¹Damanveer S.Grew,¹Rajdeep Dasgupta,¹Sanath Aithala
Earth and Planetary Science Letters 571, 117090 Link to Article [https://doi.org/10.1016/j.epsl.2021.117090]
¹Department of Earth, Environmental, and Planetary Sciences, Rice University, 6100 Main Street, MS 126, Houston, TX 77005, USA
Copyright Elsevier

Partitioning of carbon (C) into the cores of rocky protoplanets and planets is one of the primary causes of its depletion in their bulk silicate reservoirs. Most of the experimental studies that determined the alloy to silicate melt partition coefficient of carbon () have been conducted in graphite-saturated conditions. Because carbon is a minor element in all known protoplanetary and planetary cores, it is not known whether graphite-saturated values are applicable to core-mantle differentiation in rocky bodies which likely occurred in C-poor conditions. In this study we experimentally determined in MgO capsules with variable bulk C contents between oxygen fugacity (fO2) of IW–6.35 and IW–2.59 at a fixed P (3 GPa)-T (1700 °C). A mafic-ultramafic (NBO/T = 1.23-1.72) and mildly hydrous (bulk H = 44-161 ppm) nature of the silicate melts caused anhydrous C species ( + CO) to dominate over a wider fO2 range (>IW–4.2) in comparison to previous studies. This resulted in an increase in with decreasing fO2 from IW–2.6 to IW–4.2 followed by a drop at more reduced conditions due to the formation of C-H species. Importantly, increases with increasing bulk C content of the system at a given fO2. Partitioning of C between alloy and silicate melts follows non-Henrian behavior (i.e., it depends on bulk C content) because the activity coefficient of C in the alloy melt () varies with C content in the alloy. Therefore, in addition to other intensive (P, T, fO2) and extensive variables (alloy and silicate melt compositions), also depends on the bulk C content available during core-mantle differentiation. Consequently, previously determined for C-rich alloys are not directly applicable for core-mantle differentiation in relatively C-poor magma oceans (MOs). Because the experiments from the present study more realistically simulate C-poor cores and mildly hydrous, mafic-ultramafic silicate MOs, our data can be used to more accurately predict C fractionation between MOs and cores in inner Solar System rocky bodies. Our study suggests that closed system MO-core equilibration should have led to less severe depletion of C in the silicate reservoirs of inner Solar System rocky bodies than previously predicted.

¹Jennifer T.Mitchell,¹Andrew G.Tomkins,²Christopher Newton,³Tim E.Johnson
Earth and Planetary Science Letters (in Press) Link to Article [https://doi.org/10.1016/j.epsl.2021.117105]
¹School of Earth, Atmosphere & Environment, Monash University, Melbourne, Australia
²School of Physics & Astronomy, Monash University, Melbourne, Australia
³School of Earth & Planetary Sciences, The Institute for Geoscience Research, Curtin University, Perth, Australia
Copyright Elsevier

Combined phase equilibrium and thermal modelling has been used to investigate the evolution of asteroid 4 Vesta. Orthopyroxene compositions of 200 natural diogenite meteorites are used as a basis for constructing a staged mantle melting model for Vesta, which is then used to develop a staged thermal evolution model. Our pMELTS models find that removal of 15–20% of a mean eucrite component from an initial Vestan mantle composition allows a second stage of melting that crystallises low-calcium orthopyroxenes that match the observed compositions of those in natural diogenites, whereas single stage melting produces orthopyroxenes that are too calcic. Using the compositions generated by the pMELTS modelling, THERMOCALC models were created for an initial Vestan mantle composition and an evolved composition generated by a melt extraction stage. These models suggest that melt production for second-stage diogenite generation required considerably hotter temperatures (>1340 °C) than for eucrites (<1240 °C). Staged and layered thermal evolution models developed using these composition and temperature constraints, based on the decay of 26Al and 60Fe, suggest that Vesta accreted 1.50 to 1.75 Myr after calcium-aluminium inclusion (CAI) formation. Earlier accretion results in conditions that are inconsistent with the petrology of the HED meteorites, whereas later accretion predicts temperatures that are insufficient to produce diogenites. We suggest that upward migration of 26Al-rich melt initially created a convecting shallow magma ocean of <20 km depth that rapidly crystallised to form a 26Al-rich eucritic crust that acted as a hot insulating lid. The second stage of crust formation began once the depleted mantle residue reached high enough temperatures to produce diogenite-forming magmas. These results further support the view that diogenites likely formed as crustal intrusions rather than as magma ocean cumulates.

