Argon–argon dating

Argon–argon dating estimates the age of potassium-bearing rocks by comparing argon-39 produced from potassium-39 during neutron irradiation with naturally occurring argon-40.

Potassium-40: A naturally occurring radioactive isotope of potassium that decays to argon-40 and calcium-40. Its decay supplies the radiogenic argon-40 measured against irradiation-produced argon-39.
Radiometric dating: A method of determining age from predictable changes in radioactive isotopes. Argon–argon dating is one isotope-based approach to estimating geological time.
Volcanic ash dating: Dating volcanic ash deposits to establish the timing of eruptions and surrounding geological events. Sanidine and other potassium-bearing minerals in ash can yield precise eruption ages.
Potassium–argon dating: A radiometric method that dates rocks by measuring potassium-40 and radiogenic argon-40 separately. Argon–argon measures both isotopes in one sample, avoiding separate potassium analysis.
Excess argon: Argon trapped in a mineral beyond the amount expected from radioactive decay of its potassium. It can make an apparent argon–argon age older than the rock’s true formation age.
Argon-39: A radioactive argon isotope produced from potassium-39 by neutron capture followed by radioactive decay. Its measured abundance acts as a proxy for the potassium originally present in the sample.
Isotope: A form of an element whose atoms have the same proton number but different neutron numbers. The method distinguishes argon isotopes by mass and compares their abundances.
Sanidine: A high-temperature potassium feldspar commonly found in volcanic rocks. Its potassium content and often rapid argon retention make it a favored dating mineral.
Uranium–lead dating: A radiometric dating method based on uranium isotopes decaying into lead isotopes. It provides an independent clock with different minerals, decay systems, and disturbance sensitivities.
Argon loss: The escape of radiogenic argon from a mineral through diffusion or geological alteration. Loss can yield ages younger than crystallization or produce discordant heating spectra.

Linked from 12 pages