¹Ray D.,¹Baliyan S.,²Nayak C.
Advances in Space Research 68, 3233-321 Link to Article [DOI 10.1016/j.asr.2021.06.009]
¹Planetary Sciences Division, Physical Research Laboratory, Ahmedabad, 380 009, India
²Atomic & Molecular Physics Division, Bhabha Atomic Research Centre, Mumbai, 400085, India

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

¹Tiwari K.,¹Ghosh S.,²Miyahara M.,³Ray D.
Geophysical Research Letters 48, e2021GL093592 Link to Article [DOI 10.1029/2021GL093592]
¹Department of Geology and Geophysics, Indian Institute of Technology Kharagpur, Kharagpur, India
²Graduate School of Advanced Science and Engineering, Hiroshima University, Hiroshima, Japan
³Planetary Sciences Division, Physical Research Laboratory, Ahmedabad, India

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

¹Mason Neuman,^1,2Astrid Holzheid,¹Katharina Lodders,¹Bruce FegleyJr.,¹Bradley L.Jolliff,¹Piers Koefoed,³Heng Chen,¹Kun Wang王昆
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.09.035]
¹Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130, USA
²Institute of Geosciences, Kiel University, 24098 Kiel, Germany
³Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA
Copyright Elsevier

The chemical and isotopic signatures of moderately volatile elements are useful for understanding processes of volatile depletion in planetary formation and differentiation. However, the fractionation factors between gas and melt phases during evaporation that are required to model these planetary volatile depletion processes are still sparse. In this study, twenty heating experiments were conducted in 1 atm gas-mixing furnaces to constrain the behavior of K, Cu, and Zn evaporation and isotopic fractionation from basaltic melts at high temperatures. The temperatures range from 1300 °C to 1400 °C, and durations are from 2 to 8 days. Oxygen fugacities (fO₂) range from one log unit below to ten log units above that of the iron-wüstite buffer (IW–1 to IW+10, corresponding to logfO₂ of –10.7 to –0.68 at 1400 °C). The conditions were selected to achieve an evaporation-dominated regime (where timescales of diffusion << evaporation for trace elements) in order to avoid diffusion-limited evaporation. Our results show during evaporation Zn behaved as the most volatile, followed by Cu and then K, regardless of temperature and oxygen fugacity. Partitioning of Zn into spinel layers within experimental capsules, however, has been observed, which has substantial effects on the Zn isotope fractionation factor. Therefore, Zn results are presented but further discussion is excluded. Element loss depends on both temperature and oxygen fugacity, where higher temperatures and lower oxygen fugacities promote evaporation. However, with varying temperature and oxygen fugacity, the kinetic isotopic fractionation factors, α (where, RR0=fα-1), for K and Cu remain constant, thus these factors can be applied to a wider range of conditions than those in this study. The experimentally determined fractionation factors for K, and Cu during evaporation from basaltic melts are 0.9944, and 0.9961, respectively. The fractionation factors for these elements with varying volatilities are all significantly larger than the “apparent observed fractionation factors,” which approach one and are inferred from lunar basalts relative to the Bulk Silicate Earth. This observation suggests near-equilibrium conditions during volatile-element loss from the Moon as the “apparent observed fractionation factors” of lunar basalts are similar for all three elements.

¹Dennis Marcel Vanderliek,¹Harry Becker,²Alexander Rocholl
Earth and Planetary Science Letters 576, 117216 Link to Article [https://doi.org/10.1016/j.epsl.2021.117216]
¹Institut für Geologische Wissenschaften, Freie Universität Berlin, Malteserstraße 74-100, 12249 Berlin, Germany
²Deutsches GeoForschungsZentrum GFZn, Telegrafenberg, D-14473 Potsdam, Germany
Copyright Elsevier

Because of their robustness against resetting, in situ U-Pb ages of zircons in lunar impactites have the potential to provide constraints on the lunar bombardment history that may complement the more common K-Ar ages. Most previous work has focused on relatively large zircons that show growth zoning and ages were mostly interpreted as early igneous crystallization ages. Here we combine high-resolution mineralogical imaging and in situ U-Pb dating by ion microprobe to identify, characterize and date <20 μm size zircons in thin sections of lunar impact breccias. Several tens of grains of zircons of this size range were identified in thin sections of impactites from the Apollo 15 and 16 landing sites. Small zircons are more abundant in both noritic and evolved clinopyroxene, SiO2 or K-feldspar bearing lithologies compared to anorthositic bulk compositions. Both granular zircon aggregates and overgrowth on existing zircon or baddeleyite (in breccias 15455 and 67915) are interpreted to reflect high-temperature recrystallization of zircons or its high-temperature-pressure precursor phases, following shock heating events by impact. In contrast, conchoidal or poikilitic zircons <10 μm in Fe-Ni metal bearing noritic clasts or matrix (67915, 67955) crystallized in situ from impact melt. Most U-Pb ages of the 24 analyzed grains are either concordant or reverse discordant with 207Pb-206Pb ages ranging from 4.15 to 4.25 Ga. The small age range, combined with a large textural spectrum and the frequent presence of Fe-Ni metal suggest zircon crystallization from impact melt and recrystallization of pre-existing zirconium-bearing minerals by impact heating. Such ‘impact’ zircons with 4.2 Ga ages have now been reported from most Apollo landing sites, suggesting widespread formation and modification of zircons by basin-forming impacts at this time. The contrast between U-Pb zircon (predominantly 4.2 Ga) and K-Ar feldspar ages (predominantly 3.9 Ga) likely reflects resetting of the latter chronometer by impact heating.

