^1,3Andreas T. Hertwig,²Makoto Kimura,¹Céline Defouilloy,¹Noriko T. Kita
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13379]
¹WiscSIMS, Department of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA 2
²National Institute of Polar Research, Meteorite Research Center, Midoricho 10-3, Tachikawa Tokyo 190-8518, Japan 3
³Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles,
Los Angeles, California 90095, USA
Published by arrangement with John Wiley & Sons

We performed in situ oxygen three-isotope measurements of chondrule olivine,pyroxenes, and plagioclase from the newly described CVRedchondrite NWA 8613.Additionally, oxygen isotope ratios of plagioclase in chondrules from the Kaba CV3OxBchondrite were determined to enable comparisons of isotope ratios and degree of alterationof chondrules in both CV lithologies. NWA 8613 was affected by only mild thermalmetamorphism. The majority of oxygen isotope ratios of olivine and pyroxenes plot along aslope-1 line in the oxygen three-isotope diagram, except for a type II and a remolten barredolivine chondrule. When isotopic relict olivine is excluded, olivine, and low- and high-Capyroxenes are indistinguishable regardingD17O values. Conversely, plagioclase in chondrulesfrom NWA 8613 and Kaba plot along mass-dependent fractionation lines. Oxygen isotopicdisequilibrium between phenocrysts and plagioclase was caused probably by exchange ofplagioclase with16O-poor fluids on the CV parent body. Based on an existing oxygenisotope mass balance model, possible dust enrichment and ice enhancement factors wereestimated. Type I chondrules from NWA 8613 possibly formed at moderately high dustenrichment factors (509to 1509CI dust relative to solar abundances); estimates for waterice in the chondrule precursors range from 0.29to 0.69the nominal amount of ice in dustof CI composition. Findings agree with results from an earlier study on oxygen isotopes inchondrules of the Kaba CV chondrite, providing further evidence for a relatively dry andonly moderately high dust-enriched disk in the CV chondrule-forming region.

^1,2,3S. N. Valencia,¹B. L. Jolliff,¹R. L. Korotev
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13370]
¹Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, Missouri 63130, USA
²Current address: Department of Astronomy, University of Maryland, College Park, Maryland 20742, USA
¹NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
Published by arrangement with John Wiley & Sons

The Northwest Africa (NWA) 773 clan of lunar meteorite stones are coarse‐grained breccias that provide an opportunity to examine a lunar igneous system that includes inferred intrusive and extrusive lithologies, possibly related through a common liquid line of descent from a single source region. Such extensive sampling of a single very low‐Ti (VLT) magmatic system on the Moon is unprecedented among the lunar samples. This study focuses on the olivine gabbro (OG), anorthositic gabbro (AG), and ferroan gabbro (FG) lithologies variably contained in NWA 773, NWA 2727, NWA 3160, NWA 3170, NWA 7007, and NWA 10656. Mineral compositions in the three gabbros indicate the crystallization sequence OG → AG → FG. Petrologic modeling of these three lithologies, and an olivine phyric basalt that also occurs in the NWA 773 clan, however, suggests that the relationship among the lithologies is more complex. The OG and basalt can be modeled as originating from a VLT KREEP‐bearing parental melt similar to the Apollo 14 Green Glass b1 composition through mainly equilibrium crystallization. The AG and FG, however, do not fit this simple model and require either a more complex crystallization sequence involving fractional crystallization, magma chamber recharge, or perhaps heterogeneity in the source region.