^1,2Brant M.Jones,¹Aleksandr Aleksandrov,³Charles A.Hibbitts,^1,2,4Thomas M.Orlando
Earth and Planetary Science Letters (in Press) Link to Article [https://doi.org/10.1016/j.epsl.2021.117107]
¹School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA, United States of America
²Center for Space Technology and Research, Georgia Institute of Technology, Atlanta, GA, United States of America
³John Hopkins Applied Physics Laboratory, Laurel, MD, United States of America
⁴School of Physics, Georgia Institute of Technology, Atlanta, GA, United States of America
Copyright Elsevier

The evolution of water and molecular hydrogen from Apollo lunar sample 15221, a mature mare soil, was examined by temperature program desorption (TPD) experiments conducted under ultra-high vacuum conditions. Desorption at the grain/vacuum interface with re-adsorption as water transports though the void space of the grains and activated sub-surface diffusion were found to reproduce the experimental TPD signal. Signal from the grain/vacuum interface yielded the second order desorption activation energies and site probability distributions. Water from sample 15221 exhibited a broad distribution of activation energies peaking at 130 kJ mol−1 extending up to 350 kJ mol−1 at zero coverage limit with an onset of 110 kJ mol−1 at full coverage. Our results suggest that water and hydrogen originating from lunar regolith contributes a minor amount to the observed mass in the LCROSS impact event. The abnormal amount of molecular hydrogen observed in the ejecta plume of the LCROSS impact may indicate that the radiolytic production of H2 from electron and galatic cosmic rays of physisorbed water is a contributor to the vast quantity of molecular hydrogen detected.

¹Sergey N. Britvin,¹Maria G. Krzhizhanovskaya, ¹Andrey A. Zolotarev, ¹Liudmila A. Gorelova,³Edita V. Obolonskaya,⁴Natalia S. Vlasenko,^4,5Vladimir V. Shilovskikh,¹Mikhail N. Murashko
The American Mineralogist 106, 1520–1529 Link to Article [http://www.minsocam.org/msa/ammin/toc/2021/Abstracts/AM106P1520.pdf]
¹Institute of Earth Sciences, St. Petersburg State University, Universitetskaya Nab. 7/9, 199034 St. Petersburg, Russia
²Kola Science Center, Russian Academy of Sciences, Fersman Str. 14, 184209 Apatity, Russia
³The Mining Museum, Saint Petersburg Mining University, 2, 21st Line 199106 St. Petersburg, Russia
⁴Centre for Geo-Environmental Research and Modelling, St. Petersburg State University, Ulyanovskaya ul. 1, 198504 St. Petersburg, Russia
⁵Institute of Mineralogy, Urals Branch of Russian Academy of Science, Miass 456317, Russia
Copyright: The Mineralogical Society of America

