Dear Tanya Srivastava this is a very interesting and important technical question. In this context please have a look at the following potentially useful literature references which might help you in your analysis:
Using Th-U-Pb geochronology to extract crystallization ages of Paleozoic metamorphic monazite contaminated by initial Pb
Article Using Th-U-Pb geochronology to extract crystallization ages ...
and
U–Pb dating of monazite and its application to geological problems
Article U-Pb dating of monazite and its application to geological problems
Fortunately the first articles has been posted by the authors as public full text on RG, so that you can freely download it as pdf file. The author of the second paper is an RG member. Thus you can easily contact him via RG and request the full text directly from this author.
Good luck with your work and please stay safe and healthy!