Core-mantle fractionation of carbon in Earth and Mars: The effects of sulfur

1Kyusei Tsuno, 1Damanveer S.Grewal, 1Rajdeep Dasgupta
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.07.010]
1Department of Earth, Environmental, and Planetary Sciences, Rice University, 6100 Main Street, MS 126, Houston, TX 77005, USA
Copyright Elsevier

Constraining carbon (C) fractionation between silicate magma ocean (MO) and core-forming alloy liquid during early differentiation is essential to understand the origin and early distribution of C between reservoirs such as the crust-atmosphere, mantle, and core of Earth and other terrestrial planets. Yet experimental data at high pressure (P)-temperature (T) on the effect of other light elements such as sulfur (S) in alloy liquid on alloy-silicate partitioning of C and C solubility in Fe-alloy compositions relevant for core formation is lacking. Here we have performed multi-anvil experiments at 6–13 GPa and 1800–2000 °C to examine the effects of S and Ni on the solubility limit of C in Fe-rich alloy liquid as well as partitioning behavior of C between alloy liquid and silicate melt (DCalloy/silicate). The results show that C solubility in the alloy liquid as well as DCalloy/silicate decreases with increasing in S content in the alloy liquid. Empirical regression on C solubility in alloy liquid using our new experimental data and previous experiments demonstrates that C solubility significantly increases with increasing temperature, whereas unlike in S-poor or S-free alloy compositions, there is no discernible effect of Ni on C solubility in S-rich alloy liquid.

Our modelling results confirm previous findings that in order to satisfy the C budget of BSE, the bulk Earth C undergoing alloy-silicate fractionation needs to be as high as those of CI-type carbonaceous chondrite, i.e., not leaving any room for volatility-induced loss of carbon during accretion. For Mars, on the other hand, an average single-stage core formation at relatively oxidized conditions (1.0 log unit below IW buffer) with 10-16 wt.% S in the core could yield a Martian mantle with a C budget similar to that of Earth’s BSE for a bulk C content of ∼0.25-0.9 wt.%. For the scenario where C was delivered to the proto-Earth by a S-rich differentiated impactor at a later stage, our model calculations predict that bulk C content in the impactor can be as low as ∼0.5 wt.% for an impactor mass that lies between 9-20% of present day Earth’s mass. This value is much higher than 0.05-0.1 wt.% bulk C in the impactor predicted by Li et al. (2016) because C-solubility limit of 0.3 wt.% in a S-rich alloy predicted by their models is significantly lower than the experimentally derived C-solubility of ∼1.6 wt. % for the relevant S-content in the core of the impactor.

Effect of target properties and impact velocity on ejection dynamics and ejecta deposition

1Robert Luther, 1,2Meng‐Hua Zhu, 3Gareth Collins, 1,4Kai Wünnemann
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13143]
1Museum für Naturkunde Berlin, Leibniz Institute for Evolution and Biodiversity ScienceBerlin, Germany
2Space Science Institute, Macau University of Science and TechnologyTaipa, Macau
3Department of Earth Science & Engineering, Imperial College LondonLondon, UK
4Institute of Geological Sciences, Freie Universität BerlinBerlin, Germany
Published by arrangement with John Wiley & Sons

Impact craters are formed by the displacement and ejection of target material. Ejection angles and speeds during the excavation process depend on specific target properties. In order to quantify the influence of the constitutive properties of the target and impact velocity on ejection trajectories, we present the results of a systematic numerical parameter study. We have carried out a suite of numerical simulations of impact scenarios with different coefficients of friction (0.0–1.0), porosities (0–42%), and cohesions (0–150 MPa). Furthermore, simulations with varying pairs of impact velocity (1–20 km s−1) and projectile mass yielding craters of approximately equal volume are examined. We record ejection speed, ejection angle, and the mass of ejected material to determine parameters in scaling relationships, and to calculate the thickness of deposited ejecta by assuming analytical parabolic trajectories under Earth gravity. For the resulting deposits, we parameterize the thickness as a function of radial distance by a power law. We find that strength—that is, the coefficient of friction and target cohesion—has the strongest effect on the distribution of ejecta. In contrast, ejecta thickness as a function of distance is very similar for different target porosities and for varying impact velocities larger than ~6 km s−1. We compare the derived ejecta deposits with observations from natural craters and experiments.

