Ag isotopic and chalcophile element evolution of the terrestrial and martian mantles during accretion: New constraints from Bi and Ag metal-silicate partitioning

1K.Righter,21M.Schönbächler,3K.Pando,4R.RowlandII,5M.Righter,5T.Lapene
Earth and Planetary Science Letters 552, 116590 Link to Article [https://doi.org/10.1016/j.epsl.2020.116590]
1NASA-JSC, 2101 NASA Parkway, Houston, TX 77058, United States of America
2ETH Zürich, Inst. Isotope Geology and Mineral Resources, 8092 Zürich, Switzerland
3Jacobs JETS, NASA JSC, Houston, TX 77058, United States of America
4Los Alamos National Laboratory, Mail Stop P952, Los Alamos, NM 87545, United States of America
5Dept. of Earth and Atmospheric Sciences, University of Houston, Houston, TX 77204, United States of America
Copyright Elsevier

The Earth’s timing of accretion and acquisition of moderately volatile compounds is uncertain. Hafnium-W and Mn-Cr isotopic data can bracket the timing of early planetary differentiation and core formation. The Ag-Pd system has also been utilized but its application has been limited by a lack of high pressure and temperature metal-silicate partitioning for Pd and Ag. Because Ag (and Bi) are volatile chalcophile siderophile elements, understanding their early distribution can constrain the origin of volatile elements in differentiated bodies and planets. Unfortunately, neither Ag or Bi have been studied across the wide range of pressure and temperature conditions that are relevant to accretion and core-mantle differentiation. Here, new high-pressure and temperature multi-anvil metal-silicate equilibrium experiments for Bi and Ag have been carried out at conditions relevant to planetary accretion and metal silicate differentiation that allow a more refined and complete understanding of element partitioning during core formation. The new metal-silicate partitioning data are combined with previously reported data, and utilized to predict the distributions of Bi, Pd, and Ag at conditions of accretion relevant for Earth and Mars. Application of the new partitioning results to Earth shows that D(Bi) and D(Ag) (D = metal/silicate concentration ratio) are lowered due to the effect of pressure and Si alloyed in the metallic liquid, resulting in higher predicted mantle Bi and Ag abundances than in the bulk silicate Earth (BSE), as well as high and variable Pd/Ag. The unradiogenic Ag isotopic composition of the BSE could have been generated by early accretion of volatile-poor (high Pd/Ag) pre-cursors, followed by later accretion of volatile–rich (low Pd/Ag) material, in agreement with earlier studies of Pd-Ag and Mn-Cr (Schönbächler et al., 2010). However, these main accretion phases would have to be followed by segregation of a sulfide liquid (at least 1.5% of magma ocean) at high pressures (>30 GPa), to explain the primitive upper mantle (PUM) Bi, Pd, and Ag, as well as Au, Pt, Cu and Ni concentrations as proposed previously. If the early accreted bulk Earth was volatile depleted with high Pd/Ag ratios, portions of the mantle may contain ancient domains that developed positive 107Ag isotopic anomalies (as also argued by noble gases, Nd, W, and Os isotopes). In comparison, Bi, Pd, and Ag concentrations in the martian mantle could have been set by simple metal-silicate equilibrium. Mars accreted and differentiated relatively rapidly, while also developing a deep magma ocean with a high Pd/Ag ratio that could have evolved positive 107Ag anomalies, in contrast to Earth. Measurements on shergottites may reveal these predicted Ag isotopic anomalies.

Kaitianite, Ti3+2Ti4+O5, a new titanium oxide mineral from Allende

1Chi Ma,1John R. Beckett
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13576]
1Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, 91125 USA
Published by arrangement with John Wiley & Sons

