Fission Track Dating - Applications

Applications

Unlike many other dating techniques, fission-track dating is uniquely suited for determining low-temperature thermal events using common accessory minerals over a very wide geological range (typically 0.1 Ma to 2000 Ma). Apatite, sphene, zircon, micas and volcanic glass typically contain enough uranium to be useful in dating samples of relatively young age (Mesozoic and Cenozoic) and are the materials most useful for this technique. Additionally low-uranium epidotes and garnets may be used for very old samples (Paleozoic to Precambrian). The fission-track dating technique is widely used in understanding the thermal evolution of the upper crust, especially in mountain belts. Fission tracks are preserved in a crystal when the ambient temperature of the rock falls below the annealing temperature. This annealing temperature varies from mineral to mineral and is the basis for determining low-temperature vs. time histories. While the details of closure temperatures are complicated, they are approximately 70 to 110 °C for typical apatite, c. 230 to 250 °C for zircon, and c. 300°C for titanite.

Because heating of a sample above the annealing temperature causes the fission damage to heal or anneal, the technique is useful for dating the most recent cooling event in the history of the sample. This resetting of the clock can be used to investigate the thermal history of basin sediments, kilometer-scale exhumation caused by tectonism and erosion, low temperature metamorphic events, and geothermal vein formation. The fission track method has also been used to date archaeological sites and artifacts. It was used to confirm the potassium-argon dates for the deposits at Olduvai Gorge.