¹Guillaume Siron,¹Kohei Fukuda,²Makoto Kimura,¹Noriko T.Kita
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.02.010]
¹WiscSIMS, Department of Geoscience, University of Wisconsin-Madison, Madison, WI 53706, USA
²National Institute of Polar Research, Meteorite Research Center, Midoricho 10-3, Tachikawa, Tokyo 190-8518, Japan
Copyright Elsevier

Chondrules in ordinary chondrites are considered to form in high density environments, likely related to the evolution of protoplanets and large planetesimals. In order to determine the timing of their formation at high time resolution (≤0.1 Ma), we conducted high precision Al-Mg chronology of 17 porphyritic chondrules from 6 different unequilibrated ordinary chondrites (UOCs) of low petrologic subtypes (3.00-3.05). Detailed petrology, mineralogy, and oxygen isotope ratios of individual chondrules were also obtained that include 10 additional chondrules without Al-Mg ages. Seventeen chondrules for Al-Mg chronology consist of 14 chondrules with plagioclase (An₁-An₈₇) and three chondrules with Na-rich glassy mesostasis, all of which have high ²⁷Al/²⁴Mg ratios (30-3,000). The inferred initial (²⁶Al/²⁷Al)₀ ratios range between (6.5 ± 0.6)×10^–6 to (9.5 ± 1.0)×10^–6, corresponding to chondrule formation ages of 1.74 ± ^0.12/_0.11 Ma to 2.13 ± 0.09 Ma after CAIs, which have a canonical (²⁶Al/²⁷Al)₀ ratio of 5.25×10^–5. Six albite-bearing chondrules (An_<30) show a much more restricted ages range, spanning between 2.00 ± ^0.11/_0.10 Ma and 2.07 ± ^0.11/_0.10 Ma. Including 14 anorthite-bearing chondrules studied previously, chondrules in ordinary chondrites have a restricted range of formation ages from 1.8 Ma to 2.2. Ma after CAIs.

Based on the newly acquired oxygen isotope data and previous high precision studies, chondrules in L and LL chondrites do not show systematic difference in their δ¹⁸O and δ¹⁷O signatures. Majority of plagioclase-bearing chondrules studied for Al-Mg chronology show similar oxygen isotope ratios to those of glass-bearing chondrules. There is no obvious difference in Al-Mg ages of chondrules between L and LL chondrites. Thus, chondrules in L and LL chondrites would have formed in common environments and processes, though they accreted to two separate parent bodies by 2.2 Ma after CAIs, which timing is consistent with the proposed thermal model for ordinary chondrite parent bodies. Onset of chondrule formation at 1.8 Ma after CAIs may be caused by the delay of Jupiter formation or the formation of protoplanets in ordinary chondrite chondrule forming regions if chondrules formed by large scale disk shock or impact jetting of protoplanets. Alternatively, early formed chondrules would not be preserved before 1.8 Ma if chondrules formed by the impacts of molten planetesimals.

^1,2,3Jangmi Han,⁴Changkun Park,¹Adrian J.Brearley
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.02.007]
¹Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, USA
²Lunar and Planetary Institute, USRA, 3600 Bay Area Boulevard, Houston, TX 77058, USA
³Astromaterials Research and Exploration Science, NASA Johnson Space Center, 2101 NASA Parkway, Houston, TX 77058, USA
⁴Division of Earth Sciences, Korea Polar Research Institute, 26 Songdomirae-ro, Yeonsu-gu, Incheon 21990, South Korea
Copyright Elsevier

