¹Yoko Kebukawa,²Hanae Kobayashi,²Norio Urayama,²Naoki Baden,³Masashi Kondo,⁴Michael E. Zolensky,²Kensei Kobayashi
Proceedings of the National Academy of Sciences of the United States of America 116, 753-758 Link to Article [https://doi.org/10.1073/pnas.1816265116]
¹Faculty of Engineering, Yokohama National University, 240-8501 Yokohama, Japan;
²Nihon Thermal Consulting Co., Ltd., 160-0023 Tokyo, Japan
³Instrumental Analysis Center, Yokohama National University, 240-8501 Yokohama, Japan
⁴Astromaterials Research and Exploration Science, National Aeronautics and Space Administration Johnson Space Center, Houston, TX 77058

Organic matter in carbonaceous chondrites is distributed in fine-grained matrix. To understand pre- and postaccretion history of organic matter and its association with surrounding minerals, microscopic techniques are mandatory. Infrared (IR) spectroscopy is a useful technique, but the spatial resolution of IR is limited to a few micrometers, due to the diffraction limit. In this study, we applied the high spatial resolution IR imaging method to CM2 carbonaceous chondrites Murchison and Bells, which is based on an atomic force microscopy (AFM) with its tip detecting thermal expansion of a sample resulting from absorption of infrared radiation. We confirmed that this technique permits ∼30 nm spatial resolution organic analysis for the meteorite samples. The IR imaging results are consistent with the previously reported association of organic matter and phyllosilicates, but our results are at much higher spatial resolution. This observation of heterogeneous distributions of the functional groups of organic matter revealed its association with minerals at ∼30 nm spatial resolution in meteorite samples by IR spectroscopy.

¹Jordan A. Hachtel,^1,2Jingsong Huang,³Ilja Popovs,³Santa Jansone-Popova,^1,4Jong K. Keum,^1,2Jacek Jakowski,⁵Tracy C. Lovejoy,⁵Niklas Dellby,⁵Ondrej L. Krivanek,¹Juan Carlos Idrobo
Science 363, 525-528 Link to Article [DOI: 10.1126/science.aav5845]
¹Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
²Computational Sciences and Engineering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
³Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
⁴Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
¹Nion R&D, Kirkland, WA 98034, USA.
Reprinted with permission from AAAS

The identification of isotopic labels by conventional macroscopic techniques lacks spatial resolution and requires relatively large quantities of material for measurements. We recorded the vibrational spectra of an α amino acid, l-alanine, with damage-free “aloof” electron energy-loss spectroscopy in a scanning transmission electron microscope to directly resolve carbon-site–specific isotopic labels in real space with nanoscale spatial resolution. An isotopic red shift of 4.8 ± 0.4 milli–electron volts in C–O asymmetric stretching modes was observed for ¹³C-labeled l-alanine at the carboxylate carbon site, which was confirmed by macroscopic infrared spectroscopy and theoretical calculations. The accurate measurement of this shift opens the door to nondestructive, site-specific, spatially resolved identification of isotopically labeled molecules with the electron microscope.

^1,2Qi, Y., ^1,2Zhang, Z.
Scientia Geologica Sinica 53, 714-725 Link to Article [DOI: 10.12017/dzkx.2018.039]
¹Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
²University of Chinese Academy of Sciences, Beijing, 100049, China

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

¹Łuszczek, K.
Mining Science 25, 71-83 Link to Article [DOI: 10.5277/msc182506]
¹Wrocław University of Science and Technology, Faculty of Geoengineering, Mining and Geology, Department of Geology and Mineral Waters, Poland

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

^1,2,3,4Takafumi Niihara,^4,5Sky P. Beard,^4,5Timothy D. Swindle,⁶Lillian A. Schaffer,^1,2Hideaki Miyamoto, ^3,4David A. Kring
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13237]
¹Department of Systems Innovation, University of Tokyo, , Tokyo, 113‐8656 Japan
²University Museum, University of Tokyo, , Tokyo, 113‐0033 Japan
³Center for Lunar Science and Exploration, Lunar and Planetary Institute, Universities Space Research Association, , Houston, Texas, 77058 USA
⁴SSERVI, NASA Ames Research Center, , Mountain View, California, 94035 USA
⁵Lunar and Planetary Laboratory, University of Arizona, , Tucson, Arizona, 85721–0092 USA
⁶Department of Earth and Atmospheric Sciences, University of Houston, , Houston, Texas, 77204–5007 USA
Published by arrangement with John Wiley & Sons

