Location of NWA 6148 and NWA 10153 in the nakhlite body and their aqueous alteration

The petrologic and mineralogical characteristics and alteration processes of the nakhlites NWA 6148 and NWA 10153 were studied. Both consist of augite, olivine, and mesostasis. Based on the characteristics of each volume fraction of the components and the chemical composition of olivine and pyroxene, NWA 6148 correspond to lava units crystallized at 1346–1391 Ma in the nakhlite body. The position of NWA 10153 in the nakhlite body is unclear. Iron oxides/hydroxides, barite, and calcite fill the fractures of NWA 6148, which are terrestrial weathering products. In NWA 10153, olivine grains are replaced by goethite, magnetite, saponite, amorphous silica, jarosite, and siderite. Although it is uncertain whether all of the alteration minerals were formed on the surface of Mars or on the surface of Earth, NWA 10153 records two different alteration environments: reducing, neutral to alkaline, and oxidizing and acidic. As in NWA 6148 and NWA 10153, the assemblage of alteration mineral species in other nakhlites is also heterogeneous even within the same lava unit. The nakhlite body was altered by the oxidizing acidic fluid after a ${\mathrm{CO}}_3^{2-}$-bearing reducing neutral to alkaline fluid. The drastic change of alteration environments may have been caused by an impact event.