Potassium 40 argon 40 dating spinal cord injury dating
Ar closure temperatures are a function of crystal diffusional length-scale, composition and structure, and cooling rate.
To address the first of these, Knapp and Heizler (1990) select multiple mineral phases to analyze.
It is also common that only the argon released from a crystal early-on is problematic, and that a plateau is reached in the argon that is released in later stages of the analysis.
This plateau must be used with caution, however, because it could have been lowered by later events and therefore may represent a minimum constraint on the age of crystallization.
In these cases, the age of the first batch of argon released is the age of the reheating event, and the age of the last argon released is the minimum age of initial crystallization.
The transition to the region of lower closure temperatures gives the timing of Miocene extension, unroofing, and cooling.
method is based upon the decay of radioactive potassium-40 to radioactive argon-40 in minerals and rocks; potassium-40 also decays to calcium-40.
Hypothetical profiles of argon concentrations through the grain, and associated step-heating results.
(a) A constant concentration profile indicates no diffusion or later heating events. (b) Recent diffusive loss of Ar yields a staircase-type profile.