^1,2Marine Paquet , ¹Frederic Moynier, ³Paolo A. Sossi, ¹Wei Dai, James M.D. Day
Earth and Planetary Science Letters 656, 119250 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2025.119250]
¹Université Paris Cité, Institut de Physique du Globe de Paris, CNRS, Paris, F-75005, France
²Université de Lorraine, CNRS, CRPG, F-54000, Nancy, France
³Institute of Geochemistry and Petrology, ETH Zürich, Clausiusstrasse 25, Zürich CH-8092, Switzerland
⁴Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0244, USA
Copyright Elsevier

The abundances and isotopic signatures of volatile elements provide critical information for understanding the delivery of water and other essential life-giving compounds to planets. It has been demonstrated that the Moon is depleted in moderately volatile elements (MVE), such as Zn, Cl, S, K and Rb, relative to the Earth. The isotopic compositions of these MVE in lunar rocks suggest loss of volatile elements during the formation of the Moon, as well as their modification during later differentiation and impact processes. Due to its moderately volatile and strongly chalcophile behaviour, copper (Cu) provides a distinct record of planetary accretion and differentiation processes relative to Cl, Rb, Zn or K. Here we present Cu isotopic compositions of Apollo 11, 12, 14 and 15 mare basalts and lunar basaltic meteorites, which range from δ65Cu of +0.55±0.01 ‰ to +3.94±0.04 ‰ (per mil deviation of the 65Cu/63Cu from the NIST SRM 976 standard), independent of mare basalt Ti content. The δ65Cu values of the basalts are negatively correlated with their Cu contents, which is interpreted as evidence for volatile loss upon mare basalt emplacement, plausibly related to the presence Cl- and S-bearing ligands in the vapour phase. This relationship can be used to determine the Cu isotopic composition of the lunar mantle to a δ65Cu of +0.57 ± 0.15 ‰. The bulk silicate Moon (BSM) is 0.5‰ heavier than the bulk silicate Earth (+0.07 ± 0.10 ‰) or chondritic materials (from -1.45 ± 0.08 ‰ to 0.07 ± 0.06 ‰). Owing to the ineffectiveness of sulfide segregation and lunar core formation in inducing Cu isotopic fractionation, the isotopic difference between the Moon and the Earth is attributed to volatile loss during the Moon-forming event, which must have occurred at- or near-equilibrium.

^1,2Matthew J. Genge, ³Matthias Van Ginneken, ⁴Chi Ma, ⁵Martin D. Suttle, ^1,2Natasha Almeida, ⁶Noriko T. Kita, ⁶Mingming Zhang, ⁷Luca Bindi
Earth and Planetary Science Letters 656, 119276 Open Access Link to Articel [https://doi.org/10.1016/j.epsl.2025.119276]
¹Department of Earth Science and Engineering, Imperial College London, Exhibition Road, London, SW7 2AZ, UK
²Planetary Materials Group, Natural History Museum, London, SW7 5BD, UK
³Department of Physics and Astronomy, Centre for Astrophysics and Planetary Science, University of Kent, Canterbury, Kent, CT2 7NH, UK
⁴Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, 91125, USA
⁵School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
⁶Department of Geoscience, University of Wisconsin-Madison, 1215W. Dayton St., Madison, WI, 53706, USA
⁷Dipartimento di Scienze della Terra, Università di Firenze, Via La Pira 4, I, 50121, Florence, Italy
Copyright Elsevier

We report the discovery of Al-Cu-alloys within a coarse-grained micrometeorite from the Congo. Oxygen isotope ratios of the sample are consistent with a CV3 source, similar to the Khatyrka meteorite. The petrology of the micrometeorite is also similar to Khatyrka and testifies to the disequilibrium impact mixing between the CV3 parent body and a differentiated body, which was the source of the Al-Cu-alloys. The oxygen isotope composition, however, suggests either limited mixing with projectile silicates or a differentiated projectile with oxygen isotopes close to the CCAM. The most plausible origin of the Al-Cu-alloys is the desilication of an aluminous igneous protolith by hydrothermal activity under highly reduced conditions. We argue that the ureilite parent body is the most likely source for the projectile owing to its silicic magmatism, late-stage reduction and similar oxygen isotope ratios. Al-Cu-alloys can, thus, be found on the disrupted remnants of such protoplanets.