¹L. V. Forman,¹N. E. Timms,¹P. A. Bland,^1,2L. Daly,¹G. K. Benedix,³P. W. Trimby
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13380]
¹Space Science & Technology Centre, School of Earth & Planetary Sciences, Curtin University, GPO Box U1987, Perth, WesternAustralia 6845, Australia
²School of Geographical and Earth Sciences, University of Glasgow, Glasgow G12 8QQ, UK
³Oxford Instruments Nanoanalysis, High Wycombe HP12 3SE, UK
Published by arrangement with John Wiley & Sons

Meteoritic matrices are commonly classified by their modal mineralogy, alteration,and shock levels. Other “textural” characteristics are not generally considered inclassification schemes, yet could carry important information about their genesis andevolution. Terrestrial rocks are routinely described by grain morphology, which has led tomorphology-driven classifications, and identification of controlling processes. This paperinvestigates three CV chondrites—Allende (CV3.2oxA), Kaba (CV3.0oxB), and Vigarano(CV3.3red)—to determine the morphologic signature of olivine matrix grains. 2D grain sizeand shape, and crystallographic preferred orientations (CPOs) are quantified via electronbackscatter diffraction mapping. Allende contains the largest and most elongate olivinegrains, while Vigarano contains the least elongate, and Kaba contains the smallest grains.Weak but notable CPOs exist in some regions proximal to chondrules and one region distalto chondrules, and CPO geometries reveal a weak flattening of the matrix grains against theedge of chondrules within Allende. Kaba contains the least plastically deformed grains, andAllende contains the most plastically deformed grains. We tentatively infer that morphologyis controlled by the characteristics of the available population of accreting grains, andaqueous and thermal alteration of the parent body. The extent of overall finite deformationis likely dictated by the location of the sample with respect to compression, the localizedenvironment of the matrix with respect to surrounding material, and the post deformationtemperature to induce grain annealing. Our systematic, quantitative process forcharacterizing meteorite matrices has the potential to provide a framework for comparisonwithin and across meteorite classes, to help resolve how parent body processing differedacross and between chondritic asteroids.

¹Paula Lindgren,²Lydia Hallis,³Fredrik S. Hage,²Martin R. Lee,⁴John Parnell,¹Anders Plan,⁵Alistair Doye,⁵Ian MacLaren
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13381]
¹Department of Geology, Lund University, S€olvegatan 12, 223 62 Lund, Sweden
²School of Geographical & Earth Sciences, University of Glasgow, Glasgow G12 8QQ, UK
³SuperSTEM Laboratory, SciTech Daresbury Campus, Daresbury WA4 4AD, UK
⁴School of Geosciences, University of Aberdeen, Aberdeen AB24 3UE, UK
⁵School of Physics & Astronomy, University of Glasgow, Glasgow G12 8QQ, UK
Published by arrangement with John Wiley & Sons

A carbon-rich melt fragment from the Gardnos impact structure has been studied for a better understanding of the preservation and structural form(s) of carbon that have been processed by impact melting. The carbon was analyzed in situ in its original petrographic context within the melt fragment, using high-resolution techniques including focused ion beam-transmission electron microscopy and electron energy loss spectroscopy. Results show that the carbon is largely uniform and has a nanocrystalline grain size. The Gardnos carbon has a graphitic structure but with a large c/a ratio indicating disorder. The disorder could be a result of rapid heating to high temperatures during impact, followed by rapid cooling, with not enough time to crystallize into highly ordered graphite. However, temperature distribution during impact is extremely heterogenous, and the disordered Gardnos carbon could also represent material that avoided extreme temperatures, and thus, it was preserved. Understanding the structure of carbon during terrestrial impacts is important to help determine if the history of carbon within extraterrestrial samples is impact related. Furthermore, the degree of preservation of carbon during impact is key for locating and detecting organic compounds in extraterrestrial samples. This example from Gardnos, together with previous studies, shows that not all carbon is lost to oxidation during impact but that impact melting can encapsulate and preserve carbon where it is available.

