¹Amy Bonsor, ¹Zoë M. Leinhardt, ¹Philip J. Carter, ²Tim Elliott, ²Michael J. Walter, ³Sarah T. Stewart
¹School of Physics, H.H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK
²School of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, UK
³Department of Earth and Planetary Sciences, University of California, Davis, One Shields Avenue, Davis, California 95616, USA

Several lines of evidence indicate a non-chondritic composition for Bulk Earth. If Earth formed from the accretion of chondritic material, its non-chondritic composition, in particular the super-chondritic 142Nd/144Nd142Nd/144Nd and low Mg/Fe ratios, might be explained by the collisional erosion of differentiated planetesimals during its formation. In this work we use an N-body code, that includes a state-of-the-art collision model, to follow the formation of protoplanets, similar to proto-Earth, from differentiated planetesimals (> 100 km) up to isolation mass (> 0.16 M⊕). Collisions between differentiated bodies have the potential to change the core-mantle ratio of the accreted protoplanets. We show that sufficient mantle material can be stripped from the colliding bodies during runaway and oligarchic growth, such that the final protoplanets could have Mg/Fe and Si/Fe ratios similar to that of bulk Earth, but only if Earth is an extreme case and the core is assumed to contain 10% silicon by mass. This may indicate an important role for collisional differentiation during the giant impact phase if Earth formed from chondritic material.

Reference
Bonsor A, Leinhardt ZM, Carter PJ, Elliott T, Walter MJ, Stewart ST (2014) A collisional origin to earth’s non-chondritic composition? Icarus (in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.10.019]

Copyright Elsevier

¹Allan H. Treiman, ²Justin Filiberto
¹Lunar and Planetary Institute, Houston, Texas, USA
²Department of Geology, Southern Illinois University, Carbondale, Illinois, USA

The chemical compositions of shergottite meteorites, basaltic rocks from Mars, provide a broad view of the origins and differentiation of these Martian magmas. The shergottite basalts are subdivided based on their Al contents: high-Al basalts (Al > 5% wt) are distinct from low-Al basalts and olivine-phyric basalts (both with Al < 4.5% wt). Abundance ratios of highly incompatible elements (e.g., Th, La) are comparable in all the shergottites. Abundances of less incompatible elements (e.g., Ti, Lu, Hf) in olivine-phyric and low-Al basalts correlate well with each other, but the element abundance ratios are not constant; this suggests mixing between components, both depleted and enriched. High-Al shergottites deviate from these trends consistent with silicate mineral fractionation. The “depleted” component is similar to the Yamato-980459 magma; approximately, 67% crystal fractionation of this magma would yield a melt with trace element abundances like QUE 94201. The “enriched” component is like the parent magma for NWA 1068; approximately, 30% crystal fractionation from it would yield a melt with trace element abundances like the Los Angeles shergottite. This component mixing is consistent with radiogenic isotope and oxygen fugacity data. These mixing relations are consistent with the compositions of many of the Gusev crater basalts analyzed on Mars by the Spirit rover (although with only a few elements to compare). Other Mars basalts fall off the mixing relations (e.g., Wishstone at Gusev, Gale crater rocks). Their compositions imply that basalt source areas in Mars include significant complexities that are not present in the source areas for the shergottite basalts.

Reference
Treiman AH, Filiberto J (2014) Geochemical diversity of shergottite basalts: Mixing and fractionation, and their relation to Mars surface basalts. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12363]

Published by arrangement with John Wiley and Sons

¹Xie, X., ^“Chen, M., ³Zhai, S., ¹Wang, F.
¹Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China
²State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China
³Key Laboratory of Orogenic Belts and Crustal Evolution, MOE, School of Earth and Space Sciences, Peking University, Beijing, China

An assemblage with FeNi metal, troilite, Fe-Mn-Na phosphate, and Al-free chromite was identified in the metal-troilite eutectic nodules in the shock-produced chondritic melt of the Yanzhuang H6 meteorite. Electron microprobe and Raman spectroscopic analyses show that a few phosphate globules have the composition of Na-bearing graftonite (Fe,Mn,Na)3(PO4)2, whereas most others correspond to Mn-bearing galileiite Na(Fe,Mn)4(PO4)3 and a possible new phosphate phase of Na2(Fe,Mn)17(PO4)12 composition. The Yanzhuang meteorite was shocked to a peak pressure of 50 GPa and a peak temperature of approximately 2000 °C. All minerals were melted after pressure release to form a chondritic melt due to very high postshock heat that brought the chondrite material above its liquidus. The volatile elements P and Na released from whitlockite and plagioclase along with elements Cr and Mn released from chromite are concentrated into the shock-produced Fe-Ni-S-O melt at high temperatures. During cooling, microcrystalline olivine and pyroxene first crystallized from the chondritic melt, metal-troilite eutectic intergrowths, and silicate melt glass finally solidified at about 950–1000 °C. On the other hand, P, Mn, and Na in the Fe-Ni-S-O melt combined with Fe and crystallized as Fe-Mn-Na phosphates within troilite, while Cr combined with Fe and crystallized as Al-free chromite also within troilite.