Amoeboid olivine aggregates (AOAs) from the Kainsaz CO3.2 chondrite were analyzed using transmission electron microscopy in order to gain a more complete understanding of thermal metamorphism on the parent body and the role of fluids during metamorphic heating. The Kainsaz AOAs are dominated by strongly zoned, fine-grained, olivine grains (Fa2-31) with heterogeneous Fe enrichments along the grain boundaries, which are interpreted as the result of Fe2+-Mg2+ interdiffusion with the matrix during thermal metamorphism. However, our diffusion calculations show that such AOA olivine zoning and compositions cannot be produced by a simple diffusional exchange during metamorphic heating, unlike chondrule olivine zoning and compositions. In addition, fine-grained ferroan olivine overgrowths occur heterogeneously in crystallographic continuity with olivines on the AOA exteriors. The overgrowths (Fa33-36) are compositionally distinct from the underlying AOA olivines and are not fully equilibrated with the matrix olivines (Fa∼20-55). The ferroan olivine overgrowths likely formed by precipitation from fluids in an epitaxial relationship with forsteritic olivine on the edges of AOAs. Texturally and compositionally diverse chromite grains are also observed along olivine grain boundaries, in olivine grains, and in pore spaces between olivine grains. They share a similar crystallographic orientation relationships with adjacent olivine, suggestive of their formation by exsolution and/or epitaxial growth. Collectively, these observations provide evidence for the mobilization of Fe, Mg, Si, Cr, and Al in the presence of fluids along olivine grain boundaries and into olivine grains during thermal metamorphism. We conclude that in Kainsaz AOAs, the strong zonation development in individual olivine grains and the formation of ferroan olivine overgrowths and chromite grains were a fluid-driven process that occurred at relatively low temperatures (<500℃), during the cooling history of the CO3 chondrite parent body, following the peak of thermal metamorphism.

¹Cocean A.,¹Postolachi C.,^1,2Cocean G.,³Bulai G.,¹Munteanu B.,^1,4Cimpoesu N.,¹Cocean I.,¹Gurlui S.
Applied Sciences 12, 983 Link to Article [DOI 10.3390/app12030983]
¹Faculty of Physics, Alexandru Ioan Cuza University of Iasi, 11 Carol I Bld, Iasi, 700506, Romania
²Rehabilitation Hospital Borsa, 1 Floare de Colt Street, Borsa, 435200, Romania
³Integrated Center of Environmental Science Studies in the North-Eastern Development Region (CERNESIM), Department of Exact and Natural Sciences, Institute of Interdisciplinary Research, Alexandru Ioan Cuza University of Iasi, Iasi, 700506, Romania
⁴Faculty of Material Science and Engineering, Gheorghe Asachi Technical University of Iasi, 59A Mangeron Bld, Iasi, 700050, Romania

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¹Seppe Lampe et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.02.008]
¹Analytical-, Environmental-, and Geo-Chemistry (AMGC), Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium
Copyright Elsevier

Micrometeorites experience varying degrees of evaporation and mixing with atmospheric oxygen during atmospheric entry. Evaporation due to gas drag heating alters the physicochemical properties of fully melted cosmic spherules (CSs), including the size, chemical and isotopic compositions and is thus expressed in its chemical and isotopic signatures. However, the extent of evaporation and atmospheric mixing in CSs often remains unclear, leading to uncertainties in precursor body identification and statistics. Several studies have previously estimated the extent of evaporation based on the contents of major refractory elements Ca and Al in combination with the determined Fe/Si atomic ratios. Similarly, attempts have been made to design classification schemes based on isotopic variations. However, a full integration of any previously defined chemical classification schemes with the observed isotopic variability has not yet been successful. As evaporation can lead to both chemical and isotope fractionation, it is important to verify whether the estimated degrees of evaporation based on chemical and isotopic proxies converge. Here, we have analysed the major and trace element compositions of 57 chondritic (mostly V-type) CSs, along with their Fe isotope ratios. The chemical (Zn, Na, K or CaO and Al2O3 concentrations) and δ56Fe isotope fractionation measured in these particles show no correlation. The interpretation of these results is twofold: (i) isotopic and chemical fractionation are governed by distinct processes or (ii) the proxies selected for chemical and isotope fractionation are inadequate. While the initial Fe isotopic ratios of chondrites are constrained within a relatively narrow range (0.005 ± 0.008‰ δ56Fe), the chemical compositions of CSs display larger variability. Cosmic spherules are thus often not chemically representative of their precursor bodies, due to their small size. As oxygen isotopes are commonly used to refine the precursor bodies of meteorites, triple oxygen isotope ratios were measured in thirty-seven of the characterized CSs. Based on the relationship between δ18O and δ57Fe, the evaporation effect on the O isotope system can be calculated, which allows for a more accurate parent body determination. Using this correction method, two ‘Group 4’ spherules with strongly variable degrees of isotope fractionation (δ56Fe of ∼1.0‰ and 29.1‰, respectively) could be distinguished. Furthermore, it was observed that all CSs that probably have a OC-like heritage underwent roughly the same degree of atmospheric mixing (∼8‰ δ18O). This highlights the potential of including Fe isotope measurements to the regular methodologies applied to CS studies.

