^1,2,3T.J. Peter,^2,3J.I. Simon,²J.H. Jones,⁴T. Usui,⁴R. Moriwaki,⁵R.C. Economos,⁵A.K. Schmitt,⁵K.D. McKeegan
¹Lunar and Planetary Institute, Houston, TX 77058, USA
²Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, TX 77058, USA
³Center for Isotope Cosmochemistry and Geochronology, NASA Johnson Space Center, Houston, TX 77058, USA
⁴Department of Earth & Planetary Sciences, Tokyo Institute of Technology, Tokyo 152-8551, Japan
⁵Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095, USA

The apparent lack of plate tectonics on all terrestrial planets other than Earth has been used to support the notion that for most planets, once a primitive crust forms, the crust and mantle evolve geochemically-independent through time. This view has had a particularly large impact on models for the evolution of Mars and its silicate interior. Recent data indicating a greater potential that there may have been exchange between the martian crust and mantle has led to a search for additional geochemical evidence to support the alternative hypothesis, that some mechanism of crustal recycling may have operated early in the history of Mars.
In order to study the most juvenile melts available to investigate martian mantle source(s) and melting processes, the trace element compositions of olivine-hosted melt inclusions for two incompatible-element-depleted olivine-phyric shergottites, Yamato 980459 (Y98) and Tissint, and the interstitial glass of Y98, have been measured by Secondary Ionization Mass Spectrometry (SIMS). Chondrite-normalized Rare Earth Element (REE) patterns for both Y98 and Tissint melt inclusions, and the Y98 interstitial glass, are characteristically light-REE depleted and parallel those of their host rock. For Y98, a clear flattening and upward inflection of La and Ce, relative to predictions based on middle and heavier REE, provides evidence for involvement of an enriched component early in their magmatic history; either inherited from a metasomatized mantle or crustal source, early on and prior to extensive host crystallization.
Comparing these melt inclusion and interstitial glass analyses to existing melt inclusion and whole-rock data sets for the shergottite meteorite suite, defines mixing relationships between depleted and enriched end members, analogous to mixing relationships between whole rock Sr and Nd isotopic measurements. When considered in light of their petrologic context, the origin of these trace element enriched and isotopically evolved signatures represents either (1) crustal assimilation during the final few km of melt ascent towards the martian surface, or (2) assimilation soon after melt segregation, through melt–rock interaction with a portion of the martian crust recycled back into the mantle.

Reference
Peters TJ, Simon JI, Jones JH, Usui T, Moriwaki R, Economos RC, Schmitt AK, McKeegan KD (2015) Tracking the source of the enriched martian meteorites in olivine-hosted melt inclusions of two depleted shergottites, Yamato 980459 and Tissint. Earth and Planetary Science Letters 418, 91–102.
Link to Article [doi:10.1016/j.epsl.2015.02.033]

Copyright Elsevier

¹Jennifer L. Claydon,¹Sarah A. Crowther,^1,2,3Vera A. Fernandes,¹Jamie D. Gilmour
¹School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Oxford Road, Manchester, M13 9PL, UK.
²Museum für Naturkunde- Berlin, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Invalidenstrasse 43, 10115 Berlin, Germany
³UNINOVA, Universidade Nova de Lisboa, Quinta da Torre, 2829-516 Monte de Caparica, Portugal
⁴The Centre for Earth Evolution and Dynamics, Univ. of Oslo, PO Box 1048 Blindern 0316 Oslo, Norway

The meteorite Graves Nunataks 06128/06129 is the only known example of felsic asteroidal crust. Knowledge of its history can help shed light on the evolution processes of planetesimals. The noble gases can be used to constrain both the chronology of meteorites and the processes that result in movements of volatile elements on asteroidal bodies. We have examined the I-Xe and Ar-Ar systems of the plagioclase-rich achondrite, Graves Nunataks 06129 by high-resolution laser step-heating of irradiated samples. Iodine and 129Xe∗ are both present but are released at different temperatures and do not show a correlation, therefore the I-Xe system in GRA 06129 has no chronological significance. We propose that radiogenic 129Xe∗ was lost from primary phases and parentless 129Xe∗ was later introduced into the rock by interaction with a fluid sourced from a reservoir that evolved with a high I/Xe ratio. This could have been the same halogen-rich fluid that induced the conversion of merrillite and pyroxene into chlorapatite. Inherited 40Ar (i.e. not generated by in situ decay of 40K) is also present in one of three fragments studied here and may have been introduced at the same time as parentless 129Xe∗.