Kaitianite, Ti3+2Ti4+O5, is a new titanium oxide mineral discovered in the Allende CV3 carbonaceous chondrite. The type grain coexists with tistarite (Ti2O3) and rutile. Corundum, xifengite, mullite, osbornite, and a new Ti,Al,Zr‐oxide mineral are also present, although not in contact. The chemical composition of type kaitianite is (wt%) Ti2O3 56.55, TiO2 39.29, Al2O3 1.18, MgO 1.39, FeO 0.59, V2O3 0.08 (sum 99.07), yielding an empirical formula of (Ti3+1.75Al0.05Ti4+0.10Mg0.08Fe0.02)(Ti4+1.00)O5, with Ti3+ and Ti4+ partitioned, assuming a stoichiometry of three cations and five oxygen anions pfu. The end‐member formula is Ti3+2Ti4+O5. Kaitianite is the natural form of γ‐Ti3O5 with space group C2/c and cell parameters a = 10.115 Å, b = 5.074 Å, c = 7.182 Å, β = 112º, V = 341.77 Å3, and Z = 4. Both the type kaitianite and associated rutile likely formed as oxidation products of tistarite at temperatures below 1200 K, but this oxidation event could have been in a very reducing environment, even more reducing than a gas of solar composition. Based on experimental data on the solubility of Ti3+ in equilibrium with corundum from the literature, the absence of tistarite in or on Ti3+‐rich corundum (0.27–1.45 mol% Ti2O3) suggests that these grains formed at higher temperatures than the kaitianite (>1579–1696 K, depending on the Ti concentration). The absence of rutile or kaitianite in or on corundum suggests that any exposure to the oxidizing environment producing kaitianite in tistarite was too short to cause the precipitation of Ti‐oxides in or on associated corundum.

Microbial community distribution in variously altered basalts: insights into astrobiology sample site selection

1Brady AL,1,5Gibbons E,2,3Sehlke A,4Renner CJ,4Kobs Nawotniak SE,2Lim DSS,1Slater GF
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2020.105107]
1School of Geography and Earth Sciences, McMaster University, Hamilton, Ontario, Canada L8S 4K1
2NASA Ames Research Center, Moffett Field, California, USA
3Bay Area Environmental Research Institute (BAERI), Moffett Field, California, USA
4Department of Geosciences, Idaho State University, Pocatello, Idaho, USA
5Present address: Department of Earth and Planetary Sciences, McGill University, Montreal, Quebec, Canada

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The fate of sulfur and chalcophile elements during crystallization of the lunar magma ocean

1,2E. S. Steenstra,2J. Berndt,2S. Klemme,3J. F. Snape,1E. S. Bullock,3W. van Westrenen
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2019JE006328]
1The Earth and Planets Laboratory, Carnegie Institution of Science, Washington D.C., U.S.A
2Institute of Mineralogy, University of Münster, Germany
3Faculty of Science, Vrije Universiteit Amsterdam, The Netherlands
Published by arrangement with John Wiley & Sons

To assess the viability of sulfide liquid saturation during crystallization of the lunar magma ocean (LMO), we present a new dataset describing both the S concentration at sulfide liquid saturation (SCSS) and sulfide liquid‐silicate melt partition coefficients of many trace elements for various differentiated lunar magmas at lunar‐relevant conditions. Using these parameterizations, we model the SCSS and the distribution of the most chalcophile elements with progressive LMO crystallization in the absence and presence of sulfide liquids. Modeling results for different modes of LMO crystallization show that for proposed lunar mantle S abundances FeS sulfide liquid saturation is expected to occur between 96 and 98 % of LMO crystallization. This is decreased to >91 % for Fe‐S liquids with 30% Ni or Cu. Saturation of S‐poor sulfide liquids can occur at >75% of LMO crystallization. The timing of sulfide liquid saturation depends most strongly on the assumed S content of the lunar mantle following formation of the lunar core and on the sulfide liquid composition. Modeled abundances of chalcophile elements indicate that sulfide‐liquid saturation during late‐stage LMO crystallization would yield much lower abundances of Ni and Cu than observed in KREEP basalts and estimated for the urKREEP reservoir, as well as lower Ni/Co than observed in the latter. Sulfide liquids therefore did not affect moderately siderophile and chalcophile element fractionation within the LMO, supporting the hypothesis that the non‐volatile, siderophile element abundances of the lunar mantle reflect a phase of core formation and/or the addition of a meteoritic late veneer.

