Uranium–lead concordia and discordance
For a closed system with corrected common lead and retained decay-chain products, radiogenic ratios satisfy ²⁰⁶Pb*/²³⁸U=e^(λ₂₃₈t)−1 and ²⁰⁷Pb*/²³⁵U=e^(λ₂₃₅t)−1.
Key knowledge
For a closed system with corrected common lead and retained decay-chain products, radiogenic ratios satisfy ²⁰⁶Pb*/²³⁸U=e^(λ₂₃₈t)−1 and ²⁰⁷Pb*/²³⁵U=e^(λ₂₃₅t)−1. Varying t traces concordia. Discordant ratios can reveal disturbance, inheritance or disequilibrium, but a discordia intersection is an age interpretation conditional on a specified geological loss/mixing history.
Values and equations
²⁰⁶Pb*/²³⁸U=e^(λ₂₃₈t)−1; ²⁰⁷Pb*/²³⁵U=e^(λ₂₃₅t)−1
- Pb*/U ratios
- radiogenic daughter/parent atom ratios after common-lead correction 1
- λ₂₃₈,λ₂₃₅
- specified chain-parent decay constants s⁻¹
- t
- common closed-system elapsed time s
Conditions and scope
- Use consistent isotopic atom ratios and decay constants, account for common lead, and justify effective chain ingrowth/equilibrium assumptions.
- A simple two-event lead-loss model is a model choice. Continuous loss, multiple domains, inherited zircon, disequilibrium and mixed analyses can require fuller treatments; not every discordant point has a unique two-age explanation.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read actual two-U-isotope/concordia and partial-Pb-loss discussion. The exponential parametric curve is explicitly derived from the stated parent-to-radiogenic-daughter model; retained no source numerical constants or universal earliest-metamorphism interpretation.
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Entry details
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