^1,2Marine Paquet, ¹James M.D. Day, ³Arya Udry
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.12.019]
¹Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92037, USA
²Université de Lorraine, CNRS, CRPG F-54000 Nancy, France
³Department of Geoscience, University of Nevada, Las Vegas, 4505 S. Maryland Parkway, NV 89154, USA
Copyright Elsevier

The nakhlite and chassignite meteorites are the only confirmed group of rocks derived from a single volcanic system on Mars, offering a unique opportunity to investigate the composition of the martian mantle and magmatic differentiation mechanisms. Nakhlites and chassignites are thought to result from low-degree partial melting of a hydrated and metasomatized depleted mantle lithosphere, unlike shergottites that predominantly sample deeper mantle reservoirs. This study presents the first comprehensive dataset on highly siderophile element (HSE: Au, Re, Pd, Rh, Pt, Ru, Ir, Os) abundances in sulfide assemblages from twelve nakhlites and two chassignites, together with siderophile (Ni, Co, W) and chalcophile (Cu, Se, Zn, Pb) element abundance data. Sulfides in chassignites exhibit relatively high total HSE abundances at ∼ 5 × carbonaceous (CI) chondrite abundances, with patterns that are generally flat, apart from notable enrichments in Pt and/or Ru. Conversely, nakhlite sulfides display more fractionated HSE patterns with total HSE abundances ∼ 1.6 × CI, characterized by lower overall abundances and enrichment in Re, Pt and Pd relative to Ru, Ir and Os. These results confirm that sulfides are the principal reservoirs of HSE in chassignites and nakhlites. Fractionation modeling suggests that the nakhlite compositions can be reproduced following up to 15 % fractional crystallization through the removal of an olivine (+Cr-spinel)-dominated cumulate, while chassignites experienced between 20 to 30 % of fractionation. The preservation of magmatic signatures in sulfide HSE compositions allows for an in-depth reconstruction of the evolution of the nakhlite-chassignite parental melt composition.