During the last days of this year, Cosmochemistry Papers will be on Christmas break (more or less). Normal service will commence on January, 2nd, after we have recovered.

Merry Christmas & Happy New Year to everyone and see you in 2015 !

¹Kazuhide Nagashima, ¹Alexander N. Krot, ¹Gary R. Huss
¹Hawai‘i Institute of Geophysics and Planetology, School of Ocean, Science and Technology, University of Hawai‘i at Mānoa, Honolulu, HI 96826, USA

To investigate a possible relationship between chondrules and matrix, we studied mineralogy, mineral chemistry, and in situ O-isotope compositions of chondrules, clastic matrix grains, and amoeboid olivine aggregates (AOAs) in the Kakangari K-grouplet chondrite. Most olivines and low-Ca pyroxenes in the Kakangari chondrules, matrix, and AOAs have similar magnesium-rich compositions, Fo∼95–97 (∼0.3−0.5 wt% MnO) and En∼90–96, respectively. These rather uniform chemical compositions of the different chondritic components are likely due to partial Fe-Mg-Mn equilibration during thermal metamorphism experienced by the host meteorite. Oxygen-isotope compositions of olivine and low-Ca pyroxene grains in chondrules and matrix plot along a slope-1 line on a three O-isotope diagram and show a range from 16O-enriched composition similar to that of the Sun to 16O-depleted composition similar to the terrestrial O-isotope composition. Most olivines and low-Ca pyroxenes in chondrules are 16O-poor and plot on or close to the terrestrial mass-fractionation line (mean Δ17O values ± 2 standard deviations: 0.0±0.8‰ and +0.2±0.9‰ for olivine and pyroxene, respectively), consistent with the previously reported compositions of bulk chondrules (Δ17O = –0.16±0.70‰). In addition to these 16O-poor grains, a coarse-grained igneous rim surrounding a porphyritic chondrule contains abundant 16O-rich relict olivines (Δ17O ∼ –24‰). Oxygen-isotope compositions of olivines and low-Ca pyroxenes in matrix show a bimodal distribution: 12 out of 13 olivine and 4 out of 17 pyroxene grains measured are similarly 16O-rich (Δ17O ∼ –23.5±2.9‰), others are similarly 16O-poor (Δ17O ∼ –0.1±1.7‰). Due to slow oxygen self-diffusion, olivines and low-Ca pyroxenes largely retained their original oxygen-isotope compositions. The nearly identical O-isotope compositions between the chondrule phenocrysts and the 16O-poor matrix grains suggest both chondrules and matrix of Kakangari sampled isotopically the same reservoirs. In addition, the presence of abundant 16O-rich grains in matrix and the chondrule igneous rim suggests both components acquired similar precursor inventories. These observations imply that chondrules and matrix in Kakangari are genetically related in the sense that material that formed matrix was one of the precursors of chondrules and chondrules and some fraction of matrix experienced the same thermal processing event. The 16O-enriched bulk matrix value compared to the bulk chondrules reported previously is likely due to presence of abundant 16O-rich grains in the Kakangari matrix.

Reference
Nagashima K, Krot AN, Huss GR (2014) Oxygen-isotope compositions of chondrule phenocrysts and matrix grains in Kakangari K-grouplet chondrite: Implication to a chondrule-matrix genetic relationship. Geochimica et Cosmochimica (in Press)
Link to Article [doi:10.1016/j.gca.2014.12.012]

Copyright Elsevier

¹J. Brian Balta, ^2,3Matthew E. Sanborn, ^1,4Arya Udry, ²Meenakshi Wadhwa, ¹Harry Y. McSween Jr.
¹Planetary Geosciences Institute, Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, Tennessee, USA
²Center for Meteorite Studies, School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, USA
³Department of Earth and Planetary Sciences, UC Davis, Davis, California, USA
⁴Department of Geoscience, University of Nevada, Las Vegas, Nevada, USA

