Mn-Precipitates Found in a Martian Crustal Rock

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 (Mn2+Mn3+2O4 ${\text{Mn}}<^>{2+}{{\text{Mn}}<^>{3+}}_{2}{\mathrm{O}}_{4}$), manganite (& gamma;-Mn3+OOH), rhodochrosite (Mn2+CO3), and a trace amount of Mn4+O2 mineral. Jarosite KFe3+3SO42(OH)6 $\left({{\text{KFe}}<^>{3+}}_{3}{\left({\text{SO}}_{4}\right)}_{2}{(\text{OH})}_{6}\right.$) is also found. Mn2+ dissolved from olivine contributes to the formation of Mn-precipitates. A weakly acidic-neutral fluid containing a trace amount of CO32- ${{\text{CO}}_{3}}<^>{2-}$ 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, Mn2+/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 Mn2+/3+-precipitates may have been triggered by the melting of permafrost caused by an impact event around & SIM;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 & SIM;633 Ma and & SIM;11 Ma. Manganese-precipitates and sulfate mineral (jarosite) are discovered in a Martian nakhlites meteorite, Yamato (Y) 000802. In Y 000802, manganese is leached from olivine and precipitates as divalent and trivalent manganese minerals. Manganese-precipitates are also found at the Endeavour and Gale craters on Mars, which is predicted to be a tetravalent manganese mineral. A strong oxidizing agent is required to form the tetravalent manganese mineral and jarosite. In contrast, a strong alkaline reducing environment is required to form the divalent and trivalent manganese minerals. Hence, Y 000802 would be altered in a deep part of the Martian subsurface where it is isolated from water containing strong oxidizing agents. A trace amount of tetravalent manganese minerals is also found in Y 000802. After the formation of divalent and trivalent manganese minerals, Y 000802 was probably brought to a shallow part of the Martian subsurface by impact, making it susceptible to water containing strong oxidizing agents. The pyrrhotite included in Y 000802 was dissolved by the water, producing a highly acidic fluid that induced the formation of jarosite and tetravalent manganese. These alterations that formed the manganese precipitates and jarosite probably occurred during middle to late Amazonian time. Mn2+/3+-precipitates: hausmannite, manganite, rhodochrosite, and a trace amount of Mn4+O2 mineral were discovered in Y 000802 nakhlitesMn2+/3+-minerals were precipitated from strong alkaline reducing fluid at the deep part of the Martian subsurfaceLater, Mn4+O2 mineral and jarosite were formed in the nakhlite by strong oxidizing agent near the Martian surface