The Abundance and Hydrogen Isotopic Composition of Water in SNC Meteorites: Implications for Water on Mars

Citation

Leshin, Laurie Ann (1995) The Abundance and Hydrogen Isotopic Composition of Water in SNC Meteorites: Implications for Water on Mars. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/36AJ-NW91. https://resolver.caltech.edu/CaltechETD:etd-11062007-091745

Abstract

The water in the current martian atmosphere contains ~5 times more deuterium (D) than water on Earth (corresponding to a δD value of ~+4000) resulting from preferential loss of hydrogen relative to deuterium from the martian atmosphere. This thesis places constraints on the D/H of other martian water reservoirs by measuring the D/H of water in hydrous phases within the SNC meteorites, thought to be samples of martian igneous rocks.

Results from vacuum extractions of volatiles from bulk SNC samples by stepwise heating show the water yields to decrease and δD values to increase to well above terrestrial values with increasing temperature, indicative of mixing between terrestrial ~+2000 for Shergotty, the most Denriched sample. However, even the highest δD values measured may represent lower limits on the true values due to partial exchange with lighter terrestrial water.

D/H and water contents of individual amphibole, biotite and apatite grains in several SNC meteorites were measured using an ion microprobe. The amphiboles contain an order of magnitude less water than previously assumed, suggesting that SNC parent magmas may have been less hydrous than previously proposed. The δD values of the phases range from ~+500 to +4300. The variability and D-enriched nature of these values imply that the primary igneous phases have not retained a martian magmatic water signature. Rather, the high and variable D/H of the water in these phases, like that released at high temperatures from bulk SNC samples, is concluded to result from the interaction of the samples with D-enriched martian crustal fluids after crystallization, probably in an environment similar to terrestrial magmatic hydrothermal systems.

The data presented in this thesis represent the first direct evidence for ubiquitous crustal water-igneous rock interaction on another planet. Moreover, the results imply that a large amount of water must have been lost from the martian system since water in the martian crust, in addition to the atmosphere, appears to reflect D-enrichment processes.

Thesis Files