Reference
Claydon CK, Crowther SA, Fernandes VA, Gilmour JD (2015) Noble gases and halogens in Graves Nunataks 06129: the complex thermal history of a felsic asteroid crust. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.03.01]

Copyright Elsevier

Pavel P. Povinec¹, Jozef Masarik¹, Ivan Sýkora¹, Andrej Kováčik¹, Juraj Beňo¹, Matthias M. M. Meier^2,3, Rainer Wieler², Matthias Laubenstein⁴ and Vladimir Porubčan^5,6

¹Department of Nuclear Physics and Biophysics, Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia
²Department of Earth Sciences, ETH Zürich, Zürich, Switzerland
³Centre de Recherches Pétrographiques et Géochimiques, CNRS Nancy, Vandœuvre les Nancy, France
⁴National Laboratory of Gran Sasso, INFN, I-67100, Assergi (AQ), Italy
⁵Department of Astronomy, Physics of the Earth and Meteorology, Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia
⁶Astronomical Institute, Slovak Academy of Sciences, Bratislava, Slovakia

Results of nondestructive gamma-ray analyses of cosmogenic radionuclides (7Be, 22Na, 26Al, 46Sc, 48V, 54Mn, 56Co, 57Co, 58Co, and 60Co) in 19 fragments of the Košice meteorite are presented and discussed. The activities varied mainly with position of fragments in the meteoroid body, and with fluxes of cosmic-ray particles in the space affecting radionuclides with different half-lives. Monte Carlo simulations of the production rates of 60Co and 26Al compared with experimental data indicate that the pre-atmospheric radius of the meteoroid was 50 ± 5 cm. In two Košice fragments, He, Ne, and Ar concentrations and isotopic compositions were also analyzed. The noble-gas cosmic-ray exposure age of the Košice meteorite is 5–7 Myr, consistent with the conspicuous peak (or doublet peak) in the exposure age histogram of H chondrites. One sample likely contains traces of implanted solar wind Ne, suggesting that Košice is a regolith breccia. The agreement between the simulated and observed 26Al activities indicate that the meteoroid was mostly irradiated by a long-term average flux of galactic cosmic rays of 4.8 particles cm−2 s−1, whereas the short-lived radionuclide activities are more consistent with a flux of 7.0 protons cm−2 s−1 as a result of the low solar modulation of the galactic cosmic rays during the last few years before the meteorite fall.

Reference
Povinec PP, Masarik J, Sýkora I, Kováčik A, Beňo J, Meier MMM, Wieler R, Laubenstein M and Porubčan V (2015) Cosmogenic nuclides in the Košice meteorite: Experimental investigations and Monte Carlo simulations. Meteoritics & Planetary Sciences (in Press)
Link to Article [doi:10.1111/maps.12380]

Published by arrangement with John Wiley & Sons

Xenia Ritter1,*, Alexander Deutsch2, Jasper Berndt1 andEric Robin3

¹Institut für Mineralogie, Westfälische Wilhelms-Universität Münster (WWU), Münster, Germany
²Institut für Planetologie, Westfälische Wilhelms-Universität Münster (WWU), Münster, Germany
³CEA-Grenoble INAC/SP2M/LEMMA, Grenoble Cedex 9, France