¹Saya Kagami,¹Makiko K. Haba,¹Tetsuya Yokoyama,^2,3Tomohiro Usui,⁴Richard C. Greenwood
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13382]
¹Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Ookayama, Tokyo 152-8551, Japan2Earth-Life Science Institute, Tokyo
²Institute of Technology, Ookayama, Tokyo 152-8550, Japan
³Department of Solar System Sciences, ISAS, JAXA, Sagamihara, Kanagawa 252-5210, Japan
⁴Planetary and Space Sciences, School of Physical Sciences, The Open University, Walton Hall, UK
Published by arrangement with John Wiley & Sons

We report the results of a detailed study of the basaltic eucrite Northwest Africa(NWA) 7188, including its mineralogical and bulk geochemical characteristics, oxygenisotopic composition, and147,146Sm-143,142Nd mineral isochron ages. The texture andchemical composition of pyroxene and plagioclase demonstrate that NWA 7188 is amonomict eucrite with a metamorphic grade of type 4. The oxygen isotopic compositionand the Fe/Mn ratios of pyroxene confirmed that NWA 7188 belongs to the howardite–eucrite–diogenite meteorite suite, generally considered to originate from asteroid 4 Vesta.Whole-rock TiO2, La, and Hf concentrations and a CI chondrite-normalized rare earthelement pattern are in good agreement with those of representative Stannern-group eucrites.The147,146Sm-143,142Nd isochrons for NWA 7188 yielded ages of 4582190 and 4554+17/19 Ma, respectively. The closure temperature of the Sm-Nd system for different fractionsof NWA 7188 was estimated to be>865°C, suggesting that the Sm-Nd decay system haseither been resistant to reheating at~800°C during the global metamorphism or onlypartially reset. Therefore, the146Sm-142Nd age of NWA 7188 corresponds to the period ofinitial crystallization of basaltic magmas and/or global metamorphism on the parent body,and is unlikely to reflect Sm-Nd disturbance by late reheating and impact events. In eithercase, NWA 7188 is a rare Stannern-group eucrite that preserves the chronologicalinformation regarding the initial crustal evolution of Vesta.

¹Cruz-Rosas, H.I.,²Riquelme, F.,³Santiago, P.,³Rendón, L.,⁴Buhse, T.,⁵Ortega-Gutiérrez, F.,⁶Borja-Urby, R.,⁷Mendoza, D.,¹Gaona, C.,¹Miramontes, P.,³Cocho, G.
PLoS ONE 14, e0218750 Link to Article [DOI: 10.1371/journal.pone.0218750]
¹Facultad de Ciencias, Universidad Nacional Autónoma de México, Ciudad Universitaria, Cd. Mx., Mexico
²Laboratorio de Sistemática Molecular, Escuela de Estudios Superiores del Jicarero, Universidad Autónoma del Estado de Morelos, Jicarero, Morelos, Mexico
³Instituto de Física, Universidad Nacional Autónoma de México, Ciudad Universitaria, Cd. Mx., Mexico
⁴Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos, Cuernavaca, Morelos, Mexico
⁵Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Cd. Mx., Mexico
⁶Centro de Nanociencias y Micro y Nanotecnologías, Instituto Politécnico Nacional, Zacatenco, Cd. Mx., Mexico
⁷Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Ciudad Universitaria, Cd. Mx., Mexico

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^1,2Naraoka, H.,¹Hashiguchi, M.,³Sato, Y.,^1,3Hamase, K.
Life 9, 62 Link to Article [DOI: 10.3390/life9030062]
¹Research Center for Planetary Trace Organic Compounds, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan
²Department of Earth and Planetary Sciences, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan
³Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8582, Japan

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¹Francis M.McCubbin,^1,2Jessica J.Barnes
Earth and Planetary Science Letters 526, 115771 Link to Article [https://doi.org/10.1016/j.epsl.2019.115771]
¹Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, 2101 NASA Parkway, Houston, TX 77058, United States
²Lunar and Planetary Laboratory, University of Arizona, 1629 E University Blvd, Tucson, AZ 85721, United States
Copyright Elsevier

