Magma oceans, iron and chromium redox, and the origin of comparatively oxidized planetary mantles

Geochimica et Cosmochimica Acta (in Press) Link to Article []
1Dept. of Earth and Environmental Sciences, University of Minnesota, Minneapolis, MN 55455 USA
Copyright Elsevier

The mantles of both Earth and Mars are more oxidized than would be expected based on low pressure equilibration of molten silicate and alloy during their magma ocean stages. High pressure silicate-alloy equilibration in a magma ocean can produce appreciable ferric iron in the silicate, leading to comparatively oxidized near surface conditions and overlying atmospheres. Upon crystallization, this may feasibly be sufficient to account for oxygen fugacities prevailing in basalt source regions of Earth and Mars. Experiments and first principles studies affirm that Fe3+ is stabilized at high pressure, but to date there has been no model that accounts accurately for the combined effects of melt composition, temperature, pressure, and oxygen fugacity on magma ocean Fe3+/FeT. We calibrate a new model for Fe3+/FeT as a function of temperature, pressure, melt composition, and fO2 which reproduces Fe3+/FeT for experimental peridotite liquids and which incorporates differences in FeO and Fe2O3 liquid heat capacities into a potentially realistic temperature function. For the effects of pressure, two versions of the model are implemented based on recent equations of state (EOS), though only the EOS of Deng et al. (2020) is applicable to pressures relevant to metal-silicate equilibration in a deep terrestrial magma ocean. For Earth, metal-silicate equilibration at 28-53 GPa, 2300-4100 K, and fO2 set by plausible mantle and core compositions produces Fe3+/FeT between 0.034 and 0.10, with variation mostly owing to differences in assumed temperatures. For Mars, different proposed mantle compositions produce Fe3+/FeT ratios that range from 0.026 for FeO* of 13.5 wt.% up to 0.038 for FeO* of 18.1 wt.%.

Although significant Fe3+ may be present in magma oceans owing to high pressure equilibration with alloy, the budget of Fe2O3 in crystallized mantles is expected to be modified from that in the molten state. An important additional factor is the influence of Cr, which is Cr2+ in molten silicate equilibrated with alloy and Cr3+ in terrestrial upper mantles. Production of Cr3+ and Fe2+ by reaction with Cr2+ and Fe3+ during crystallization can destroy much of the Fe2O3 present during the magma ocean stage. Considering the stability of Cr2+ in olivine and the temperature-dependent partitioning of Cr3+ between mantle silicates, we construct an empirical model for the fraction of Cr that is Cr2O3 in solid spinel peridotite as a function of temperature and fO2. For Earth, at least 0.35 wt.% Fe2O3 is destroyed by oxidation of magma ocean CrO and for Mars, more than 0.55 wt.% Fe2O3 should be destroyed. Consequently, either the terrestrial and martian magma oceans were significantly more enriched in Fe2O3 than their present-day upper mantles or other processes contributed to oxidation of the latter. Over-enrichment of Fe2O3 in the magma oceans is plausible only if terrestrial metal-silicate equilibration occurred above 3300 K and if the martian mantle contains >17 wt.% FeO*. Subsolidus disproportionation of ferrous iron may have contributed to the present-day redox state of the Earth’s mantle, and late accretion of chondrite-like material and hydrogen degassing also likely affected the solidified mantles of both Earth and Mars.

Petrochemistry and Oxygen Isotope of Karimati (L5) Chondrite, a 2009 Fall in Uttar Pradesh, India

1Ray D.,1Panda D.K.,1Arora G.,bGhosh S.,3Murty S.V.S.,4Chakraborty S.
Journal of the Geological Society of India 98, 323-328 Link to Article [DOI 10.1007/s12594-022-1983-4]
1Physical Research Laboratory, Ahmedabad, 380 009, India
254/3 M.B. Road, Kolkata, 700 072, India
3Lad Society Road, Ahmedabad, 380 015, India
4Department of Chemistry, University of California, Urey Hall 5112, San Diego, La Jolla, 92093-0356, United States

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Isotopic and trace element data of Tissint indicate a homogeneous strewn field, mobilization of Sr, REE, and Pb during shock metamorphism, and limits on the incorporation of martian surficial materials in impact melt glass

Geochimica et Cosmochimica Acta (in Press) Link to Article []
1Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX 77204–5007, USA
2Department of Geoscience, University of Wisconsin–Madison, Madison, WI 53706–1692, USA
3Department of Earth and Space Sciences, University of Washington, Seattle, WA 98195–1310, USA
Copyright: Elsevier

