¹Winfried H. Schwarz,¹Michael Hanel,¹Mario Trieloff
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13437]
¹Klaus‐Tschira‐Labor für Kosmochemie, Institut für Geowissenschaften, Universität Heidelberg, Im Neuenheimer Feld 234‐236, D‐69120 Heidelberg, Germany
Published by arrangement with John Wiley & Sons

In situ U‐Pb measurements on zircons of the Ries impact crater are presented for three samples from the quarry at Polsingen. The U‐Pb data of most zircons plot along a discordia line, leading to an upper intercept of Carboniferous age (331 ± 32 Ma [2σ]). Four zircons define a concordia age of 313.2 ± 4.4 Ma (2σ). This age most probably represents the age of a granite from the basement target rocks. From granular textured zircon grains (including baddeleyite and anatase/Fe‐rich phases, first identified in the Ries crater), most probably recrystallized after impact (13 analyses, 4 grains), a concordia age of 14.89 ± 0.34 Ma (2σ) and an error weighted mean ²⁰⁶Pb*/²³⁸U age of Ma 14.63 ± 0.43 (2σ) is derived. Including the youngest concordant ages of five porous textured zircon grains (24 spot analyses), a concordia age of 14.75 ± 0.22 Ma (2σ) and a mean ²⁰⁶Pb*/²³⁸U age of 14.71 ± 0.26 Ma (2σ) can be calculated. These results are consistent with previously published ⁴⁰Ar/³⁹Ar ages of impact glasses and feldspar. Our results demonstrate that even for relatively young impact craters, reliable U‐Pb ages can be obtained using in situ zircon dating by SIMS. Frequently the texture of impact shocked zircon grains is explained by decomposition at high temperatures and recrystallization to a granular texture. This is most probably the case for the observed granular zircon grains having baddeleyite/anatase/Fe‐rich phases. We also observe non‐baddeleyite/anatase/Fe‐rich phase bearing zircons. For these domains, reset to crater age is more frequently for high U,Th contents. We tentatively explain the higher susceptibility to impact resetting of high U,Th domains by enhanced Pb loss and mobilization due to higher diffusivity within former metamict domains that were impact metamorphosed more easily into porous as well as granular textures during decomposition and recrystallization, possibly supported by Pb loss during postimpact cooling and/or hydrothermal activity.

^1,2Toni Schulz,³Pavel P. Povinec,⁴Ludovic Ferrière,^5,6A. J. Timothy Jull,³Andrej Kováčik,³Ivan Sýkora,²Jonas Tusch,²Carsten Münker,⁴Dan Topa,^1,4Christian Koeberl
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13435]
¹Department of Lithospheric Research, University Vienna, Althanstrasse 14, 1090 Vienna, Austria
²Institut für Geologie und Mineralogie, Universität zu Köln, Zülpicher Strasse 49b, 50674 Köln, Germany
³Faculty of Mathematics, Physics and Informatics, Department of Nuclear Physics and Biophysics, Comenius University, SK‐84248 Bratislava, Slovakia
⁴Natural History Museum, Burgring 7, 1010 Vienna, Austria
⁵Department of Geosciences, University of Arizona, Tucson, Arizona, 85721 USA
⁶Hungarian Academy of Sciences, Institute for Nuclear Research, ICER, 4026 Debrecen, Hungary
⁷MicroStep‐MIS, 84104 Bratislava, Slovakia
Published by arrangement with John Wiley & Sons

