Linxi Li, Hejiu Hui, Sen Hu, Hao Wang, Wei Yang, Yi Chen, Shitou Wu, Lixin Gu, Lihui Jia, Fuyuan Wu
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14072]
Published by arrangement with John Wiley & Sons

The regolith samples returned by the Chang’E-5 mission (CE-5) contain the youngest radiometrically dated mare basaltic clasts, which provide an opportunity to elucidate the magmatic activities on the Moon during the late Eratosthenian. In this study, detailed petrographic observations and comprehensive geochemical analyses were performed on the CE-5 basaltic clasts. The major element concentrations in individual plagioclase grain of the CE-5 basalts may vary slightly from core to rim, whereas pyroxene has clear chemical zonation. The crystallization sequence of the CE-5 mare basalts was determined using petrographic and geochemical relations in the basaltic clasts. In addition, both fractional crystallization (FC) and assimilation and fractional crystallization models were applied to simulate the chemical evolution of melt equilibrated with plagioclase in CE-5 basalts. Our results reveal that the melt had a TiO₂ content of ~3 wt% and an Mg# of ~45 at the onset of plagioclase crystallization, suggesting a low-Ti parental melt of the CE-5 basalts. The relatively high FeO content (>14.5 wt%) in melt equilibrated with plagioclase could have resulted in extensive crystallization of ilmenite, unlike in Apollo low-Ti basalts. Furthermore, our calculations showed that the geochemical evolution of CE-5 basaltic melt could not have occurred in a closed system. On the contrary, the CE-5 basalts could have assimilated mineral, rock, and glass fragments that have higher concentrations of KREEP elements (potassium, rare earth elements, and phosphorus) in the regolith during magma flow on the Moon’s surface. The presence of the KREEP signature in the CE-5 basalts is consistent with literature remote sensing data obtained from the CE-5 landing site. These KREEP-bearing fragments could originate from KREEP basaltic melts that may have been emplaced at the landing site earlier than the CE-5 basalts.

Alexander N. Krot, Kazuhide Nagashima, Marina A. Ivanova, Dante Lauretta, Guy Libourel, Brandon C. Johnson, Frank E. Brenker, Viktoria Hoffman, Martin Bizzarro
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14072]
Published by arrangement with John Wiley & Sons

The CB (Bencubbin-like) metal-rich carbonaceous chondrites are subdivided into the CB_aand CB_b subgroups. The CB_a chondrites are composed predominantly of ~cm-sized skeletal olivine chondrules and unzoned Fe,Ni-metal ± troilite nodules. The CB_bchondrites are finer grained than the CB_as and consist of chemically zoned and unzoned Fe,Ni-metal grains, Fe,Ni-metal ± troilite nodules, cryptocrystalline and skeletal olivine chondrules, and rare refractory inclusions. Both subgroups contain exceptionally rare porphyritic chondrules and no interchondrule fine-grained matrix, and are interpreted as the products of a gas–melt impact plume formed by a high-velocity collision between differentiated planetesimals about 4562 Ma. The anomalous metal-rich carbonaceous chondrites, Fountain Hills and Sierra Gorda 013 (SG 013), have bulk oxygen isotopic compositions similar to those of other CBs but contain coarse-grained igneous clasts/porphyritic chondrule-like objects composed of olivine, low-Ca-pyroxene, and minor plagioclase and high-Ca pyroxene as well as barred olivine and skeletal olivine chondrules. Cryptocrystalline chondrules, zoned Fe,Ni-metal grains, and interchondrule fine-grained matrix are absent. In SG 013, Fe,Ni-metal (~80 vol%) occurs as several mm-sized nodules; magnesiochromite (Mg-chromite) is accessory; daubréelite and schreibersite are minor; troilite is absent. In Fountain Hills, Fe,Ni-metal (~25 vol%) is dispersed between chondrules and silicate clasts; chromite and sulfides are absent. In addition to a dominant chondritic lithology, SG 013 contains a chondrule-free lithology composed of Fe,Ni-metal nodules (~25 vol%), coarse-grained olivine and low-Ca pyroxene, interstitial high-Ca pyroxene and anorthitic plagioclase, and Mg-chromite. Here, we report on oxygen isotopic compositions of olivine, low-Ca pyroxene, and ±Mg-chromite in Fountain Hills and both lithologies of SG 013 measured in situ using an ion microprobe. Oxygen isotope compositions of olivine, low-Ca pyroxene, and Mg-chromite in these meteorites are similar to those of magnesian non-porphyritic chondrules in CB_aand CB_b chondrites: on a three-isotope oxygen diagram (δ¹⁷O vs. δ¹⁸O), they plot close to a slope-1 (primitive chondrule mineral) line and have a very narrow range of Δ¹⁷O (=δ¹⁷O–0.52 × δ¹⁸O) values, −2.5 ± 0.9‰ (avr ± 2SD). No isotopically distinct relict grains have been identified in porphyritic chondrule-like objects. We suggest that magnesian non-porphyritic (barred olivine, skeletal olivine, cryptocrystalline) chondrules in the CB_as, CB_bs, and porphyritic chondrule-like objects in SG 013 and Fountain Hills formed in different zones of the CB impact plume characterized by variable pressure, temperature, cooling rates, and redox conditions. The achondritic lithology in SG 013 represents fragments of one of the colliding bodies and therefore one of the CB chondrule precursors. Fountain Hills was subsequently modified by impact melting; Fe,Ni-metal and sulfides were partially lost during this process.

Christian Zeeden^a,b, Jacques Laskar^a, David De Vleeschouwer^d, Damien Pas^e, Anne-Christine Da Silva^c
Earth and Planetary Science Letters (in Press) Link to Article [https://doi.org/10.1016/j.epsl.2023.118348]
^aIMCCE, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, 75014 Paris, France
^bLIAG – Leibniz Institute for Applied Geophysics, Stilleweg 2, 30655 Hannover, Germany
^cPétrologie sédimentaire, B20, Allée du Six Août, 12, Quartier Agora, Liège University, Sart Tilman, 4000 Liège, Belgium
^dInstitute of Geology and Paleontology, Westfälische Wilhelms-Universität (WWU) Münster, Corrensstr 24, 48149 Münster, Germany
^eInstitute of Earth Sciences (ISTE), University of Lausanne, CH-1015 Lausanne, Switzerland
Copyright : Elsevier

Astronomical insolation forcing plays an important role in pacing Earth’s climate history, including paleoclimate dynamics, and its imprint can be seen in various geoarchives. Its signature is often evident through typical rhythmic patterns in sediments. The detailed study of those patterns led to a better understanding of orbital climate forcing, while also providing more precise constraints on the geological time scale. Due to the tidal evolution in the Earth-Moon system, the precession and obliquity periods get shorter when going back in time while the main eccentricity 405 kyr period remains stable. While several astrophysical models describe the evolution of the length of precession- and obliquity cycles, few reliable and quantitative geological information from tidalitesand astrochronology are available.

To better constrain these key astronomical parameters in the distant past, we calculate precession and obliquity properties for the Devonian (∼420-360 million years before present) as reconstructed from a suite of geological datasets. Our results show the period of precession to be 19.4-16.1 kyr, and the dominant p+s3 obliquity period to be 29.50±0.46 long. These findings are compared with and support the presence of oceanic tidal resonances at 300 and 540 Ma, as shown in the recent AstroGeo22 model of the Earth-Moon evolution of (Farhat et al., 2022).