Schreibersite, (Fe,Ni)3P, the most abundant cosmic phosphide, is a principal carrier of phosphorus in the natural Fe-Ni-P system and a likely precursor for prebiotic organophosphorus compounds at the early stages of Earth’s evolution. The crystal structure of the mineral contains three metal sites allowing for unrestricted substitution of Fe for Ni. The distribution of these elements across the structure could serve as a tracer of crystallization conditions of schreibersite and its parent celestial bodies. However, discrimination between Fe (Z = 26) and Ni (Z = 28) based on the conventional X-ray structural analysis was for a long time hampered due to the proximity of their atomic scattering factors. We herein show that this problem has been overcome with the implementation of area detectors in the practice of X-ray diffraction. We report on previously unknown site-specific substitution trends in schreibersite structure. The composition of the studied mineral encompasses a Ni content ranging between 0.03 and 1.54 Ni atoms per formula unit (apfu): the entire Fe-dominant side of the join Fe3P-Ni3P. Of 23 schreibersite crystals studied, 22 comprise magmatic and non-magmatic iron meteorites and main group pallasites. The near end-member mineral (0.03 Ni apfu) comes from the pyrometamorphic rocks of the Hatrurim Basin, Negev desert, Israel. It was found that Fe/Ni substitution in schreibersite follows the same trends in all studied meteorites. The dependencies are nonlinear and can be described by second-order polynomials. However, the substitution over the M2 and M3 sites within the most common range of compositions (0.6 < Ni <1.5 apfu) is well approximated by a linear regression: Ni(M2) = 0.84 × Ni(M3) – 0.30 apfu (standard error 0.04 Ni apfu). The analysis of the obtained results shows a strong divergence between the variation of unit-cell parameters of natural schreibersite and those of synthetic (Fe,Ni)3P. This indicates that Fe/Ni substitution trends in the mineral and its synthetic surrogates are different. A plausible explanation might be related to the differences in the system equilibration time of meteoritic schreibersite (millions of years) and synthetic (Fe,Ni)3P (~100 days). However, regardless of the reason for the observed difference, synthetic (Fe,Ni)3P cannot be considered a structural analog of natural schreibersite, and this has to be taken into account when using synthetic (Fe,Ni)3P as an imitator of schreibersite in reconstructions of natural processes

^1,2Naoya Imae,¹Makoto Kimura
American Mineralogist 106, 1470–1479 Link to Article [http://www.minsocam.org/msa/ammin/toc/2021/Abstracts/AM106P1470.pdf]
¹National Institute of Polar Research, 10-3 Midori-cho, Tachikawa-shi, Tokyo 190-8518, Japan 2
²SOKENDAI, 10-3 Midori-cho, Tachikawa-shi, Tokyo 190-8518, Japan
Copyright: The Mineralogical Society of America

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Robert M. Hazen,¹Shaunna M. Morrison
American Mineralogist 106, 1388–1419 Link to Article [http://www.minsocam.org/msa/ammin/toc/2021/Abstracts/AM106P1388.pdf]
¹Earth and Planets Laboratory, Carnegie Institution for Science, 5251 Broad Branch Road NW, Washington, D.C. 20015, U.S.A
Copyright: The Mineralogical Society of America

Part V of the evolutionary system of mineralogy explores phases produced by aqueous alteration,
metasomatism, and/or thermal metamorphism—relicts of ancient processes that affected virtually all
asteroids and that are preserved in the secondary mineralogy of meteorites. We catalog 166 historical
natural kinds of minerals that formed by alteration in the parent bodies of chondritic and non-chondritic
meteorites within the first 20 Ma of the solar system. Secondary processes saw a dramatic increase in
the chemical and structural diversity of minerals. These phases incorporate 41 different mineral-forming
elements, including the earliest known appearances of species with essential Co, Ge, As, Nb, Ag, Sn, Te,
Au, Hg, Pb, and Bi. Among the varied secondary meteorite minerals are the earliest known examples
of halides, arsenides, tellurides, sulfates, carbonates, hydroxides, and a wide range of phyllosilicates.
Keywords: Philosophy of mineralogy, classification, mineral evolution, natural kinds, meteorite

¹M.Matsuoka,²T.Nakamura,³N.Miyajima,⁴T.Hiroi,⁵N.Imae,⁵A.Yamaguchi
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.08.042]
¹ISAS/JAXA, Sagamihara, Kanagawa 252-5210, Japan
²Tohoku University, Sendai, Miyagi 980-8578, Japan
³Bayerisches Geoinstitut, University of Bayreuth, Bayreuth 95440, Germany
⁴Brown University, Providence, RI 02912, USA
⁵Research National Institute of Polar Research, Tachikawa, Tokyo 190-8518, Japan
Copyight Elsevier

