The age and early evolution of the Moon revealed by the Rb-Sr systematics of lunar ferroan anorthosites

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^1,2Jonas M. Schneider, ¹Thorsten Kleine
Earth and Planetary Science Letters 669, 119592 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2025.119592]
¹Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
²GEOMAR Helmholtz Center for Ocean Research Kiel, Wischhofstraße 1-3, 24148 Kiel, Germany
Copyright Elsevier

The formation of the Moon by a giant impact of an object called Theia onto proto-Earth marks the end of the main stage of Earth’s accretion. However, the timing of this event is controversial, with estimates ranging between ∼50 and ∼220 million years (Ma) after solar system formation. The 87Rb-87Sr system has the potential to resolve this debate, as formation of the Moon resulted in strong fractionation of rubidium from strontium. To better determine the initial 87Sr/86Sr of the Moon, we obtained Rb-Sr isotope data for several lunar ferroan anorthosites, which define an initial 87Sr/86Sr of 0.6990608±0.0000005 (2 s.e.) at 4.360±0.003 Ga. Modeling the pre-giant impact Rb-Sr isotopic evolution of Theia and the proto-Earth reveals that while in the canonical giant impact model no Rb-Sr model age can be determined, all other current impact models yield a Moon formation age of 4.502±0.020 Ga, or 65±20 Ma after solar system formation. When compared to the chronology of lunar samples, this age implies that solidication of the lunar magma ocean took ∼70 Ma, and that the Moon underwent a global re-melting event ∼150 Ma after its formation.

Modeling the early Earth: Core formation in the nebular era does not guarantee a high He/He ratio

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^1,2Madelyn Sita, ²Marvin Osorio, ²Colin Jackson, ³Sujoy Mukhopadhyay
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2025.08.022]
¹Department of Geology, University of Maryland, 8000 Regents Dr., College Park, 20742, MD, USA
²Department of Earth and Environmental Science, Tulane University, 6823 St. Charles Ave, New Orleans, 70118, LA, USA
³School of Earth and Space Exploration, Arizona State University, 781 E Terrace Mall, Tempe, 85287-6004, AZ, USA
Copyright Elsevier

Ocean island basalts (OIBs) sourced from mantle plumes contain a high ³He/⁴He component, marking the lower mantle as a potential reservoir for primordial, less degassed, material. Some of these same samples have been observed to contain low ¹⁸²W/¹⁸⁴W isotope ratios, which suggest the formation of high ³He/⁴He reservoirs occurred during the early stages of Earth’s formation and point to the core as, potentially, the ultimate source of high ³He/⁴He materials. We developed a computational model to investigate parameters that affect the time-integrated He/(U+Th) ratio present in the core in order to establish the conditions during planetary formation that favor the formation of a high ³He/⁴He reservoir in the core. The parameters investigated are representative of the processes responsible for transporting primordial ³He from the nebular atmosphere and the refractory elements U and Th from the silicate magma ocean into the protoplanets’ differentiated core. The parameters investigated include the radius of the protoplanet, timescale of accretion (), optical opacity of the atmosphere (), amount of Si in the bulk planet (), depth of magma ocean-core equilibration, magma ocean thermal gradient, and the metal-silicate partition coefficient of He (D). The model results, obtained through random sampling of the parameter space, indicated that protoplanets which undergo relatively slow accretion during the lifetime of the solar nebula but still reach sizes larger than 4500 km, protoplanets with optically thin atmospheres, and protoplanets that maintain relatively shallow and cool magma oceans will preferentially develop high ³He/⁴He cores. Overall, Earth’s core could serve as a reservoir for primordial helium, but current parameter space makes the core’s ³He/⁴He ratio highly uncertain.