The Tissint strewn field has produced over 16 kg of material that has minimal terrestrial weathering and/or contamination. Tissint, along with 16 other incompatible trace element (ITE)-depleted shergottite specimens with igneous crystallization ages spanning 327 to 2403 Ma, were ejected together from Mars 1.1 m.y. ago. Despite the geochemical similarities of fragments from the Tissint strewn field, there are reported discrepancies in age determinations from different fragments that raise the possibility that the strewn field may be heterogenous. There are also questions about whether the shock ejection event incorporated martian soil components into impact glass, and the sources of radiogenic Sr and Pb that have been measured from leachate fractions in previous studies. An impact melt-rich fragment of Tissint was analyzed by LA-ICPMS for rare-earth element (REE) and highly siderophile element (HSE) concentrations and Pb isotopic compositions. Leachate and residues from 8 specimens representing separate individual fragments collected from the strewn field were analyzed for Rb-Sr. Unleached fractions of the 8 specimens were also analyzed for Sm-Nd and Lu-Hf.

The measured REE and HSE concentrations of impact melt glass and associated sulfide measured by LA-ICPMS are consistent with bulk rock compositions of Tissint and show no evidence for incorporation of more ITE-enriched martian surface components. Measured Pb isotopic compositions confirm that the impact melt glass and associated sulfide contain no evidence for incorporation of more radiogenic materials than the Pb compositions inherited from the primary magma. In situ Pb isotopic data from sulfide likely represents the most robust method for constraining initial Pb isotopic compositions of shergottites whereas approaches that rely on leaching and digestion may not remove all mineral and/or crack surface contaminants.

Rubidium-strontium analyses of the 8 Tissint specimens indicate that labile components hosting HCl-soluble Rb and Sr are not in isotopic equilibrium with the igneous assemblage and that the washed residues are in isotopic equilibrium with the igneous assemblage. The Sr isotopic compositions of the leachate are within the range of ‘more ITE-enriched’ depleted shergottites, perhaps indicating sources from the igneous pile on Mars. The radiogenic Sr component could represent crack and mineral surface coatings of volatilized materials derived from nearby depleted shergottite rock units during the impact ejection process but are not radiogenic enough to represent ITE-enriched crust or mantle components.

The Lu-Hf isotopic data from the specimens indicate no evidence of contamination or element mobility, whereas the Rb-Sr and Sm-Nd isotopic systems show evidence for element mobility and potential mixing with an isotopic component not in equilibrium with the igneous phases. The calculated ages using data compiled from Brennecka et al. (2014), and Grosshans (2013) for Lu-Hf, Rb-Sr, and Sm-Nd are 571 ± 84 Ma, 590 ± 49 Ma and 559 ± 39 Ma, respectively. These data indicate that the specimens analyzed here are cogenetic and the Tissint strewn field appears to be homogeneous.

Atomic-scale structure and non-stoichiometry of meteoritic hibonite: A transmissionelectron microscope study

1,2Jangmi Han,3Ichiro Ohnishi,3Akira Yasuhara,2Lindsay P. Keller
American Mineralogist 107 873–884 Link to Article []
1Lunar and Planetary Institute, USRA, 3600 Bay Area Boulevard, Houston, Texas 77058, U.S.A.
2Astromaterials Research and Exploration Science, NASA Johnson Space Center, 2101 NASA Parkway, Houston, Texas 77058, U.S.A.
3JEOL Ltd., 3-1-2 Musashino, Akishima, Tokyo, 196-8558, Japan
Copyright: The Mineralogical Society of America