¹Jonathan A.Lewis,^1,2Rhian H.Jones,¹Adrian J.Brearley
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.10.004]
¹Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA
²Department of Earth and Environmental Sciences, University of Manchester, Manchester, M13 9PL, UK
Copyright Elsevier

In ordinary chondrites (OCs), feldspar is present both in chondrules as a primary, igneous phase, and as a secondary phase that results from crystallization of chondrule mesostasis glass during thermal metamorphism. To further understand the chemical and physical conditions prevailing during thermal metamorphism in OCs, we conducted a study of feldspar microtextures and compositions within chondrules, focusing on alteration and equilibration features. We included OCs representing the full metamorphic sequence (petrologic types 3-6) and all OC groups (H, L and LL). Our observations show that primary calcic plagioclase alters to sodalite, scapolite, and nepheline in petrologic types 3.2-3.9, and to albite in types 3.6-5. Plagioclase also develops alteration features such as zoning, micropores, and alteration lamellae in types 3-4. Sodic plagioclase is present in minor amounts as a primary phase, but also forms from the crystallization of chondrule mesostasis glass (types 3.2-3.9), and predominantly through albitization reactions in calcic plagioclase (types 3.6-5). K-feldspar occurs in albite in types 3.6-6 as fine-scale exsolution lamellae and as larger patches.

We combine these observations into an overall model of metasomatism during thermal metamorphism in OCs. Hydrous alteration during prograde metamorphism results in most of the alteration and equilibration features we observe in plagioclase. During retrograde metamorphism, high temperature, short duration infiltration of anhydrous, alkali- and halogen-bearing fluids causes incorporation of K into plagioclase that subsequently exsolves. Overall, we show that evidence of metasomatism is present throughout the metamorphic sequence in all the OCs, and thus was a ubiquitous process on all OC parent bodies. Recognition of the effects of fluid activity in OCs of even the lowest petrologic subtypes has important consequences for radioisotope chronometers, such as Al-Mg and I-Xe, that rely on the integrity of phases such as plagioclase and feldspathic mesostasis glass which are highly susceptible to alteration. Furthermore, the presence of aqueous alteration features in OCs implies that the non-carbonaceous chondrite isotopic reservoir must have also had ices and that models of protoplanetary disk evolution must also include the presence of ices in the inner solar system.

¹Huidobro J.,¹Aramendia J.,¹Arana G.,¹Madariaga J.M.
ACS Earth and Space Chemistry 5, 1333 – 1342 Link to Article [DOI 10.1021/acsearthspacechem.0c00329]
¹Analytical Chemistry Department, University of the Basque Country (UPV/EHU), Barrio Sarriena s/n, Leioa, 48980, Spain

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

^1,2Chen L.,^2,3Liu Y.,^2,3Li Y.,^2,3,4Li Q.-L.,^2,3,4Li X.-H.
Journal of Analytical Atomic SpectrometryVolume 36, 1431-1440 Link to Article [DOI 10.1039/d1ja00029b]
¹Institute of Earth Sciences, China University of Geosciences Beijing, Beijing, China
²State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
³Innovation Academy of Earth Science, Chinese Academy of Sciences, Beijing, China
⁴College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, China

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

¹B.S.Prince,^2,3M.J.Loeffler
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114736]
¹Department of Applied Physics and Materials Science, Northern Arizona University, Flagstaff, AZ 86011, United States of America
²Department of Astronomy and Planetary Science, Northern Arizona University, Flagstaff, AZ 86011, United States of America
³Center for Materials Interfaces in Research and Applications, Northern Arizona University, Flagstaff, AZ 86011, United States of America
Copyright Elsevier

Here we present results from pulsed laser irradiation of CI and CM simulant samples in an effort to simulate space weathering on airless bodies via micrometeorite impacts. For this study, we focused on determining what type of alteration occurs in the 3-μm absorption region, as this region will be critical to ascertain compositional information of the surface regolith of hydrated asteroids. Generally, using entirely in situ spectral analysis, we find that the laser produces similar effects in both samples. Specifically, irradiation causes the blue spectral slope to decrease until it is relatively flat and that the sample darkens initially with laser irradiation but brightens back to about half of its original level by the end of the irradiation. Furthermore, we also find that laser irradiation causes the band depth on the 3-μm absorption band to increase by as much as 30%, yet the shape of the entire absorption band does not change and the band minima of the 2.72 μm shifts less than 0.001 μm after laser irradiation. The constancy of the latter two parameters, which will be most critical to compositional analysis, suggests that this spectral region could be very useful to determine the asteroid composition on surfaces on hydrated asteroids that have undergone extensive aqueous alteration even if the surface had been subject to a significant amount of space weathering. Whether the same conclusion will be generally applicable to other surfaces containing minerals with a wide range of aqueous alteration is currently unclear but will be tested in future studies.

¹D. Gardiol et al. (>10)
Monthly Notices of the Royal Astronomical Society 501, 1215–1227 Link to Article [https://doi.org/10.1093/mnras/staa3646]
¹INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, I-10025 Pino Torinese, TO, Italy

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

¹McGeoch J.E.M.,²McGeoch M.W.
Physics of Fluids 33, 067118 Linkto Article [DOI 10.1063/5.0054860]
¹Department of Molecular and Cellular Biology, Harvard University, 52 Oxford St., Cambridge, 02138, Massachusetts, United States
²PLEX Corporation, 275 Martine St., Suite 100, Fall River, 02723, Massachusetts, United States

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