Journal cover Journal topic
Geochronology Advances in geochronological science
Journal topic
Preprints
https://doi.org/10.5194/gchron-2020-24
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/gchron-2020-24
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  28 Sep 2020

28 Sep 2020

Review status
This preprint is currently under review for the journal GChron.

Thermal Annealing of Implanted 252Cf Fission-1 Tracks in Monazite

Sean Jones, Andrew Gleadow, and Barry Kohn Sean Jones et al.
  • School of Earth Sciences, University of Melbourne, Victoria 3010, Australia

Abstract. A series of isochronal heating experiments were performed to constrain monazite fission-track thermal annealing properties. 252Cf fission-tracks were implanted into monazite crystals from the Devonian Harcourt Granodiorite (Victoria, Australia) on polished surfaces oriented parallel and perpendicular to (100) prismatic faces. Tracks were annealed over 1, 10, 100 and 1000 hour schedules at temperatures between 30 °C and 400 °C. Track lengths were measured on captured digital image stacks, and then converted to calculated mean lengths of equivalent confined fission tracks which progressively decreased with increasing temperature and time. Annealing is anisotropic, with tracks on surfaces perpendicular to the crystallographic c-axis consistently annealing faster than those on surfaces parallel to c. To investigate how the mean track lengths decreased as a function of annealing time and temperature, one parallel and two fanning models were fitted to the empirical dataset. The temperature limits of the monazite partial annealing zone (MPAZ) were defined as length reductions to 0.95 (lowest) and 0.5 (highest) for this study. Extrapolation of the laboratory experiments to geological timescales indicates that for a heating duration of 107 years, estimated temperature ranges of the MPAZ are −44 to 101 °C for the parallel model and −71 to 143 °C (both ~ 6–21 °C, 2 standard errors) for the best fitting linear fanning model (T0 = ∞). If a monazite fission-track closure temperature is approximated as the mid-point of the MPAZ, these results, for tracks with similar mass and energy distributions to those involved in spontaneous fission of 238U, are consistent with previously estimated closure temperatures (calculated from substantially higher energy particles) of < 50 °C and perhaps not much above ambient surface temperatures. Based on our findings we estimate that this closure temperature (Tc) for fission tracks in monazite ranges between ~ 45 and 25 °C over geological timescales of 106–107 years making this system potentially useful as an ultra-low temperature thermochronometer.

Sean Jones et al.

Interactive discussion

Status: open (until 09 Nov 2020)
Status: open (until 09 Nov 2020)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
[Subscribe to comment alert] Printer-friendly Version - Printer-friendly version Supplement - Supplement

Sean Jones et al.

Sean Jones et al.

Viewed

Total article views: 138 (including HTML, PDF, and XML)
HTML PDF XML Total BibTeX EndNote
100 34 4 138 1 1
  • HTML: 100
  • PDF: 34
  • XML: 4
  • Total: 138
  • BibTeX: 1
  • EndNote: 1
Views and downloads (calculated since 28 Sep 2020)
Cumulative views and downloads (calculated since 28 Sep 2020)

Viewed (geographical distribution)

Total article views: 107 (including HTML, PDF, and XML) Thereof 107 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 

Cited

Saved

No saved metrics found.

Discussed

No discussed metrics found.
Latest update: 19 Oct 2020
Publications Copernicus
Download
Short summary
We present the results of a series of experiments that constrain the temperature sensitivity of fission tracks in monazite over geological time. It was concluded that over a heating duration of ten million years the estimated closure temperature is < 50 °C and perhaps not much above ambient surface temperatures. Monazite fission track thermochronology has the potential to understand the thermal history of the Earth's upper crust (< 1–2 km) and constrain the timing of geological processes.
We present the results of a series of experiments that constrain the temperature sensitivity of...
Citation