Fisson track dating
The partial annealing zone for apatite lies between 60°C and 120°C (Green and Duddy, 1989; Corrigan, 1993), with a mean effective closure temperature constrained at 110 ± 10°C.Fission track dating was applied to a large number of apatites for the first time. Apatites taken from different types of rocks from the Odenwald (Germany) were studied.Layer counting - essentially counting back through annually deposited layers within a rock.Can be very accurate, but is only applicable to extremely limited material such as speleothems that have grown continuous or varved lake sediments with continuous deposition and are still actively being formed. Marine oxygen isotope records can be 'tuned' to orbital forcing of glacial/interglacial cycles.Accurate and precise age estimates can be obtained on glass by use of the isothermal plateau fission-track (ITPFT) dating method.Correction for partial track fading is achieved by heating the natural sample and its irradiated aliquot for 30 days at 150°C.FT thermochronology is widely used for reconstruction of low-temperature thermal histories in upper crustal rocks.The method has found particular application in estimating temperature history and long-term denudation rates in orogenic belts, rifted margins and more stable areas, providing a means of assessing the timing and volume of sediment being delivered to sedimentary basins, and as an estimator of hydrocarbon maturity potential.
The fission track (FT) method is a single crystal technique and has several advantages in comparison to other dating methods: (1) any loss of daughter products due to increase of temperature can be detected through track-length measurements and (2) the low temperature range covered by the FT method (~300 – 60°C) is out of detection of most other radiometric dating systems.
Orbital forcing (essentially how variations in the Earth's orbit, axis etc.
affect the amount of sunlight received) can be calculated, so the oxygen isotope startigraphy can be used to determine absolute ages.
In apatite it is easy to identify fission tracks on the (0001) face if one uses the oil immersion technique. The fission track ages obtained have to be interpreted individually.
The apatites taken from volcanic rocks yield crystallization ages.