Thermochemical modelling of the alteration assemblage in Martian Meteorite ALH84001 at low temperature (15–25 °C)

Melwani Daswani, M.; Schwenzer, S. P.; Wright, I. P. and Grady, M. M. (2013). Thermochemical modelling of the alteration assemblage in Martian Meteorite ALH84001 at low temperature (15–25 °C). In: The 3rd UK in Aurora Meeting: Advances in Mars Science, 8 Feb 2013, London, UK.

URL: http://www.ras.org.uk/

Abstract

The origin of secondary carbonate minerals in the martian meteorite ALH84001 has been intensely debated in the literature, with widely different thermal origins considered: from hydrothermal [e.g. 1] to low temperature alteration [e.g. 2]. Isotopic evidence suggests the carbonates precipitated from evaporating water at 18±4 ºC under near-surface conditions [3]. We tested this latter scenario with the thermochemical modelling program CHIM-XPT at 15, 20 and 25 ºC; and pressures of 1 and 2 bar of atmospheric CO₂. The water-to-rock ratio (W/R) was varied to obtain alteration precipitates. Isothermal evaporation scenarios were also modelled starting from W/R≤5. The composition of the ALH84001 host rock was obtained from [5] and the secondary phases were not included in the unaltered rock composition modelled. The composition of the starting fluid consisted of water equilibrated with 1 or 2 bar of atmospheric CO₂.