^1,2Tim Cunningham,^1,2Peter J. Wheatley,^1,2Pier-Emmanuel Tremblay,^1,2Boris T. Gänsicke,³George W. King,^4,5Odette Toloza,^1,2Dimitri Veras
Nature 602, 219-222 Link to Areticle [DOI https://doi.org/10.1038/s41586-021-04300-w]
¹Department of Physics, The University of Warwick, Coventry, UK
²Centre for Exoplanets and Habitability, University of Warwick, Coventry, UK
³Department of Astronomy, University of Michigan, Ann Arbor, MI, USA
⁴Departamento de Física, Universidad Técnica Federico Santa María, Valparaíso, Chile
⁵Millennium Nucleus for Planet Formation (NPF), Valparaíso, Chile

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¹Keisuke Fukushi,^1,2Yasuhito Sekine,³Elizabeth B.Rampe
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.02.005]
¹Institute of Nature and Environmental Technology, Kanazawa University, Kakuma, Kanazawa, Ishikawa 920-1192 Japan
²Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550 Japan
³Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, Houston, TX77058, USA
Copyright Elsevier

Mars once possessed liquid water on its surface. In investigations of aqueous conditions on early Mars, the Mars Science Laboratory rover Curiosity has provided mineralogical and geochemical data from lacustrine sediments of Gale Crater, site of a former lake. Recently, the top-down method for quantitative reconstruction of the chemical parameters of ancient pore water, based on exchangeable cation compositions in smectite and secondary minerals, was developed and applied to the Yellowknife Bay sediments in Gale Crater. Here we report the application of this method to lacustrine sediment from the Quela drill site in Gale Crater, in the Karasburg member of the Murray formation. The results show that the final pore water to interact with the sediments had the following chemistry: pH = 3.6–5.6, Eh > 0.22 V, molality of Na ({Na}) = 0.14–2.2 mol/kg, {K} = 0.0080–0.31 mol/kg, {Ca} = 0.021–0.21 mol/kg, {Mg} < 0.14 mol/kg, {Fe(II)} < 0.063 mol/kg, {Cl} = 0.096–2.6 mol/kg and {SO4} = 0.048–0.33 mol/kg. At two adjacent drill sites (Marimba and Sebina), the comparable mineral assemblages and smectite interlayer compositions imply that they have water chemistry similar to that of the Quela sediment. The inferred pore water was undersaturated with respect to halite by an order of magnitude, although the sediment contains halite. This suggests that the final water in the Quela sediment disappeared by freezing and sublimation rather than evaporation. One interpretation of the high Na and Cl concentrations of the final pore water at Quela is that the sediment was deposited in an arid climate at around 3.5 Ga. The high salinity of the final pore water at Quela relative to that at Yellowknife Bay suggests that climate may have shifted from semi-arid when the Yellowknife Bay formation was deposited to arid when the Karasburg member was deposited. Alternatively, the high salinity at Quela suggests that the post-depositional fluids at 2–3 Ga was enriched in Na. In contrast to low Na in the post-depositional fluids in the underlying Yellowknife Bay, the high salinity of the post-depositional fluids of the Quela suggests different origin and/or timing of the re-wetting events between these two sites. The acidic pH and high Eh suggest that the Quela sediment was intensively affected by oxidizing and acidic post-depositional fluids. The pH of the final pore water would not have allowed the preservation of Ca and Mg carbonates under attainable CO2 partial pressures, which is consistent with the scenario of carbonate dissolution by acidic post-depositional fluids on Mars.

