The most popular papers in November on Cosmochemistry Papers were:

1-Howard KT, Alexander CMOD, Schrader DL, Dyl KA (2014) Classification of hydrous meteorites (CR, CM and C2 ungrouped) by phyllosilicate fraction: PSD-XRD modal mineralogy and planetesimal Environments. Geochimica et Cosmochimica Acta (in Press) Link to Article [DOI: 10.1016/j.gca.2014.10.025]

2-Hartmann WK (2014) The giant impact hypothesis: past, present (and future?). Philosophical Transactions of the Royal Society A 13,372, 2024 Link to Article [doi: 10.1098/rsta.2013.0249]

3-Kovacs J, István Sajób, Márton Z, Jáger V, Hegedüs T, Berecz T, Tóth T, Gyenizse P, Podobni A (2014) Csátalja, the largest H4-5 chondrite from Hungary. Planetary and Space Science (in Press) Link to Article [doi:10.1016/j.pss.2014.11.009]

4-Shahar A, Hillgren VJ, Horan MF, Mesa-Garcia J, Kaufman LA, Mock TD (2014) Sulfur-controlled iron isotope fractionation experiments of core formation in planetary bodies. Geochimica et Cosmochinica Acta (in Press) Link to Article [DOI: 10.1016/j.gca.2014.08.011]

5-Khan R, Yokozuka Y, Terai S, Shirai N, Ebihara M (2014) Accurate determination of Zn in geological and cosmochemical rock samples by isotope dilution inductively coupled plasma mass spectrometry. Journal Analytical Atomic Spectrometry (in Press) Link to Article [DOI: 10.1039/C4JA00344F]

¹Erik H. Hauri,²Alberto E. Saal,²Malcolm J. Rutherford, ³James A. Van Orman
¹Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA
²Department of Geological Sciences, Brown University, Providence, RI 02912, USA
³Department of Earth, Environmental and Planetary Sciences, Case Western Reserve University, Cleveland, OH 44106, USA

Geochemical data for H2O and other volatiles, as well as major and trace elements, are reported for 377 samples of lunar volcanic glass from three chemical groups (A15 green, A15 yellow, A17 orange 74 220). These data demonstrate that degassing is a pervasive process that has affected all extrusive lunar rocks. The data are combined with published data to estimate the total composition of the bulk silicate Moon (BSM). The estimated BSM composition for highly volatile elements, constrained by H2O/Ce ratios and S contents in melt inclusions from orange glass sample 74 220, are only moderately depleted compared with the bulk silicate Earth (avg. 0.25X BSE) and essentially overlap the composition of the terrestrial depleted MORB source. In a single giant impact origin for the Moon, the Moon-forming material experiences three stages of evolution characterized by very different timescales. Impact mass ejection and proto-lunar disk evolution both permit system loss of H2O and other volatiles on timescales ranging from days to centuries; the early Moon is likely to have accreted from a thin magma disk of limited volume embedded in, but largely displaced from, the extended distribution of vapor around the Earth. Only the protracted evolution of the lunar magma ocean (LMO) presents a time window sufficiently long (10–200 Ma) for the Moon to gain water during the tail end of accretion. This “hot start” to lunar formation is however not the only model that matches the lunar volatile abundances; a “cold start” in which the proto-lunar disk is largely composed of solid material could result in efficient delivery of terrestrial water to the Moon, while a “warm start” producing a disk of 25% volatile-retentive solids and 75% volatile-depleted magma/vapor is also consistent with the data. At the same time, there exists little evidence that the Moon formed in a singular event, as all detailed planetary accretion models predict several giant impacts in the terrestrial planet region in which the Earth forms. It is thus conceivable that the Moon, like the Earth, experienced a history of heterogeneous accretion.

