Annealing of ion tracks in apatite under pressure characterized in situ by small angle x-ray scattering

Rodney C Ewing,Nigel Kirby,Boshra Afra,Pablo Mota-Santiago,Christina Trautmann,Daniel Schauries,Patrick Kluth,Maik Lang

doi:10.1038/s41598-020-57600-y

Abstract

Fission track thermochronology is routinely used to investigate the thermal history of sedimentary basins, as well as tectonic uplift and denudation rates. While the effect of temperature on fission track annealing has been studied extensively to calibrate the application of the technique, the effect of pressure during annealing is generally considered to be negligible. However, a previous study suggested elevated pressure results in a significantly different annealing behaviour that was previously unknown. Here, we present a method to study track annealing in situ under high pressure by using synchrotron-based small angle x-ray scattering (SAXS). To simulate fission tracks in a controlled environment, ion tracks were created in apatite from Durango, Mexico using 2 GeV Au or Bi ions provided by an ion accelerator facility. Samples were annealed at 250 °C at approximately 1 GPa pressure using diamond anvil cells (DACs) with heating capabilities. Additional in situ annealing experiments at ambient pressure and temperatures between 320 and 390 °C were performed for comparison. At elevated pressure a significantly accelerated annealing rate of the tracks was observed compared with annealing at ambient pressure. However, when extrapolated to geologically relevant temperatures and pressures, the effects become very small. The measurement methodology presented provides a new avenue to study materials behaviour in extreme environments.

Highlights

Fission track thermochronology is routinely used to investigate the thermal history of sedimentary basins, as well as tectonic uplift and denudation rates
Applications of fission track thermochronology include the investigation of the thermal histories of sedimentary basins, as well as studies of tectonic uplift and denudation rates, and dating of volcanic ashes[7]
We present a new methodology for studying the annealing of ion tracks under high-pressure in situ by means of synchrotron based small angle x-ray scattering (SAXS)

Summary

Introduction

Fission track thermochronology is routinely used to investigate the thermal history of sedimentary basins, as well as tectonic uplift and denudation rates. As the minerals are generally exposed to elevated pressures in the Earths’ crust, the influence of pressure on the annealing behaviour of fission tracks has already been discussed since the 1960s While this effect was generally considered to be negligible[10,11], a study by Wendt el al. Has challenged this assumption and suggested slower annealing rates under elevated pressure[12] These results remained controversial[13,14] and a more recent investigation by Schmidt et al has found an accelerated annealing behaviour of fission tracks under very high pressures that becomes negligible at geologically relevant values[7]

Methods

Results

Conclusion