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NWA 11562: A Unique Ureilite with Extreme Mg-rich Constituents

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1,2Mingbao Li,3,4Ke Zhu,1,5Yan Fan,6P. M. Ranjith,7Chao Wang,1Wen Yu, 1,8,9Shijie Li
The Planetary Science Journal 5, 178 Open Access Link to Article [DOI 10.3847/PSJ/ad6154]
1Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 55021, People’s Republic of China
2State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau 999078, People’s Republic of China
3Freie Universität Berlin, Institut für Geologische Wissenschaften, Malteserstr. 74-100, Berlin 12249, Germany
4Bristol Isotope Group, School of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, Bristol BS8 1RJ, UK
5State Key Laboratory of Continental Dynamics and Department of Geology, Northwest University, Xi’an 710069, People’s Republic of China
6Graduate School of Advanced Science and Technology, Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa, 923-1292, Japan
7School of Earth and Space Sciences, Peking University, Beijing 100871, People’s Republic of China
8CAS Center for Excellence in Comparative Planetology, Hefei, 230022, People’s Republic of China

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Fe, Zn, and Mg stable isotope systematics of acapulcoite lodranite clan meteorites

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1,2Stepan M. Chernonozhkin,3Lidia Pittarello,4Genevieve Hublet,5Philippe Claeys,4Vinciane Debaille,1Frank Vanhaecke,5Steven Goderis
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14258]
1Atomic & Mass Spectrometry—A&MS Research Unit, Department of Chemistry, Ghent University, Ghent, Belgium
2Isotope Ratio Analysis Research Group, Chair of General and Analytical Chemistry, Montanuniversität Leoben, Leoben, Austria
3Naturhistorisches Museum Wien – NHMW, Vienna, Austria
4Laboratoire G-Time, Université Libre de Bruxelles, Brussels, Belgium
5Archaeology, Environmental Changes, and Geo-Chemistry (AMGC), Vrije Universiteit Brussel, Brussels, Belgium
Published by arrangement with John Wiley & Sons

The processes of planetary accretion and differentiation, whereby an unsorted mass of primitive solar system material evolves into a body composed of a silicate mantle and metallic core, remain poorly understood. Mass-dependent variations of the isotope ratios of non-traditional stable isotope systems in meteorites are known to record events in the nebula and planetary evolution processes. Partial melting and melt separation, evaporation and condensation, diffusion, and thermal equilibration between minerals at the parent body (PB) scale can be recorded in the isotopic signatures of meteorites. In this context, the acapulcoite–lodranite meteorite clan (ALC), which represents the products of thermal metamorphism and low-degree partial melting of a primitive asteroid, is an attractive target to study the processes of early planetary differentiation. Here, we present a comprehensive data set of mass-dependent Fe, Zn, and Mg isotope ratio variations in bulk ALC species, their separated silicate and metal phases, and in handpicked mineral fractions. These non-traditional stable isotope ratios are governed by mass-dependent isotope fractionation and provide a state-of-the-art perspective on the evolution of the ALC PB, which is complementary to interpretations based on the petrology, trace element composition, and isotope geochemistry of the ALC. None of the isotopic signatures of ALC species show convincing co-variation with the oxygen isotope ratios, which are considered to record nebular processes occurring prior to the PB formation. Iron isotopic compositions of ALC metal and silicate phases broadly fall on the isotherms within the temperature ranges predicted by pyroxene thermometry. The isotope ratios of Mg in ALC meteorites and their silicate minerals are within the range of chondritic meteorites, with only accessory spinel group minerals having significantly different compositions. Overall, the Mg and Fe isotopic signatures of the ALC species analyzed are in line with their formation as products of high-degree thermal metamorphism and low-degree partial melting of primitive precursors. The δ66/64Zn values of the ALC meteorites demonstrate a range of ~3.5‰ and the Zn is overall isotopically heavier than in chondrites. The superchondritic Zn isotopic signatures have possibly resulted from evaporative Zn losses, as observed for other meteorite parent bodies. This is unlikely to be the result of PB differentiation processes, as the Zn isotope ratio data show no covariation with the proxies of partial melting, such as the mass fractions of the platinum group and rare earth elements.

