¹Rappenglück M.A.
Minerals 12, 188 Open Access Link to Article [DOI 10.3390/min12020188]
¹Adult College and Observatory Gilching, Gilching, 82205, Germany

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

¹Cox M.A.,¹Cavosie A.J.,¹Orr K.J.,²Daly L.,³Martin L.,¹Lagain A.,^1,4Benedix G.K.,¹Bland P.A.
Science Advances 8, eabl7497 Open Access Link to Article [DOI 10.1126/sciadv.abl7497]
¹Space Science and Technology Centre (SSTC), School of Earth and Planetary Science, Curtin University, Perth, 6102, WA, Australia
²School of Geographical and Earth Sciences, University of Glasgow, Glasgow, G12 8QQ, United Kingdom
³Centre for Microscopy, Characterisation and Analysis (CMCA), The University of Western Australia, 6 Verdun Street, Perth, 6009, WA, Australia
⁴Department of Earth and Planetary Sciences, Western Australia Museum, WA, Australia

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

¹Nicolas Schnuriger,¹Camille Cartier,¹Johan Villeneuve,²Valentina Batanova,¹Maxence Regnault,¹Yves Marrocchi
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13802]
¹Université de Lorraine, CRPG, CNRS, UMR 7358, Vandœuvre-lès-Nancy, 54501 France
²Université Grenoble Alpes, ISTerre, CNRS, UMR 5275, Grenoble, 38000 France
Published by arrangement with John Wiley & Sons

In carbonaceous chondrites, Mg-spinel (MgAl2O4) grains are ubiquitous in refractory inclusions but rarely reported in chondrules, where they may correspond to minerals either (i) inherited from chondrule precursors or (ii) crystallized from chondrule melts. Here, we report high-current quantitative electron microprobe measurements and secondary ion mass spectrometry oxygen isotopic analyses of Mg-spinel-bearing chondrules in the CV3 carbonaceous chondrites Northwest Africa 10235 and Allende. Compared to spinels in refractory inclusions, chondrule spinels are characterized by higher Cr contents and 16O-poorer oxygen isotopic signatures (∆17O ≡ δ17O−0.52 × δ18O, from −2 to −6‰). Because the similar Δ17O values of chondrule olivine and spinel crystals imply their comagmatic origin, we applied a geothermometer based on the Al-Cr distribution between these minerals to determine their crystallization temperatures. The calculated temperatures range from 1200 to 1640 °C (mean = 1470 °C), most being lower than the estimated liquidus temperature of porphyritic chondrules (~1600 °C). Our results suggest that chondrules experienced relatively slow cooling rates (slower than a few hundreds of °C h−1), which is in good agreement with models of chondrule formation invoking nonlinear or two-stage cooling rates.

¹J.Eschrig,¹L.Bonal,²M.Mahlke,²B.Carry,¹P.Beck,³J.Gattacceca
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115012]
¹Institut de Planétologie et d’Astrophysique de Grenoble, Université Grenoble Alpes, CNRS CNES, 38000 Grenoble, France
²Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, France
³CNRS, Aix Marseille Univ, IRD, Coll France, CEREGE, Aix-en-Provence, France
Copyright Elsevier

The search for asteroidal parent bodies of chondrites through various techniques is an ongoing endeavor. A link between ordinary chondrites (OCs) and S-type asteroids has previously been established by the sample return of the Hayabusa space mission. OCs are the class with the most abundant samples in our meteorite collection. We present an in-depth study of the reflectance spectra of 39 equilibrated and 41 unequilibrated ordinary chondrites (EOCs and UOCs). We demonstrate that consistent measuring conditions are vital for the direct comparison of spectral features between chondrites, otherwise hampering any conclusions. We include a comparison with a total of 466 S-type asteroid reflectance spectra from various databases. We analyze (i) if a difference between EOCs and UOCs as well as between H, L and LL can be seen, (ii) if it is possible to identify unequilibrated and equilibrated S-type asteroid surfaces and (iii) if we can further constrain the match between OCs and S-type asteroids all based on reflectance spectra.