¹Bidong Zhang,²Nancy L.Chabot,^1,3Alan E.Rubin⁴Munir Humayun,⁵Joseph S.Boesenberg,⁶Deonvan Niekerk
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.02.004]
¹Department of Earth, Planetary & Space Sciences, University of California, Los Angeles, CA 90095-1567, USA
²Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA
³Maine Mineral & Gem Museum, 99 Main Street, P.O. Box 500, Bethel, ME 04217, USA
⁴National High Magnetic Field Laboratory and Department of Earth, Ocean & Atmospheric Science, Florida State University, Tallahassee, FL 32310, USA
⁵Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, USA
⁶Department of Geology, Rhodes University, Makhanda 6140, South Africa
Copyright Elsevier

Group IIIF was established as a magmatic iron-meteorite group based on similar Ga and Ge abundances, unusually high Ga/Ge ratios, and the IIIAB-like interelement trends in its members; recent Mo and Ru isotopic data indicate that three of its members exhibit the isotopic signature of carbonaceous-chondrite (CC) irons. Here we report the elemental chemistry of this group and model its crystallization history. Included are new elemental data for IIIF irons acquired by both instrumental neutron activation analysis (INAA) and laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS). A fractional-crystallization model was used to evaluate the IIIF compositional trends for 19 elements and was unable to explain the observed fractionation trends for several key elements (Co, Ga, Ge). In particular, the inability of this model to match Co in the IIIF irons is striking because (1) group IIIF has the widest Co variation among all magmatic iron groups and (2) none of the tested initial S contents (0−20 wt.%) explains both the wide Co variation and steep Co-As slope. Attempts to fit subsets of the IIIF irons were also unsuccessful. In addition, group IIIF has the greatest variety of structural classes and kamacite bandwidths among all established magmatic iron groups. If the IIIF irons constitute a coherent group, they were derived from a parent body that experienced more complex processes than simple fractional crystallization of the core.

The Zinder and Northwest Africa (NWA) 1911 pyroxene-bearing pallasites were recently suggested to be related to group IIIF based on their Ga and Ge contents, and we completed a petrographic study of the pallasite silicates and LA-ICP-MS analyses of their metal fractions. The two pallasites are related to one another: they have nearly identical mineralogical, elemental and O-isotopic compositions in their silicates and metals. Their metallic compositions resemble those of the IIIF irons Moonbi, St. Genevieve County, and Cerro del Inca, but their O-isotopic compositions resemble those of non-carbonaceous (NC) achondrites. Additional isotopic measurements are needed to test the potential genetic relationship to group IIIF.

^1,2Hu J.,²Sharp T.G.
Progress in Earth and Planetary Science 9, 6 Link to Article [DOI 10.1186/s40645-021-00463-2]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, 91125, CA, United States
²School of Earth and Space Exploration, Arizona State University, Tempe, 85287, AZ, United States

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¹Jean-Guillaume Feignon,^1,2Toni Schulz,³Ludovic Ferrière,⁴Steven Goderis,^4,5Sietze J.de Graaff,^4,5Pim Kaskes,^4,5Thomas Déhais,⁴Philippe Claeys,¹Christian Koeberl
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.02.006]
¹Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A-1090, Vienna, Austria
²Institute for Geology und Mineralogy, University of Cologne, Zülpicher Strasse 49b, 50674 Cologne, Germany
³Natural History Museum, Burgring 7, 1010 Vienna, Austria
⁴Research Unit: Analytical, Environmental & Geo-Chemistry, Department of Chemistry, Vrije Universiteit Brussel, AMGC-WE-VUB, Pleinlaan 2, 1050 Brussels, Belgium
⁵Laboratoire G-Time, Université Libre de Bruxelles, Av. F.D. Roosevelt 50, 1050 Brussels, Belgium
Copyright Elsevier

Constraining the degree of preservation of a meteoritic signature within an impact structure provides vital insights in the complex pathways and processes that occur during and after an impact cratering event, providing information on the fate of the projectile. The IODP-ICDP Expedition 364 drilling recovered a ∼829 m continuous core (M0077A) of impactites and basement rocks within the ∼200-km diameter Chicxulub impact structure peak ring. No highly siderophile element (HSE) data have been reported for any of the impact melt rocks of this drill core to date. Previous work has shown that most Chicxulub impactites contain less than 0.1% of a chondritic component. Only few impact melt rock samples in previous drill cores recovered from the Chicxulub might contain such a signal. Therefore, we analyzed impact melt rock and suevite samples, as well as pre-impact lithologies of the Chicxulub peak ring, with a focus on the HSE concentrations and Re–Os isotopic compositions.

