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A primer on apatite fission track dating. Apatite commonly contains a little bit of 238 U. When 238 U decays, the ejected alpha particle creates a track of damage inside the apatite grain. How does this occur?. A fission track.
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A primer on apatite fission track dating • Apatite commonly contains a little bit of 238U. • When 238U decays, the ejected alpha particle creates a track of damage inside the apatite grain.
How does this occur? A fission track Use dilute nitric acid to etch the tracks on the apatite surface so they are visible. Etched fission tracks
So, what determines how many tracks are made? • Directly related to two variables: • 1) time • 2) uranium content • So, we must determine how much U is present in each apatite to eliminate it as a variable. • Then, we can calculate the age.
What age are we calculating? • Apatite tracks anneal at elevated temperature! • Cold temperatures stop apatite from recrystallizing. • Let’s look at the age of tracks vs temperature:
So, what does this mean:? • If the U content is known, and the tracks are counted, then time since passing through the 100°C ± 20°C isotherm can be calculated. This is an apatite fission track age. Gives information on uplift rate for rocks. • Also, mean track length gives information on how slowly or rapidly the sample came through this isotherm (i.e. fast = all long tracks; slow = many short tracks).