Correlated isotopic and chemical evidence for condensation origins of olivine in comet 81P/Wild 2 and in AOAs from CV and CO chondrites

1KoheiFukuda,2Donald E.Brownlee,2David J.Joswiak,3Travis J.Tenner,4Makoto Kimura,1Noriko T.Kita
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.09.036]
1WiscSIMS, Department of Geoscience, University of Wisconsin-Madison, Madison, WI 53706, USA
2Department of Astronomy, University of Washington, Seattle, WA 98195, USA
3Chemistry Division, Nuclear and Radiochemistry, Los Alamos National Laboratory, MSJ514, Los Alamos, NM 87545, USA
4National Institute of Polar Research, Tokyo 190-8518, Japan
Copyright Elsevier
Magnesium stable isotope ratios and minor element abundances of five olivine particles from comet 81P/Wild 2 were examined by secondary ion mass spectrometry (SIMS). Wild 2 olivine particles exhibit only small variations in δ25MgDSM-3 values from –1.0 +0.4/–0.5 ‰ to 0.6 +0.5/–0.6 ‰ (2σ). This variation can be simply explained by mass-dependent fractionation from Mg isotopic compositions of the Earth and bulk meteorites, suggesting that Wild 2 olivine particles formed in the chondritic reservoir with respect to Mg isotope compositions. We also determined minor element abundances, and O and Mg isotope ratios of olivine grains in amoeboid olivine aggregates (AOAs) from Kaba (CV3.1) and DOM 08006 (CO3.01) carbonaceous chondrites. Our new SIMS minor element data reveal uniform, low FeO contents of ∼0.05 wt% among AOA olivines from DOM 08006, suggesting that AOAs formed at more reducing environments in the solar nebula than previously thought. Furthermore, the SIMS-derived FeO contents of the AOA olivines are consistently lower than those obtained by electron microprobe analyses (∼1 wt% FeO), indicating possible fluorescence from surrounding matrix materials and/or Fe,Ni-metals in AOAs during electron microprobe analyses. For Mg isotopes, AOA olivines show more negative mass-dependent fractionation (–3.8 ± 0.5‰ ≤ δ25MgDSM-3 ≤ –0.2 ± 0.3‰; 2σ) relative to Wild 2 olivines. Further, these Mg isotope variations are correlated with their host AOA textures. Large negative Mg isotope fractionations in olivine are often observed in pore-rich AOAs, while those in compact AOAs tend to have near-chondritic Mg isotopic compositions. These observations indicate that pore-rich AOAs preserved their gas-solid condensation histories, while compact AOAs experienced thermal processing in the solar nebula after their condensation and aggregation. Importantly, one 16O-rich Wild 2 LIME olivine particle (T77/F50) shows negative Mg isotope fractionation (δ25MgDSM-3 = –0.8 ± 0.4‰, δ26MgDSM-3 = –1.4 ± 0.9‰; 2σ) relative to bulk chondrites. Minor element abundances of T77/F50 are in excellent agreement with those of olivines from pore-rich AOAs in DOM 08006. The observed similarity in O and Mg isotopes, and minor element abundances suggest that T77/F50 formed in an environment similar to AOAs, probably near the proto-Sun, and then was transported to the Kuiper belt, where comet 81P/Wild 2 likely accreted.

Surface weathering on Venus: Constraints from kinetic, spectroscopic, and geochemical data

1,2M. Darby Dyar,3Jörn Helbert,4Reid F.Cooper,1Elizabeth C.Sklute,3Alessandro Maturilli,3Nils T.Mueller,3David Kappel,5Suzanne E.Smrekar
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.114139]
1Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719, USA
2Department of Astronomy, Mount Holyoke College, 50 College St., South Hadley, MA 01075, USA
3German Aerospace Center (DLR) Institute for Planetary Research, Rutherfordstr 2, Berlin 12489, Germany
4Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, RI, 02912, USA
5Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
Copyright Elsevier