Reference
Hauri EH, Saal AE, Rutherford MJ, Van Orman JA (2014) Water in the Moon’s interior: Truth and consequences. Earth and Planetary Science Letters 409, 252–264
Link to Article [doi:10.1016/j.epsl.2014.10.053]

Copyright Elsevier

¹Shuo Ding, ¹Rajdeep Dasgupta, ¹Cin-Ty A. Lee, ²Meenakshi Wadhwa
¹Department of Earth Science, Rice University, 6100 Main street, MS 126, Houston, TX 77005, USA
²School of Earth and Space Exploration, Arizona State University, AZ, USA

Sulfur storage and transport between different reservoirs such as core, mantle, crust and atmosphere of Mars are tied to igneous processes. Martian meteorites carry a record of mantle melting and subsequent differentiation history of Martian magmas. Investigation of S geochemistry of Martian meteorites can thus provide an understanding of how S is transferred from the Martian interior to the exosphere. In this study we measured bulk S concentration of 7 Martian meteorites and modeled the behavior of S during both isobaric crystallization of primary Martian magmas and isentropic partial melting of Martian mantle. Comparisons between measured data and modeled results suggest that (1) sulfides may become exhausted at the source during decompression melting of the mantle and mantle-derived basalts may only become sulfide-saturated after cooling and crystallization at shallow depths and (2) in addition to degassing induced S loss, mixing between these differentiated sulfide-saturated basaltic melts and cumulus minerals with/without cumulate sulfides could also be responsible for the bulk sulfur contents in some Martian meteorites. In this case, a significant quantity of S could remain in Martian crust as cumulate sulfides or in trapped interstitial liquid varying from 2 to 95 percent by weight. Our modeling also suggests that generation of sulfide-undersaturated parental magmas requires that the mantle source of Martian meteorites contain <700–1000 ppm S if melting degree estimation of 2–17 wt.% based on compositions of shergottites is relevant.

Reference
Ding S, Dasgupta R, Lee CTA, Wadhwa M (2014) New bulk sulfur measurements of Martian meteorites and modeling the fate of sulfur during melting and crystallization – Implications for sulfur transfer from Martian mantle to crust–atmosphere System. Earth and Planetary Science Letters 409, 157–167
Link to Article [doi:10.1016/j.epsl.2014.10.046]

Copyright Elsevier

¹Paola Vannucchi, ¹Jason P. Morgan, ¹Damiano Della Lunga,
²Christopher L. Andronicos, ³W. Jason Morgan
¹Earth Sciences Department, Royal Holloway, University of London, UK
²Earth, Atmospheric and Planetary Sciences Department, Purdue University, IN, USA
³Department of Earth and Planetary Sciences, Harvard, Cambridge, MA, USA

Shock metamorphism is rarely found at the surface of the Earth. The most used structures to identify shock metamorphism are “true Planar Deformation Features” (PDFs) in quartz, now accepted as diagnostic indicators of a meteorite impact. Here we present several lines of evidence for shock metamorphism and PDFs developed in quartz occurring on samples centered on a circular geological structure on Mount Stojkovic (60°54′06″N; 101°55′40″E), which lies within southern surface exposures of the Siberian Traps. The shock event appears to have occurred during the eruption of the surface Siberian Traps basalts that cover this region. Curiously, Mount Stojkovic lies within ∼3 km of the tree fall epicenter of the 1908 Tunguska event. Based on current estimates of the Phanerozoic impact distribution, there is at most a 1 in ∼17 000 chance that the 1908 bolide would randomly fall on the site of a previous impact structure capable of creating shocked quartz. Just as improbable would be an airbust event, incapable of creating a small crater, that could have produced shock metamorphism. Our preferred least implausible hypothesis is that the shock-metamorphism here was associated with a terrestrial event, a hyperexplosive volcanic gas eruption called ‘Verneshot’.

