Origin of aubrites and their parent bodie(s): a petrological, geochemical and cosmochemical study
Context / funding: This PhD is part of the IMPAcToR (Aubrite meteorites: relicts of a large protoplanet Mercury?) project led by Camille Cartier, funded by the ANR for the period 2025-2029. This project aims at unraveling the link between aubrites meteorites, planet Mercury, and E-type asteroids through a multi-disciplinary approach. IMPAcToR brings together a team of 8 researchers from various disciplines, working at CRPG or other French research institutes, who will all interact with the student. This PhD is an analytical and geochemical modeling project, but bridges could be established with the other parts of the ANR project, particularly the experimental and the dating parts. In addition to the PhD student, the project includes the internships of two Master 2 students.
Supervisors: Camille Cartier (CRPG, Université de Lorraine), François Faure (CRPG, Université de Lorraine)
Contact: camille.cartier@univ-lorraine.fr / francois.faure@univ-lorraine.fr.
Contact Camille Cartier for more information on the ANR IMPAcToR project and/or PhD logistical details.
Keywords: Cosmochemistry, Planetary Science, Meteoritics, Modeling
Expected start date and duration: 3 years starting October 2025
Location: This PhD will be hosted at CRPG (Nancy) and will include missions in France and abroad.
Application deadline: Applications will be accepted until May 23, 2025.
Application process: Candidates should contact the two supervisors with a cover letter and a CV.
Desired profile: Candidates should be in the final year of a Master’s degree, in Geosciences or Planetary Science. Candidates should be highly motivated by the study of meteorites and early solar system Science, with advanced knowledge in igneous petrology and geochemistry, background in cosmochemistry, an excellent level of written expression, and a sense of initiative. Knowledge of low oxygen fugacity environments and/or reduced meteorites is a plus, as well as experience with one or several of the numerous methods that will be used.
Summary: Mercury stands out as an outlier in our Solar System, characterized by its unique lithologies formed in an ultra-reducing, sulfur-rich environment (Cartier and Wood, 2019). Despite being the smallest planet, Mercury intriguingly has the largest core proportionately (Charlier and Namur, 2019). Thus, a long-standing hypothesis suggests that Mercury originally had a much larger rocky mantle, largely pulverized during massive impact(s). However, due to insufficient constraints, this scenario has never been confirmed and the origin of Mercury remains a highly elusive and debated topic. Aubrites, rare achondrites with mineralogies particularly similar to that of Mercury, are known to originate from E-type asteroids, small “rubble piles” located in the innermost asteroid belt (Keil, 2010). The present project aims to evaluate the original hypothesis according to which aubrites would be remnants of the shallow mantle/crust of a large proto-Mercury, pulverized by one or more giant impacts, and of which a small fraction of the debris would have been implanted in the asteroid belt in the form of E-type asteroids (Cartier et al., 2022).
The aim of this PhD project is to comprehensively characterize the petrography, the chemical compositions and some isotopic compositions of a unique collection of aubrites and possibly related meteorites as a fundamental prerequisite for understanding their formation conditions and unravel the geological history of their parent bodie(s).
