Rhenium depletion age

Cratonic mantle peridotites. Over 230 whole-rock cratonic xenoliths have now been analyzed for Re-Os isotope compositions. Given that many peridotite xenoliths have experienced relatively recent rhenium introduction, it is generally best to use rhenium-depletion model ages (Trd) that do not rely on the measured rhenium content of the rock for model age calculation. For cratonic peridotite xenoliths, the frequency distribution of rhenium-depletion ages shows a wide range, with a pronounced mode at 2.5-2.75 Gyr and some samples that have ages of >3.5 Gyr... 

Figure 9.7 Schematic illustration of the concept of mantle extraction ages (Tma) and rhenium depletion ages (Trd) for a residue of partial melting, of which the present day Os/ Os ratio is indicated by the circle on the y-axis. The mantle extraction age uses the measured Re/ Os ratio to calculate the age at which the Os/ Os ratio of the sampl was the same as that of the chondritic mantle. The rhenium depletion age assumes that all rhenium was removed during the partial melting event, and that any rhenium present in the sample now was added recently.

In this case, it is assumed that the residue lost all of its rhenium during the partial melting event, and that any rhenium present was added recently, and therefore did not contribute any radiogenic Os. The rhenium depletion age is always younger than the mantle extraction age. 

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