Hibonite (CaAl12O19) is a common refractory mineral in Ca-Al-rich inclusions (CAIs) in primitive
meteorites. Transmission electron microscope (TEM) studies have identified enigmatic planar defects
in different occurrences of hibonite in the Allende meteorite that give rise to strong streaking along c*
in electron diffraction patterns. Atomic resolution high-angle annular dark-field (HAADF) imaging and
energy-dispersive X-ray (EDX) analyses were used to determine the nature and origin of these planar
features. HAADF images of hibonite grains reveal lamellar intergrowths of common 1.6 nm spacing,
and less commonly 2.0 and 2.5 nm spacings, interspersed in stoichiometric hibonite showing 1.1 nm
(002) spacing. Stoichiometric hibonite consists of alternating Ca-containing (“R”) and spinel-structured
(“S”) blocks stacked in a sequence RS. In contrast, the 1.6 nm layers result from a doubled S block
such that the stacking sequence is RSS, while in the widest defect observed, the stacking sequence is
RSSSS. These intergrowths are epitaxial and have coherent, low-strain boundaries with the host hibonite
Meteoritic hibonite shows common Ti and Mg substitution for Al in its structure. Atomic-resolution
EDX maps of hibonite grains in the Allende CAI confirm the preferred site occupancy of Mg on
tetragonal M3 sites in S blocks and of Ti on trigonal bipyramidal M2 and octahedral M4 sites in R
blocks. Mg is highly concentrated, but Ti is absent in the planar defects where wider S blocks show
Al-rich compositions compared to stoichiometric MgAl2O4 spinel. Therefore, Mg likely played the
major role in the formation and metastability of planar defects in hibonite. Electron energy loss spec-
troscopy data from the Ti L2,3 edge show the presence of mixed Ti oxidation states with ~15–20% of Ti
as Ti3+ in hibonite, suggesting a direct substitution of Ti3+ ↔ Al3+ in hibonite. The remaining ~80–85%
of Ti is present as Ti4+ and corresponding EDX analyses are consistent with the well-known coupled
substitution 2Al3+ ↔ Ti4+ + Mg2+ being the major mechanism for Ti and Mg substitution in hibonite.
The formation of planar defects in hibonite occurred during high-temperature nebular condensa-
tion or melting/crystallization processes. The occurrence of non-stoichiometric hibonite in the Allende
CAI deviates from the mineral formation sequence predicted from equilibrium condensation models.
Overall, our atomic resolution TEM observations signify non-equilibrium, kinetic-controlled crystal
growth during the high-temperature formation of refractory solids in the early solar nebula.

Overview of the Morphology and Chemistry of Diagenetic Features in the Clay‐Rich Glen Torridon Unit of Gale Crater, Mars

1Patrick J. Gasda et al. (>10)
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article []
1Los Alamos National Laboratory, Los Alamos, New Mexico, USA
Published by arrangement with John Wiley & Sons

The clay-rich Glen Torridon region of Gale crater, Mars, was explored between sols 2300 and 3007. Here, we analyzed the diagenetic features observed by Curiosity, including veins, cements, nodules, and nodular bedrock, using the ChemCam, Mastcam, and Mars Hand Lens Imager instruments. We discovered many diagenetic features in Glen Torridon, including dark-toned iron- and manganese-rich veins, magnesium- and fluorine-rich linear features, Ca-sulfate cemented bedrock, manganese-rich nodules, and iron-rich strata. We have characterized the chemistry and morphology of these features, which are most widespread in the higher stratigraphic members in Glen Torridon, and exhibit a wide range of chemistries. These discoveries are strong evidence for multiple generations of fluids from multiple chemical endmembers that likely underwent redox reactions to form some of these features. In a few cases, we may be able to use mineralogy and chemistry to constrain formation conditions of the diagenetic features. For example, the dark-toned veins likely formed in warmer, highly alkaline, and highly reducing conditions, while manganese-rich nodules likely formed in oxidizing and circumneutral conditions. We also hypothesize that an initial enrichment of soluble elements, including fluorine, occurred during hydrothermal alteration early in Gale crater history to account for elemental enrichment in nodules and veins. The presence of redox-active elements, including Fe and Mn, and elements required for life, including P and S, in these fluids is strong evidence for habitability of Gale crater groundwater. Hydrothermal alteration also has interesting implications for prebiotic chemistry during the earliest stages of the crater’s evolution and early Mars.

Geochemical and mineralogical classification of four new shergottites: NWA 10441, NWA 10818, NWA 11043, and NWA 12335

1Kenneth J. Orr,1Lucy V. Forman,2Kai Rankenburg,2Noreen J. Evans,2Bradley J. McDonald,3Belinda Godel,1,4,5Gretchen K. Benedix
Meteoritics & Planetary Science (in Press) Open Access Link to Article []
1Space Science and Technology Centre, School of Earth and Planetary Science, Curtin University, GPO Box 1987, Perth, Western Australia, 6845 Australia
2School of Earth and Planetary Science/John de Laeter Centre, Curtin University, GPO Box 1987, Perth, Western Australia, 6845 Australia
3CSIRO Mineral Resources, ARRC, Kensington, Western Australia, Australia
4Department of Earth and Planetary Science, Western Australia Museum, Locked Bag 49, Welshpool, Western Australia, 6986 Australia
5Planetary Science Institute, 1700 E. Fort Lowell, Suite 106, Tucson, Arizona, 85719 USA
Published by arrangement with John Wiley & Sons