Characterization of hydrogen in basaltic materials with laser‐induced breakdown spectroscopy (LIBS) for application to MSL ChemCam data

1N.H.Thomas et al. (>10)
Journal of Geophysical Research Planets (in Press) Link to Article [https://doi.org/10.1029/2017JE005467]
1Division of Geological and Planetary Sciences, California Institute of TechnologyPasadena, California, USA
Published by arrangement with John Wiley & Sons

The Mars Science Laboratory rover, Curiosity, is equipped with ChemCam, a Laser‐Induced Breakdown Spectroscopy (LIBS) instrument, to determine the elemental composition of nearby targets quickly and remotely. We use a laboratory sample set including prepared mixtures of basalt with systematic variation in hydrated mineral content and compositionally well‐characterized, altered basaltic volcanic rocks to measure hydrogen by characterizing the H‐alpha emission line in LIBS spectra under martian environmental conditions. The H contents of all samples were independently measured using thermogravimetric analysis. We found that H peak area increases with weight percent H for our laboratory mixtures with basaltic matrices. The increase is linear with weight percent H in the mixtures with structurally bound H up to about 1.25 wt. % H and then steepens for higher H‐content samples, a non‐linear trend not previously reported but potentially important for characterizing high water content materials. To compensate for instrument, environmental, and target matrix related effects on quantification of H content from the LIBS signal, we examined multiple normalization methods. The best performing methods utilize O 778 nm and C 248 nm emission lines. The methods return comparable results when applied to ChemCam data of H‐bearing materials on Mars. The calibration and normalization methods tested here will aid in investigations of H by LIBS on Mars with ChemCam and SuperCam. Further laboratory work will aid quantification across different physical matrices and heterogeneous textures because of differences we observed in H in pelletized and natural rock samples of the same composition.

Detection of meteoroid impacts by the Geostationary Lightning Mapper on the GOES‐16 satellite

1,2Peter Jennikens et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13137]
1SETI Institute, Carl Sagan CenterMountain View, California, USA
2NASA Ames Research CenterMoffett Field, California, USA
Published by arrangement with John Wiley & Sons

Bolides are detected by the Geostationary Lightning Mapper onboard the GOES‐16 weather satellite, which takes images of Earth at a rate of 500 Hz in a 1.1 nm wide pass band centered on 777.4 nm wavelength. Ten case studies are discussed. These initial results were obtained using the Level 0 data received during the nonoperational in‐orbit postlaunch test period. GLM positions and timings are sufficiently accurate to assist in trajectory and orbit reconstruction. GLM samples the light curve nearly completely, unaffected by onboard and downlink processes tailored to lightning data. Sufficient data on the instantaneous background scene are provided to reconstruct the baseline drift in the brightest pixels. The agreement to within a factor of 2–3 between measured total radiated energy from GLM and that derived from other space‐borne observations implies that during the bolide’s peak brightness the GLM pass band is dominated by continuum emission, rather than O I line emission. The reported flux is corrected for angle‐from‐nadir shifts in the central wavelength of the pass band, which overestimates continuum flux by only up to 20% for most of the GLM field of view, but more so if the bolide is observed far from nadir. Assuming a 6000 K blackbody spectrum, GLM is able to detect bolides with peak visual magnitude (at a normalized 100 km distance) brighter than about −14 in nighttime, and slightly brighter in daytime.

First evidence for silica condensation within the solar protoplanetary disk

1,2Mutsumi Komatsu, 2Timothy J. Fagan, 3Alexander N. Krot, 3Kazuhide Nagashima, 4,5Michail I. Petaev, 6,7Makoto Kimura, 6,8Akira Yamaguchi
Proceedings of the National Academy of Sciences of the United States of America
Link to Article [https://doi.org/10.1073/pnas.1722265115]
1The Graduate University for Advanced Studies (SOKENDAI), Hayama, 240-0193 Kanagawa, Japan
2Department of Earth Sciences, Waseda University, Shinjuku, 169-8050 Tokyo, Japan
3Hawai‘i Institute of Geophysics and Planetology, School of Ocean, Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, HI 96822
4Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138
5Harvard–Smithsonian Center for Astrophysics, Cambridge, MA 02138
6National Institute of Polar Research, Tachikawa, 190-8518 Tokyo, Japan
7Ibaraki University, 310-8512 Mito, Japan
8Department of Polar Science, School of Multidisciplinary Science, SOKENDAI, Tachikawa, 190-8518 Tokyo, Japan

