¹Ashley J. King,¹Jake R. Solomon, ¹Paul F. Schofield, ¹Sara S. Russell
¹Department of Earth Sciences, Natural History Museum

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Reference
King AJ, Solomon JR, Schofield PF, Russell SS (2015) Characterising the CI and CI-like carbonaceous chondrites using thermogravimetric analysis and infrared spectroscopy. Earth, Planets and Space 67, 198
Link to Article [DOI: 10.1186/s40623-015-0370-4]

^1,2Arya Udry, ¹Harry Y. McSween Jr., ³Richard L. Hervig,¹Lawrence A. Taylor
¹Department of Earth and Planetary Sciences, Planetary Geosciences Institute, University of Tennessee, Knoxville, Tennessee, USA
²Department of Geoscience, University of Nevada, Las Vegas, Nevada, USA
³School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, USA

Degassed magmatic water was potentially the major source of surficial water on Mars. We measured Li, B, and Be abundances and Li isotope profiles in pyroxenes, olivines, and maskelynite from four compositionally different shergottites—Shergotty, QUE 94201, LAR 06319, and Tissint—using secondary ion mass spectrometry (SIMS). All three light lithophile elements (LLE) are incompatible: Li and B are soluble in H2O-rich fluids, whereas Be is insoluble. In the analyzed shergottites, Li concentration decreases and Be concentration increases from cores to rims in pyroxenes. However, B concentrations do not vary consistently with Li and Be abundances, except in QUE 94201 pyroxenes. Additionally, abundances of these three elements in olivines show a normal igneous-fractionation trend consistent with the crystallization of olivine before magma ascent and degassing. We expect that kinetic effects would lead to fractionation of 6Li in the vapor phase compared to 7Li during degassing. The Li isotope profiles, with increasing δ7Li from cores to rims, as well as Li and B profiles indicate possible degassing of hydrous fluids only for the depleted shergottite QUE 94201, as also supported by degassing models. Conversely, Shergotty, LAR 06319, and Tissint appear to have been affected by postcrystallization diffusion, based on their LLE and Li isotope profiles, accompanied by diffusion models. This process may represent an overlay on a degassing pattern. The LLE profiles and isotope profiles in QUE 94201 support the hypothesis that degassing of some basaltic shergottite magmas provided water to the Martian surface, although evidence may be obscured by subsolidus diffusion processes.

Reference
Udry A, McSween Jr. HY, Hervig RL, Taylor LA (2015) Lithium isotopes and light lithophile element abundances in shergottites: Evidence for both magmatic degassing and subsolidus diffusion. Meteoritics & Planetary Sciences (in Press)
Link to Article [DOI: 10.1111/maps.12582]

Published by arrangement with John Wiley & Sons

¹Ohgo S, ¹Nishido H, ¹Ningawa K
¹Department of Biosphere–Geosphere Science, Okayama University of Science 2) Department of Applied Physics, Okayama University of Science

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Reference
Ohgo S, Nishido H, Ningawa K (2015) Cathodoluminescence characterization of enstatite. Journal of Mineralogical and Petrological Sciences 110, 241-246
Link to Article [http://doi.org/10.2465/jmps.150713b]

¹Robin M. Canup,^1,2Channon Visscher,¹Julien Salmon,³Bruce Fegley Jr
¹Planetary Sciences Directorate, Southwest Research Institute, Boulder, Colorado 80302, USA
²Chemistry and Planetary Sciences, Dordt College, Sioux Center, Iowa 51250, USA
³Department of Earth and Planetary Sciences and McDonnell Center for Space Sciences, Washington University, St Louis, Missouri 63130, USA

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Reference
Canup RM, Visscher C, Salmon J, Fegley Jr B (2015) Lunar volatile depletion due to incomplete accretion within an impact-generated disk. Nature Geoscience 8, 918 – 921
Link to Article [doi:10.1038/ngeo2574]

¹P. Bonnand, ²H.M. Williams, ^3,4I.J. Parkinson, ¹B.J. Wood, ¹A.N. Halliday
¹Department of Earth Sciences, University of Oxford, South Parks Road, Oxford, OX1 3AN, United Kingdom
²Department of Earth Sciences, Durham University, Sciences Labs, Durham, DH1 3LE, United Kingdom
³School of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, United Kingdom
⁴Department of Environment, Earth and Ecosystems, CEPSAR, The Open University, Walton Hall, Milton Keynes, MK7 6AA, United Kingdom

