Chrome-rich spinels in micrometeorites from modern Antarctic sedimentary deposits

• Published in: Earth and Planetary Science Letters
• Main Authors: Van Maldeghem, Flore, Maeda, Ryoga, Soens, Bastien, Suttle, Martin D., Ruggiu, Lisa Krämer, Cordier, Carole, Yamaguchi, Akira, Schmitz, Birger, Claeys, Philippe, Folco, Luigi, Goderis, Steven
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2024
• Subjects: Geology; Chromite; Cosmic spherules; Cr-spinel; Micrometeorites; Oxygen isotope ratios; Parent bodies; Antarctic; Sør Rondane Mountains; Sør-Rondane; Transantarctic Mountains; Antarc*; Antarctica
• Online Access: https://lup.lub.lu.se/record/05c0f2c5-e084-44c5-aa35-1fe3fda0f7fb; https://doi.org/10.1016/j.epsl.2024.118837

Each year, approximately 5000 tons of extraterrestrial material reaches the Earth's surface as micrometeorites, cosmic dust particles ranging from 10 to 2000 μm in size. These micrometeorites, collected from diverse environments, mainly deep-sea sediments, Antarctic ice, snow and loose sediments, and hot deserts, are crucial in understanding our Solar System's evolution. Chrome-rich spinel (Cr-spinel) minerals have gained attention as proxies for studying the extraterrestrial flux in sedimentary deposits, because these robust minerals occur, in various extraterrestrial materials, with compositions characteristic of their parent bodies. A total of 27 Cr-spinel bearing micrometeorites within the size range of 185–800 μm, were identified from approximately 6000 micrometeorites from the Transantarctic Mountains (n = 23) and the Sør Rondane Mountains (n = 4), in Antarctica, containing Cr-spinel (8–120 μm), were examined in this study for geochemical composition and high-precision oxygen isotope ratios to assess alteration and identify potential parent bodies. Oxygen isotopes in the micrometeorite groundmass and in Cr-spinel grains reveal a predominance of ordinary chondritic precursors, with only 1 in 10 micrometeorites containing Cr-spinel minerals showing a carbonaceous chondritic signature. This may be further confirmed by an elevated Al content (> 12 wt% Al2O3) in Cr-spinel from specific carbonaceous chondrite types, but a more extensive dataset is required to establish definitive criteria. The first Cr-spinel bearing particle, in an Antarctic micrometeorite, that can be linked to R-chondrites based on oxygen isotopes, has been documented, demonstrating the potential for R-chondrites as a source of chrome-rich spinels. The study also highlights the potential for chemical modifications and alteration processes that Cr-spinel minerals may undergo during their time on the parent body, atmospheric entry, and terrestrial residence. In the context of the broader micrometeorite flux, the results align with previous ...