Louis MO 63130
^dMaterials Science and Technology Division, Naval Research Laboratory, 4555 Overlook Ave. SW, Washington DC 20375

Reference
Zega TJ, Nittler LR, Gyngard F, Alexander CMO’D, Stroud RM and Ernst K. Zinner EK (accepted manuscript) A Transmission Electron Microscopy Study of Presolar Spinel. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2013.09.010]
Copyright Elsevier

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A. Compère¹, D. Farrelly², A. Lemaître¹ and D. Hestroffer³

¹naXys, University of Namur, Rempart de la Vierge 8, 5000 Namur, Belgium
²Utah State University, 0300 Old Main Hill, Logan, UT 84322-0300, USA
³IMCCE, Observatoire de Paris, UPMC, CNRS, 77 av. Denfert Rochereau, 75014 Paris, France

Reference
Compère A, Farrelly D Lemaître A and Hestroffer D (in press) A possible mechanism to explain the lack of binary asteroids among the Plutinos. Astronomy & Astrophysics
[doi:10.1051/0004-6361/201321137]
Reproduced with permission © ESO

Link to Article