Date

5-1-2017

Document Type

Thesis

Degree

Master of Science

Department

Earth and Environmental Sciences

First Adviser

Peter K. Zeitler

Abstract

Apatite (U-Th)/He thermochronology is among the most powerful techniques used to resolve low-temperature near-surface thermal histories, but issues remain regarding the interpretation of age data that must be addressed as the method continues to move forward. These issues crop up as the problem of age dispersion: the fact that some rocks have wide variations in the apatite (U-Th)/He (AHe) ages they yield, often far outside the analytical error expected. These unresolvable data sets thus cast doubt the usability of AHe dating in certain geologic environments. New AHe ages, analyzed by the continuous ramped heating (CRH) method (Idleman et al., 2017; McDannell et al., 2017) show a range of different possible diffusive behaviors of helium, and correspondingly different levels of age dispersion. Using a newly developed sample characterization method, geometrically necessary dislocation (GND) densities have been calculated from apatites from these same samples. These measurements were made in order to understand the role dislocations or other crystallographic microstructures play in causing age dispersion. The data from this method do not show any simple correlation between GND density and average age or any other metric used to characterized apatite samples. Further work will be needed to develop this method and generate a larger dataset.

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