EARTH221 Lecture Notes - Lecture 10: Uranium-238, Uranium-235, Zircon

• School: University of Waterloo
• Department: Earth Sciences
• Course: EARTH221
• Professor: Brian Kendall

Document Summary

Lecture 10: u (238 and 235) are the long-lived radioactive isotopes that decay into a final stable daughter isotope pb (206 and 207 respectively) Intermediate radioactive daughters are short lived: undergo positron and negatron decays, uranium 238 has a much greater half life compared to uranium 235, if geological material < 2 million yeas old. Can use intermediate daughters for geochronology: if geological material > 2 million years old. Can treat u isotopes as decaying directly to pb: zircon. Provides time of volcanism or magma crystallization: u-pb concordia diagram. The isochron diagram is only used when there is one parent and one daughter. Positron decay will release enough energy (he 4) to cause radiation damage (pb loss) Pb has a high charge and radius so it is not compatible with the zircon crystal system and so under high temp and metamorphism pb is easily lost compared to the parent (goldschmidts rules)