The presence of H2O within differentiated terrestrial bodies in the inner Solar System is well established; however, the source(s) of this H2O and the time of its arrival to the inner Solar System is an area of active study. At present, the prevailing model for the origin of inner Solar System H2O calls upon carbonaceous chondrites as the source. This is largely based on reported observations that H- and N-isotopic compositions of differentiated planetary bodies are largely the same and within a range of values that overlaps with carbonaceous chondrites as opposed to comets or the Sun. In this contribution, we evaluate the efficacy of this model and other models for the origin of inner Solar System H2O by considering geochronological constraints on early Solar System history, constraints on primary building blocks of differentiated bodies based on nucleosynthetic isotope anomalies, and constraints from dynamical models of planet formation. In addition to H- and N-isotopic data, these constraints indicate that an interstellar source of H2O was present in the inner Solar System within the first 4 Ma of CAI formation. Furthermore, the most H2O-rich carbonaceous chondrites are unlikely to be the source of H2O for the earliest-formed differentiated bodies based on their minimally overlapping primary accretion windows and the separation of their respective isotopic reservoirs by Jupiter in the timespan of about 1–4 Ma after CAI formation. The presence of deuterium-rich, non-nebular H2O sources in the inner Solar System prior to the formation of carbonaceous chondrites or comets implies early contributions of interstellar ices to both the inner and outer Solar System portions of the protoplanetary disk. Evidence for this interstellar ice component in the inner Solar System may be preserved in LL chondrites and in the mantle of Mars. In contrast to the earlier-formed bodies within the inner Solar System, Earth’s protracted accretion window may have facilitated incorporation of H2O in its interior from both the inner and outer Solar System, helping the Earth to become a habitable planet.

^1,2Asmaa Boujibar,^3,4,5Mya Habermann,¹Kevin Righter,^6,7D. Kent Ross,⁶Kellye Pando,⁸Minako Righter,⁹Bethany A. Chidester,⁶Lisa R. Danielson
American Mineralogist 104, 1221-1237 Link to Article [https://doi.org/10.2138/am-2019-7000]
¹NASA Johnson Space Center, 2101 E NASA Parkway, Houston, Texas 77058, U.S.A.
²Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington, D.C. 20015, U.S.A.
³Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, Texas 77058, U.S.A.
⁴HX5, NASA Johnson Space Center, 2101 E NASA Parkway, Houston, Texas 77058, U.S.A.
⁵Department of Earth and Planetary Sciences, University of New Mexico, 221 Yale Boulevard NE, Albuquerque, New Mexico 87131, U.S.A.
⁶Jacobs, NASA Johnson Space Center, 2101 E NASA Parkway, Houston, Texas 77058, U.S.A.
⁷UTEP-CASSMAR, 500 W University Avenue, El Paso, Texas 79968, U.S.A.
⁸Department of Earth and Atmospheric Sciences, University of Houston, 3507 Cullen Boulevard, Houston, Texas 77004, U.S.A.
⁹Department of the Geophysical Sciences, University of Chicago, 5734 S Ellis Avenue, Chicago, Illinois 60637, U.S.A.
Copyright: The Mineralogical Society of America

