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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.

Rb-Sr constraints on the age of Moon formation

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Elsa Yobregat, Caroline Fitoussi, Bernard Bourdon
Icarus (in Press) Open Access
Link to Article [https://doi.org/10.1016/j.icarus.2024.116164]
Laboratoire de Géologie de Lyon, ENS Lyon, CNRS, UCBL, France

Determining the age of the Moon, which is commonly considered as the termination of Earth accretion has been a complex challenge for geochronology. A number of methods have been used to delineate the age of the Moon based either on absolute chronology of lunar rocks or have relied on more indirect methods using short-lived nuclides such as 182Hf that was present in the early history of the Solar System. Model ages usually require some assumptions that are sometimes controversial or harder to verify.

In this study, new high precision Sr isotope data (2.4 ppm, 2SD) were obtained for a well-dated lunar anorthosite (60025) in order to better constrain the initial 87Sr/86Sr of the bulk silicate Moon. This new data is then used to model the Sr isotope evolution of the Earth-Moon starting from the beginning of the Solar System. To comply with the Hfsingle bondW and stable isotope constraints, we then assume that the Earth and Moon were equilibrated at the time of Moon formation. By investigating systematically all the sources of uncertainties in our model, we show that compared with previous work on anorthosite, one can tighten the constraints on the youngest age of Moon formation to no >79 Ma after the beginning of the Solar System, i.e. the Moon cannot be younger than 4488 Ma.

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.

Nucleosynthetic isotope variations in chondritic meteorites and their relationship to bulk chemistry

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1Herbert Palme,2,3Klaus Mezger
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14127]
1Forschungsinstitut und Naturmuseum Senckenberg, Frankfurt am Main, Germany
2Institut für Geologie, Universität Bern, Bern, Switzerland
3Center for Space and Habitability, Universität Bern, Bern, Switzerland
Published by arrangement with John Wiley & Sons

The relationship of mass-independent stable isotope anomalies with the chemistry of chondritic meteorites provides constraints on mixing and fractionation processes in the early solar nebula. The present study emphasizes the strong correlation of nucleosynthetic isotope variations among ordinary chondrites (OC), enstatite chondrites (EC), Earth, CI-chondrites, and Ca, Al-rich inclusions (CAI) in ε50Ti versus ε54Cr space. This correlation indicates variable contamination of chondritic reservoirs with material from a single source providing neutron-rich nuclei such as 50Ti, 54Cr, and 62Ni. The well-defined linear relationship of ε50Ti versus ε54Cr indicates that all reservoirs on the correlation line (“chondrite reference line”) started with a CI-chondritic (solar) Cr/Ti ratio, irrespective of the present Cr/Ti ratio of the samples falling on the chondrite reference line. The isotope compositions of carbonaceous chondrites (CC) do not fit the chondrite reference line. Their isotope composition is consistent with a mixture of chondritic meteorites originally falling on the chondrite reference line and volatile element depleted CAIs. However, CC cannot result from addition of CAIs to OC or EC. Neither can OC and EC be produced by loss of refractory components from CI-meteorites. Also, stable isotopes are inconsistent with OC being derived from EC, and vice versa, by a chemical fractionation process. The enrichment of the Earth in refractory lithophile elements is not the result of addition of a refractory component to a chondritic reservoir. It is rather the result of internal fractionation of a chondritic reservoir.