In a histogram of lunar impact ages from the Apollo 16 site, there is a spike circa 3.9 Ga that has been interpreted to represent either a large number of nearly synchronous events or an abundance of samples that were affected slightly differently by the event that produced the Imbrium basin. To further scrutinize those age relationships, we extracted six centimeter‐sized clasts of impact melt from ancient regolith breccia 60016 and performed petrological and geochronological (40Ar‐39Ar) analyses. Three clasts have similar poikilitic textures, while others have porphyritic, aphanitic, or intergranular textures. Compositions and abundances of relict minerals are different in all six clasts and variously imply Mg‐suite and ferroan anorthosite target sequences. Estimated bulk compositions of four clasts are similar to previously defined group 1 Apollo 16 impact melt rocks, while the other two have higher Al2O3 and lower FeO+MgO compositions. All six clasts have similar K2O and P2O5 concentrations, which could have been derived from a KREEP‐bearing component among target sequences. Eighteen 40Ar/39Ar analyses of the six clasts produced an age range from 3823 ± 75 to 4000 ± 23 Ma, consistent with estimates for the proposed late heavy bombardment. Four clasts have multiple temperature steps that define plateau ages. These ages are distinct, so they cannot be explained by a single impact event, such as the one that produced the Imbrium impact basin. The conclusion that these represent distinct ages remains after considering the possibility of artifacts in defining plateaus.

¹Weijia Gao,¹Ruining Zhao,¹Jian Gao,¹Biwei Jiang,¹Jun Li
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2018.12.010]
¹Department of Astronomy, Beijing Normal University, Beijing, 100875, China

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

¹Jia Liu,^1,2Liping Qina,¹Jiuxing Xia,³Richard W.Carlson,⁴Ingo Leya,⁵Nicolas Dauphas,²Yongsheng He
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.01.032]
¹CAS Key Laboratory of Crust – Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China
²State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China
³Department of Terrestrial Magnetism, Carnegie Institution for Science, 5241 Broad Branch Road, NW, Washington, DC 20015, USA
⁴Space Research and Planetology, University of Berne, Sidlerstrasse 5, 3012 Berne, Switzerland
⁵Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago IL 60637, USA
Copright Elsevier

The ⁵³Mn-⁵³Cr short-lived radionuclide decay system is a powerful tool to investigate the timescales of early solar system processes. A complication arises, however, from the fact that spallation and thermal/epithermal neutron capture processes induced by cosmic rays can significantly alter ⁵³Cr/⁵²Cr ratios in solar system objects that have long exposure ages and high Fe/Cr ratios. Quantifying these cosmogenic effects helps constrain the cosmic ray exposure history of extraterrestrial samples. The isotopic shifts produced by cosmic ray irradiation also need to be corrected before the Cr isotope systematics can be used as a dating tool and as a tracer of nucleosynthetic provenance. To investigate the impact of cosmogenic production on Cr, the Cr isotopic compositions of 25 samples from 16 iron meteorites belonging to nine different chemical groups were measured. The measurements show that exposure to cosmic rays can cause large coupled excesses in ε⁵³Cr (-0.04 ± 0.44 to +268.29 ± 0.14; 2SE) and ε⁵⁴Cr (+0.28 ± 0.72 to +1053.78 ± 0.72; 2SE) with a best fit line of ε⁵⁴Cr= (3.90 ± 0.03) × ε⁵³Cr. The magnitude of Cr isotope production is controlled by various factors including the exposure age, the chemical composition (i.e., Cr concentration and Ni/Fe ratio) and shielding conditions. Nevertheless, the correlation of ε⁵³Cr and ε⁵⁴Cr is independent of these factors, which provides an effective method to evaluate the cosmogenic contribution to ⁵³Cr by monitoring the cosmogenic variations in ε⁵⁴Cr in meteoritic irons. The results are compared with modeling results that yield a slightly shallower slope of 3.6 ± 0.2. Modeling results for the olivine in stony meteorites yield a higher slope (∼5.4). However, the previous estimated results for lunar samples (stony targets for comic ray irradiation) exhibit an observably shallower slope (∼2.62). The reason for the different slopes is that the production rates of different cosmogenic Cr isotopes in iron meteorites and lunar samples are in different proportions. The differences may not be completely controlled by the higher thermal and epithermal neutron fluencies in lunar samples than in iron meteorites, but instead may largely reflect different radiation geometry between the two. More studies are needed to solve this open question.