Reference
Xie X, Chen M, Zhai S, Wang, F (2014) Eutectic metal + troilite + Fe-Mn-Na phosphate + Al-free chromite assemblage in shock-produced chondritic melt of the Yanzhuang chondrite. Meteoritics & Planetary Science (in Press)
Link to Article [doi: 10.1111/maps.12379]

Published by arrangement with John Wiley & Sons

^1,2M.M.M. Meier, ³A. Reufer, ²R. Wieler
¹Centre de Recherches Pétrographiques et Géochimiques, CNRS Nancy, France
²Department of Earth Sciences, ETH Zurich, Switzerland
³School of Earth & Space Exploration, Arizona State University, AZ 85287-6004, USA

Knowing the isotopic composition of Theia, the proto-planet which collided with the Earth in the Giant Impact that formed the Moon, could provide interesting insights on the state of homogenization of the inner Solar System at the late stages of terrestrial planet formation. We use the known isotopic and modeled chemical compositions of the bulk silicate mantles of Earth and Moon and combine them with different Giant Impact models, to calculate the possible ranges of isotopic composition of Theia in O, Si, Ti, Cr, Zr and W in each model. We compare these ranges to the isotopic composition of carbonaceous chondrites, Mars, and other Solar System materials. In the absence of post-impact isotopic re-equilibration, the recently proposed high angular momentum models of the Giant Impact (“impact-fission”, Cúk, M., Stewart, S.T. [2012]. Science 338, 1047; and “merger”, Canup, R.M. [2012]. Science 338, 1052) allow – by a narrow margin – for a Theia similar to CI-chondrites, and Mars. The “hit-and-run” model (Reufer, A., Meier, M.M.M., Benz, W., Wieler, R. [2012]. Icarus 221, 296–299) allows for a Theia similar to enstatite-chondrites and other Earth-like materials. If the Earth and Moon inherited their different mantle FeO contents from the bulk mantles of the proto-Earth and Theia, the high angular momentum models cannot explain the observed difference. However, both the hit-and-run as well as the classical or “canonical” Giant Impact model naturally explain this difference as the consequence of a simple mixture of two mantles with different FeO. Therefore, the simplest way to reconcile the isotopic similarity, and FeO dissimilarity, of Earth and Moon is a Theia with an Earth-like isotopic composition and a higher (∼20%) mantle FeO content.

Reference
Meier MMM, Reufer A, Wieler R (2014) On the origin and composition of Theia: Constraints from new models of the Giant Impact. Icarus 242, 316–328 Link to Article [DOI: 10.1016/j.icarus.2014.08.003]

Copyright Elsevier

¹Alian Wang, ¹Randy L. Korotev, ¹Bradley L. Jolliff, ²Zongcheng Ling
¹Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St. Louis, USA
²School of Space Science and Physics, Shandong University, Weihai Campus, China

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Reference
Wang A, Korotev RL, Jolliff BL,Ling Z (2014) Raman imaging of extraterrestrial Materials. Planetary and Space Science (in Press)
Link to Article [DOI: 10.1016/j.pss.2014.10.005]

^1,2Michael N. Mautner
¹Department of Chemistry, Virginia Commonwealth University, Richmond, VA 23284-2006, USA
²Soil and Physical Sciences Department, Lincoln University, Lincoln, New Zealand

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Reference
Mautner MN (2014) In situ biological Resources: Soluble Nutrients and Electrolytes in carbonaceous asteroids/meteorites. Implications for astroecology and space populations. Planetary and Space Science (in Press)
Link to Article [DOI: 10.1016/j.pss.2014.10.001]

¹J. Mortimer, ¹A.B. Verchovsky, ^1,2M. Anand, ¹I. Gilmour,¹C.T. Pillinger,
¹Planetary and Space Sciences, Department of Physical Sciences, The Open University, Milton Keynes, MK7 6AA, UK
²Department of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD, UK