Calcium-aluminum–rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs), a refractory component of chondritic meteorites, formed in a high-temperature region of the protoplanetary disk characterized by approximately solar chemical and oxygen isotopic (Δ17O ∼ −24‰) compositions, most likely near the protosun. Here we describe a 16O-rich (Δ17O ∼ −22 ± 2‰) AOA from the carbonaceous Renazzo-type (CR) chondrite Yamato-793261 containing both (i) an ultrarefractory CAI and (ii) forsterite, low-Ca pyroxene, and silica, indicating formation by gas–solid reactions over a wide temperature range from ∼1,800 to ∼1,150 K. This AOA provides direct evidence for gas–solid condensation of silica in a CAI/AOA-forming region. In a gas of solar composition, the Mg/Si ratio exceeds 1, and, therefore, silica is not predicted to condense under equilibrium conditions, suggesting that the AOA formed in a parcel of gas with fractionated Mg/Si ratio, most likely due to condensation of forsterite grains. Thermodynamic modeling suggests that silica formed by condensation of nebular gas depleted by ∼10× in H and He that cooled at 50 K/hour at total pressure of 10−4 bar. Condensation of silica from a hot, chemically fractionated gas could explain the origin of silica identified from infrared spectroscopy of remote protostellar disks.

The Dingle Dell meteorite: A Halloween treat from the Main Belt

1Hadrien A.R. Devillepoix et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13142]
1School of Earth and Planetary Sciences, Curtin UniversityBentley, WA, Australia
Published by arrangement with John Wiley & Sons

We describe the fall of the Dingle Dell (L/LL 5) meteorite near Morawa in Western Australia on October 31, 2016. The fireball was observed by six observatories of the Desert Fireball Network (DFN), a continental‐scale facility optimized to recover meteorites and calculate their pre‐entry orbits. The 30 cm meteoroid entered at 15.44 km s−1, followed a moderately steep trajectory of 51° to the horizon from 81 km down to 19 km altitude, where the luminous flight ended at a speed of 3.2 km s−1. Deceleration data indicated one large fragment had made it to the ground. The four person search team recovered a 1.15 kg meteorite within 130 m of the predicted fall line, after 8 h of searching, 6 days after the fall. Dingle Dell is the fourth meteorite recovered by the DFN in Australia, but the first before any rain had contaminated the sample. By numerical integration over 1 Ma, we show that Dingle Dell was most likely ejected from the Main Belt by the 3:1 mean motion resonance with Jupiter, with only a marginal chance that it came from the ν6 resonance. This makes the connection of Dingle Dell to the Flora family (currently thought to be the origin of LL chondrites) unlikely.

1.34 billion-year-old magmatism on Mars evaluated from the co-genetic nakhlite and chassignite meteorites

1Arya Udry, 2James M.D.Day
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.07.006]
1Department of Geoscience, University of Nevada Las Vegas, Las Vegas NV 89154, USA
2Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0244, USA
Copyright Elsevier

Nakhlite and chassignite martian meteorites have similar crystallization (1340 ± 40 Ma) and ejection (∼11 Ma) ages, and 87Rb-87Sr and 143Sm-144Nd compositions. Using a near-comprehensive suite of these rocks, we place further constraints on nakhlite and chassignite petrogenesis, utilizing bulk rock and mineral major- and trace-element compositions, and quantitative textural data for 17 samples, including three recent finds (Northwest Africa [NWA] 10153, NWA 10645, and NWA 11013). Bulk rock and mineral compositions indicate that nakhlites and chassignites originated from <5% partial melting of a highly depleted source, in the presence of residual garnet. Significant fractionation of olivine and pyroxene from parental magmas led to formation of cumulate dunites (chassignites), and augite-rich cumulates with relatively low abundances of interstitial material (nakhlites). We show that two nakhlite groups exist with high and low absolute trace-element abundances, which are consistent with groupings from previous studies based on mesostasis content and volatile element contents. The discrepancy between the parental melt and cumulate bulk rock compositions indicates that a missing fractionated melt composition complementary to nakhlites and chassignites should exist on Mars. Quantitative textural analyses of both nakhlites and chassignites are consistent with emplacement as distinct lava flows and/or magmatic bodies close to the martian surface, rather than from a single sill or lava flow sequence. Although originating from the same parental melt to nakhlites, chassignites likely represent cumulates that were either erupted as xenoliths, or occurred as crystal settling pods within dikes or sills and thus represent a different batch of flow/magma from the nakhlites. Determination of an ancient 207Pb-206Pb age (3.95 ± 0.16 Ga) for an apatite grain in NWA 998 is consistent with hydrothermal alteration of nakhlites by ancient crustal-derived fluids immediately following their emplacement. We interpret the apatite age, which is highly distinct from the crystallization age of nakhlites, to indicate addition of Cl-rich fluids driven by hydrothermal circulation of martian crustal brines during emplacement of the nakhlites and chassignites. Although the spatial location of nakhlites and chassignites at the martian surface remains unconstrained, our results indicate similar emplacement features to those observed in terrestrial volcano-magmatic systems.