Secondary Minerals in the Nakhlite Meteorite Yamato 000593: Distinguishing Martian from Terrestrial Alteration Products

• Main Authors: Breton, H., Lee, M.R., Mark, D.F.
• Format: Conference Object
• Language: English
• Published: 2015
• Subjects: Antarctic; Yamato; Antarc*; Antarctica
• Online Access: http://eprints.gla.ac.uk/102426/; http://eprints.gla.ac.uk/102426/1/102426.pdf

The nakhlites are olivine-bearing clinopyroxenites that formed in a Martian lava flow or shallow intrusion 1.3 Ga ago [1, 2]. They are scientifically extremely valuable because they interacted with water-bearing fluids on Mars [3]. Fluid-rock interactions led to the precipitation of secondary minerals, many of which are hydrous. The secondary minerals consist in a mixture of poorly crystalline smectitic material and Fe-oxide, collectively called “iddingsite”, but also carbonate and sulphate [4]. The proportion, chemistry and habit of the secondary minerals vary between members of the Nakhlite group, which is thought to reflect compositional variation of the fluid within the Martian crust [5]. However, some secondary minerals are quite similar to terrestrial alteration products and thus the chemical and textural variations could also reflect terrestrial contamination (deposition or exchange). Identifying the origin of the secondary minerals is not straightforward but essential to unravel the Martian fluid chemistry and conditions. Yamato 000593 (Y-000593) is a nakhlite meteorite that was discovered in Antarctica near the Yamato Mountains by the Japanesse Antarctic Research Expedition in 2000-2001 [6]. Most of the meteorite is covered by a black shiny fusion crust but it also has deep erosion features in its underside that probably formed by freeze- thaw cycles. As in most other Nakhlites, Y 000593 contains iddingsite-like alteration products believed to have been formed on Mars because they have devolatilization features at the vicinity of the fusion crust [7]. Additional evidence of Martian aqueous alteration is the presence of laihunite, a high temperature oxidative alteration product of fayalitic olivine [8]. The secondary minerals in Y-000593 can provide a powerful insight into the Martian hydrosphere from high to low temperature environments with implications for the origin, cycling, and availability of water on Mars. However, it is highly likely that some secondary minerals have formed on Earth which can biased our understanding of the Martian groundwater chemistry. With this in mind, we are trying to identify all the different secondary minerals and document their spatial and textural relations, their mineralogy and chemistry to better constrain their possible origin and the impact that terrestrial fluids may have had on the Martian alteration products.