Olivine fabric and microstructure in Northwest Africa (NWA) 7059 and Nova 018: Insights into ureilite deformation

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^1,2A. I. Sheen,^1,2C. K. F. Tirona,^1,2K. T. Tait,^1,2,3L. F. White,^1,2B. C. Hyde,^1,2S. Korchinos
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70028]
¹Department of Natural History, Royal Ontario Museum, Toronto, Ontario, Canada
²Department of Earth Sciences, University of Toronto, Toronto, Ontario, Canada
³School of Physical Sciences, The Open University, Milton Keynes, UK
Published by arrangement with John Wiley & Sons

Olivine is a major constituent in ureilites and commonly defines macroscopic fabric via shape-preferred orientation of elongate grains. In this study, we examined olivine fabric (crystallographic preferred orientation, or CPO) and microstructures in the unbrecciated olivine-pigeonite ureilites Northwest Africa (NWA) 7059 and Nova 018 using electron backscatter diffraction (EBSD) analysis. Point-per-grain orientation data of NWA 7059 indicate a <010> lineation subparallel to grain elongation. Misorientation data of two grains in NWA 7059 indicate dominant activity of (010) [100], (001) [100], (100) [001], and {hk0} [001] slip systems. Nova 018 displays an axial-[010] fabric, with misorientations indicating (010) [001], {hk0} [001] slips, and formation of (010) twist boundaries. Axial-[010] fabric in Nova 018 is consistent with compaction of residual olivine during melt extraction. The <010> lineation in NWA 7059 is unlike typical ureilite fabric and requires a [010] Burgers vector, uncommon in terrestrial samples. Rotational axis analysis of 2°–10° misorientations in olivine shows that the relative proportion of [001] slips and [100] slips in both ureilites are similar to warm-shocked ordinary chondrites, which were deformed at subsolidus temperatures. However, subsolidus deformation temperatures for both studied ureilites are inconsistent with a “hot disruption” model for the ureilite parent body (UPB). The further lack of correlation between 2°–10° misorientation metrics and olivine core Fo content argues against deformation temperature as the main control on olivine slip systems in ureilites. Our findings highlight the use of olivine petrofabric to gain insights into ureilite deformation, as well as complexities in interpreting olivine deformation data with respect to the history of the UPB.

Secondary corundum-bearing assemblages in Allende Ca,Al-rich inclusions: Mineralogy, petrology, oxygen, and aluminum–magnesium isotope systematics

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¹A. N. Krot,¹K. Nagashima,²M. I. Petaev,¹E. Dobrică,³C. Ma,⁴B. Jacobsen
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70036]
¹Hawai‘i Institute of Geophysics & Planetology, School of Ocean and Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i, USA
²Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
³Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
⁴Lawrence Livermore National Laboratory, Livermore, California, USA
Published by arrangement with John Wiley & Sons

We report on the mineralogy, petrology, oxygen, and aluminum–magnesium isotopic systematics of the secondary corundum-bearing assemblages in type B CAIs 3529Z and 3529G and fluffy type A (FTA) CAI ALH-2 from Allende (CV > 3.6). In 3529Z and 3529G, 2–5 μm-sized euhedral-to-subhedral corundum grains associate with secondary alumoåkermanite [(Ca,Na)2AlSi2O7], grossular, spinel, grossite, celsian, kushiroite, and wadalite. In ALH-2, 2–5 μm-sized euhedral-to-subhedral corundum grains associate with secondary grossular, nepheline, spinel, and kushiroite. In 3529Z and 3529G, corundum and associated secondary grossite, spinel, alumoåkermanite, grossular, and kushiroite have similar 16O-poor compositions (Δ17O = −2.2 ± 1.5‰); primary spinel is 16O-rich (Δ17O ~ −23‰); Al,Ti-diopside shows a range of Δ17O (from ~ −24‰ to ~ −15‰); anorthite and melilite are 16O-depleted to various degrees (−6.5‰ ≤ Δ17O ≤ −4.5‰ and Δ17O = −2.7 ± 0.8‰, respectively). In ALH-2, corundum shows a range of Δ17O, from ~ −9‰ to ~ −1‰; primary hibonite and spinel are 16O-rich (Δ17O ~ −23‰); melilite and perovskite are 16O-poor (Δ17O = −2.6 ± 1.5‰ and −3.1 ± 1.3‰, respectively). On the Al-Mg isotope diagram (26Mg* versus 27Al/24Mg), primary Al,Ti-diopside, hibonite, melilite, and spinel in the Allende CAIs studied along the canonical isochron with inferred initial 26Al/27Al ratio [(26Al/27Al)0] of ~5 × 10−5. All secondary minerals have resolved excesses of 26Mg*: alumoåkermanite, corundum, and grossite plot below the canonical isochron, whereas most spinel analyses plot above it. An internal isochron defined by the coexisting secondary corundum and alumoåkermanite in 3529Z has (26Al/27Al)0 = (7.5 ± 2.6) × 10−7. We conclude that the corundum-bearing assemblages in Allende CAIs resulted from metasomatic alteration of primary melilite and anorthite, ~4–5 Ma after their crystallization. Metasomatic alteration of CAIs in the Allende parent asteroid by an aqueous fluid having Δ17O of ~ −3 ± 2‰ modified the O-isotope composition of their primary melilite, anorthite, and Ti-rich pyroxene; O-isotope compositions of primary hibonite, spinel, and low-Ti pyroxene escaped this modification.

