¹Addi Bischoff,^1,2Mike Komnik,¹Jakob Storz,³Jasper Berndt
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14052]
¹Institut für Planetologie, University of Münster, Münster, Germany
²Institut für Geologie und Paläontologie, University of Münster, Münster, Germany
³Institut für Mineralogie, University of Münster, Münster, Germany
Published by arrangement with John Wiley & Sons

The lunar regolith breccia Dhofar 1769, which was found in 2012 as a single 125 g piece in the Zufar desert area of Oman, contains a relatively large, dark-colored impact melt breccia embedded in a fine-grained clastic matrix. The internal texture of the fragment indicates the repeated melt breccia formation on the lunar surface, their repeated brecciation, and mixing in second, third, and fourth generations of brecciated rock types. The chemical and mineralogical data reveal the incorporation of a feldspar-rich subophitic crystalline melt within a feldspar-rich microporphyritic crystalline melt breccia. This lithic paragenesis itself is embedded within a mafic, crystalline melt breccia. The entire breccia with the three different impact melts has been finally incorporated into the whole rock breccia. The three impact melts are mixtures of different source rocks and impact projectiles, based on the obtained minor and trace element compositions (in particular of Ni and the rare earth elements [REE]) of the impact melt lithologies. For all processes of impact melt formation, additional steps of their brecciation and re-lithification require a minimum number of seven impact processes.

¹Mazumdar, Amulya Chandra,^2,3Pati, Jayanta Kumar,²Singh, Anuj Kumar,¹Bhagabaty, Balen,¹Phukan, Sarat,¹Borah, Pritom
Geological Journal (in Press) Link to Article [DOI 10.1002/gj.4776]
¹Department of Geological Sciences, Gauhati University, Guwahati, India
²Department of Earth and Planetary Sciences, Nehru Science Centre, University of Allahabad, Prayagraj, India
³National Centre of Experimental Mineralogy and Petrology, University of Allahabad, Prayagraj, India

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¹Savina, Michael R.,¹Shulaker, Danielle Ziva,¹Isselhardt, Brett H.,¹Brennecka, Gregory A.
Journal of Analytical Atomic Spectrometry 38, 1205-1212 Open Access Link to Article [DOI
10.1039/d3ja00096f]
¹Lawrence Livermore National Laboratory, Nuclear and Chemical Sciences Division, United States

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¹R. Keerthana,¹R. Annadurai,²K.N. Kusuma
Planetary and Space Science (in Press) Link to Article [https://www.sciencedirect.com/science/article/abs/pii/S0032063323001150]

¹Department of Civil Engineering, SRM Institute of Science and Technology, Kattankulathur, 603 203, India
²Department of Earth Sciences, Pondicherry University, Puducherry, 605 014, India

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^1,2Marina Martínez,^1,3Charles K. Shearer,¹Adrian J. Brearley
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14042]
¹Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA
²Universitat Autònoma de Barcelona, Edifici Cs, Av. de l’Eix Central, s/n, 08193 Cerdanyola del Vallès, Barcelona,
Spain.
³Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico, USA
Copyright Elsevier

Secondary minerals in martian nakhlites provide a powerful tool for investigating the nature, composition, and duration of aqueous activity in the martian crust. Northwest Africa (NWA) 998 crystallized early from the nakhlite magmatic source and has evidence of minimal signatures of the late hydrothermal alteration event that altered the nakhlites. Using FIB-TEM techniques to study a cumulus apatite grain in NWA 998, we report the first evidence of a submicron-scale vein consisting of fluorapatite and an SiO2-rich phase. Fluorapatite grew epitaxially on the walls of an opened cleavage plane of host F-bearing chlorapatite and the SiO2-rich phase filled the center of the vein. The presence of nanoporosity and nanometer-scale amorphous material and the sharp interface between the vein and the host apatite indicate the vein represents a coupled dissolution–reprecipitation process that generated apatite of a different composition that was more stable with the fluid. Using experimental data and diffusion coefficients of Cl in apatite from the literature, we conclude that the vein was caused by a low temperature (~300°C), slightly acidic, F-, Si-rich, aqueous fluid that acted as a closed system. Based on the characteristics of the vein (formation by rapid injection of fluid) and the fluid (composition, temperature, pH), and the lack of terrestrial weathering products in our SEM and TEM images, we infer that the vein is pre-terrestrial in origin. Our observations support the hypothesis that the heat source triggering a hydrothermal system was a low-shock velocity impact and rule out a magmatic origin. Finally, the vein could have formed from a late-stage fluid different from that reported in other nakhlites, but formation during the same magmatic event by, for example, a less evolved fluid might also be plausible.