We present new mass independent and mass dependent Cr isotope compositions for meteorites measured by double spike thermal ionisation mass spectrometry. Small differences in both mass independent 53Cr and 54Cr relative to the Bulk Silicate Earth are reported and are very similar to previously published values. Carbonaceous chondrites are characterised by an excess in 54Cr compared to ordinary and enstatite chondrites which make mass independent Cr isotopes a useful tool for distinguishing between meteoritic groups. Mass dependent stable Cr isotope compositions for the same samples are also reported. Carbonaceous and ordinary chondrites are identical within uncertainty with average δ53Crδ53Cr values of −0.118±0.040‰−0.118±0.040‰ and −0.143±0.074‰−0.143±0.074‰ respectively. The heaviest isotope compositions are recorded by an enstatite chondrite and a CO carbonaceous chondrite, both of which have relatively reduced chemical compositions implying some stable Cr isotope fractionation related to redox processes in the circumstellar disk. The average δ53Crδ53Cr values for chondrites are within error of the estimate for the Bulk Silicate Earth (BSE) also determined by double spiking. The lack of isotopic difference between chondritic material and the BSE provides evidence that Cr isotopes were not fractionated during core formation on Earth. A series of high-pressure experiments was also carried out to investigate stable Cr isotope fractionation between metal and silicate and no demonstrable fractionation was observed, consistent with our meteorites data. Mass dependent Cr isotope data for achondrites suggest that Cr isotopes are fractionated during magmatic differentiation and therefore further work is required to constrain the Cr isotopic compositions of the mantles of Vesta and Mars.

Reference
Bonnand P,Williams HM, Parkinson IJ,Wood BJ,Halliday AN (2016) Stable chromium isotopic composition of meteorites and metal–silicate experiments: Implications for fractionation during core formation. Earth and Planetary Science Letters 435, 14–21
Link to Article [doi:10.1016/j.epsl.2015.11.026]
Copyright Elsevier

¹M. C. De Sanctis et al. (>10)*
¹Istituto di Astrofisica e Planetologia Spaziali, INAF, Via del Fosso del Cavaliere 100, 00133 Roma, Italy
*Find the extensive, full author and affiliation list on the publishers website

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Reference
De Sanctis MC et al. (2015) Ammoniated phyllosilicates with a likely outer Solar System origin on (1) Ceres. Nature 528, 241–244
Link to Article [doi:10.1038/nature16172]

¹Yann Sonzogni, ¹Georgiana Y. Kramer, ¹Allan H. Treiman
¹Lunar and Planetary Institute, Houston, Texas, USA

Clast 100 in regolith breccia 15295 could be a key to resolving the relationship(s) between mare basalts and lunar picritic glasses. The clast is basaltic, with texture, mineralogy, mineral compositions, and calculated bulk composition suggesting that it crystallized in a thick lava flow or shallow intrusive body from a very-low-titanium (VLT) basaltic magma. The estimated bulk composition of clast 15295,100 is primitive (i.e., magnesian) compared to those of known VLT basalts, and is very close to those of VLT picritic green glasses, especially the Apollo 14 A green glass. From these similarities, we infer that clast 15295,100 is a crystalline product of a picritic magma similar to the Apollo 14 A glass. Clementine and M3 remotely sensed data of the lunar surface were used to find areas that have chemical compositions consistent with those of clast 15295,100, not only near the Apollo 15 site, but in a broad region surrounding the site. Two regions are consistent with clast’s 15295,100 compositional data. The larger region is in southern Mare Imbrium, and a smaller region is in the eastern half of Sinus Aestuum. These locations should be considered as candidates for future missions focusing on sample science.

Reference
Sonzogni Y, Kramer GY, Treiman AH(2015) Petrology and provenance of a very-low-titanium picrite clast in lunar highland regolith breccia 15295. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12579]
Published by arrangement with John Wiley & Sons

¹R. T. Pidgeon, ¹R. E. Merle, ¹M. L. Grange, ^1,2A. A. Nemchin,²M. J. Whitehouse
¹Department of Applied Geology, Curtin University, Perth, Western Australia, Australia
²Swedish Museum of Natural History, Stockholm, Sweden

Impact breccia 14311, was collected from the Apollo 14 landing site as a potential sample of the underlying Fra Mauro Formation. Published zircon U-Pb ages of >4000 Ma date the source material of the breccia and the apatite U-Pb age of ~3940 Ma is interpreted as dating thermal resetting of the apatite U-Pb systems. In this contribution we present new age information on the late stage thermal history of the breccia based on the annealing of radiation damage in the zircons. From Raman spectroscopic determination of the radiation damage within SIMS analytical spots on the zircons and the U and Th concentrations determined on these spots, we demonstrate that the radiation damage in the zircons has been annealed and we estimate the age of annealing at 3410 ± 80 Ma. This age is interpreted as a cooling age following heating of the breccia to above the annealing temperature of ~230 °C for stage 1 radiation damage in zircon, but below the temperature needed to reset the U-Pb system of apatite (~500 °C). It is proposed that this thermal event was associated with the prolonged period of Mare volcanism, from 3150 to 3750 Ma, that generated massive basalt flows in the vicinity of the sample location.

