Antarctic Alteration of Meteorites

Steer, Elisabeth (2016). Antarctic Alteration of Meteorites. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000bc50

Abstract

The discovery of large accumulations of meteorites in Antarctica is comparably recent, with annual collection expeditions beginning in 1974. Since then, over 50,000 meteorites have been recovered from the icefields of Antarctica. Many of those meteorites have had long residence times of up to 2 Ma mostly encased in ice; during which many of the meteorites have undergone considerable alteration. Understanding the paths of alteration allows reconstruction of original features, but additionally it gives a unique opportunity to examine a natural laboratory of cold, water-restricted alteration environments similar to those on Mars today and in its history.

To fully understand the weathering of meteorites in these environments, six L6 chondrites in a variety of weathering states have been examined and characterised petrologically, chemically, and magnetically. Chemical analyses undertaken are major and trace elements measured in bulk and in spatially resolved analysis and bulk oxygen isotopes.

Petrology has proven to control the weathering patterns and alteration state of the meteorite. A chemical weathering index has been developed to characterise the state of weathering using bulk chemical data, which also links with the petrological findings. This is especially evident in micro features created by shock, which promote rapid mineral breakdown and acidification of alteration fluids, which, fundamentally changes the nature and speed of the alteration. Shock generated features have created increased vulnerability to weathering and so areas that have undergone significant shock on Mars are more vulnerable to weathering and breakdown. However, the heterogeneity that is inherent to alteration environments of low water to rock ratios results in short transport distances for elements, resulting in little bulk chemical change with significant mineralogical alteration.

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