Reference
Vannucchi P, Morgan JP, Lunga DD, Andronicos CL, Morgan WJ (2014) Direct evidence of ancient shock metamorphism at the site of the 1908 Tunguska Event. Earth and Planetary Science Letters 409, 168–174
Link to Article [doi:10.1016/j.epsl.2014.11.001]

Copyright Elsevier

^1,2Tsuyoshi Iizuka, ^3,4Akira Yamaguchi, ³Makiko K. Haba, ²Yuri Amelin, ²Peter Holden, ²Sonja Zink, ²Magdalena H. Huyskens, ²Trevor R. Ireland
¹Department of Earth and Planetary Science, The University of Tokyo, Hongo 7-3-1, Bunkyo, Tokyo 113-0033, Japan
²Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia
³National Institute of Polar Research, Tokyo, Japan
⁴Department of Polar Science, School of Multidisciplinary Science, Graduate University for Advanced Sciences, Tokyo, Japan

Non-cumulate eucrites represent basaltic crust that experienced a complex thermal history involving multistage metamorphism and metasomatism, probably on asteroid Vesta. To better constrain the thermal history of these rocks and their parent body, we have integrated high-precision U–Pb age and trace element data for zircon grains with sizes up to 80 μm in the eucrite Agoult. All analyzed zircon grains yielded concordant U–Pb dates that correspond to the precise 207Pb/206Pb age of 4554.5±2.0 Ma4554.5±2.0 Ma. The Ti contents in these zircon grains indicate their crystallization at subsolidus temperatures of ca. 900 °C, which are similar to the inferred conditions of pyroxene exsolution in most basaltic eucrites that occurred during protracted thermal metamorphism. The zircon crystallization temperatures, together with the presence of baddeleyite needles and variable Zr concentration in Agoult ilmenite grains, indicate metamorphic origin of the Agoult zircon through Zr release from ilmenite followed by reaction with silica. We therefore consider the zircon 207Pb/206Pb age as the timing of the widespread thermal metamorphism in Vesta’s crust. The metamorphic age is coincident with the oldest Mn–Cr date for cumulate eucrites, supporting the view that the thermal metamorphism is a result of burial of basaltic crust and subsequent heating from the hot interior rather than collision of asteroids. The zircon rare earth element patterns with restricted Ce positive anomalies suggest that the metamorphism occurred at an oxygen fugacity below the iron–wüstite buffer, implying the absence of oxidizing agents such as aqueous fluid within the crust at that time.

Reference
Iizuka T, Yamaguchi A, Haba MK, Amelin Y, Holden P, Zink S, Huyskens MH, Ireland TR (2014)Timing of global crustal metamorphism on Vesta as revealed by high-precision U–Pb dating and trace element chemistry of eucrite zircon. Earth and Planetary Science Letters 409,182–192
Link to Article [doi:10.1016/j.epsl.2014.10.055]

Copyright Elsevier

¹Takaaki Noguchi, ²Noriaki Ohashi, ²Shinichi Tsujimoto, ²Takuya Mitsunari, ³John P. Bradley, ⁴Tomoki Nakamura,
⁵Shoichi Toh, ⁶Thomas Stephan, ⁷Naoyoshi Iwata, ⁸Naoya Imae
¹Faculty of Arts and Science, Kyushu University, 744, Motooka, Nishi-ku, Fukuoka 819-0395, Japan
²College of Science, Ibaraki University, 2-1-1 Bunkyo, Mito 310-8512, Japan
³University of Hawaii at Manoa, Hawaii Institute of Geophysics and Planetology, Honolulu, HI 96822, USA
⁴Department of Earth Science, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai 980-8578, Japan
⁵Department of Applied Physics, Fukuoka University, 8-19-1 Nanakuma, Fukuoka 814-0180, Japan
⁶Department of the Geophysical Sciences, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA
⁷Department of Earth and Environmental Sciences, Yamagata University, 1-4-12 Kojirakawa-machi, Yamagata 990-8560, Japan
⁸National Institute of Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan

