The age is calculated using macros which iterate the age equations until a solution is reached to 0. Most other geochronometers usually have a much lower closure temperature. All three minerals preferentially fractionate Y, yet they form and break down at different stage of metamorphism. Monazite may be present as elongate grains aligned in foliation. If all Pb are suddenly removed from monazite by a geological event replacing batterythe age become zero
However, it can also be interpreted that the monazite grew along the foliation of other minerals long after the shearing.