The fall and recovery of the Tissint meteorite in 2011 created a rare opportunity to examine a Martian sample with a known, short residence time on Earth. Tissint is an olivine-phyric shergottite that accumulated olivine antecrysts within a single magmatic system. Coarse olivine grains with nearly homogeneous cores of Mg# >80 suggest slow re-equilibration. Many macroscopic features of this sample resemble those of LAR 06319, including the olivine crystal size distribution and the presence of evolved oxide and olivine compositions. Unlike LAR 06319, however, no magmatic hydrous phases were found in the analyzed samples of Tissint. Minor and trace element compositions indicate that the meteorite is the product of closed-system crystallization from a parent melt derived from a depleted source, with no obvious addition of a LREE-rich (crustal?) component prior to or during crystallization. The whole-rock REE pattern is similar to that of intermediate olivine-phyric shergottite EETA 79001 lithology A, and could also be approximated by a more olivine-rich version of depleted basaltic shergottite QUE 94201. Magmatic oxygen fugacities are at the low end of the shergottite range, with log fO2 of QFM-3.5 to -4.0 estimated based on early-crystallized minerals and QFM-2.4 estimated based on the Eu in pyroxene oxybarometer. These values are similarly comparable to other depleted shergottites, including SaU 005 and QUE 94201. Tissint occupies a previously unsampled niche in shergottite chemistry: containing olivines with Mg# >80, resembling the enriched olivine-phyric shergottite LAR 06319 in its crystallization path, and comparable to intermediate olivine-phyric shergottite EETA 79001A, depleted olivine-phyric shergottite DaG 476, and depleted basaltic shergottite QUE 94201 in its trace element abundances and oxygen fugacity. The apparent absence of evidence for terrestrial alteration in Tissint (particularly in trace element abundances in the whole-rock and individual minerals) confirms that exposure to the arid desert environment results in only minimal weathering of samples, provided the exposure times are brief.

Reference
Balta JB, Sanborn ME, Udry A, Wadhwa M, McSween Jr. HY (2014) Petrology and trace element geochemistry of Tissint, the newest shergottite fall. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12403]

Published by arrangement with John Wiley&Sons

¹Winfried H. Schwarz, ^2,3Martin Schmieder, ^4,5Elmar Buchner, ¹Mario Trieloff, ⁶Jarmo Moilanen, ⁷Teemu Öhman
¹Institut für Geowissenschaften, Universität Heidelberg, Heidelberg, Germany
²School of Earth and Environment, University of Western Australia, Crawley, WA, Australia
³Western Australian Argon Isotope Facility, Department of Applied Geology and JdL Centre, Curtin University, Perth, WA, Australia
⁴HNU Neu-Ulm University, Neu-Ulm, Germany
⁵Institut für Mineralogie und Kristallchemie, Universität Stuttgart, Stuttgart, Germany
⁶Oulu, Finland
⁷Arctic Planetary Science Institute, Rovaniemi, Finland

A recrystallized band of pale feldspathic impact melt in a gneissic impact breccia from the approximately 10 km Paasselkä impact structure in southeast Finland was dated via 40Ar/39Ar step-heating. The newly obtained plateau age of 228.7 ± 1.8 (2.2) Ma (2σ) (MSWD = 0.32; p = 0.93) is equal to the previously published pseudoplateau age of 228.7 ± 3.0 (3.4) (2σ) for the impact event. According to the current international chronostratigraphic chart and using the most recent published suggestions for the K decay constants, a Carnian (Late Triassic) age for the Paasselkä impact structure of 231.0 ± 1.8 (2.2) Ma (2σ) is calculated and considered the most precise and accurate age for this impact structure. The new plateau age for Paasselkä confirms the previous dating result but is, based on its internal statistics, much more compelling.

Reference
Schwarz WH, Schmieder M, Buchner E, Trieloff M, Moilanen J, Öhman T (2014) A Carnian 40Ar/39Ar age for the Paasselkä impact structure (SE Finland)—An update. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12407]

Published by arrangement with John Wiley & Sons

^1,2Michael A. Antonelli, ²Sang-Tae Kim, ¹Marc Peters, ³Jabrane Labidi, ³Pierre Cartigny, ¹Richard J. Walker, ⁴James R. Lyons, ¹Joost Hoek, ^1,5James Farquhar
¹Department of Geology, University of Maryland, College Park, MD 20742;
²School of Geography and Earth Sciences, McMaster University, Hamilton, ON L8S 4K1, Canada;
³Laboratoire de Géochimie des Isotopes Stables, Institut de Physique du Globe de Paris, UMR 7154 CNRS, Universite Paris Denis-Diderot, Sorbonne Paris Cite, 75005 Paris, France;
⁴School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287; and
⁵Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD 20742

Achondrite meteorites have anomalous enrichments in 33S, relative to chondrites, which have been attributed to photochemistry in the solar nebula. However, the putative photochemical reactions remain elusive, and predicted accompanying 33S depletions have not previously been found, which could indicate an erroneous assumption regarding the origins of the 33S anomalies, or of the bulk solar system S-isotope composition. Here, we report well-resolved anomalous 33S depletions in IIIF iron meteorites (<−0.02 per mil), and 33S enrichments in other magmatic iron meteorite groups. The 33S depletions support the idea that differentiated planetesimals inherited sulfur that was photochemically derived from gases in the early inner solar system (<∼2 AU), and that bulk inner solar system S-isotope composition was chondritic (consistent with IAB iron meteorites, Earth, Moon, and Mars). The range of mass-independent sulfur isotope compositions may reflect spatial or temporal changes influenced by photochemical processes. A tentative correlation between S isotopes and Hf-W core segregation ages suggests that the two systems may be influenced by common factors, such as nebular location and volatile content.