On Venus, understanding of surface-atmosphere interactions resulting from chemical weathering is both critically important for constraining atmospheric chemistry and relative ages of surface features and multifaceted, requiring integration of diverse perspectives and disciplines of study. This paper evaluates the issue of surface alteration on Venus using multiple lines of evidence. Surface chemistry from Venera and Vega landers is inconsistent with significant breakdown from atmospheric interactions, with <2.0 wt% S or less observed. Consideration of kinetics and breakdown of basalt under Venus conditions indicates diffusion of Ca > Fe > Mg toward the oxidizing Venus atmosphere, favoring creation of anhydrite and carbonate-rich surfaces on basalts with minor addition of hematite. When related to Venus-analog experiments, the kinetic calculations suggest a maximum coating of ~30 μm over 500,000 years. These changes would result in an overall volume increase in the outermost surface materials, which in turn decreases surface rock FeO contents. Those variations can be detected from orbit because emissivity is correlated with total FeO, and the predicted magnitudes are consistent with Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) observations. Models of anhydrite and hematite coatings on basalt mixtures suggest that changes in emissivity (ε) spectra due to chemical weathering can result in ca. <0.08 shifts in total emissivity. Such gradations are small compared to the first-order effect of bulk composition on emissivity, which can cause up to ~0.80 emissivity shifts. For all these reasons, there is at present no evidence to suggest that emissivity spectra should show impenetrable coatings of either hematite (ε = 0.8) or anhydrite (ε = 0.1) are present on Venus. Orbital measurements of surface emissivity on a global scale could therefore produce not only a map of rock type and surface composition based on transition metal contents (largely FeO) (Helbert et al., 2020) but also provide local scale assessments of fresh vs. mature lava flows on the surface.

Visible and near-infrared reflectance of hyperfine and Hyperporous particulate surfaces

1R.Sultana,1O.Poch,1,2P.Becka,1B.Schmitt,1E.Quirico
Icarus (in Press) Link to Journal [https://doi.org/10.1016/j.icarus.2020.114141]
1Université Grenoble Alpes, CNRS, Institut de Planétologie et d’Astrophysique de Grenoble, Grenoble, France
2Institut Universitaire de France, Paris, France
Copyright Elsevier

The composition of Solar System surfaces can be inferred through reflectance and emission spectroscopy, by comparing these observations to laboratory measurements and radiative transfer models. While several populations of objects appear to be covered by sub-micrometre sized particles (D < 1 μm) (referred to as hyperfine), there are limited studies on reflectance and emission of particulate surfaces composed of particles smaller than the visible and infrared wavelengths. We have undertaken an effort to determine the reflectance of hyperfine particulate surfaces in conjunction with high-porosity, in order to simulate the physical state of cometary surfaces and their related asteroids (P- and D-types). In this work, we present a technique developed to produce hyperfine particles of astrophysical relevant materials (silicates, sulphides, macromolecular organics). This technique is used to prepare hyperfine powders that were measured in reflectance in the 0.4–2.6 μm range. These powders were then included in water ice particles, sublimated under vacuum, in order to produce a hyperporous sample of hyperfine material (refers as to sublimation residue). When grinded below one micrometre, the four materials studied (olivine, smectite, pyroxene and amorphous silica), show strong decrease of their absorption features together with a blueing of the spectra. This “small grain degeneracy” implies that surfaces covered by hyperfine grains should show only shallow absorption features if any (in the case of moderately absorbing particles as studied here). These two effects, decrease of band depth and spectral blueing, appear magnified when the grains are incorporated in the hyperporous residue. We interpret the distinct behaviour between hyperporous and more compact surfaces by the distancing of individual grains and a decrease in the size of the elemental scatterers. This work implies that hyperfine grains are unabundant at the surfaces of S- or V-type asteroids, and that the blue nature of B-type may be related to a physical effect rather than a compositional effect.

Probing the nature of extraterrestrial dust reaching the Earth’s surface collected from the Maitri station, Antarctica

1N. G. Rudraswami,1D. Fernandes,1M. Pandey
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13574]
1National Institute of Oceanography (Council of Scientific and Industrial Research), Dona Paula, Goa, 403004 India
Published by arrangement with John Wiley & Sons

Micrometeorites (MMs) are extraterrestrial dust particles, in the size range of tens of µm to mm, recovered from the Earth’s surface primarily from deep‐sea sediments, Antarctica, and also from space. The present collection of MMs (>50 µm) obtained by melting ~50 t of ice near the Maitri station, Antarctica, has allowed us to investigate the abundance and properties of the particles by an unbiased collection technique. The collection reveals a large quantity of extraterrestrial material in the ~80−140 µm size range. Previous collections have shown an abundance of particles at diameter ~200 µm, which is in contrast to our findings. This can either be explained by movement of material within the ice or a recent influx of smaller particles. The smaller particles (<80 µm) typically undergo atmospheric entry heating, contrary to earlier observations, which have suggested that they reach the Earth’s surface unmelted. Chondrules and refractory inclusions are rare in the collected MMs indicating that their contribution is only a small percentage. The Maitri station collection does not have a well‐constrained ice accumulation rate and terrestrial age. Nevertheless, based on matching the previous well‐documented flux calculation of Antarctica, we suggest a slow ice accumulation rate of <1.0 g cm−2 yr−1 near Maitri station.