¹Jason C.Lai,²Briony Horgan,¹James F.Bell III,¹Danika F.Wellington
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.01.019]
¹School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
²Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, USA
Copyright Elsevier

Much of Mars’ surface is mantled by bright dust, which masks the spectral features used to interpret the mineralogy of the underlying bedrock. Despite the wealth of near-infrared (NIR) and thermal infrared (TIR) data returned from orbiting spacecraft in recent decades, the detailed bedrock composition of approximately half of the Martian surface remains relatively unknown due to dust cover. To address this issue, and to help gain a better understanding of the bedrock mineralogy in dusty regions, Dust Cover Index results from the Mars Global Surveyor Thermal Emission Spectrometer (TES) and analysis of images from the Mars Reconnaissance Orbiter Mars Color Imager (MARCI) were used to identify 63 small localized areas within the classical bright dusty regions of Arabia Terra, Elysium Planitia, and Tharsis Montes as potential “windows” through the dust; that is, areas where the dust cover is thin enough to permit infrared remote sensing of the underlying materials. The mineralogy of each candidate window was inferred using spectra from the Mars Express Observatoire pour la Mineralogie, l’Eau, les Glaces et l’Activité (OMEGA) NIR spectrometer and, where possible, TES. Twelve areas of interest returned spectra that are consistent with mineral species expected to be present at the regional scale, such as high- and low-calcium pyroxene, olivine, and iron-bearing glass. Distribution maps were created using previously defined index parameters for each species present within an area. High-quality TES spectra, if present within an area of interest, were deconvolved to estimate modal mineralogy and to support NIR interpretations. OMEGA data from Arabia Terra and Elysium Planitia are largely similar and indicate the presence of high-calcium pyroxene with significant contributions of glass and olivine, while TES data suggest an intermediate between the established compositions of the southern highlands and Syrtis Major. Limited data from Tharsis are consistent with low-calcium pyroxene mixed with lesser amounts of glass and high-calcium pyroxene. TES data from southern Tharsis correlate well with the previously inferred compositions of the Aonium and Mare Sirenum highlands immediately to the south. Of particular note is the detection of iron-bearing glass as a significant component of all three analyzed regions, especially in Tharsis. Overall, the underlying compositions of the classically dust-covered regions of Mars appear consistent with the compositions of adjacent and other low-albedo (not dust covered) regions of the planet identified in previous studies, with the noted contribution from iron-bearing glass.

¹Sarah E.Roberts,¹Clive R.Neal
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.01.023]
¹Department of Civil & Env. Eng. & Earth Sciences, University of Notre Dame, Notre Dame, IN 46556, USA
Copyright Elsevier

Very high potassium or VHK basalts have been described from the Apollo 14 landing site at Fra Mauro on the lunar near side. Many of the known samples are clasts in polymict breccias with a few as <1 cm rocklets in the regolith samples. VHK basalts are distinct from the high-Al basalts that are more common at the Apollo 14 site in that they are enriched in the alkali/alkaline earth elements (e.g., K, Rb, Ba, etc.). The source of this enrichment was initially proposed to be through assimilation of granite by a crystallizing high-Al basaltic magma. However, with the discovery of more VHK basalt clasts from three Apollo 14 polymict breccias, the number of different AFC episodes and granite assimilants had to increase in order to explain the whole rock compositional diversity within the VHK basalt suite.
New work completed on fourteen VHK basalts include Crystal Size Distributions (CSDs) and in-situ chemical analyses and element maps collected by electron probe microanalysis (EPMA). CSDs completed on three VHK basalt samples indicate that these basalts are not impact melts and represent endogenous melts of the lunar interior. Potassium Kα element maps reveal the spatial relationship between the K-rich material and the basalt clasts with attached breccia matrix if present. In-situ EPMA analyses have identified two distinct types of K-rich material: K-feldspar and K-rich glass. With these new data, an additional mechanism for an exogenic petrogenesis of VHK basalts is proposed that involves the impact process. VHK basalts can be divided into two groups based on density and viscosity. VHK-1 basalts formed when a hot impact ejecta covered the granite/felsite-rich matrix material containing high-Al basalt clasts. Heat from the impact ejecta partially melted and possibly evaporated nearby K-bearing materials, which then infiltrated and contaminated the high-Al clasts. VHK-2 basalts are consistent with the hypothesis of granite assimilation by a high-Al magma, as seen in the higher abundances of network-forming elements.