Spectral and mineralogical analyses were performed using nine naturally hydrated and dehydrated carbonaceous chondrite samples which were classified into heating stages (HS) from I to IV based on previous X-ray diffraction results. In-situ heating of samples at 120–400 °C was performed during spectral measurements and successfully removed absorbed water and part of rehydrated water from chondrite samples. Reflectance spectra of HS-I samples show the positive slope in visible (Vis)-infrared (IR) range and the significant 0.7- and 3-μm absorption bands. The 0.7-μm band appears in only HS-I sample spectra. With increasing temperature of heating, (1) Vis-IR slope decreases, (2) the 3-μm band becomes shallower, and (3) Christiansen feature (CF) and Reststrahlen bands (RB) shift toward longer wavelength. TEM-EDX analyses showed that the matrix of strongly-heated chondrites consists of tiny olivine, low-Ca pyroxene, and FeNi metallic particles mostly smaller than 100 nm in diameter, instead of Fe-rich serpentines and tochilinite observed in the HS-I chondrite. Therefore, in proportion to the heating degree, amorphization and dehydration of serpentine and tochilinite from HS-I to HS-II may cause the 0.7- and 3-μm band weakening, spectral bluing and darkening of chondrite spectra. In addition, formation of secondary anhydrous silicates and FeNi-rich metal grains at HS-IV would be responsible for the 3-μm band depth decrease, spectral reddening and brightening, CF peak shift, and RB changes of chondrite spectra. Those spectral changes in response to mineralogical alteration processes will be useful to interpret planetary surface composition by remote-sensing observations using ground-based or airborne/space telescopes or spacecraft missions.

^1,2Denis Fougerouse,^1,3Aaron J.Cavosie,^1,4Timmons Erickson,^1,2Steven M.Reddy,^1,3Morgan A.Cox,²David Saxey,²William Rickard,⁵Michael T.D.Wingate
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.08.025]
¹School of Earth and Planetary Sciences, Curtin University, Perth, Australia
²Geoscience Atom Probe Facility, John de Laeter Centre, Curtin University, Perth, Australia
³Space Science and Technology Centre, Curtin University, Perth, Australia
⁴Jacobs – JETS, Astromaterials Research and Exploration Science division, NASA Johnson Space Center, Houston, USA
⁵Geological Survey of Western Australia, Department of Mines, Industry Regulation and Safety, Perth, Australia
Copyright Elsevier

To test the potential of deformation twins to record the age of impact events, micrometre-scale size mechanical twins in shocked monazite grains from three impact structures were analyzed by atom probe tomography (APT). Shocked monazite from Vredefort (South Africa; ∼300 km crater diameter), Araguainha (Brazil; ∼40 km diameter), and Woodleigh (Australia; 60 to 120 km diameter) were studied, all from rocks which experienced pressures of ∼30 GPa or higher, but each with a different post-impact thermal history. The Vredefort sample is a thermally recrystallised foliated felsic gneiss and the Araguainha sample is an impact melt-bearing bedrock. Both Vredefort and Araguainha samples record temperatures > 900 °C, whereas the Woodleigh sample is a paragneiss that experienced lower temperature conditions (350 – 500 °C). A combined 208Pb/232Th age for common {1} twins and shock-specific (01) twins in Vredefort monazite was defined at 1979 ± 150 Ma, consistent with the accepted impact age of ∼2020 Ma. Irrational η1 [0] shock-specific twins in Araguainha monazite yielded a 260 ± 48 Ma age, also consistent with the accepted 250-260 Ma impact age. However, the age of a common (001) twin in Araguainha monazite is 510 ± 87 Ma, the pre-impact age of igneous crystallisation. These results are explained by the occurrence of common (001) twins in tectonic deformation settings, in contrast to the (01) and irrational η1 [0] twins, which have only been documented in shock-deformed rocks. In Woodleigh monazite, APT age data for all monazite twins [(001), (01), newly identified 102°/<23> twin], and host monazite are within uncertainty at 1048 ± 91 Ma, which is interpreted as a pre-impact age of regional metamorphism. We therefore are able to further constrain the poorly known age of the Woodleigh impact to < 1048 ± 91 Ma. These results provide evidence that Pb is expelled from monazite during shock twin formation at high temperature (Vredefort and Araguainha), and also that Pb is not mobilised during twinning at lower temperature (Woodleigh). Our study suggests that twins formed during shock metamorphism have the potential to record the age of the impact event in target rocks that are sufficiently heated during the cratering process.

