^1,2Neha,¹S. Natrajan,¹K. K. Marhas
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2025JE009101]
¹Physical Research Laboratory, Ahmedabad, Gujarat, India
²Gujarat University, Ahmedabad, Gujarat, India
Published by arrangement with John Wiley & Sons

Raman spectroscopic investigation of chemically separated insoluble organic matter (IOM) from six aubrites and five enstatite chondrites revealed a bimodal range of temperatures spanning from ∼200 to ∼1,000°C points toward heterogeneously altered organics. Temperatures derived from graphitized or partially graphitized IOM from aubrites are similar to those reported earlier by mineral thermometry (∼900–1,000°C) and their presence in our samples, despite peak temperatures falling significantly below the temperature threshold for graphitization, suggests the involvement of metal-catalyzed graphitization processes. The absence of an exciton peak in X-ray absorption near edge structure spectra and the temperatures inferred from Raman spectroscopy suggest short-term heating of IOM, potentially linked to impact-related heating within the aubrite parent body (AuPB). The diverse temperature obtained for the aubrites in this study possibly indicates that the source of these organics could either be indigenous, that is, preserved during partial melting (incomplete differentiation of AuPB) or exogenous, that is, delivered through impact. High-resolution transmission electron microscopy analysis reveals diverse IOM structures ranging from amorphous carbon to highly graphitic lamellar carbon phases and nanoglobules. Notably, the identification of nanoglobules, a feature typically associated with primitive chondrites, within one aubrite sample suggests the incorporation of exogenous organic material, possibly derived from primitive chondritic impactors.

^1,2Ke Zhu, ³Martijn Klaver, ^4,5,6Wei-Biao Hsu, ⁷Harry Becker, ⁸Lu Chen, ⁹Qi Chen
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.10.009]
¹Bristol Isotope Group, School of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, Bristol BS8 1RJ, United Kingdom
²State Key Laboratory of Geological Processes and Mineral Resources, Hubei Key Laboratory of Planetary Geology and Deep-Space Exploration, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China
³Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Corrensstraße 24, 48149 Münster, Germany
⁴CAS Center for Excellence in Comparative Planetology, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210023, China
⁵State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Avenida Wai Long, Taipa, Macau
⁶School of Earth Sciences and Engineering, International Center for Isotope Effects Research, Nanjing University, Nanjing 210023, China
⁷Freie Universität Berlin, Institut für Geologische Wissenschaften, Malteserstr. 74-100, 12249 Berlin, Germany
⁸Wuhan SampleSolution Analytical Technology Co., Ltd, Wuhan, China
⁹Department of Earth Science & Environmental Change, University of Illinois at Urbana Champaign, Urbana, IL, United States
Copyright Elsevier

To understand accretion and differentiation of Mars, we report high-precision mass-dependent Ni (siderophile and chalcophile) isotope data of 37 bulk Martian meteorites. Large δ60/58Ni variations observed among these Martian meteorites are attributed primarily to magmatism and Ni diffusion in zoned olivine and sulfide. Shergottites show systematically higher Mg# and lower δ60/58Ni values relative to nakhlites, which can be caused by olivine crystallization, consistent with the Ni isotope fractionation factor between olivine and melt. Two Ni-rich chassignites (Martian dunites) provide the best current estimate of the upper limit of δ60/58Ni of bulk silicate Mars (BSM): 0.110 ± 0.031 ‰, since olivine crystallization causes Ni isotope fractionation. Subtracting a presumably chondritic contribution by late accretion, the proto-BSM should possess a δ60/58Ni of ≤ 0.074 ‰ that is lower than the average of chondrites (∼0.24 ‰). This sub-chondritic value of Martian mantle suggests the sulfur-rich core formation has not caused Ni isotope fractionation, because the sulfide and Martian sulfur-rich core is believed to enrich in light Ni isotopes. Instead, Ni isotope differences between Earth, Mars, Vesta, and the ureilites can be inherited from non-bulk chondritic precursor materials.