¹Zachary A. Torrano, ²Michelle K. Jordan, ²Lori N. Willhite, ²Richard W. Carlson
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2026.03.015]
¹Los Alamos National Laboratory, Nuclear and Radiochemistry Group, Los Alamos, NM, USA
²Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC, USA
Copyright Elsevier

We report Nd and Sm isotopic compositions of a sample returned from asteroid (101955) Bennu by the NASA OSIRIS-REx mission to evaluate potential genetic relationships between Bennu, known meteorite groups, and returned samples from asteroid Ryugu, and to track the cosmic ray exposure history of Bennu. We measured Nd and Sm isotopic compositions via thermal ionization mass spectrometry using 1013 Ω amplifiers. We also explore the constraints that determine the sample sizes where such high-gain amplifiers can be expected to provide improved analytical precision to that of 1011 Ω amplifiers. Bennu exhibits negative µ142Nd and µ144Sm isotopic compositions, both consistent with the nucleosynthetic anomalies previously documented for carbonaceous chondrites and Ryugu. Bennu also exhibits a resolvable deficit in 149Sm that is the result of exposure to galactic cosmic rays as demonstrated by the correlation between 150Sm/152Sm and 149Sm/152Sm ratios that fall along the expected neutron capture correlation line. The 149Sm deficit is consistent with an exposure age of 4.4 ± 1.2 Myr assuming sampling of near surface material, which overlaps with the CRE ages inferred for Bennu from other parameters.

¹Himela Moitra, ¹Sujoy Ghosh, ¹Tamalkanti Mukherjee, ¹Saibal Gupta, ²Kuljeet Kaur Marhas
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2026.03.008]
¹Department of Geology & Geophysics, Indian Institute of Technology Kharagpur, Kharagpur 721302, India
²Planetary Science Division, Physical Research Laboratory Navrangpura, Ahmedabad 380009, India
Copyright Elsevier

High-pressure layered and mixed experiments were performed at pressures of 1–3 GPa and temperatures of 1075–1500 °C in a piston cylinder apparatus to study the interaction between a novel (fayalite-rich) ilmenite-bearing cumulate (IBC) composition and ambient lunar mantle (represented by San Carlos olivine with XMg of 0.91), to investigate the origin of intermediate- and high-Ti mare basalts (6–18 wt% TiO2). The partial melts generated in the layered experiments show TiO2 contents (9–19 wt%) similar to high-Ti mare basalts, but low MgO (<6 wt%). Thermodynamic modelling shows that high-temperature, moderately Ti-rich partial melts (6–8 wt% TiO2) of the IBC layer can directly fractionate to generate intermediate-Ti lunar basalts. Lower-temperature, high-Ti partial melts (11–19 wt% TiO2) may first fractionate to more Ti-rich, Mg-poor compositions, then mix with ascending low-Ti, picritic magmas and undergo subsequent fractionation during ascent to generate high-Ti basalt compositions. Our model successfully reproduces the observed evolution of MgO, TiO2, SiO2, and FeO in high-Ti basalts, although it underestimates their Al2O3 and CaO contents. Incorporation of pockets of plagioclase-rich melts from the mantle may resolve this discrepancy. High-pressure density calculations suggest that at 1 GPa, high-Ti partial melts can ascend to the lunar surface. At 2–3 GPa, some partial melts may ascend to the surface after fractionation and assimilation, while some may sink through the lunar mantle. These findings provide new insights on the role of lunar mantle overturn, IBC melting and mantle interactions in the formation of lunar high-Ti basalts and offer a viable mechanism for their generation throughout the history of mare volcanism.