Martian subsurface fluid pathways and 3D mineralogy of the Nakhla meteorite

The three dimensional structure of the Nakhla meteorite has been investigated in order to provide a detailed picture of the fluid pathways in the volcanic subsurface of Mars. A combination of computed tomography and electron microscopy have been used to identify, characterise and interpret the distribution, size, interconnectivity and secondary mineralisation of fractures through which water flowed. Secondary minerals which formed during aqueous alteration are found as fracture-filling silicates in olivine grains and a range of carbonates, sulfates and halite are found throughout olivine, pyroxene and mesostasis. The fractures which acted as fluid pathways are highly interconnected, branching and reconnecting at multiple locations, leading to a pervasive and homogeneous distribution of secondary minerals throughout the sample. Miniature topographic basins have been identified and provide a unique method of identifying the true orientation of the meteorite while on its host planetary surface. Halite and sulfate are found to be related to one another, likely formed in the same episode of fluid flow, and are found to postdate both carbonate and olivine-hosted silicate-alteration products. Later episodes of fluid flow may have interacted with, and potentially eroded, earlier generations of secondary minerals. Nakhla, and by implication the other nakhlite meteorites, therefore preserves a complex record of multiple episodes of fluid flow on Mars in the past billion years.