We have investigated six impact glass spherules from the K-Pg event bed at Beloc, Haiti, using optical and electron microscopy, electron microprobe and in situ laser ablation–mass spectrometry (LA-ICP-MS; 37 trace elements, spot size 90–35 μm), in order to understand geochemical changes during alteration. The mm-sized glass spherules are partly or totally altered to smectite, but original textural features are preserved. The average trace-element composition of glass matches that one of the upper continental crust. Hints for a “meteoritic component” are lacking (Ni/Cr < 1.3; Pt below detection limit). Compared to this fresh glass, smectites are strongly depleted in trace elements, except for Li, Sc, V, Ni, Ga, Ge, and Ba. The chondrite-normalized REE distribution patterns are flat with subchondritic abundances, related to their very low degree of crystallinity. We observe a positive Eu and a strong negative Ce anomaly; the latter is explained by formation of an organic Ce4+-complex, soluble under reducing conditions. Zr/Hf of glasses and smectites is chondritic to superchondritic (35–40), whereas Nb/Ta in smectite is subchondritic (5–12) compared to Nb/Ta in the glass (~14–18). The low Nb/Ta is due to the low Nb concentrations in the smectite. Using in situ techniques with high spatial resolution, we have documented for the first time the significant changes in diagnostic elemental ratios during alteration of glass spherules. This has to be taken into account in the interpretation of geochemical data of not only impact materials but also volcanic glass, especially if bulk rock methods are used.

Reference
Ritter X, Deutsch A, Berndt J and Robin E (2015) Impact glass spherules in the Chicxulub K-Pg event bed at Beloc, Haiti: Alteration patterns. Meteoritics & Planetary Sciences (in Press)
Link to Article [doi:10.1111/maps.12432]

Published by arrangement with John Wiley & Sons

Li Li^1,2, Zongyu Yue¹, Kaichang Di¹ and Man Peng¹

¹State Key Laboratory of Remote Sensing Science, Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing, China
²University of Chinese Academy of Sciences, Beijing, China

The formation mechanism of layered ejecta craters on Mars has remained a topic of intense debate since their discovery. In this study, we perform a global morphological analysis of Martian layered ejecta craters using Thermal Emission Imaging System (THEMIS) images and Mars Orbiter Laser Altimeter (MOLA) data. The study focuses on the ejecta morphologies and well-defined distal rampart characteristics associated with 9945 layered ejecta craters with a diameter greater than 1.5 km distributed across the entire Martian surface. Data analysis based on the new database provides new information on the distribution and morphological details of the three major layered ejecta morphologies (single layer ejecta [SLE], double layer ejecta [DLE], and multiple layer ejecta [MLE]). Global analysis is applied to the latitudinal distribution of characteristic parameters, including the ejecta mobility, lobateness values, and onset diameter. Our survey of the distribution and characteristics of layered ejecta craters reveals that strong correlations exist between ejecta mobility and latitude, and there is a latitudinal dependence of onset diameter. Our study of Martian layered ejecta craters provides more detailed information and insights of a connection between the layered ejecta morphologies and the subsurface volatiles.

Reference
Li L, Yue Z, Di K and Peng N (2015) Observations of Martian layered ejecta craters and constraints on their formation mechanisms. Meteoritics & Planetary Sciences (in Press)
Link to Article [doi:10.1111/maps.12438]

Published by arrangement with John Wiley & Sons

J. H. Jones

KR, NASA/JSC, Houston, Texas, USA

Several controversies are associated with the age and origin of the shergottite meteorites, a suite of basaltic samples from Mars. Here, it will be argued that (1) the shergottites have a young igneous age, ≤600 Myr, (2) their parent magmas were relatively dry, (3) the range of initial isotopic compositions in shergottites is most likely due to assimilation of crustal materials by mantle-derived basaltic magmas, and (4) the intercumulus liquid compositions of shergottites such as Shergotty and Zagami are relatively well constrained.

Reference
Jones JH (2015) Various aspects of the petrogenesis of the Martian shergottite meteorites. Meteoritics & Planetary Sciences (in Press)
Link to Article [doi:10.1111/maps.12421]

Published by arrangement with John Wiley & Sons

Annelies Van Hoesel^1,2, Wim Z. Hoek², Gillian M. Pennock¹, Knut Kaiser³, Oliver Plümper¹, Michal Jankowski⁴, Maartje F. Hamers¹, Norbert Schlaak⁵, Mathias Küster⁶, Alexander V. Andronikov⁷ and Martyn R. Drury¹

¹Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands
²Department of Physical Geography, Utrecht University, Utrecht, The Netherlands
³GFZ German Research Centre for Geosciences, Potsdam, Germany
⁴Department of Soil Science and Landscape Management, Nicolaus Copernicus University, Toruń, Poland
⁵State Agency for Mining, Geology and Resources Brandenburg (LBGR), Cottbus, Germany
⁶Institute of Geography and Geology, University of Greifswald, Greifswald, Germany
⁷Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA

The Younger Dryas impact hypothesis suggests that multiple airbursts or extraterrestrial impacts occurring at the end of the Allerød interstadial resulted in the Younger Dryas cold period. So far, no reproducible, diagnostic evidence has, however, been reported. Quartz grains containing planar deformation features (known as shocked quartz grains), are considered a reliable indicator for the occurrence of an extraterrestrial impact when found in a geological setting. Although alleged shocked quartz grains have been reported at a possible Allerød-Younger Dryas boundary layer in Venezuela, the identification of shocked quartz in this layer is ambiguous. To test whether shocked quartz is indeed present in the proposed impact layer, we investigated the quartz fraction of multiple Allerød-Younger Dryas boundary layers from Europe and North America, where proposed impact markers have been reported. Grains were analyzed using a combination of light and electron microscopy techniques. All samples contained a variable amount of quartz grains with (sub)planar microstructures, often tectonic deformation lamellae. A total of one quartz grain containing planar deformation features was found in our samples. This shocked quartz grain comes from the Usselo palaeosol at Geldrop Aalsterhut, the Netherlands. Scanning electron microscopy cathodoluminescence imaging and transmission electron microscopy imaging, however, show that the planar deformation features in this grain are healed and thus likely to be older than the Allerød-Younger Dryas boundary. We suggest that this grain was possibly eroded from an older crater or distal ejecta layer and later redeposited in the European sandbelt. The single shocked quartz grain at this moment thus cannot be used to support the Younger Dryas impact hypothesis.

Reference
Van Hoesel A, Hoek WZ, Pennock GM, Kaiser K, Plümper O, Jankowski M, Hamers MF, Schlaak N, Küster M, Andronikov AV and Drury MR (2015) A search for shocked quartz grains in the Allerød-Younger Dryas boundary layer. Meteoritics & Planetary Sciences (in Press)
Link to Article [doi:10.1111/maps.12435]

Published by arrangement with John Wiley & Sons

Luigi Folco¹, Massimo D’Orazio¹, Agnese Fazio¹, Carole Cordier^2,3, Antonio Zeoli⁴, Matthias van Ginneken⁵ and Ahmed El-Barkooky⁶

¹Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy
²Université de Grenoble Alpes, Grenoble, CEDEX 9, France
³CNRS, Istitute des Sciences de la Terre (ISTerre), Grenoble, CEDEX 9, France
⁴Museo Nazionale dell’Antartide, Università di Siena, Siena, Italy
⁵Department of Earth Science and Engineering, Imperial College, London, UK
⁶Department of Geology, Faculty of Sciences, Cairo University, Giza, Egypt

We report on the microscopic impactor debris around Kamil crater (45 m in diameter, Egypt) collected during our 2010 geophysical expedition. The hypervelocity impact of Gebel Kamil (Ni-rich ataxite) on a sandstone target produced a downrange ejecta curtain of microscopic impactor debris due SE–SW of the crater (extending ~300,000 m2, up to ~400 m from the crater), in agreement with previous determination of the impactor trajectory. The microscopic impactor debris include vesicular masses, spherules, and coatings of dark impact melt glass which is a mixture of impactor and target materials (Si-, Fe-, and Al-rich glass), plus Fe-Ni oxide spherules and mini shrapnel, documenting that these products can be found in craters as small as few tens of meters in diameter. The estimated mass of the microscopic impactor debris (20 t, likely 50–60 t).

Reference
Luigi Folco L, D’Orazio M, Fazio A, Cordier C, Zeoli A, van Ginneken M and El-Barkooky A (2015) Microscopic impactor debris in the soil around Kamil crater (Egypt): Inventory, distribution, total mass, and implications for the impact scenario. Meteoritics & Planetary Sciences (in Press)
Link to Article [doi:10.1111/maps.12427]