Reference
Antonelli MA, Kim S-T, Peters M, Labidi J, Cartigny P, Walker RJ, Lyons JR, Hoek J, Farquhar J (2014) Early inner solar system origin for anomalous sulfur isotopes in differentiated protoplanets. Proceedings of the National Academy of Sciences 111, 17749-17754
Link to Article [doi:10.1073/pnas.1418907111]

¹Dennis Harries, ¹Falko Langenhorst
¹Analytical Mineralogy of Micro- and Nanostructures, Institute of Geoscience, Friedrich Schiller University Jena, Carl-Zeiss-Promenade 10, 07745 Jena,Germany

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

Reference
Harries D, Langenhorst F (2014) The mineralogy and space weathering of a regolith grain from 25143 Itokawa and the possibility of annealed solar wind damage. Earth, Planets and Space 2014, 66:163
Link to Article [doi:10.1186/s40623-014-0163-1]

¹ A. Kereszturi, ²I. Gyollai, ³M. Szabó
¹Konkoly Thege Miklos Astronomical Institute, Research Center for Astronomy and Earth Sciences, H-1121 Budapest, Konkoly Thege Miklos 15-17Hungary
²Department of Lithospheric Research, University of Vienna, A-1091, Althanstrasse 14., Vienna, Austria
³Institute of Geological and Geochemical Research, Research Center for Astronomy and Earth Sciences, H-1112 Budapest, 45 Budaörsi street

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

Reference
Kereszturi A, Gyollai I, Szabó M (2014) Case study of chondrule alteration with IR spectroscopy in NWA 2086 CV3 Meteorite. Planetary and Space Science (in Press)
Link to Article [doi:10.1016/j.pss.2014.12.015]

^1,2S. Fornasier, ^1,3I.N. Belskaya, ¹D. Perna
¹LESIA, Observatoire de Paris, CNRS, UPMC Univ Paris 06, Univ. Paris Diderot, 5 Place J. Janssen, 92195 Meudon Pricipal Cedex, France
²Univ. Paris Diderot, Sorbonne Paris Cité, 4 rue Elsa Morante, 75205 Paris Cedex 13
³Astronomical Observatory of Kharkiv National University, 35 Sumska str., 61022 Kharkiv, Ukraine Submitted to Icarus: September 2014

In this paper we present the results on the polarimetric and spectroscopic observations of the Potentially Hazardous Asteroid (214869) 2007 PA8 obtained during its favorable apparition in October-November 2012, when it approached the Earth at the minimal distance of 0.043 AU. Polarimetry was carried out at the NOT in the B, V, R, and I bands covering both low (12-23°) and large phase angles (88-99°). Spectroscopy in the visible and near infrared range was obtained at the TNG telescope.

The spectrum of 2007 PA8 shows silicates absorption features and a behavior consistent with a Q-type classification. The olivine and pyroxene BI band is centered at 0.9578±0.0042 μm, with a band depth of 16.5%, the BII band is centered at 1.95±0.01 μm, and it has a band depth of about 3.9%. The 2007 PA8 spectral parameters are consistent with those of L chondrites. Also the spectral comparison with meteorites gives the L-type chondrites, and L6 in particular, as best match.

The NEA (214869) 2007 PA8 is the forth moderate albedo asteroid and the first Q-type asteroid for which the value of the polarization maximum is determined. The inversion angle of the polarization curve in the V filter is 19.0±1.1°, the corresponding slope parameter (h ) is of 0.078±0.010%/°, the maximum value of polarization is 5.99±0.16%, and the extreme value of negative polarization is estimated to be lower than -0.52%. Using the polarimetric slope we derive a geometric albedo of 0.29±0.08 in the V band, that gives an estimated diameter of 1.4±0.2 km, assuming an absolute HvHv magnitude of 16.2 mag. We find a strong dependence of the polarization in the B, V, R, and I bands with wavelength, and the polarimetric albedo in the four bands is strongly correlated with the asteroid’s spectrum. The 2007 PA8 polarimetric properties resemble those of other 2 NEAs, 1566 Icarus and 25143 Itokawa, which are both S(IV)/Q type.