The sub-μm petrography of the observed meteorite fall Winchcombe—A complex array of pristine and altered chondrite components

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¹Johannes Lier,¹Christian Vollmer,¹Linus Risthaus,^2,3Demie Kepaptsoglou,^2,4Quentin M. Ramasse,²Aleksander B. Mosberg,⁵Ashley J. King,^5,6Charlotte L. Bays,⁵Paul F. Schofield
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70027]
¹Institut für Mineralogie, Universität Münster, Münster, Germany
²SuperSTEM Laboratory, Daresbury, UK
³School of Physics, Engineering and Technology, University of York, Heslington, UK
⁴School of Chemical and Process Engineering and School of Physics and Astronomy, University of Leeds, Leeds, UK
⁵Planetary Materials Group, Natural History Museum, London, UK
⁶Department of Earth Sciences, Royal Holloway, University of London, Egham, UK
Published by arrangement with JohnWiley & Sons

Samples of observed meteorite falls provide important constraints on alteration histories of Solar System materials. Due to its rapid collection, terrestrial alteration in the observed Mighei-type (CM) carbonaceous chondrite fall Winchcombe was minimal. In this work, the petrography and mineralogy of three Winchcombe lamellae, two from the matrix and one from a lithological clast, were analyzed by transmission electron microscopy. Our results demonstrate that the matrix of Winchcombe is dominated by Mg-Fe-rich serpentine-type phyllosilicates and tochilinite-cronstedtite intergrowth (TCI)-like phases with variable, but generally high (petrologic type 2.0–2.3) alteration degrees that agree with petrologic types acquired on TCIs on larger scales in other work. However, we also located pristine areas in investigated lamellae such as homogeneous amorphous silicates and glassy particles with sulfide and metal inclusions that resemble altered cometary GEMS (glass with embedded metal and sulfides). One distinct GEMS-like domain shows Fe-rich metal and sulfide grains with oxygen-enriched rims in a Mg-rich amorphous groundmass embedded in organic matter, which likely shielded it from more severe alteration. Fe-Ni-sulfides are mainly pentlandite and concentrated in matrix lamellae. In addition to the sub-μm scale brecciated texture, the three lamellae show different alteration extents, further demonstrating the complex alteration nature of this CM2 meteorite.

Chondrule formation by collisions of planetesimals containing volatiles triggered by Jupiter’s formation

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¹Sin-iti Sirono,²Diego Turrini
Scientific Reports 15, 30919 Open Access Link to Article [DOI https://doi.org/10.1038/s41598-025-12643-x]
¹Graduate School of Earth and Environmental Sciences, Nagoya University, Nagoya, Japan
²Turin Astrophysical Observatory, National Institute of Astrophysics (INAF), Pino Torinese, Italy