Characterization of shocked quartz grains from Chicxulub peak ring granites and shock pressure estimates

1Jean‐Guillaume Feignon,2Ludovic FerriÈre,3Hugues Leroux,1Christian Koeberl
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13570]
1Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A‐1090 Vienna, Austria
2Natural History Museum, Burgring 7, A‐1010 Vienna, Austria
3Univ‐Lille, CNRS, INRAE, Centrale Lille, UMR 8207 – UMET – Unité Matériaux et transformations, 59655 Villeneuve d’Ascq, France
Published by arrangement with John Wiley & Sons

Planar deformation features (PDFs) in quartz are a commonly used and well‐documented indicator of shock metamorphism in terrestrial rocks. The measurement of PDF orientations provides constraints on the shock pressure experienced by a rock sample. A total of 963 PDF sets were measured in 352 quartz grains in 11 granite samples from the basement of the Chicxulub impact structure’s peak ring (IODP‐ICDP Expedition 364 drill core), with the aim to quantify the shock pressure distribution and a possible decay of the recorded shock pressure with depth, in the attempt to better constrain shock wave propagation and attenuation within a peak ring. The investigated quartz grains are highly shocked (99.8% are shocked), with an average of 2.8 PDF sets per grain; this is significantly higher than in all previously investigated drill cores recovered from Chicxulub and also for most K‐Pg boundary samples (for which shocked quartz data are available). PDF orientations are roughly homogenous from a sample to another sample and mainly parallel to {10urn:x-wiley:10869379:media:maps13570:maps13570-math-00013} and {10urn:x-wiley:10869379:media:maps13570:maps13570-math-00024} orientations (these two orientations representing on average 68.6% of the total), then to {10urn:x-wiley:10869379:media:maps13570:maps13570-math-00032} orientation, known to form at higher shock pressure. Our shock pressure estimates are within a narrow range, between ~16 and 18 GPa, with a slight shock attenuation with increasing depth in the drill core. The relatively high shock pressure estimates, coupled with the rare occurrence of basal PDFs, i.e., parallel to the (0001) orientation, suggest that the granite basement in the peak ring could be one of the sources of the shocked quartz grains found in the most distal K‐Pg boundary sites.

Murrili meteorite’s fall and recovery from Kati Thanda

1Eleanor K. Sanson et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13566]
1School of Earth and Planetary Sciences, Curtin University, Bentley, Western Australia, 6102 Australia
Published by arrangement with John Wiley & Sons

On November 27, 2015, at 10:43:45.526 UTC, a fireball was observed across South Australia by 10 Desert Fireball Network observatories lasting 6.1 s. An ~37 kg meteoroid entered the atmosphere with a speed of 13.68 ± 0.09 km s−1 and was observed ablating from a height of 85 km down to 18 km, having slowed to 3.28 ± 0.21 km s−1. Despite the relatively steep 68.5° trajectory, strong atmospheric winds significantly influenced the darkflight phase and the predicted fall line, but the analysis put the fall site in the center of Kati Thanda–Lake Eyre South. Kati Thanda has meters‐deep mud under its salt‐encrusted surface. Reconnaissance of the area where the meteorite landed from a low‐flying aircraft revealed a 60 cm circular feature in the muddy lake, less than 50 m from the predicted fall line. After a short search, which again employed light aircraft, the meteorite was recovered on December 31, 2015 from a depth of 42 cm. Murrili is the first recovered observed fall by the digital Desert Fireball Network (DFN). In addition to its scientific value, connecting composition to solar system context via orbital data, the recovery demonstrates and validates the capabilities of the DFN, with its next generation remote observatories and automated data reduction pipeline.