¹A. Nakamura,¹M. Miyahara,^2,3H. Suga,⁴A. Yamaguchi,⁵D. Wakabayashi,⁵S. Yamashita,^5,6Y. Takeichi,¹K. Kukihara,²Y. Takahashi,⁷E. Ohtani
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2023JE007951]

¹Graduate School of Advanced Science and Engineering, Hiroshima University, Higashi-Hiroshima, Japan
²Department of Earth and Planetary, Graduate School of Science, The University of Tokyo, Tokyo, Japan
³Japan Synchrotron Radiation Research Institute, Hyogo, Japan
⁴National Institute of Polar Research, Tokyo, Japan
⁵Institute of Materials Structure Science, High-Energy Accelerator Research Organization (KEK), Tsukuba, Japan
⁶School of Engineering, Osaka University, Osaka, Japan
⁷Department of Earth Sciences, Graduate School of Science, Tohoku University, Sendai, Japan
Published by arrangement with John Wiley & Sons

Alteration minerals in one of the Martian meteorite nakhlites, Yamato (Y) 000802, were studied to understand the alteration process and conditions. Mn-precipitates are discovered between altered plagioclase grains in Y 000802. Mn-precipitates consist of hausmannite (), manganite (γ-Mn³⁺OOH), rhodochrosite (Mn²⁺CO₃), and a trace amount of Mn⁴⁺O₂ mineral. Jarosite ) is also found. Mn²⁺ dissolved from olivine contributes to the formation of Mn-precipitates. A weakly acidic-neutral fluid containing a trace amount of  altered the olivine, and Mn²⁺ was dissolved into the fluid. The fluid also reacted with plagioclase and probably induced dealkalization of plagioclase, causing a local strong alkaline environment. Plagioclase was altered to ferroan saponite-nontronite + amorphous SiO₂ under alkaline conditions. Simultaneously, Mn^2+/3+-precipitates were formed from the Mn²⁺-containing fluid in the interstices between the altered plagioclase grains under the strong alkaline reducing environment. These alterations occurred in the deep part of the nakhlite body, where they are isolated from Martian subsurface water, including strong oxidants. The formation of Mn^2+/3+-precipitates may have been triggered by the melting of permafrost caused by an impact event around ∼633 Ma. Later, the nakhlite body was probably excavated by another impact, making it susceptible to water including strong oxidants. Pyrrhotite was dissolved and a highly acidic oxidizing fluid was formed, which would induce the formation of jarosite and the Mn⁴⁺O₂ mineral between ∼633 Ma and ∼11 Ma.