¹Masashi Shidare,^bRyoichi Nakada,^3,4Tomohiro Usui,¹Minato Tobita,²Kenji Shimizu,⁵Yoshio Takahashi,¹Tetsuya Yokoyama
Geochimica et Cosmochinica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.08.026]
¹Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Tokyo 152-8551, Japan
²Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 200 Monobe, Nankoku, Kochi 783-8501, Japan
³Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Tokyo 152-8551, Japan
⁴Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA), 3-1-1 Yoshinodai, Sagamihara, Kanagawa 252-5210, Japan
⁵Department of Earth and Planetary Science, the University of Tokyo, 7-3-1 Hongo, Tokyo 113-8654, Japan
Copyright Elsevier

The surface of Mars has experienced progressive oxidation, resulting in the formation of sulfate minerals as evidenced from surface exploration missions. However, no clear evidence for the presence of sulfate minerals has been reported within Martian meteorites. This study examined sulfur speciation in impact glasses of three basaltic shergottites, Elephant Moraine (EETA) 79001, Larkman Nunatak (LAR) 06319, and Dhofar 019, using X-ray absorption near-edge structure (XANES) spectroscopy. The measured XANES spectra were classified into four types: (1) sulfide, (2) highly reduced sulfide glass (∼IW+1), (3) mixture of sulfide and sulfate, and (4) sulfate. The sulfate spectra observed from EETA79001 and LAR 06319 were mixed with sulfide from the reduced igneous host rock as impact glasses were formed by shock on the surface of Mars, both sulfide and sulfate would have possibly originated on Mars. Besides, highly reduced sulfide present in the same impact glasses is inconsistent with secondary alteration on the oxic Earth’s environment. In contrast to EETA79001 and LAR 06319, all of the XANES spectra from Dhofar 019 showed the only sulfate, whose origin is most likely from terrestrial alteration. Combining with the geochemical signatures of volatile elements (e.g., D/H, C, and halogens) in impact glasses of EETA79001 and LAR 06319, we propose two possible scenarios for the formation of sulfate species to the shergottite host-rocks: (i) oxidation of sulfide minerals by subsurface oxic water in Mars, or (ii) precipitation of sulfate mineral derived from Martian subsurface water. The difference between the two models is the source of S(VI) species, whether it originated from (i) magmatic sulfide in shergottite or (ii) sulfate ion in the subsurface water/ice. Both models indicate that the ancient (∼4 Ga) water reservoir might have already been oxic, and it requires post-magmatic water–rock interaction that formed sulfate minerals whose oxidized signatures were incorporated into impact glass.

¹A. J. King,^1,2E. Mason,^1,3H. C. Bates,¹P. F. Schofield,^3,4K. L. Donaldson Hanna,³N. E. Bowles,¹S. S. Russell
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13734]
¹Planetary Materials Group, Department of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD UK
²Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London, SW7 2AZ UK
³Planetary Spectroscopy Facility, Atmospheric, Oceanic and Planetary Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford, OX1 3PU UK
⁴Department of Physics, University of Central Florida, Orlando, Florida, 32816–2385 USA
Published by arrangement with John Wiley & Sons

The CM carbonaceous chondrites are an important resource in our efforts to understand the role of volatiles in the formation of planetary systems. We report the bulk mineralogy, water abundance, and infrared (IR) reflectance spectra of the CM chondrites LaPaz Icefield (LAP) 04514, LAP 04796, LAP 04565, and LAP 02333. They contain abundant Fe- and Mg-rich serpentines (˜70–80 vol%), and based on their phyllosilicate fractions, we classify LAP 04514, LAP 04796, and LAP 04565 as petrologic subtype 1.6 and LAP 02333 as 1.4. This is consistent with estimated water abundances of 9.9 (±1.1) wt% for LAP 04796, 10.4 (±0.1) wt% for LAP 04565, and 11.5 (±0.5) wt% for LAP 02333. However, LAP 04514 contains less water (8.8 ± 0.3 wt%), has a shallower 3 µm band depth, and lacks tochilinite having experienced posthydration temperatures of ˜300–400 °C. We conclude that LAP 04514, LAP 04796, and LAP 04565 are among the least altered CM chondrites, which retain primitive features from the initial building blocks of the CM parent body. Finally, we use the IR spectral features of LAP 04514, LAP 04796, and LAP 04565 to identify C-complex asteroid surfaces that record mild levels of hydration.