Assessing Zircon Fission Track Analysis as a Paleotemperature Tool for Sedimentary Basins

Paul F. Green, Kerry A. Hegarty, Ian R. Duddy, and Sara A. Foland

Apatite Fission Track Analysis (AFTA) is well established for investigating thermal histories in sedimentary basins, in the time-temperature realm relevant to generation of oil and gas. An advantage of AFTA is the ability to provide direct determination of the timing, as well as the magnitude of maximum paleotemperatures. This timing information often cannot be obtained from other methods. Zircon is also suitable for fission track analysis, being a common uranium-bearing detrital mineral, and fission track ages can readily be determined. However for many years, the precise thermal stability of fission tracks in zircon has been uncertain. Estimates of the temperature required to remove or "anneal" tracks over timescales of the order of 1 Ma vary from 175°C or less, to 250°C or above.

We have investigated the thermal stability of fission tracks in zircon in geological conditions by comparing ZFTA data with Vitrinite Reflectance (VR) data from sedimentary sequences which have been subjected to profound geological heating. Onset of significant fission track age reduction occurs at VR values of approximately ~6%, while total annealing is equivalent to approximately ~8% R₀max. These results are consistent with extrapolation of recently published laboratory-based kinetic models which suggest that tracks in zircon should be stable to temperatures in excess of 300°C for 1 to 10 Ma. Such paleotemperatures are outside the range normally encountered in hydrocarbon exploration provinces, although ZFTA has found practical application in a number of areas where improved knowledge of the thermal stability has provided new insights.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California