¹Leire Coloma, ¹Fernando Alberquilla, ¹Julene Aramendia, ¹Gorka Arana, ²Ed Cloutis, ¹Juan Manuel Madariaga
Journal of Geophysical Research: Planets (in Press) Open Source Link to Article [DOI: 10.1029/2026JE009954]
¹Faculty of Science and Technology, Department of Analytical Chemistry, University of the Basque Country, Leioa, Spain
²Department of Geography, University of Winnipeg, Winnipeg, MB, Canada
Published by arrangement with John Wiley & Sons

The presence of minor minerals is a key factor distinguishing meteorite types, as they provide valuable insights into the formation processes, surface conditions, and evolutionary history of their parent bodies. In Martian nakhlites, one of the most distinctive minor phases is iron-titanium oxides forming characteristic skeletal textures. However, their mineralogical nature remains debated, with most studies identifying them as titanomagnetite, whereas others suggest ilmenite skeletal textures. This study uses Raman imaging to investigate the mineralogical distribution of these skeletal textures. Additionally, scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) was used to assess titanium concentration gradients from the exterior to the core of the structures. Chemometric methods were applied to differentiate and represent the mineralogical distribution. Furthermore, similar skeletal textures observed in terrestrial analogs from the Timanfaya and Maciot volcanoes (Lanzarote, Canary Islands, Spain) were analyzed using Raman imaging to evaluate potential similarities or differences in composition and formation processes with those found in the paired meteorites studied. The results show that the skeletal textures in the MIL nakhlites consist of ilmenite surrounded by titanomagnetite and magnetite. In contrast, in the analogs, two types of skeletal textures were identified: some composed of ilmenite and others of magnetite. These findings indicate that skeletal oxide textures in Martian and terrestrial samples from two field sites formed through distinct processes and constitute sensitive recorders of the evolution of mafic magmatic systems. These differences reflect restricted redox conditions and limited subsolidus re-equilibration in the MIL nakhlites, versus oxidation and faster cooling histories in the terrestrial analogs.

¹B.G. Rider-Stokes, ^1,2A. Stephant, ³M. Nottingham, ⁴J. Gamblin, ⁴E. Füri, ^5,6S.S. Russell, ¹X. Zhao, ¹M. Anand, ⁴M.J. Whitehouse, ¹M.M. Grady
Geochimica et Cosmochimica Acta (in Press) Open Source Link to Article [DOI: 10.1016/j.gca.2026.07.047]
¹School of Physical Sciences, The Open University, Milton Keynes MK7 6AA, UK
²Istituto di Astrofisica e Planetologia Spaziali – INAF, 00111 Rome, Italy
³School of Geographical & Earth Sciences, University of Glasgow, G12 8QQ, UK
⁴Université de Lorraine, CNRS, CRPG, F-54000 Nancy, France
⁵Department of Earth Sciences, The Natural History Museum, London SW7 5BD, UK
⁶Department of Geosciences, Swedish Museum of Natural History, SE-104 05 Stockholm, Sweden
Copyright Elsevier

Evidence for SiO₂-rich melts on the ureilite parent body (UPB) stems from feldspathic clasts within polymict ureilites and has been additionally preserved and recorded in rare fragments of the Almahata Sitta meteorite suite, which originated from the asteroid 2008 TC₃. These unique fragments demonstrated that ancient crust-forming volcanism on small planetary bodies was not simply restricted to basaltic lithologies. Two recent Northwest Africa finds (NWA) 15,820 and NWA 16789 expand the known quantity of SiO₂-rich material from the UPB, allowing for a more representative investigation into the chemical and isotopic variations among these unique lithologies. Here, we measured the H abundance and isotopic composition (δD) of NWA 15820 and NWA 16789 to evaluate the bulk UPB water content, resulting in a revised minimum bulk water content of 13 µg/g H₂O. Furthermore, we report the δD of water in the UPB. While the D/H ratio of late-stage phosphates and glass is highly fractionated as a result of magmatic degassing, nominally anhydrous silicate pyroxene better records the original δD of the UPB. In particular, the pyroxene within NWA 16789 records a δD value of 83 ± 79‰, which we infer is the best estimate for the original δD of water in the UPB.