Martian meteorites are rare; therefore, the discovery of new meteorites has the potential to significantly expand our current understanding of Mars. In this study, we describe four new shergottites, all found within the past 5 yr, in Northwest Africa (NWA): NWA 10441, NWA 10818, NWA 11043, and NWA 12335. To determine the geochemical and mineralogical composition of these new shergottites, a number of traditional and nontraditional analytical techniques were utilized, such as high-resolution X-ray computed tomography (for 3-D modal abundance determination) and electron backscattered diffraction (for identification of shock features). This enabled a comprehensive, nondestructive investigation of the in situ and bulk characteristics of these meteorites. From the results, we confirm the preliminary classifications of NWA 10441 and NWA 12335 as basaltic (diabasic), and NWA 10818 and NWA 11043 as poikilitic, shergottites. Chondrite-normalized rare earth element (REE) patterns of shergottites distinguish likely source reservoirs in the Martian mantle. NWA 10441 and NWA 12335 have bulk enriched REE patterns. NWA 10818 has an intermediate REE pattern, being slightly depleted in the light REE. Although published data for bulk rock REE in NWA 11043 indicate an enriched pattern, here we show that targeted in situ analyses of unaltered minerals reveal an intermediate REE pattern, suggesting that terrestrial weathering combined with shock processes experienced by these meteorites on ejection may affect the bulk analysis. Extensive fracturing in NWA 11043 likely acted as conduits for terrestrial alteration products. We suggest that in situ spot checking of REE in meteorites will constrain any weathering effect on the REE pattern of the bulk rock.

Determination of olivine fayalite–forsterite composition in ordinary chondrites by X-ray diffraction

1V. E. Di Cecco,1,2B. C. Hyde,1K. T. Tait,1R. I. Nicklin
Meteoritics & Planetary Science (in Press) Link to Article []
1Department of Natural History – Mineralogy, Royal Ontario Museum, Toronto, Ontario, M5S 2C6 Canada
2Department of Geological Sciences and Geological Engineering, Queen’s University, Kingston, Ontario, K7L 2N8 Canada
Published by arrangement with John Wiley & Sons

Ordinary chondrites account for the majority of the described meteorites on Earth. To expand the toolbox of analytical techniques available to describe such specimens, this study evaluates the application of a previously described fayalite determination method by X-ray diffraction (XRD) to equilibrated ordinary chondrites. A suite of ordinary chondrites, ranging from petrologic type 4 to 6, and types H, L, and LL were analyzed by both XRD and electron probe microanalysis. A comparison of the results shows good agreement between the two methods with an R2 of 0.95 and better agreement for homogenous ordinary chondrites above petrographic grade 4. The differences between the two methods can largely be attributed to analytical uncertainty, as well as differences between point and bulk sampling techniques. These differences were used to identify two polymict breccia samples, Peace River and Northwest Africa 10946. Of note is the effect of exposure of the ordinary chondrites to room temperature and humidity conditions after sample preparation (powdering) and the impact on measured fayalite content by XRD. As such, it is recommended that XRD analyses of meteorites be performed immediately after sample preparation.

GRO 95577 (CR1) as a mineralogical analogue for asteroid (101955) Bennu

1Victoria E.Hamilton,2Hannah H.Kaplan,3,4Harold C.ConnollyJr,5Cyrena A.Goodrich,6Neyda M.Abreu,2Amy A.Simon
Icarus (in Press) Link to Article []
1Southwest Research Institute, Boulder, CO, United States of America
2NASA Goddard SpaceFlight Center, Greenbelt, MD, United States of America
3Rowan University, Glassboro, NJ, United States of America
4American Museum of Natural History, New York, NY, United States of America
5Lunar and Planetary Institute, USRA, Houston, TX, United States of America
6NASA Langley Research Center, Hampton, VA, United States of America
Copyright Elsevier