¹J.J.Bellucci,^1,2A.A.Nemchin,²M.Grange,^3,4K.L.Robinson,⁵G.Collins,¹M.J.Whitehouse,^1,6J.F.Snape,⁷M.D.Norman,^3,4D.A.Kring
Earth and Planetary Science Letters 510, 173-185 Link to Article [https://doi.org/10.1016/j.epsl.2019.01.010]
¹Department of Geosciences, Swedish Museum of Natural History, SE-104 05 Stockholm, Sweden
²Department of Applied Geology, Curtin University, Perth, WA 6845, Australia
³Lunar and Planetary Institute, Universities Space Research Association, 3600 Bay Area Blvd., Houston, TX 77058, United States of America
⁴Center for Lunar Science and Exploration, NASA Solar System Exploration Research Virtual Institute, United States of America
⁵Department of Earth Science & Engineering, Imperial College London, Kensington, London SW7 2AZ, UK
⁶Department of Earth Sciences, Faculty of Science, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, the Netherlands
⁷Research School of Earth Sciences, The Australian National University, 142 Mills Road, Acton ACT, 2601, Australia
Copyright Elsevier

A felsite clast in lunar breccia Apollo sample 14321, which has been interpreted as Imbrium ejecta, has petrographic and chemical features that are consistent with formation conditions commonly assigned to both lunar and terrestrial environments. A simple model of Imbrium impact ejecta presented here indicates a pre-impact depth of 30–70 km, i.e. near the base of the lunar crust. Results from Secondary Ion Mass Spectrometry trace element analyses indicate that zircon grains recovered from this clast have positive Ce/Ce^⁎ anomalies corresponding to an oxygen fugacity +2 to +4 log units higher than that of the lunar mantle, with crystallization temperatures of 771±88 to 810 ± 37 °C (2σ) that are unusually low for lunar magmas. Additionally, Ti-in-quartz and zircon calculations indicate a pressure of crystallization of 6.9±1.2 kbar, corresponding to a depth of crystallization of 167±27 km on the Moon, contradicting ejecta modelling results. Such low-T, high-fO₂, and high-P have not been observed for any other lunar clasts, are not known to exist on the Moon, and are broadly similar to those found in terrestrial magmas.

The terrestrial-like redox conditions inferred for the parental magma of these zircon grains and other accessory minerals in the felsite contrasts with the presence of Fe-metal, bulk clast geochemistry, and the Pb isotope composition of K-feldspar grains within the clast, all of which are consistent with a lunar origin. The dichotomy between redox conditions and the depth of origin inferred from the zircon compositions compared to the ejecta modelling necessitates a multi-stage petrogenesis. Two, currently unresolvable hypotheses for the origin and history of the clast are allowed by these data. The first postulates that the relatively oxidizing conditions were developed in a lunar magma, possibly by fractional crystallization and enrichment of incompatible elements in a fluid-rich, phosphate-saturated magma, at the base of the lunar crust to form the zircon grains and their host felsite. Subsequent excavation by the Imbrium impact introduced more typical lunar features to the clast but preserved primary chemical characteristics in zircon and some other accessory minerals. However, this hypothesis fails to explain the high P of crystallization. Alternatively, the felsite and its zircon crystallized on Earth at a modest depth of 19±3 km in the continental crust where oxidizing, low-T, fluid-rich conditions are common. Subsequently, the clast was ejected from the Earth during a large impact, entrained in the lunar regolith as a terrestrial meteorite with the evidence of reducing conditions introduced during its incorporation into the Imbrium ejecta and host breccia.