¹Christian Liebske, ^1,3Amir Khan, ^1,2Scott M. McLennan, ¹Paolo A. Sossi
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2025.116666]
¹Institute of Geochemistry and Petrology, ETH Zürich, Switzerland
²Department of Geosciences, Stony Brook University, Stony Brook, NY, USA
³Institute of Geophysics, ETH Zürich, Switzerland
Copyright Elsevier

The terrestrial planets are believed to have accreted from chondritic meteorites of widely varying composition. Yet, making planets from known meteoritic material has proved elusive, be it their nucleosynthetic isotopic anomalies, bulk chemistry or geophysical properties. Because of the inherent non-uniqueness of meteoritic mixing models based on isotopes alone, combining geochemical and geophysical observations is key to identifying the nature of the building blocks of the terrestrial planets. Here, we integrate the recent proliferation of data in the form of geophysical measurements pertaining to Mars’s interior structure from the recent InSight mission including its astronomic-geodetic response, the chemical and isotopic compositions of undifferentiated and differentiated meteorites, and observational constraints on trace element abundances (K/Th ratio) in order to make new inferences on the constitution and provenance of Mars. Using stochastic mixing models of meteoritic material, we find that
0.02% of mixtures, consisting primarily of ordinary- and enstatite chondrites and, to a lesser extent, achondritic material, are able to reproduce the isotopic signature of Mars. Of these, however, none match the geophysical or Mg/Si and K/Th constraints, indicating that Mars is unlikely to have formed from known unmodified meteoritic material. Instead, relatively oxidised building blocks that are intrinsic to the inner solar system and underwent evaporation/condensation processes that lead to volatile-element depletion patterns unlike those in any known meteorite group, would be consistent with the isotopic, geochemical and geophysical properties of Mars.

¹G. Florin, ¹P. Gleißner, ¹H. Becker
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.06.006]
¹Freie Universität Berlin, Institut für Geologische Wissenschaften, Malteserstr. 74-100, 12249 Berlin, Germany
Copyright Elsevier

In the last decade, several studies have reported enrichments of the heavy isotopes of moderately volatile elements in lunar mare basalts. However, the mechanisms controlling the isotope fractionation are still debated and may differ for elements with variable geochemical behaviour. Here, we present a new comprehensive dataset of mass-dependent copper isotope compositions (δ65Cu) of 30 mare basalts sampled during the Apollo missions. The new δ65Cu data range from +0.14 ‰ to +1.28 ‰ (with the exception of two samples at 0.01 ‰ and –1.42 ‰), significantly heavier than chondrites and the bulk silicate Earth. A comparison with mass fractions of major and trace elements and thermodynamic constraints reveals that Cu isotopic variations within different mare basalt suites are mostly unrelated to fractional crystallisation of silicates or oxides and late-stage magmatic degassing. Instead, we propose that the δ65Cu average of each suite is representative of the composition of its respective mantle source. The observed differences across geographically and temporally distinct mare basalt suites, suggest that this variation relates to large-scale processes that formed isotopically distinct mantle sources. Based on a Cu isotope fractionation model during metal melt saturation in crystal mush zones of the lunar magma ocean, we propose that distinct δ65Cu compositions and Cu abundances of mare basalt mantle sources reflect local metal melt–silicate equilibration and trapping of metal in mantle cumulates during lunar magma ocean solidification. Differences in δ65Cu and mass fractions and ratios of siderophile elements between low- and high-Ti mare basalt sources reflect the evolving compositions of both metal and silicate melt during the late cooling stages of the lunar magma ocean.