Sound velocities in lunar mantle aggregates at simultaneous high pressures and temperatures: Implications for the presence of garnet in the deep lunar interior

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Marisa C. Wood1, Steeve Gréaux1, Yoshio Kono1, Sho Kakizaw1,2, Yuta Ishikawa1, Sayako Inoué1, Hideharu Kuwahara1, Yuji Higo2, Noriyoshi Tsujino2, Tetsuo Irifune1
Earth and Planetary Science Letters 641, 118792
Link to Article [https://doi.org/10.1016/j.epsl.2024.118792]
1Geodynamics Research Center, Ehime University, Matsuyama, Japan
2Japan Synchrotron Radiation Research Institute, SPring-8, Hyogo, Japan
Copyright Elsevier

Recent experimental and theoretical studies on lunar magma ocean crystallisation have suggested the presence of significant proportions of garnet in the deep lunar interior. While phase relation studies indicate a deep lunar mantle consisting of olivine, pyroxene, and garnet, the compatibility of such an assemblage with seismic models of the lunar interior is yet untested. In this study we report compressional and shear wave velocities in an iron-rich assemblage consisting of olivine, orthopyroxene, clinopyroxene, and garnet up to ∼8 GPa and 1300 K, by means of ultrasonic interferometry measurements combined with synchrotron techniques using the multi-anvil press apparatus. Sound velocity and density models of lunar mantle rocks along a selenotherm based on our experimental results find good agreement with the seismic and density profiles at lunar interior depths of 740–1260 km. Further models are constructed, allowing for the variation of chemical composition, phase proportion, and temperature; these suggest that a garnet-rich deep lunar mantle is compatible with present-day lower lunar mantle temperatures of between 1400–1800 K. Our results show that lunar mantle rocks with up to 33 wt.% garnet may provide an explanation for the observed high velocities of the lower lunar mantle. The presence of garnet in the lowermost part of the Moon’s mantle has significant implications for the depth and temperature of the Moon’s magma ocean as well as the composition, structure and internal dynamics of the solid Moon.

Accretion of warm chondrules in weakly metamorphosed ordinary chondrites and their subsequent reprocessing

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aAlex M. Ruzicka, aRichard C. Hugo, b,cJon M. Friedrich, aMichael T. Ream
Geochimica et Cosmochimica Acta (in Press)
Link to Article [https://doi.org/10.1016/j.gca.2024.05.031]
aCascadia Meteorite Laboratory, Department of Geology, Portland State University, 1721 SW Broadway, Portland, OR 97207, USA
bDepartment of Chemistry, Fordham University, Bronx, NY 10458, USA
cDepartment of Earth and Planetary Science, American Museum of Natural History, New York, NY 10024, USA
Copyright Elsevier

To better understand chondrite accretion and subsequent processes, the textures, crystallography, deformation, and compositions of some chondrite constituents in ten lithologies of different cluster texture strength were studied in seven weakly metamorphosed (Type 3) and variably shocked ordinary chondrites (Ragland—LL3 S1, Tieschitz—H/L3 S1, NWA 5421—LL3 S2, NWA 5205—LL3 S2, NWA 11905—LL3-5 S3, NWA 5781—LL3 S3, NWA 11351—LL3-6 S4) using optical and electron microscopy and microtomography techniques.

Results support a four-stage model for chondrite formation. This includes 1) limited annealing following collisions during chondrule crystallization and rapid cooling in space prior to accretion, as evidenced by olivine microstructures consistent with dislocation recovery and diffusion; 2) initial accretion of still-warm chondrules into aggregates at an effective chondrite accretion temperature of ∼900-950 °C with nearly in situ impingement deformation between adjacent chondrules in strongly clustered lithologies (NWA 5781, Tieschitz, NWA 5421, NWA 5205 Lithology A), as evidenced by intragranular lattice distortions in olivine consistent with high-temperature slip systems, and by evidence that some olivine-rich objects in Tieschitz accreted while partly molten; 3) syn- or post-accretion bleaching of chondrule mesostases, which transferred feldspathic chondrule mesostasis to an interchondrule glass deposit found in strongly clustered lithologies, as evidenced by chemical data and textures; and 4) post-bleaching weak or strong shocks that resulted in destruction of interchondrule glass and some combination of brecciation, foliation of metal and sulfide, and melting and shock-overprinting effects, as evidenced by poor cluster textures and presence of clastic texture, alignment of metal and sulfide grains caused by shock compression, presence of impact-generated glass, and changes in olivine slip systems. The data support the model of Metzler (2012), who suggested that chondrules in ordinary chondrites accreted while still warm to form cluster chondrite textures as a “primary accretionary rock” (our Stage 2), and that subsequent brecciation destroyed this texture to create chondrites with weak cluster texture (our Stage 4).