Similar to the concentrations of the other major and trace elements, those of the moderately siderophile elements (Cr, Co, Ni) of impact melt rock samples primarily reflect mixing between a mafic (dolerite) and felsic (granite) components, with the incorporation of carbonate material in the upper impact melt rock unit (from 715.60 to 747.02 meters below seafloor). The HSE concentrations of the impact melt rocks and suevites are generally low (<39 ppt Ir, <96 ppt Os, <149 ppt Pt), comparable to the values of the average upper continental crust, yet three impact melt rock samples exhibit an enrichment in Os (125–410 ppt) and two of them also in Ir (250–324 ppt) by one order of magnitude relative to the other investigated samples. The 187Os/188Os ratios of the impact melt rocks are highly variable, ranging from 0.18 to 2.09, probably reflecting heterogenous target rock contributions to the impact melt rocks. The significant amount of mafic dolerite (mainly ∼20–60% and up to 80–90%) , which is less radiogenic (187Os/188Os ratio of 0.17), within the impact melt rocks makes an unambiguous identification of an extraterrestrial admixture challenging. Granite samples have unusually low 187Os/188Os ratios (0.16 on average), while impact melt rocks and suevites broadly follow a mixing trend between upper continental crust and chondritic/mantle material. Only one of the investigated samples of the upper impact melt rock unit could also be interpreted in terms of a highly diluted (∼0.01–0.05%) meteoritic component. Importantly, the impact melt rocks and pre-impact lithologies were affected by post-impact hydrothermal alteration processes, probably remobilizing Re and Os. The mafic contribution, explaining the least radiogenic 187Os/188Os values, is rather likely. The low amount of meteoritic material preserved within impactites of the Chicxulub impact structure may result from a combination of the assumed steeply-inclined trajectory of the Chicxulub impactor (enhanced vaporization, and incorporation of projectile material within the expansion plume), the impact velocity, and the volatile-rich target lithologies.

^1,2,3Mark C. Nottingham,⁴Finlay M. Stuart,⁴Biying Chen,⁴Marta Zurakowska,⁴Jamie D. Gilmour,^1,2Louise Alexander,^1,2Ian A. Crawford,³Katherine H. Joy
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13783]
¹Department of Earth and Planetary Science, Birkbeck College, University of London, Malet Street, London, WC1E 7HX UK
²The Centre for Planetary Sciences at UCL-Birkbeck, Gower Street, London, WC1E 6BT UK
³Department of Earth and Environmental Sciences, The University of Manchester, Oxford Road, Manchester, M13 9PL UK
⁴Isotope Geosciences Unit, Scottish Universities Environmental Research Centre (SUERC), East Kilbride, G75 0QF UK
Published by arrangement with John Wiley & Sons

We report the concentrations and isotope ratios of light noble gases (He, Ne, Ar) in 10 small basalt fragments derived from lunar regolith soils at the Apollo 12 landing site. We use cosmic ray exposure (CRE) and shielding condition histories to consider their geological context. We have devised a method of using cosmogenic Ne isotopes to partition the CRE history of each sample into two stages: a duration of “deep” burial (shielding of 5–500 g cm−2) and a duration of near-surface exposure (shielding of 0 g cm−2). Three samples show evidence of measurable exposure at the lunar surface (durations of between 6 ± 2 and 7 ± 2 Myr). The remaining seven samples show evidence of a surface residence duration of less than a few hundred thousand years prior to collection. One sample records a single-stage CRE age range of between 516 ± 36 and 1139 ± 121 Myr, within 0–5 g cm−2 of the lunar surface. This is consistent with derivation from ballistic sedimentation (i.e., local regolith reworking) during the Copernicus crater formation impact at ~800 Myr. The remaining samples show CRE age clusters around 124 ± 11 Myr and 188 ± 15 Myr. We infer that local impacts, including Surveyor crater (180–240 Ma) and Head crater (144 Ma), may have brought these samples to depths where the cosmic ray flux was intense enough to produce measurable cosmogenic Ne isotopes. More recent small impacts that formed unnamed craters may have exhumed these samples from their deep shielding conditions to the surface (i.e., ~0–5 g cm−2) prior to collection from the lunar surface during the Apollo 12 mission.