^1,2Alex Ruzicka, ¹Ryan Brown, ^3,4Jon Friedrich, ^1,2 Melinda Hutson, ² Richard Hugo, ⁵Mark Rivers
¹Cascadia Meteorite Laboratory, Portland State University, 1721 SW Broadway, Portland, Oregon 97207, U.S.A.
²Department of Geology, Portland State University, 17 Cramer Hall, 1721 SW Broadway, Portland, Oregon 97207, U.S.A.
³Department of Chemistry, Fordham University, Bronx, New York 10458, U.S.A.
⁴Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York 10024, U.S.A.
⁵Consortium for Advanced Radiation Sources, University of Chicago, Argonne, Illinois 60439, U.S.A.

The conditions under which metal cores formed in silicate-metal planetary bodies in the early Solar System are poorly known. We studied the Buck Mountains 005 (L6) chondrite with serial sectioning, X-ray computed microtomography, and optical and electron microscopy to better understand how metal and troilite were redistributed as a result of a moderately strong (shock stage S4) shock event, as an example of how collisional processes could have contributed to differentiation. The chondrite was recovered on Earth in multiple small pieces, some of which have a prominent, 1.5–3 mm wide holocrystalline shock melt dike that forms a jointed, sheet-like structure, as well as an associated shock vein network. The data suggest that metal and troilite within the dike were melted, sheared, and transported as small parcels of melt, with metal moving out of the dike and along branching veins to become deposited as coarser nodules and veins within largely unmelted host. Troilite also mobilized but partly separated from metal to become embedded as finer-grained particles, vein networks, and emulsions intimately intergrown with silicates. Rock textures and metal compositions imply that shock melts cooled rapidly against relatively cool parent body materials, but that low-temperature annealing occurred by deep burial within the parent body. Our results demonstrate the ability of shock processes to create larger metal accumulations in substantially unmelted meteorite parent bodies, and they have implications for the formation of iron meteorites and for core formation within colliding planetesimals.

Reference
Ruzicka A, Brown R, Friedrich J, Hutson M, Hugo R, Rivers M(2015) Shock-induced mobilization of metal and sulfide in planetesimals: Evidence from the Buck Mountains 005 (L6 S4) dike-bearing chondrite. American Mineralogist 100, 2725-2738, Link to Article [doi:10.2138/am-2015-5225]
Copyright: The Mineralogical Society of America

¹Sandra Pizzarello, ¹Maitrayee Bose
¹Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287-1604, USA

Large isotopic anomalies are found in meteoritic insoluble organic materials (IOMs) and, for nitrogen, show 15N-excesses up to ${\delta }^{15}$N ~ 5000‰. These 15N-enrichments are commonly ascribed to presolar origins, but the attribution seems contradicted by available data on N-isotopes’ cosmic distribution. We report here that 15N hotspots in several IOMs are reduced by hydrothermal treatment and their loss correlates with 15N values of ammonia released upon treatment. Because released ammonia’s 15N-enrichments also relate with meteorites’ mineralogy, i.e., asteroidal processes, and no current models offer plausible explanations for the finding, we account for our data with a novel scenario whereby 15N-enriched ammonia produced in the solar nebula is incorporated by carbonaceous materials and delivered to early Earth by comets and meteorites. The proposal also implies that abundant reduced nitrogen, a required element in origins of life theories, could reach our nascent planet and other planetary systems affecting their habitability.

Reference
Pizzarello S, Bose M (2015) THE PATH OF REDUCED NITROGEN TOWARD EARLY EARTH: THE COSMIC TRAIL AND ITS SOLAR SHORTCUTS. The Astrophysical Journal 814, 2
Link to Article [http://dx.doi.org/10.1088/0004-637X/814/2/107]