This section will introduce two alternative methods for calculating average ages, and the next section will add a third.Each of these new methods is more appropriate than the arithmetic mean age in specific applications.
However, in the presence of -emitting zircon inclusion contained in an apatite without U and Th.
The inclusion ejects He into the surrounding apatite that is measured following degassing by heating with a laser or in a resistance furnace.
“Pooling” several grains boosts the signal strength and sometimes averages out -ejection correction errors caused by zoning and mineral inclusions. (2007) introduced the “pooled age” as the best way to compare multiple single-grain ages with one or more multi-grain ages, or to compare two sets of multi-grain ages with each other (Figure 1).
The pooled age is calculated by adding the respective U, Th and He abundances (in moles) of several measurements together, thereby generating one “synthetic” multi-grain measurement.
This problem can be detected with the (U-Th)/He isochron.
In the absence of mineral inclusions, the isochron goes through the origin (P=[He]=0).
The only cost of the new procedure is computational complexity.
To facilitate the calculations, they are implemented in an online calculator () and illustrated on a published dataset of inclusion-bearing apatites.
(a) According to the linear age equation, (U-Th)/He ages are given by the slopes of lines connecting each point (P,[He]) with the origin; (b) the “pooled” age is a “synthetic multi-grain age” calculated from the summed production rates and helium-abundances of all the measurements. The pooled age of the sample is 11.28 The previous section showed that (U-Th)/He data can be visualized on a two-dimensional plot of helium abundance or concentration versus -production (Figure 1).
To calculate a pooled age, it is important that [U], [Th] and [He] are elemental .
Because such bias can be associated with anomalous grains affected by radiation damage or implanted helium, the pooled age may be wrong by effectively giving extra weight to outliers.