Chondritic porous interplanetary dust particles (CP IDPs) collected in the stratosphere are regarded as possibly being cometary dust, and are therefore the most primitive solar system material that is currently available for analysis in laboratories. In this paper we report the discovery of more than 40 chondritic porous micrometeorites (CP MMs) in the surface snow and blue ice of Antarctica, which are indistinguishable from CP IDPs. The CP MMs are botryoidal aggregates, composed mainly of sub-micrometer-sized constituents. They contain two components that characterize them as CP IDPs: enstatite whiskers and GEMS (glass with embedded metal and sulfides). Enstatite whiskers appear as <2-μm-long acicular objects that are attached on, or protrude from the surface, and when included in the interior of the CP MMs are composed of a unit-cell scale mixture of clino- and ortho-enstatite, and elongated along the [100] direction. GEMS appear as 100–500 nm spheroidal objects containing <50 nm Fe–Ni metal and Fe sulfide. The CP MMs also contain low-iron–manganese-enriched (LIME) and low-iron–chromium-enriched (LICE) ferromagnesian silicates, kosmochlor (NaCrSi2O6)-rich high-Ca pyroxene, roedderite (K, Na)2Mg5Si12O30, and carbonaceous nanoglobules. These components have previously been discovered in primitive solar system materials such as the CP IDPs, matrices of primitive chondrites, phyllosilicate-rich MMs, ultracarbonaceous MMs, and cometary particles recovered from the 81P/Wild 2 comet. The most outstanding feature of these CP MMs is the presence of kosmochlor-rich high-Ca pyroxene and roedderite, which suggest that they have building blocks in common with CP IDPs and cometary dust particles and therefore suggest a possible cometary origin of both CP MMs and CP IDPs. It is therefore considered that CP MMs are CP IDPs that have fallen to Earth and have survived the terrestrial environment.

Reference
Noguchia T, Ohashi N, Tsujimoto S, Mitsunari T, Bradley JP, Nakamura T, Toh S, Stephan T, Iwata N, Imae N (2014) Cometary dust in Antarctic ice and snow: Past and present chondritic porous micrometeorites preserved on the Earth’s surface. Earth and Planetary Science Letters 410,l 1-11
Link to Article [doi:10.1016/j.epsl.2014.11.012]

Copyright Elsevier

¹M. Hässig et al. (>10)*
¹Southwest Research Institute, Space Science and Engineering, 6220 Culebra Rd., San Antonio, TX 78238, USA
*Find the extensive, full author and affiliation list on the publishers website

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Reference
Hässig M (2014) The capabilities of ROSINA/DFMS to measure argon isotopes at comet 67P/Churyumov-Gerasimenko. Planetary and Space Science (in Press)
Link to Article [doi:10.1016/j.pss.2014.11.015]

¹Sandra Pizzarello
¹Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85018-1604, USA

HCN is ubiquitous in extraterrestrial environments and is central to current theories on the origin of early solar system organic compounds such as amino acids. These compounds, observed in carbonaceous meteorites, were likely important in the origin and/or evolution of early life. As part of our attempts to understand the origin(s) of meteoritic CN–, we have analyzed the 15N/14N isotopic composition of HCN gas released from water extracts of the Murchison meteorite and found its value to be near those of the terrestrial atmosphere. The findings, when evaluated viz-a-viz molecular abundances and isotopic data of meteoritic organic compounds, suggest that HCN formation could have occurred during the protracted water alteration processes known to have affected the mineralogy of many asteroidal bodies during their solar residence. This was an active synthetic stage, which likely involved simple gasses, organic molecules, their presolar precursors, as well as mineral catalysts and would have lead to the formation of molecules of differing isotopic composition, including some with solar values.

