Open AccessIncorporating 3‐D parent nuclide zonation for apatite 4 He/ 3 He thermochronometry: An example from the A ppalachian M ountains
Author(s) -
Fox Matthew,
McKeon Ryan E.,
Shuster David L.
Publication year - 2014
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1002/2014gc005464
Subject(s) - apatite , nuclide , geology , thermochronology , crystal (programming language) , thermal diffusivity , tectonics , cosmogenic nuclide , diffusion , mineralogy , physics , thermodynamics , seismology , astrophysics , nuclear physics , cosmic ray , computer science , programming language
The ability to constrain km‐scale exhumation with apatite 4 He/ 3 He thermochronometry is well established and the technique has been applied to a range of tectonic and geomorphic problems. However, multiple sources of uncertainty in specific crystal characteristics limit the applicability of the method, especially when geologic problems require identifying small perturbations in a cooling path. Here we present new 4 He/ 3 He thermochronometric data from the Appalachian Mountains, which indicate significant parent nuclide zonation in an apatite crystal. Using LA‐ICPMS measurements of U and Th in the same crystal, we design a 3‐D model of the crystal to explore the effects of intracrystal variability in radiation damage accumulation. We describe a numerical approach to solve the 3‐D production‐diffusion equation. Using our numerical model and a previously determined time temperature path for this part of the Appalachians, we find excellent agreement between predicted and observed 4 He/ 3 He spectra. Our results confirm this time‐temperature path and highlight that for complex U and Th zonation patterns, 3‐D numerical models are required to infer an accurate time‐temperature history. In addition, our results provide independent and novel evidence for a radiation damage control on diffusivity. The ability to exploit intracrystal differences in 4 He diffusivity [i.e., temperature sensitivity) greatly increases the potential to infer complex thermal histories.