Published by arrangement with John Wiley & Sons

M. Alvaro1^1,†, M. C. Domeneghetti², A. M. Fioretti³, F. Cámara^4,5 and L. Marinangeli⁶

¹Dipartimento di Geoscienze, Università degli Studi di Padova, Padova, Italy
²Dipartimento di Scienze della Terra e dell’Ambiente, Università degli Studi di Pavia, Pavia, Italy
³Instituto di Geoscienze e Georisorse CNR, UOS di Padova, Padova, Italy
⁴Dipartimento di Scienze della Terra, Università di Torino, Torino, Italy
⁵CrisDi, Interdepartmental Centre for the Research and Development of Crystallography, Torino, Italy
⁶International Research School of Planetary Sciences, Università G. d’Annunzio, Chieti, Italy
^†Dipartimento di Scienze della Terra e dell’Ambiebnte, Università degli Studi di Pavia, Pavia, Italy

Recently it has been shown that the relatively low closure temperature (Tc) of 500 (100)°C calculated for augite from Miller Range nakhlite (MIL 03346,13) using the available geothermometers would correspond to a slow cooling rate inconsistent with the petrologic evidence for an origin from a fast-cooled lava flow. Moreover, previous annealing experiments combined with HR-SC-XRD on an augite crystal from MIL 03346 clearly showed that at 600 °C, the Fe2+-Mg degree of order remained unchanged, thus suggesting that the actual Tc is close to this temperature. In order to clarify this discrepancy, we undertook an ex situ annealing experimental study at 700, 800, and 900 °C, until the equilibrium in the intracrystalline Fe2+-Mg exchange is reached, using an augite crystal from Miller Range nakhlite (MIL 03346,13) with a composition of about En36Fs24Wo40. These data allowed us to calculate the following new geothermometer calibration for Martian nakhlites:

where The application of this new equation to other Martian nakhlites (NWA 988 and Nakhla) suggests that for augite with composition close to that of MIL 03346, the Tc is up to 170 °C higher with respect to the one calculated using the previous available geothermometer equation, thus suggesting a significantly faster cooling in agreement with petrologic evidence.

Reference
Alvaro M, Domeneghetti MC, Fioretti AM, Cámara F and Marinangeli L (2015) A new calibration to determine the closure temperatures of Fe-Mg ordering in augite from nakhlites. Meteoritics & Planetary Sciences (in Press)
Link to Article [doi:10.1111/maps.12436]

Published by arrangement with John Wiley & Sons

Agata Krzesińska¹, Jérôme Gattacceca², Jon M. Friedrich^3,4 and Pierre Rochette²

¹Institute of Geological Sciences, Polish Academy of Sciences INGPAN, Wrocław, Poland
²CEREGE UM34, CNRS, Aix-Marseille University, Aix-en-Provence, France
³Department of Chemistry, Fordham University, Bronx, New York, USA
⁴Department of Earth and Planetary Science, American Museum of Natural History, New York, USA

Petrofabrics in chondrites have the potential to yield important information on the impact evolution of chondritic parent asteroids, but studies involving chondritic petrofabrics are scarce. We undertook an analysis of the Pułtusk H chondrite regolith breccia. Measurements of anisotropy of magnetic susceptibility and quantitative tomographic examination of metal grains are presented here and the results are compared with petrographic observations. The major fabric elements are in Pułtusk shear fractures cutting the light-colored chondritic clasts as well as brittly and semibrittly deformed, cataclased fragments in dark matrix of regolith breccia. Cataclasis is accompanied by rotation of silicate grains and frictional melting. Fabric of metal grains in chondrite is well defined and coherently oriented over the breccia, both in the clasts and in the cataclastic matrix. Metal grains have prolate shapes and they are arranged into foliation plane and lineation direction, both of which are spatially related and kinematically compatible to shear-dominated deformational features. We argue that the fabric of Pułtusk was formed in response to impact-related noncoaxial shear strain. Deformation promoted brittle cataclastic processes and shearing of silicates, and, simultaneously, allowed for ductile metal to develop foliation and lineation. We suggest that plastic flow is the most probable mechanism for the deformation of metal grains in the shear-dominated strain field. The process led also to the formation of large metal nodules and bands in the dark matrix of breccia.

Reference
Krzesińska A, Gattacceca J, Friedrich JM and Rochette P (2015) Impact-related noncoaxial deformation in the Pułtusk H chondrite inferred from petrofabric analysis. Meteoritics & Planetary Sciences (in Press)
Link to Article [doi:10.1111/maps.12429]

Published by arrangement with John Wiley & Sons