¹H. C. Bates,¹A. J. King,²K. S. Shirley,³E. Bonsall,³C. Schröder,⁴F. Wombacher,⁵T. Fockenberg,¹R. J. Curtis,¹N. E. Bowles
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14043]
¹Planetary Materials Group, Natural History Museum, London, UK
²Atmospheric, Oceanic and Planetary Physics, University of Oxford, Oxford, UK
³Biological and Environmental Sciences, Faculty of Natural Sciences, University of Stirling, Stirling, UK
⁴Institut für Geologie und Mineralogie, Universität zu Köln, Köln, Germany
⁵Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, Bochum, Germany
Published by arrangement with John Wiley & Sons

On the microscale, the Winchcombe CM carbonaceous chondrite contains a number of lithological units with a variety of degrees of aqueous alteration. However, an understanding of the average hydration state is useful when comparing to other meteorites and remote observations of airless bodies. We report correlated bulk analyses on multiple subsamples of the Winchcombe meteorite, determining an average phyllosilicate fraction petrologic type of 1.2 and an average water content of 11.9 wt%. We show the elemental composition and distribution of iron and iron oxidation state are consistent with measurements from other CM chondrites; however, Winchcombe shows a low Hg concentration of 58.1 ± 0.5 ng g⁻¹. We demonstrate that infrared reflectance spectra of Winchcombe are consistent with its bulk modal mineralogy, and comparable to other CM chondrites with similar average petrologic types. Finally, we also evaluate whether spectral parameters can estimate H/Si ratios and water abundances, finding generally spectral parameters underestimate water abundance compared to measured values.

^1,2Alan E. Rubin,^2,3Tasha L. Dunn,³Kyla Garner,³Malena Cecchi,³Mitchel Hernandez
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14046]
¹Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California, USA
²Maine Mineral & Gem Museum, Bethel, Maine, USA
³Department of Geology, Colby College, Waterville, Maine, USA
Published by arrangement with John Wiley & Sons

In general, barred olivine (BO) chondrules formed from completely melted precursors. Among BO chondrules in unequilibrated ordinary chondrites, there are significant positive correlations among chondrule diameter, bar thickness, and rim thickness. In the nebula, smaller BO precursor droplets cooled faster than larger droplets (due to their higher surface area/volume ratios) and grew thinner bars and rims. There is a bimodal distribution in the olivine FeO content in BO chondrules, with a hiatus between 11 and 19 wt% FeO. The ratio of (FeO rich)/(FeO poor) BO chondrules decreases from 12.0 in H to 1.6 in L to 1.3 in LL. This is the opposite of the case for porphyritic chondrules: the mean (FeO rich)/(FeO poor) modal ratio increases from 0.8 in H to 1.8 in L to 2.8 in LL. During H chondrite agglomeration, most precursor dustballs were small with low bulk FeO/(FeO + MgO) ratios and moderately high melting temperatures. The energy available for chondrule melting from flash heating was relatively low, capable of completely melting many ferroan dusty precursors (to form FeO-rich BO chondrules), but incapable of completely melting many magnesian dusty precursors (to form FeO-poor BO chondrules). When L and LL chondrites agglomerated somewhat later, significant proportions of precursor dustballs were relatively large and had moderately high bulk FeO/(FeO + MgO) ratios. The energy available from flash heating was higher, capable of completely melting higher proportions of magnesian dusty precursors to form FeO-poor BO chondrules. These differences may have resulted from an increase in the amplitude of lightning discharges in the nebula caused by enhanced charge separation.

¹Hadrien Pirotte,²Camille Cartier,³Olivier Namur,⁴Anne Pommier,³Yishen Zhang,⁵Jasper Berndt,⁵Stephan Klemme,¹Bernard Charlier
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115699]
¹Department of Geology, University of Liège, 4000 Sart Tilman, Belgium
²Centre de Recherches Pétrographiques et Géochimiques, Université de Lorraine, 54501 Vandœuvre-lès-Nancy, France
³Department of Earth and Environmental Sciences, KU Leuven, 3001 Leuven, Belgium
⁴Carnegie Institution for Science, Earth and Planets Laboratory, Washington, DC 20015, USA
⁵Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Münster 48149, Germany
Copyright Elsevier