In this PhD project, ≈ 35 meteorites will be studied, part of which will be studied for the first time. The student will conduct the first in-situ comprehensive geochemical study (trace elements in all phases in all samples will be investigated using LA-ICPMS and SIMS) of aubrites. A particular focus will be made on vitrophyric clasts (Fogel, 2005; Keil et al., 2011), very rare objects containing magmatic glass that have never been studied in-situ. A preliminary work allowed us to discover several new vitrophyre clasts in aubrites (Lacheux et al., 2024). The data will make it possible to test, through geochemical modelling, the equilibrium relationship between the different phases, to trace the thermodynamic conditions of this equilibrium (composition of the system, pressure, temperature, oxygen fugacity). This will lead to unravelling the controversial origin of metal and sulphide grains in aubrites, and assess the nature of the aubrite parent body, in particular its size. We will also measure H, C and N contents of glasses using SIMS, to unravel the controversial volatile element content of aubrites (Piani et al., 2020; Peterson et al., 2023). The analyses will be complemented by a textural study of aubrites. In particular, the characterisation of dendrites in glassy objects will permit inferring the thermal history of the vitrophyre clast, supporting a volcanic origin or not (Keil et al. 2011). Also, some aubrites have pegmatitic textures with cm-sized enstatite crystals containing thousands of vesicles and silicate/sulphide/metal inclusions mainly oriented along their crystallographic axes, and which origins are unknown (Lorenz et al., 2020; Wilbur et al., 2022). The aim will be to understand if these inclusions are formed early, during the crystallisation of aubrites or later, during impact processes. Finally, aubrites are extremely brecciated meteorites which contain clasts and dust of extraneous material (chondritic, achondritic), and whose highly reduced nature makes them very susceptible to terrestrial oxidation. In this task, O-isotopic compositions will be measured for the first time in-situ in aubrites using SIMS. The data will be integrated all together with literature data to build a petrological model of aubrite formation in their parent bodie(s), and unravel the properties of this parent body
Methods: SEM-EDS, EPMA, LA-ICPMS, SIMS, Raman Spectroscopy, X-ray tomography, petrological/geochemical modeling.
References:
Cartier C., Charlier B., Boyet M., Spalding C. and Namur O. (2022) A large Proto-Mercury as the Aubrite Parent Body. In 53rd Lunar and Planetary Science Conference
Cartier C. and Wood B. J. (2019) The role of reducing conditions in building Mercury. Elements 15, 39–45.
Charlier B. and Namur O. (2019) The Origin and Differentiation of Planet Mercury. Elements 15, 9–14.
Fogel R. A. (2005) Aubrite basalt vitrophyres: The missing basaltic component and high-sulfur silicate melts. Geochim Cosmochim Acta 69, 1633–1648.
Keil K. (2010) Enstatite achondrite meteorites (aubrites) and the histories of their asteroidal parent bodies. Chemie der Erde 70, 295–317.
Keil K., Mccoy T. J., Wilson L., Barrat J. A., Rumble D., Meier M. M. M., Wieler R. and Huss G. R. (2011) A composite Fe,Ni-FeS and enstatite-forsterite-diopside-glass vitrophyre clast in the Larkman Nunatak 04316 aubrite: Origin by pyroclastic volcanism. Meteorit Planet Sci 46, 1719–1741.
Lacheux M., Cartier C., Loth L., Faure F., Villeneuve J., Piani L. and Namur O. (2024) Petrological And Geochemical Study Of Aubrite Vitrophyres: Insights Into Aubrite Origin. In 86th annual meeting of The Meteoritical Society
Lorenz C. A., Buikin A. I., Shiryaev A. A. and Kuznetsova O. V (2020) Composition and origin of the volatile components released from the Pesyanoe aubrite by stepwise crushing and heating. Geochemistry.
Peterson L. D., Newcombe M. E., Alexander C. M. O. D., Wang J., Klein F., Bekaert D. V and Nielsen S. G. (2023) The H content of aubrites : An evaluation of bulk versus in situ methods for quantifying water in meteorites. 620.
Piani L., Marrocchi Y., Rigaudier T., Vacher L., Thomassin D. and Marty B. (2020) Earth’s water may have been inherited from material similar to enstatite chondrite meteorites. Science (1979) 369, 1110–1113.
Wilbur Z. E., Udry A., McCubbin F. M., vander Kaaden K. E., DeFelice C., Ziegler K., Ross D. K., McCoy T. J., Gross J., Barnes J. J., Dygert N., Zeigler R. A., Turrin B. D. and McCoy C. (2022) The effects of highly reduced magmatism revealed through aubrites. Meteorit Planet Sci 57, 1387–1420.