Articles | Volume 3, issue 2
Geochronology, 3, 561–575, 2021
Geochronology, 3, 561–575, 2021

Research article 21 Dec 2021

Research article | 21 Dec 2021

Deconvolution of fission-track length distributions and its application to dating and separating pre- and post-depositional components

Peter Klint Jensen1 and Kirsten Hansen2 Peter Klint Jensen and Kirsten Hansen
  • 1Department of Civil Engineering, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
  • 2Natural History Museum of Denmark, University of Copenhagen, 1350 Copenhagen, Denmark

Abstract. To enable the separation of pre- and postdepositional components of the length distribution of (partially annealed) horizontal confined fission tracks, the length distribution is corrected by deconvolution. Probabilistic least-squares inversion corrects natural track length histograms for observational biases, considering the variance in data, modelization, and prior information. The corrected histogram is validated by its variance–covariance matrix. It is considered that horizontal track data can exist with or without measurements of angles to the c axis. In the latter case, 3D histograms are introduced as an alternative to histograms of c-axis-projected track lengths. Thermal history modelling of samples is not necessary for the calculation of track age distributions of corrected tracks. In an example, the age equations are applied to apatites with predepositional (inherited) tracks in order to extract the postdepositional track length histogram. Fission tracks generated before deposition in detrital apatite crystals are mixed with post-depositional tracks. This complicates the calculation of the post-sedimentary thermal history, as the grains have experienced different thermal histories prior to deposition. Thereafter, the grains share a common thermal history. Thus, the extracted post-depositional histogram without inherited tracks may be used for thermal history calculation.

Short summary
Fission tracks are generated in minerals due to spontaneous fission of uranium-238. The initial track length decreases with time due to recrystallization. The age of a track can be calculated by counting the number of the shorter tracks per volume and including the decay constant. However, the theoretical order of the track length versus time is disrupted by uncertainties. We shown how the order can be re-established. The age of tectonic events such as uplift and burial can then be determined.