Charlier, B. L. A.; Needham, A. W. and Grady, M. M.
Dating of secondary minerals in nakhlites.
In: 74th Annual Meeting of the Meteoritical Society, 8-12 August 2011, London, UK.
Nakhlites are a group of martian clinopyroxenites, currently 13 in number, that have a tightly-constrained crystallization age of 1320 ± 40 Ma. They are thought to emanate from either a single lava flow, or closely-allied series of flows, and following their crystallization, have experienced aqueous alteration. Secondary alteration products include clay minerals, carbonates, sulphates and halite, which form complex assemblages and intergrowths. It is not clear what the relationship is between the different minerals: they may have formed by gradual evaporation following a single episode of fluid incursion , or over an extended period of time following several episodes of aqueous activity. The latter case is supported by spectral data from widespread regions of the martian surface, where overlying units of secondary minerals have been employed to produce a relative chronology. Direct measurement of the age of the secondary products in the meteorites has been difficult – the minerals are fine-grained and not easy to separate from their host silicates. Where results have been obtained, they indicate formation ages of around 600 Ma for phyllosilicates. We have used Rb-Sr dating of Nakhla and Y 000593 in an attempt to determine a series of ages for different components within the meteorites.
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