Orbital spectra collected of asteroid (101955) Bennu by NASA’s Origins, Spectral Interpretation, Resource Identification, Security–Regolith Explorer (OSIRIS–REx) spacecraft have identified ungrouped C, CI, and CM meteorites having petrologic types 1, 1/2, and 2 as the best mineralogical analogues to Bennu to date. Here we present spectral evidence that Grosvenor Mountains (GRO) 95,577, a CR1, is a better analogue for Bennu’s bulk surface mineralogy. CR-like parent bodies are targets of interest because they contain some of the most pristine materials from the solar nebula and can contain substantial amounts of H2O and OH− in addition to exotic organics. Unfortunately, terrestrial weathering makes constraining their indigenous mineralogy and organics challenging. Analysis of samples retrieved directly from an asteroid would help us disentangle the effects of terrestrial weathering and asteroidal aqueous alteration and hence whether some of the exotic organics and large populations of presolar grains were affected by terrestrial processes in meteorites. If Bennu is comprised of CR1(−like) material, in whole or in part, the OSIRIS–REx returned sample represents a tremendous opportunity to explore in depth what is currently a unique material among carbonaceous chondrites.

Reflectance spectra (1–5 μm) at low temperatures and different grain sizes of ammonium-bearing minerals relevant for icy bodies

Icarus (in Press) Link to Article []
1Department of Physics and Geology, University of Perugia, I-06123 Perugia, Italy
2Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
3Department of Chemistry, Biology and Biotechnology, University of Perugia, Via Elce di sotto 8, 06123 Perugia, Italy
Copyright Elsevier

It has been proposed that ammonium-bearing minerals are present in a varying amount in icy planetary bodies. Their observation at the surface of large objects was related to the upwelling and cryovolcanism of ammoniated water from possible subsurface oceans forming ammonium-bearing minerals (NH4+) mixed with ice at the surface. We analyzed the temperature evolution of the near-infrared spectra of a selected number of anhydrous and hydrated ammonium-bearing minerals containing different anions and water content. Reflectance spectra were collected in the 1–4.8 μm spectral range at cryogenic temperatures ranging from 293 K to ~65 K and the effect of sample’s grain size between 32 and 150 μm was also investigated at room temperature. Reflectance spectra of anhydrous samples show well-defined absorption bands in the 1–2.5 μm range. The bands located at ~1.06, 1.3, 1.56, 2.02, and 2.2 μm could be useful to discriminate these salts and their characteristics are examined in detail in this work. On the other hand, the reflectance spectra of water-rich samples show H2O fundamental absorption bands strongly overlapping the NH4+ bands, thus dominating the spectra from 1 to 2.8 μm and fully saturating above 2.8 μm. The position of the absorption bands changes with temperature and grain size, shifting to higher frequencies as temperature decreases. The low-temperature spectra also reveal a fine structure compared to the room temperature ones and display narrower and more defined absorption bands. Granulometry mainly affects the band depth and band area parameters. Moreover, mascagnite, salammoniac, ammonium phosphate, tschermigite, and ammonium nitrate are subjected to a reversible low-temperature phase transition, which is manifested in the spectra by a progressive growth and shift of the bands towards shorter wavelengths with an abrupt change in their depth. This new set of spectra at cryogenic temperatures can be directly compared with remote sensing data to detect the presence of ammonium-bearing minerals on the surface of icy bodies. Their identification can impact our knowledge of the internal composition and dynamics of these bodies as well as their potential habitability.

Arpu Kuilpu: An H5 from the outer main belt

1Patrick M. Shober et al. (>10)
Meteoritics & Plantetary Science (in Press) Open Access Link to Article []
1Space Science & Technology Centre, School of Earth and Planetary Sciences, Curtin University, Bentley, Western Australia, 6102 Australia
Published by arrangement with John Wiley & Sons

On June 1, 2019, just before 7:30 p.m. local time, the Desert Fireball Network (DFN) detected a −9.3 magnitude fireball over South Australia near the Western Australia border. The event was observed by six fireball observatories, and lasted for 5 s. One station was nearly directly underneath the trajectory, greatly constraining the trajectory solution. This trajectory’s backward numerical integrations indicate that the object originated from the outer main belt with a semimajor axis of 2.75 au. A light curve was also extracted and showed that the body experienced very little fragmentation during its atmospheric passage. A search campaign was conducted with several DFN team members and other volunteers. One 42 g fragment was recovered within the predicted fall area based on the dark flight model. Based on measurements of short-lived radionuclides, the fragment was confirmed to be a fresh fall. The meteorite, Arpu Kuilpu, has been classified as an H5 ordinary chondrite. This marks the fifth fall recovered in Australia by the DFN, and the smallest meteoroid (≃2 kg) to ever survive entry and be recovered as a meteorite.