As a first step, we checked the classification of the 31 Antarctic UOCs analyzed in the present work, using petrography and magnetic measurements, and evidenced that 74% of them were misclassified. Reflectance spectra were compared between EOCs and UOCs as well as between H, L and LL chondrites using a set of spectral features including band depths and positions, peak reflectance values, spectral slopes and the Ol/(Ol + Px) ratio. UOCs and EOCs reflectance spectra show no clear-cut dichotomy, but a continuum with some EOCs showing stronger absorption bands and peak reflectance values, while others are comparable to UOCs. Moreover, we show by the example of 6 EOCs that their band depths decrease with decreasing grain size. Based on reflectance spectra alone, it is thus highly challenging to objectively identify an unequilibrated from an equilibrated S-type surface. There is no clear distinction of the chemical groups: only LL EOCs of petrographic type >4 can be distinguished from H and L through less deep 2000 nm band depths and 1000 nm band positions at longer wavelengths. No dichotomy of S-type asteroids can be seen based on the Ol/(Ol + Px) ratio. Their average Ol/(Ol + Px) ratio matches EOCs better than UOCs. A principal component analysis (PCA) was performed illustrating that both the unknown degree of space weathering and the unknown regolith grain size on asteroid surfaces hinder the distinction between equilibrated and unequilibrated surfaces. Lastly, an anti-correlation between the diameter of the asteroids and their 1000 nm band depth is found indicating that larger sized S-type asteroids show finer grained surfaces.

¹Bernard Marty
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.115020]
¹Université de Lorraine, CNRS, CRPG, F-54000 Nancy, France
Copyright Elsevier

The elemental and isotopic compositions of noble gases trapped in primitive meteorites have the potential to yield stringent constraints on the origin of matter in the solar system. The isotopic compositions of key elements like O, Ti, Ru, Mo suggest that the Earth accreted from material having similarities with two classes of meteorites, carbonaceous chondrites (CC) and non‑carbonaceous chondrites (NC), in particular enstatite chondrites (EC). In this contribution, I examine published noble gas (neon and argon) data for CI-CM as representative of CCs, and ECs as representative of NC terrestrial building blocks. Data were corrected for contributions of cosmic ray-produced isotopes in order to identify the trapped component compositions. For both CCs and ECs, corrected noble gas data indicate that high temperature objects such as chondrules were evolving in a dusty environment. The dust consisted of refractory phases including nanodiamonds, impacts-related debris, medium to low temperature phases mainly made of organics and, in the case of CC, hydrated minerals and icy grains. Remnants of such a dust are found as rims around chondrules and as a matrix between high temperature assemblages. The dust was probably the main source of volatiles on Earth.

In terrestrial reservoirs, covariations of 20Ne/22Ne ratios with 36Ar/22Ne ratios are consistent with mixing between a solar-like neon component trapped in the mantle and a chondritic Ne–Ar component mainly present in the atmosphere and hydrosphere. The chondritic end-member is clearly of the CC type and excludes EC-like material as the source of atmospheric volatiles. In addition to CC-like material, the isotopic composition of heavy noble gases (Kr and Xe) in the atmosphere points to a ~ 20% contribution of cometary material akin of the composition of comet 67P/Churyumov-Gerasimenko. In contrast, comets might have contributed less than 1% terrestrial water, C and N. Solar-like neon in the terrestrial mantle might have originated from solar irradiation of free-floating dust before parent body compaction, but this would require a cleared, dust-free environment. Trapping of nebular gas into forming solids during the gas epoch of the nascent solar system appears a more promising possibility. For other mantle volatiles, the stable isotopes of H, N, Ar, Kr and Xe point to a chondritic origin. The hydrogen and nitrogen isotopic signatures of mantle rocks and minerals are consistent with an EC-like contribution whereas those of heavy noble gases are still too imprecise to conclude. Further progress in the field will require high precision analysis of noble gases (in particular, Kr and Xe) trapped in the terrestrial (and martian) mantle(s), as well as documenting the composition of the Venusian atmosphere.

¹Chi Ma,²Oliver Tschauner,³Mihye Kong,¹John R. Beckett,⁴Eran Greenberg,⁴Vitali B. Prakapenka,³Yongjae Lee
American Mineralogist 107, 625-630 Link to Article [http://www.minsocam.org/msa/ammin/toc/2022/Abstracts/AM107P0625.pdf]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A.
²Department of Geoscience, University of Nevada, Las Vegas, Nevada 89154, U.S.A.
³Department of Earth System Sciences, Yonsei University, Seoul 03722, Republic of Korea
⁴GSECARS, University of Chicago, Argonne National Laboratory, Chicago, Illinois 60637, U.S.A
Copyright: The mineralogical Society of America
Clinopyroxenes with excess Si have been described in run products from high-pressure experi –
ments and inferred to have existed in nature from retrograde transformation phases. Here, we present
the discovery of albitic jadeite, (Na,Ca,1/4)(Al,Si)Si2O6—the first natural, sodic clinopyroxene with
excess Si occupying the octahedral cation site, M1, and a corresponding ¼ vacancy on the M2-site
in the Ries impact structure and in a suite of L6 ordinary chondrites, EET 13014, EET 13052, NWA
1662, and TIL 08001. Garnet compositions in these samples indicate shock pressures of 18–22 GPa.
Based on our survey, albitic jadeite is likely to be rather common in terrestrial and meteoritic shock-
metamorphic environments. Shock-generated jadeite should be reexamined with respect to excess