Our spectral and polarimetric analysis indicate that 2007 PA8 has a young and fresh surface almost unweathered, similar to L-type chondrites. These results, together with dynamical simulations made by Nedelcu et al., 2014 and Nesvorny et al., 2009, indicate that 2007 PA8 may be a member of the Gefion family recently ejected from the 5:2 resonance and a potential source of L chondrites.

Reference
Fornasier S, Belskaya IN, Perna D (2014) The potentially hazardous asteroid (214869) 2007 PA8: an unweathered L chondrite analogue surface. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2014.12.015]

Copyright Elsevier

¹Joke Belza, ^1,2Steven Goderis, ³Jan Smit, ²Frank Vanhaecke, ⁴Kitty Baert, ⁴Herman Terryn, ¹Philippe Claeys
¹Department of Analytical Environmental and Geo-Chemistry, Vrije Universiteit Brussel, Pleinlaan 2, BE-1050 Brussels, Belgium
²Department of Analytical Chemistry, Universiteit Gent, Krijgslaan 281-S12, BE-9000 Ghent, Belgium
³Department of Sedimentology, Vrije Universiteit Amsterdam, de Boelelaan 1085, 1081HV Amsterdam, Netherlands
⁴Department of Electrochemical and Surface Engineering, Vrije Universiteit Brussel, Pleinlaan 2, BE-1050 Brussels, Belgium

Using laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS), we have conducted spatially resolved trace element analysis on fresh, unaltered microtektite glasses linked to the Cretaceous-Paleogene (K-Pg) boundary Chicxulub crater and on their surrounding alteration phases. This unique approach offers the opportunity to study in situ and at high spatial resolution both the mixing of different target lithologies and the variation of the major and trace element budget during the alteration process. In addition, two-dimensional element distribution maps reveal important geochemical information beyond the capabilities of single spot laser drilling. Glasses from two localities in opposite quadrants from the source crater were studied. At the Beloc locality (Haiti), the glass population is dominated by the presence of yellow high-Ca glass and black andesitic glass formed by admixture of carbonate/dolomite/anhydrite platform lithologies with crystalline basement. These glasses alter according to the well-established hydration-palagonitisation model postulated for mafic volcanic glasses. REEs become progressively leached from the glass to below the detection limit for the applied spot size, while immobile Zr, Hf, Nb, and Ta passively accumulate in the process exhibiting both inter-element ratios and absolute concentrations similar to those for the original glass. In contrast, The Arroyo El Mimbral locality (NE Mexico) is characterized by abundant green glass fragments high in Si, Al and alkalis, and low in Mg, Ca, Fe. Low Si black glass is less abundant though similar in composition to the black glass variety at Beloc. The alteration pattern of high-Si, Al green glass at the Mimbral locality is more complex, including numerous competing reaction processes (ion-exchange, hydration, dissolution, and secondary mineral precipitation) generally controlled by the pH and composition of the surrounding fluid. All green, high-Si, Al glasses are hydrated and variably enriched in Sr, Ba, and Cs, indicating preferred adsorption from seawater during hydration. Despite the onset of ion-exchange reactions, which only seem to have affected the alkalis, the trace element composition of the green high-Si, Al glass is still largely representative of the original melt composition. Refining the geochemical signature of (altered) melt lithologies may advance our current understanding of glass stability in the natural environment and provide insight into the origin and emplacement of ejecta material during crater formation.

Reference
Belza J, Goderis S, Smit J, Vanhaecke F, Baert K, Terryn H, Claeys P (2014) High spatial resolution geochemistry and textural characteristics of ‘microtektite’ glass spherules in proximal Cretaceous-Paleogene sections: insights into glass alteration patterns and precursor melt lithologies. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2014.12.013]

Copyright Elsevier

¹P. A. Bland,²G. S. Collins,²T. M. Davison,³N. M. Abreu,⁴F. J. Ciesla,²A. R. Muxworthy, ²J. Moore
¹Department of Applied Geology, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia
²Impacts & Astromaterials Research Centre (IARC), Department of Earth Science & Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
³Earth Science Program, Pennsylvania State University—Du Bois Campus, Du Bois, Pennsylvania 15801, USA N. M. Abreu
⁴Department of Geophysical Science, University of Chicago, 5734 South Ellis Avenue, Chicago, Illinois 60430, USA

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

Reference
Bland PA, Collins GS, Davison TM, Abreu NM, Ciesla FJ, Muxworthy AR, Moore J (2014) Pressure–temperature evolution of primordial solar system solids during impact-induced compaction. Nature Communications 5, 5451
Link to Article [doi:10.1038/ncomms6451]