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A helium-based model for the effects of radiation damage annealing on helium diffusion kinetics in apatite

Willett, CD; Fox, M; Shuster, DL; (2017) A helium-based model for the effects of radiation damage annealing on helium diffusion kinetics in apatite. Earth and Planetary Science Letters , 477 pp. 195-204. 10.1016/j.epsl.2017.07.047. Green open access

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Abstract

Widely used to study surface processes and the development of topography through geologic time, (U–Th)/He thermochronometry in apatite depends on a quantitative description of the kinetics of 4He diffusion across a range of temperatures, timescales, and geologic scenarios. Empirical observations demonstrate that He diffusivity in apatite is not solely a function of temperature, but also depends on damage to the crystal structure from radioactive decay processes. Commonly-used models accounting for the influence of thermal annealing of radiation damage on He diffusivity assume the net effects evolve in proportion to the rate of fission track annealing, although the majority of radiation damage results from α-recoil. While existing models adequately quantify the net effects of damage annealing in many geologic scenarios, experimental work suggests different annealing rates for the two damage types. Here, we introduce an alpha-damage annealing model (ADAM) that is independent of fission track annealing kinetics, and directly quantifies the influence of thermal annealing on He diffusivity in apatite. We present an empirical fit to diffusion kinetics data and incorporate this fit into a model that tracks the competing effects of radiation damage accumulation and annealing on He diffusivity in apatite through geologic time. Using time–temperature paths to illustrate differences between models, we highlight the influence of damage annealing on data interpretation. In certain, but not all, geologic scenarios, the interpretation of low-temperature thermochronometric data can be strongly influenced by which model of radiation damage annealing is assumed. In particular, geologic scenarios involving 1–2 km of sedimentary burial are especially sensitive to the assumed rate of annealing and its influence on He diffusivity. In cases such as basement rocks in Grand Canyon and the Canadian Shield, (U–Th)/He ages predicted from the ADAM can differ by hundreds of Ma from those predicted by other models for a given thermal path involving extended residence between ∼40–80 °C.

Type: Article
Title: A helium-based model for the effects of radiation damage annealing on helium diffusion kinetics in apatite
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.epsl.2017.07.047
Publisher version: http://doi.org/10.1016/j.epsl.2017.07.047
Language: English
Additional information: © 2017 Elsevier B.V. All rights reserved. This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Science & Technology, Physical Sciences, Geochemistry & Geophysics, apatite, radiation damage, annealing, helium, diffusion kinetics, thermochronometry, GRAND-CANYON, FISSION TRACKS, (U-TH)/HE THERMOCHRONOMETRY, COLORADO PLATEAU, ZIRCON, TEMPERATURE, INCISION, HE-4/HE-3, HISTORY, BURIAL
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10027175
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