The Tissint meteorite fell on July 18, 2011 in Morocco and was quickly recovered, allowing the investigation of a new unaltered sample from Mars. We report new high‐field strength and highly siderophile element (HSE) data, Sr‐Nd‐Hf‐W‐Os isotope analyses, and data for cosmogenic nuclides in order to examine the history of the Tissint meteorite, from its source composition and crystallization to its irradiation history. We present high‐field strength element compositions that are typical for depleted Martian basalts (0.174 ppm Nb, 17.4 ppm Zr, 0.7352 ppm Hf, and 0.0444 ppm W), and, together with an extended literature data set for shergottites, help to reevaluate Mars’ tectonic evolution in comparison to that of the early Earth. HSE contents (0.07 ppb Re, 0.92 ppb Os, 2.55 ppb Ir, and 7.87 ppb Pt) vary significantly in comparison to literature data, reflecting significant sample inhomogeneity. Isotope data for Os and W (¹⁸⁷Os/¹⁸⁸Os = 0.1289 ± 15 and an ε¹⁸²W = +1.41 ± 0.46) are both indistinguishable from literature data. An internal Lu‐Hf isochron for Tissint defines a crystallization age of 665 ± 74 Ma. Considering only Sm‐Nd and Lu‐Hf chronometry, we obtain, using our and literature values, a best estimate for the age of Tissint of 582 ± 18 Ma (MSWD = 3.2). Cosmogenic radionuclides analyzed in the Tissint meteorite are typical for a recent fall. Tissint’s pre‐atmospheric radius was estimated to be 22 ± 2 cm, resulting in an estimated total mass of 130 ± 40 kg. Our cosmic‐ray exposure age of 0.9 ± 0.2 Ma is consistent with earlier estimations and exposure ages for other shergottites in general.

¹A. J. G. Jurewicz et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13439]
¹Center for Meteorite Studies, Arizona State University, m/c 6004, Tempe, Arizona, 85287 USA
Published by arrangement with John Wiley & Sons

NASA’s Genesis Mission returned solar wind (SW) to the Earth for analysis to derive the composition of the solar photosphere from solar material. SW analyses control the precision of the derived solar compositions, but their ultimate accuracy is limited by the theoretical or empirical models of fractionation due to SW formation. Mg isotopes are “ground truth” for these models since, except for CAIs, planetary materials have a uniform Mg isotopic composition (within ≤1‰) so any significant isotopic fractionation of SW Mg is primarily that of SW formation and subsequent acceleration through the corona. This study analyzed Mg isotopes in a bulk SW diamond‐like carbon (DLC) film on silicon collector returned by the Genesis Mission. A novel data reduction technique was required to account for variable ion yield and instrumental mass fractionation (IMF) in the DLC. The resulting SW Mg fractionation relative to the DSM‐3 laboratory standard was (−14.4‰, −30.2‰) ± (4.1‰, 5.5‰), where the uncertainty is 2ơ SE of the data combined with a 2.5‰ (total) error in the IMF determination. Two of the SW fractionation models considered generally agreed with our data. Their possible ramifications are discussed for O isotopes based on the CAI nebular composition of McKeegan et al. (2011).

¹A.‐J. Soini,¹I. T. Kukkonen,¹T. Kohout,²A. Luttinen
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13441]
¹Department of Geosciences and Geography, University of Helsinki, PO Box 64, FI‐00014 Helsinki, Finland
²Finnish Museum of Natural History, University of Helsinki, PO Box 44, FI‐00014 Helsinki, Finland
Published by arrangement with John Wiley & Sons

We report direct measurements of thermal diffusivity and conductivity at room temperature for 38 meteorite samples of 36 different meteorites including mostly chondrites, and thus almost triple the number of meteorites for which thermal conductivity is directly measured. Additionally, we measured porosity for 34 of these samples. Thermal properties were measured using an optical infrared scanning method on samples of cm‐sizes with a flat, sawn surface. A database compiled from our measurements and literature data suggests that thermal diffusivities and conductivities at room temperature vary largely among samples even of the same petrologic and chemical type and overlap among, for example, different ordinary chondrite classes. Measured conductivities of ordinary chondrites vary from 0.4 to 5.1 W m⁻¹ K⁻¹. On average, enstatite chondrites show much higher values (2.33–5.51 W m⁻¹ K⁻¹) and carbonaceous chondrites lower values (0.5–2.55 W m⁻¹ K⁻¹). Mineral composition (silicates versus iron‐nickel) and porosity control conductivity. Porosity shows (linear) negative correlation with conductivity. Variable conductivity is attributed to heterogeneity in mineral composition and porosity by intra‐ and intergranular voids and cracks, which are important in the scale of typical meteorite samples. The effect of porosity may be even more significant for thermal properties than that of the metal content in chondrites.