¹Joseph A. Petrus, ²Doreen E. Ames,³Balz S. Kamber
¹Department of Earth Sciences, Laurentian University, Sudbury, Canada
²Geological Survey of Canada, Ottawa, Canada
³Department of Geology, Trinity College Dublin, Dublin 2, Ireland

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

Reference
Petrus JA, Ames DE, Kamber BS (2014) On the track of the elusive sudbury impact: geochemical evidence for a chondrite or comet Bolide. Terra Nova (in Press)
Link to Article [DOI: 10.1111/ter.12125]

¹Brad Jolliff
¹Department of Earth and Planetary Sciences Washington University in St. Louis, Campus Box 1169, One Brookings Drive, St. Louis, Missouri 63130, U.S.A.

Merrillite, Ca18(Ca,□)Mg2(PO4)14–Ca18 Na2Mg2(PO4)14–Ca16REE2(Mg,Fe)2(PO4)14 occurs as a primary phosphate along with apatite, in lunar and martian rocks, and in meteorites. It is nominally anhydrous, but attempts to directly measure H in this mineral have not previously been reported. Because of the occurrence on Earth of whitlockite, Ca18(Mg,Fe2+)2(PO4)12[HPO4]2, and the apparent incorporation in whitlockite of a merrillite component, the lack of a whitlockite component in extraterrestrial merrillite could be taken as an indicator of low hydrogen fugacity, and this implication has been applied to lunar merrillite. On the other hand, for martian rocks, where magmatic OH or H2O contents were likely higher, apatite accordingly contains higher OH contents, yet coexists with anhydrous, Na-rich merrillite. With direct measurements by SIMS, McCubbin et al. (2014), which is in the July issue of American Mineralogist (p. 1347–1354), show that Shergotty merrillite is anhydrous and infer that the high T of crystallization of Shergotty precluded incorporation of a whitlockite component. The mineral pair apatite-merrillite in extraterrestrial rocks constitutes a powerful pair for recording magmatic conditions; however, as McCubbin et al. show, the implications of these minerals and their compositions must be interpreted in light of careful and complete analyses and crystal chemical constraints.

Reference
Jolliff B (2014) Merrillite and apatite as recorders of planetary magmatic processes. American Mineralogist 99, 2161-2162
Link to Article [doi: 10.2138/am-2014-5075]

Copyright: The Mineralogical Society of America

¹Vacheslav V. Emel’yanenko, ¹Sergey A. Naroenkov, ^2,3Peter Jenniskens,⁴Olga P. Popova
¹Institute of Astronomy of the Russian Academy of Sciences, Moscow, Russia
²SETI Institute, Carl Sagan Center, Mountain View, California, USA
³NASA Ames Research Center, Moffett Field, California, USA
⁴Institute for Dynamics of Geospheres of the Russian Academy of Sciences, Moscow, Russia

The orbit of the Chelyabinsk object is calculated, applying the least-squares method directly to astrometric positions. The dynamical evolution of this object in the past is studied by integrating equations of motion for particles with orbits from the confidence region. It is found that the majority of the Chelyabinsk clones reach the near-Sun state. Sixty-seven percent of these objects have collisions with the Sun for 15 Myr in our numerical simulations. The distribution of minimum solar distances shows that the most probable time for the encounters of the Chelyabinsk object with the Sun lies in the interval from −0.8 Myr to −2 Myr. This is consistent with the estimate of a cosmic ray exposure age of 1.2 Myr (Popova et al. 2013). A parent body of the Chelyabinsk object should experience strong tidal and thermal effects at this time. The possible association of the Chelyabinsk object with 86039 (1999 NC43) and 2008 DJ is discussed.

Reference
Emel’yanenko VV, Naroenkov SA, Jenniskens P, Popova OP (2014) The orbit and dynamical evolution of the Chelyabinsk object. Meteoritics & Planetary Science (in Press)
Link to Article [doi: 10.1111/maps.12382]

Published by arrangement with John Wiley&Sons

¹Nancy L. Chabot, ²E. Alex Wollack, ³Munir Humayun,¹Ellen M. Shank
¹Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
²Department of Physics, Princeton University, Princeton, New Jersey, USA
³Department of Earth, Ocean and Atmospheric Science and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida, USA

Oxygen has been considered a potentially important light element in metallic liquids during a range of planetary processes, yet the influence of O in a metallic melt on element partitioning behavior is largely unknown. To investigate the effect of O in such systems, we conducted experiments in the Fe-S-O system, doped with 25 trace elements, which produced two immiscible metallic liquids. Our results indicate that the presence of O in the metallic liquid produces a distinctive chemical signature for W and Ga in particular. Tungsten shows an affinity for O in the metallic liquid and partitions more strongly into the metallic melt in the presence of O. The partitioning of Ga is relatively constant despite the presence of O, which is in contrast to the majority of the other siderophile elements in the study. Our experiments from 1400 to 1600 °C show no significant effect from temperature on the partitioning behavior of any trace elements over this limited temperature range. This distinctive chemical signature due to the presence of O in the metallic liquid has potential implications for modeling core formation, evaluating isotopic signatures produced by core crystallization, and interpreting chemical assemblages observed in meteorites.

Reference
Chabot NL, Wollack EA, Humayun M, Shank EM (2014) The effect of oxygen as a light element in metallic liquids on partitioning behavior. Meteoritics & Planetary Science (in Press)
Link to Article [doi: 10.1111/maps.12383]

Published by arrangement with John Wiley&Sons