Simultaneous static-mode mass spectrometric measurements of nitrogen, carbon, helium, neon, and argon extracted from the same aliquot of sample by high-resolution stepped combustion have been made for a suite of six lunar basalts.
Collecting abundance and isotopic data for several elements simultaneously from the same sample aliquot enables more detailed identification of different volatile components present in the basalts by comparing release patterns for volatiles across a range of temperature steps. This approach has yielded new data, from which new insights can be gained regarding the indigenous volatile inventory of the Moon.
By taking into account N and C data for mid-temperature steps, unaffected by terrestrial contamination or cosmogenic additions, it is possible to determine the indigenous N and C signatures of the lunar basalts. With an average δ15N value of around +0.35 ‰, the indigenous N component seen in these samples is similar within error to other (albeit limited in number) isotopic measurements of indigenous lunar N. Average C/N ratios for indigenous volatiles in these six basalt samples are much lower than those of the terrestrial depleted mantle, or bulk silicate Earth, possibly suggesting much less C in the lunar interior, relative to N, than on Earth.
Cosmogenic isotopes in these samples are well-correlated with published sample exposure ages, and record the rate of in situ production of spallogenic volatiles within material on the lunar surface.

Reference
Mortimer J, Verchovsky AB, M. Anand M, Gilmour I, Pillinger CT (2014) IcaruSimultaneous analysis of abundance and isotopic composition of nitrogen, carbon, and noble gases in lunar basalts: insights into interior and surface processes on the Moon. Icarus (in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.10.006]

Copyright Elsevier

¹Subrata Chakraborty, ²B. H. Muskatel, ¹Teresa L. Jackson, ³Musahid Ahmed, ^2,4R. D. Levine,¹Mark H. Thiemens
¹Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093-0356
²The Fritz Haber Research Center for Molecular Dynamics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
³Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
⁴Department of Chemistry and Biochemistry, Crump Institute for Molecular Imaging, and Department of Molecular and Medical Pharmacology, University of California, Los Angeles, CA 90095

Nitrogen isotopic distributions in the solar system extend across an enormous range, from −400‰, in the solar wind and Jovian atmosphere, to about 5,000‰ in organic matter in carbonaceous chondrites. Distributions such as these require complex processing of nitrogen reservoirs and extraordinary isotope effects. While theoretical models invoke ion-neutral exchange reactions outside the protoplanetary disk and photochemical self-shielding on the disk surface to explain the variations, there are no experiments to substantiate these models. Experimental results of N2 photolysis at vacuum UV wavelengths in the presence of hydrogen are presented here, which show a wide range of enriched δ15N values from 648‰ to 13,412‰ in product NH3, depending upon photodissociation wavelength. The measured enrichment range in photodissociation of N2, plausibly explains the range of δ15N in extraterrestrial materials. This study suggests the importance of photochemical processing of the nitrogen reservoirs within the solar nebula.

Reference
Chakraborty S, Muskatel BH, Jackson TL, Ahmed M, Levine RD, Thiemens MH (2014) Massive isotopic effect in vacuum UV photodissociation of N2 and implications for meteorite data. Proceedings of the National Academy of Sciences 111, 41
Link to Article [doi: 10.1073/pnas.1410440111]

¹D. Ray, ²S. Misra
¹PLANEX, Physical Research Laboratory, Ahmedabad, 380009, India
²Discipline of Geological Sciences, SAEES, University of KwaZulu-Natal, Durban, 4000, South Africa

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Reference
Ray D, Misra S (2014) Contrasting Aerodynamic Morphology and Geochemistry of Impact Spherules from Lonar Crater, India: Some Insights into Their Cooling History. Earth, Moon and Planets (in Press)
Link to Article [10.1007/s11038-014-9451-9]

¹Pavel Spurný, ^2,3Jakub Haloda, ¹Jiří Borovička, ¹Lukáš Shrbený,²Patricie Halodová
¹Astronomical Institute, Academy of Sciences, 25165 Ondřejov, Czech Republic
²Czech Geological Survey, Geologická 6, 15200 Praha 5, Czech Republic
³Oxford Instruments NanoAnalysis, Halifax Road, High Wycombe, HP12 3SE, UK

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Reference
Spurný P, Haloda J, Borovička J, Shrbený L, Halodová P (2014) Reanalysis of the Benešov bolide and recovery of polymict breccia meteorites – old mystery solved after 20 years. Astronomy&Astrophysics 570.
Link to Article [http://dx.doi.org/10.1051/0004-6361/201424308]