Reference
Pidgeon RT, Merle RE, Grange ML, Nemchin AA, Whitehouse MJ (2015) Annealing of radiation damage in zircons from Apollo 14 impact breccia 14311: Implications for the thermal history of the breccia.
Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12572]
Published by arrangement with John Wiley & Sons

^1,2Hiroshi Nagaoka, ³Yuzuru Karouji, ⁴Hiroshi Takeda, ⁵Timothy J. Fagan, ⁶Mitsuru Ebihara, ^1,2Nobuyuki Hasebe
¹Research Institute for Science and Engineering, Waseda University, Shinjuku 169-8555, Tokyo, Japan
²School of Advanced Science and Engineering, Waseda University, Shinjuku 169-8555, Tokyo, Japan
³Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), Sagamihara 252-5210, Kanagawa, Japan
⁴Department of Earth and Planetary Science, University of Tokyo, Hongo 113-0033, Tokyo, Japan
⁵Department of Earth Science School of Education, Waseda University, Shinjuku 169-8050, Tokyo, Japan
⁶Department of Chemistry, Tokyo Metropolitan University, Hachioji 192-0397, Tokyo, Japan

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Reference
Nagaoka H, Karouji Y, Takeda H, Fagan TJ, Ebihara M, Hasebe N (2015)
Mineralogy and petrology of lunar meteorite Northwest Africa 2977 consisting of olivine cumulate gabbro including inverted pigeonite. Earth, Planets and Space 67, 200

Link to Article [doi:10.1186/s40623-015-0368-y]

¹Lars E. Borg, ^1,2Gregory A. Brennecka, ³Steven J.K. Symes
¹Chemical Sciences Division, Lawrence Livermore National Laboratory, 7000 East Avenue L-231, Livermore CA 94550 USA
²Institut für Planetologie, Westfälische Wilhelms-Universität Munster, Wilkhekm-Klemm-Str. 10, 48149 Münster Germany
³Department of Chemistry, University of Tennessee-Chattanooga, Chattanooga, TN 37403, USA

High precision Sm−Nd isotopic analyses have been completed on a suite of 11 martian basaltic meteorites in order to better constrain the age of silicate differentiation on Mars associated with the formation of their mantle sources. These data are used to evaluate the merits and disadvantages of various mathematical approaches that have been employed in previous work on this topic. Ages determined from the Sm−Nd isotopic systematics of individual samples are strongly dependent on the assumed Nd isotopic composition of the bulk planet. This assumption is problematic given differences observed between the Nd isotopic composition of Earth and chondritic meteorites and the fact that these materials are both commonly used to represent bulk planetary Nd isotopic compositions. Ages determined from the slope of 146Sm−142Nd whole rock isochrons are not dependent on the assumed 142Nd/144Nd ratio of the planet, but require the sample suite to be derived from complementary, contemporaneously-formed reservoirs. In this work, we present a mathematical expression that defines the age of formation of the source regions of such a suite of samples that is based solely on the slope of a 143Nd−142Nd whole rock isochron and is also is independent of any a priori assumptions regarding the bulk isotopic composition of the planet. This expression is also applicable to mineral isochrons and has been used to successfully calculate 143Nd−142Nd model crystallization ages of early refractory solids as well as lunar samples. This permits ages to be obtained using only Nd isotopic measurements without the need for 147Sm/144Nd isotope dilution determinations. When used in conjunction with high-precision Nd isotopic measurements completed on martian meteorites this expression yields an age of formation of the martian basaltic meteorite source regions of 4504 ± 6 Ma. Because the Sm−Nd model ages for the formation of martian source regions are commonly interpreted to record the age at which large scale mantle reservoirs formed during planetary differentiation associated with magma ocean solidification, the age determined here implies that magma ocean solidification occurred several tens of millions of years after the beginning of the Solar System. Recent thermal models, however, suggest that Mars-sized bodies cool rapidly in less than ∼5 Ma after accretion ceases, even in the presence of a thick atmosphere. Assuming these models are correct, an extended period of accretion is necessary to provide a mechanism to keep portions of the martian mantle partially molten until 4504 Ma. Late accretional heating of Mars could either be associated with protracted accretion occurring at a quasi-steady state or alternatively be associated with a late giant impact. If this scenario is correct, then accretion of Mars-sized bodies takes up to 60 Ma and is likely to be contemporaneous with the core formation and possibly the onset of silicate differentiation. This further challenges the concept that isotopic equilibrium is attained during primordial evolution of planets, and may help to account for geochemical evidence implying addition of material into planetary interiors after core formation was completed.

Reflectance
Borg LE, Brennecka GA, Symes SJK (2015) Accretion Timescale and Impact History of Mars Deduced from the Isotopic Systematics of Martian Meteorites. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.12.002]
Copyright Elsevier