^1,3Eve L. Berger, ²Lindsay P. Keller,¹Dante S. Lauretta
¹Lunar and Planetary Laboratory, The University of Arizona, Tucson, Arizona, USA
²NASA Johnson Space Center, Houston, Texas, USA
³GeoControl Systems, Inc. — Jacobs JETS contract — NASA Johnson Space Center, Houston, Texas, 77058, USA

The low-temperature form of CuFe2S3, cubanite, has been identified in the CI chondrite and NASA Stardust mission collections. The presence of this mineral constrains the maximum temperature to 210 °C since the time of its formation. However, until now, the conditions under which cubanite forms were less well constrained. In order to refine the history of the time-varying, low-temperature fluids which existed on the CI-chondrite parent body and Comet 81P/Wild 2 (Wild 2), we synthesized cubanite. The experimental synthesis of this mineral was achieved, for the first time, under low-temperature aqueous conditions relevant to the CI-chondrite parent body. Using a variant of in situ hydrothermal recrystallization, cubanite formed in aqueous experiments starting with temperatures of 150 and 200 °C, pH approximately 9, and oxygen fugacities corresponding to the iron-magnetite buffer. The composition and structure of the cubanite were determined using electron microprobe and transmission electron microscopy techniques, respectively. The combined compositional, crystallographic, and experimental data allow us to place limits on the conditions under which the formation of cubanite is feasible, which in turn constrains the nature of the fluid phase on the CI-chondrite parent body and Wild 2 when cubanite was forming.

Reference
Berger EL, Keller LP, Lauretta DS (2014) An experimental study of the formation of cubanite (CuFe2S3) in primitive meteorites. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12399]

Published by arrangement with John Wiley&Sons

¹Yangting Lin et al. (>10)*
¹Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
*Find the extensive, full author and affiliation list on the publishers website

Two petrographic settings of carbonaceous components, mainly filling open fractures and occasionally enclosed in shock-melt veins, were found in the recently fallen Tissint Martian meteorite. The presence in shock-melt veins and the deuterium enrichments (δD up to +1183‰) of these components clearly indicate a pristine Martian origin. The carbonaceous components are kerogen-like, based on micro-Raman spectra and multielemental ratios, and were probably deposited from fluids in shock-induced fractures in the parent rock of Tissint. After precipitation of the organic matter, the rock experienced another severe shock event, producing the melt veins that encapsulated a part of the organic matter. The C isotopic compositions of the organic matter (δ13C = −12.8 to −33.1‰) are significantly lighter than Martian atmospheric CO2 and carbonate, providing a tantalizing hint for a possible biotic process. Alternatively, the organic matter could be derived from carbonaceous chondrites, as insoluble organic matter from the latter has similar chemical and isotopic compositions. The presence of organic-rich fluids that infiltrated rocks near the surface of Mars has significant implications for the study of Martian paleoenvironment and perhaps to search for possible ancient biological activities on Mars.

Reference
Lin Y et al. (2014) NanoSIMS analysis of organic carbon from the Tissint Martian meteorite: Evidence for the past existence of subsurface organic-bearing fluids on Mars. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12389]

Published by arrangement with John Wiley&Sons

¹Jean-Yves Bonnet et al. (>10)*
¹Univ. Grenoble Alpes, IPAG, F-38000 Grenoble, France, CNRS, IPAG, F-38000 Grenoble, France
*Find the extensive, full author and affiliation list on the publishers website

Nitrogen-rich refractory organics are scarce phases recovered as a fraction of stratospheric IDPs and constitute the bulk of the organic matter of some ultracarbonaceous Antarctic micrometeorites. They are likely formed under very specific conditions within a nitrogen-rich environment and may provide valuable clues on the origin of the population of interplanetary dusts accreted by Earth. In this study, we produced relevant analogs of such refractory organics characterized in three ultracarbonaceous Antarctic micrometeorites, starting from the carbonization of an HCN polymer and a tholin. Indeed, carbonization is a process that can increase the polyaromatic character toward a structure similar to that observed in these cosmomaterials. Both these precursors were degraded in an Ar atmosphere at 300, 500, 700 and 1000°C over ∼1 hour and characterized by elemental analysis, micro-FTIR and Raman micro-spectroscopy (at 244 and 514 nm excitation wavelengths). Our results show that the precursors evolve along distinct chemical and structural pathways during carbonization and that the influence of the precursor structure is still very strong at 1000°C. Interestingly, these different carbonization routes appear in the spectral characteristics of the G and D bands of their Raman spectra. Several of the residues present chemical and structural similarities with three recently studied ultracarbonaceous micrometeorites [Dobrica et al. (2011)Meteoritics Planet. Sci.46, 1363; Dartois et al. (2013)Icarus224, 243] and with N-rich inclusions in stratospheric IDPs. However the residues do not simultaneously account for the carbon structure (Raman) and the chemical composition (IR, N/C ratio). This indicates that the precursors and/or heating conditions in our experiments are not fully relevant. Despite this lack of full relevancy, the formation of a polyaromatic structure fairly similar to that of UCAMMs and IDPs suggests that the origin of N-rich refractory organics lies in a thermal process in the proto-solar disk, however radiolysis cannot be excluded.

Reference
Bonnet J-Y et al. (2014) Formation of analogs of cometary nitrogen-rich refractory organics from thermal degradation of tholin and hcn polymer. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2014.11.006]

Copyright Elsevier

¹Oliver Tschauner, ²Chi Ma, ²John R. Beckett, ³Clemens Prescher, ³Vitali B. Prakapenka, ²George R. Rossman
¹Department of Geoscience and High Pressure Science and Engineering Center, University of Nevada, Las Vegas, NV 89134, USA.
²Division of Geology and Planetary Science, California Institute of Technology, Pasadena, CA 91125, USA.
³Center of Advanced Radiation Sources, University of Chicago, Chicago, IL 60632, USA.

Meteorites exposed to high pressures and temperatures during impact-induced shock often contain minerals whose occurrence and stability normally confine them to the deeper portions of Earth’s mantle. One exception has been MgSiO3 in the perovskite structure, which is the most abundant solid phase in Earth. Here we report the discovery of this important phase as a mineral in the Tenham L6 chondrite and approved by the International Mineralogical Association (specimen IMA 2014-017). MgSiO3-perovskite is now called bridgmanite. The associated phase assemblage constrains peak shock conditions to ~ 24 gigapascals and 2300 kelvin. The discovery concludes a half century of efforts to find, identify, and characterize a natural specimen of this important mineral.

Reference
Tschauner O, Ma C, Beckett JR, Prescher C, Prakapenka VB, Rossman GR (2014) Discovery of bridgmanite, the most abundant mineral in Earth, in a shocked Meteorite. Science 346, 1100-1102
Link to Article [DOI: 10.1126/science.1259369]

Reprinted with permission from AAAS

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