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Improved measurement of fission-track annealing in apatite using c-axis projection

¹ Jackson School of Geosciences, University of Texas, Austin, Texas, U.S.A.
² Research School of Earth Sciences at University College of London, U.K.
³ Apatite to Zircon, Inc., Viola, Idaho, U.S.A.
⁴ Département des Sciences de la Terre, Université Paris Sud, Orsay-Cedex, France

Correspondence: ^* E-mail: ketcham{at}mail.utexas.edu

Apatite fission-track length data are used extensively for thermal history inversion. However, several studies have documented instances of poor reproducibility of length data. We address this problem by using c-axis projection to normalize track lengths for crystallographic angle in the extensive laboratory annealing data set acquired by Barbarand et al. (2003a, 2003b). A new simplification reduces the c-axis projection model from six to four fitted parameters. Normalizing for track angle using c-axis projection improves every aspect of length measurement reproducibility examined. It accelerates convergence of mean length in single analyses; increases consistency among replicate measurements by a single analyst; enhances consistency of measurements of the same mounts by different analysts; and improves the match between analyses conducted with and without Cf-irradiation. C-axis projection is also shown to enhance the thermal sensitivity of length data. Based on these results, we assert that c-axis projection is a good means of compensating for observer bias, although it does not overcome differences caused by experimental error.

Key Words: Fission-track • apatite • annealing • anisotropy • thermochronology

This article has been cited by other articles:

				F. Lisker, B. Ventura, and U. A. Glasmacher Apatite thermochronology in modern geology Geological Society, London, Special Publications, January 1, 2009; 324(1): 1 - 23. [Abstract] [Full Text] [PDF]