The distribution of heat-producing elements (HPE) potassium (K), uranium (U), and thorium (Th) within planetary interiors has major implications for the thermal evolution of the terrestrial planets and for the inventory of volatile elements in the inner solar system. To investigate the abundances of HPE in Mercury’s interior, we conducted experiments at high pressure and temperature (up to 5 GPa and 1900 °C) and reduced conditions (IW-1.8 to IW-6.5) to determine U, Th, and K partitioning between metal, silicate, and sulfide (D^met/sil and D^sulf/sil). Our experimental data combined with those from the literature show that partitioning into sulfide is more efficient than into metal and that partitioning is enhanced with decreasing FeO and increasing O contents of the silicate and sulfide melts, respectively. Also, at low oxygen fugacity (log f_O2 < IW-5), U and Th are more efficiently partitioned into liquid iron metal and sulfide than K. D^met/sil for U, Th, and K increases with decreasing oxygen fugacity, while Dmet/silUDUmet/sil and Dmet/silKDKmet/sil increase when the metal is enriched and depleted in O or Si, respectively. We also used available data from the literature to constrain the concentrations of light elements (Si, S, O, and C) in Fe metal and sulfide. We calculated chemical compositions of Mercury’s core after core segregation, for a range of f_O2 conditions during its differentiation. For example, if Mercury differentiated at IW-5.5, its core would contain 49 wt% Si, 0.02 wt% S, and negligible C. Also if core-mantle separation happened at a f_O2 lower than IW-4, the bulk Mercury Fe/Si ratio is likely to be chondritic. We calculated concentrations of U, Th, and K in the Fe-rich core and possible sulfide layer of Mercury. Bulk Mercury K/U and K/Th were calculated taking all U, Th, and K reservoirs into account. Without any sulfide layer, or if Mercury’s core segregated at a higher f_O2 than IW-4, bulk K/U and K/Th would be similar to those measured on the surface, confirming more elevated volatile K concentration than previously expected for Mercury. However, Mercury could fall on an overall volatile depletion trend where K/U increases with the heliocentric distance if core segregation occurred near IW-5.5 or more reduced conditions, and with a sulfide layer of at least 130 km thickness. At these conditions, the bulk Mercury K/Th ratio is close to Venus’s and Earth’s values. Since U and Th become more chalcophile with decreasing oxygen fugacity, to a higher extent than K, it is likely that at an f_O2 close to, or lower than, IW-6 both K/U and K/Th become lower than values of the other terrestrial planets. Therefore, our results suggest that the elevated K/U and K/Th ratios of Mercury’s surface should not be exclusively interpreted as the result of a volatile enrichment in Mercury, but could also indicate a sequestration of more U and Th than K in a hidden iron sulfide reservoir, possibly a layer present between the mantle and core. Hence, Mercury could be more depleted in volatiles than Mars with a K concentration similar to or lower than the Earth’s and Venus’s, suggesting volatile depletion in the inner solar system. In addition, we show that the presence of a sulfide layer formed between IW-4 and IW-5.5 decreases the total radioactive heat production of Mercury by up to 30%.

^1,2Julian Alfing,¹Markus Patzek,¹Addi Bischoff
Geochemistry (Chemie der Erde) Link top Article [https://doi.org/10.1016/j.chemer.2019.08.004]
¹Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm Str. 10, D-48149, Münster, Germany
²Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Corrensstr. 24, D-48149, Münster, Germany
Copyright Elsevier

For the bulk rocks of CI chondrites, various values are given for the modal abundance of matrix (95–100 vol%) and the accompanying mineral constituents. Here, we have determined the modal abundance of phases >5 μm in the CI chondrites Orgueil, Ivuna, Alais, and Tonk. Considering this cut-off grain-size to distinguish between matrix and coarse-grained constituents, then, we find the modal abundance of the minor phases magnetite, pyrrhotite, carbonate, olivine, and pyroxene to be 6 vol% in total, and these phases are embedded within the fine-grained, phyllosilicate-rich matrix, making up 94 vol%. The values vary slightly from meteorite to meteorite. Considering all four chondrites, the most abundant phase is – by far – magnetite (4.3 vol%) followed by pyrrhotite (∼1.1 vol%). All four CI chondrites are complex breccias, and their degree of brecciation decreases in the sequence: Orgueil > Ivuna > Alais ∼ Tonk. Because these meteorites contain clasts with highly variable modal abundances, we therefore also studied individual clasts with high abundances of specific coarse-grained phases. In this respect, in Orgueil we found a fragment with a 21.5 vol% of magnetite as well as a clast having 31.8 vol% phosphate. In Ivuna, we detected an individual clast with a 21.5 vol% of carbonates. Thus, since the CI composition is used as a geochemical standard for comparison, one also should keep in mind that sufficiently large sample masses are required to reveal a homogeneous CI composition. Small aliquots with one dominating lithology may significantly deviate from the suggested standard CI composition.