Reference
Pizzarello S (2014) The Nitrogen Isotopic Composition of Meteoritic HCN. Astrophysical Journal 796, L25
Link to Article [doi:10.1088/2041-8205/796/2/L25]

¹Nirmala Jain, ¹Prakash Chauhan
¹Planetary Sciences & Marine Biology Division, Biological and Planetary Sciences and Applications Group, Space Applications Centre (SAC), Indian Space Research Organization (ISRO), Ahmedabad, Gujarat, India, 380 015

Spectral reflectance data from the MRO-CRISM (Mars Reconnaissance Orbiter-Compact Reconnaissance Imaging Spectrometer for Mars) of Capri Chasma, a large canyon within Valles Marineris on Mars, have been studied. Results of this analysis reveal the presence of minerals, such as, phyllosilicates (illite, smectite (montmorillonite)) and carbonates (ankerite and manganocalcite). These minerals hint of the aqueous history of Noachian time on Mars. Phyllosilicates are products of chemical weathering of igneous rocks, whereas carbonates could have formed from local aqueous alteration of olivine and other igneous minerals. Four different locations within the Capri Chasma region were studied for spectral reflectance based mineral detection. The study area also shows the spectral signatures of iron-bearing minerals, e.g. olivine with carbonate, indicating partial weathering of parent rocks primarily rich in ferrous mineral. The present study shows that the minerals of Capri Chasma are characterized by the presence of prominent spectral absorption features at 2.31 μm, 2.33 μm, 2.22 μm, 2.48 μm and 2.52 μm wavelength regions, indicating the existence of hydrous minerals, i.e., carbonates and phyllosilicates. The occurrence of carbonates and phyllosilicates in the study area suggests the presence of alkaline environment during the period of their formation. Results of the study are important to understand the formation processes of these mineral assemblages on Mars, which may help in understanding the evolutionary history of the planet.

Reference
Jain N, Chauhan P (2014) Study of phyllosilicates and carbonates from the Capri Chasma region of Valles Marineris on Mars based on Mars Reconnaissance Orbiter-Compact Reconnaissance Imaging Spectrometer for Mars (MRO-CRISM) observations. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2014.11.018]

Copyright Elsevier

¹Lars E. Borg, ¹Amy M. Gaffney, ²Charles K. Shearer
¹Chemical Sciences Division, Lawrence Livermore National Laboratory, Livermore, California, USA
²Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico, USA

Data obtained from Sm-Nd and Rb-Sr isotopic measurements of lunar highlands’ samples are renormalized to common standard values and then used to define ages with a common isochron regression algorithm. The reliability of these ages is evaluated using five criteria that include whether: (1) the ages are defined by multiple isotopic systems, (2) the data demonstrate limited scatter outside uncertainty, (3) initial isotopic compositions are consistent with the petrogenesis of the samples, (4) the ages are defined by an isotopic system that is resistant to disturbance by impact metamorphism, and (5) the rare-earth element abundances determined by isotope dilution of bulk of mineral fractions match those measured by in situ analyses. From this analysis, it is apparent that the oldest highlands’ rock ages are some of the least reliable, and that there is little support for crustal ages older than approximately 4.40 Ga. A model age for ur-KREEP formation calculated using the most reliable Mg-suite Sm-Nd isotopic systematics, in conjunction with Sm-Nd analyses of KREEP basalts, is 4389 ± 45 Ma. This age is a good match to the Lu-Hf model age of 4353 ± 37 Ma determined using a subset of this sample suite, the average model age of 4353 ± 25 Ma determined on mare basalts with the 146Sm-142Nd isotopic system, with a peak in Pb-Pb ages observed in lunar zircons of approximately 4340 ± 20 Ma, and the oldest terrestrial zircon age of 4374 ± 6 Ma. The preponderance of ages between 4.34 and 4.37 Ga reflect either primordial solidification of a lunar magma ocean or a widespread secondary magmatic event on the lunar nearside. The first scenario is not consistent with the oldest ages reported for lunar zircons, whereas the second scenario does not account for concordance between ages of crustal rocks and mantle reservoirs.

Reference
Borg LE, Gaffney AM, Shearer CK (2014) A review of lunar chronology revealing a preponderance of 4.34–4.37 Ga Ages. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12373]

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