Understanding the behavior of elements under highly reduced conditions is fundamental to explain the differentiation, crust formation, and volatile budget of Mercury. Here we report experiments on a synthetic composition representative of the bulk silicate Mercury (BSM), at pressure up to 3 GPa, temperature up to 1720 °C, and under highly reduced conditions (~IW − 8 to ~IW − 1, with IW the iron-wüstite oxygen fugacity buffer). We determined partition coefficients for >30 minor and trace elements between silicate melt, metal melt (Fesingle bondSi), sulfide melt (FeS), and MgS solid sulfides. Based on these results and published literature, we modeled the behavior of heat-producing elements (HPE: U, Th, and K) during Mercury’s early differentiation and mantle partial melting and estimated their concentrations in the mantle and crust. We found that U, K and especially Th are principally concentrated in the BSM and did not partition into the core because they are not siderophile elements. Uranium is chalcophile under highly reduced conditions, and so our model suggests that an FeS layer at the core-mantle boundary formed during Mercury’s primordial differentiation would likely have incorporated large amounts of U, significantly increasing the Th/U ratio of the BSM. However, this is inconsistent with the chondritic or slightly sub-chondritic Th/U ratios of Mercury’s lavas. In addition, the likely presence of mantle sulfides, such as MgS, would have also fractionated U and Th, increasing the mantle Th/U. It is possible to have an FeS layer if Mercury formed under less reduced conditions, or if the building blocks of Mercury had Th/U ratios close to the lower end of chondritic data. If, as suggested by our model, no FeS layer formed during differentiation, it means that the majority of HPE are concentrated in Mercury’s thin silicate part. Based on the compatibility of U, Th and K, we also show that surface K/Th and K/U ratios are respectively 2–4 times and 3–6 times lower than expected for initial K/Th and K/U ratios similar to enstatite chondrites, implying that the planet suffered an important volatile loss via mechanisms that remain undetermined.

¹Arthur Goodwin,¹Romain Tartèse,¹Russell J. Garwood,¹Rhodri Jerrett,¹Katherine H. Joy
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14035]
¹Department of Earth and Environmental Sciences, The University of Manchester, Manchester, UK
Published by arrangement with John Wiley & Sons

The Stac Fada Member (Stoer Group) is a ~1.2 Ga melt-rich impact breccia preserved and intermittently exposed along the NW coast of Scotland. Using a combination of x-ray diffraction and micro-Raman spectroscopy, we identify potential coesite that is spatially associated with micron-sized diamonds, as well as disordered carbon phases. Comparing the graphite G-band of disordered carbon phases in the impact breccia to samples from underlying units indicates that most of the carbon in the Stoer Group was ultimately derived from the underlying Lewisian basement. Disordered carbon phases within the Stac Fada Member have been modified by mild heating within a hot ejecta blanket rather than shock pressure. We also report the first evidence for impact diamonds discovered within the Stac Fada Member. These diamonds have an average Raman shift of 1328.5 cm−1 and are present within both the impact breccia and the shocked gneiss clasts that are present in sandstones directly underlying the Stac Fada Member contact, and within sandstone rafts entrapped in the unit. These findings have implications for the timing of deposition of the Stac Fada Member, which must have occurred after ballistic ejection of Lewisian basement clasts during the impact event.

¹Laura B. Seifert,¹Pierre Haenecour,²Tarunika Ramprasad,^1,2Thomas J. Zega
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14040]
¹Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA
²Department of Materials Science and Engineering, University of Arizona, Tucson, Arizona, USA
Copyright Elsevier

Here we report in situ structural and chemical analyses of four presolar grains and the matrices of the Meteorite Hills (MET) 00526 L3.05 and Queen Alexandra Range (QUE) 97008 L3.05 unequilibrated ordinary chondrites (UOCs). The presolar grains in MET 00526 include one Fe-rich single crystal olivine, and one olivine grain that contains both amorphous and polycrystalline material. The single crystal olivine likely has origins in the circumstellar envelope (CSE) of a red giant branch (RGB) or asymptotic giant branch (AGB) star, and the amorphous/polycrystalline olivine has an O-isotopic composition consistent with origins in a type II supernova. The presolar grains from QUE 97008 are Fe rich and include one crystalline, stoichiometric olivine that contains a Ca-rich core and one crystalline, stoichiometric pyroxene grain, both of which have O-isotopic compositions consistent with origins in the CSEs of low-mass AGB/RGB stars. The matrices of both UOCs are mineralogically diverse with evidence for unaltered material in the form of amorphous silicates and a C-rich nanoglobule and altered material in the form of Ni-rich sulfides, abundant Fe-rich olivine, and Fe-Mg zoning in matrix silicates. No phyllosilicates were observed. The Fe-rich olivine grains are the dominant alteration phase in both UOCs and likely replaced primary amorphous silicates in the presence of an Fe-rich fluid during parent body alteration. Our work suggests that the ordinary and carbonaceous chondrites received a similar inventory of dust with comparable structures and chemistries.