U-Th-Pb Dating

General. Three independent ages may be obtained in the U-Th-Pb system or and 

Stieff and Stern (1961) and Stieff et al. (1963) considered plots of data similar to the concordia plot wherein the common lead was not first removed in the age calculation. These plots allow calculation of the initial ° Pb/ ° Pb. Also valuable are plots of ° Pb/ Pb versus U/ Pb and ° Pb/ Pb versus U/ Pb, similar to the strontium isochron plot (or Bernard Price Institute plots), which also allow the initial values of ° Pb/ Pb and Pb/ ° Pb to be determined. These plots are best suited to situations in which there is not great radiogenic enrichment. One good example of this application is given by Mirkina and Makarochkin (1966). 

Though considerable data have been obtained on Th-Pb dating, this dating has received less emphasis because of the lack of a companion radioactive parent isotope to go with Th. The theoretical behavior is, however, given by Steiger and Wasserburg (1966). 

A table of equations and parameters used in age calculations is given in Table 1. The decay constants are those preferred from the 

Initial ratio is that ratio which the phase contained when it was formed. 

---

We do, however, also include brief discussion of the principles and application of U-Th-Pb dating which can theoretically be applied to material up to the age of the Earth. 

Criteria for successful U-Th-Pb dating are similar to those of standard U-series techniques, but in addition (1) sufficient amounts of ° Pb and ° Pb must have accumulated by radiogenic ingrowth to be distinguished from the initial Pb that is always present at the time of formation and (2) the decay scheme must be closed for all intermediate daughters from °Th and Pa to stable ° Pb and ° Pb, respectively. 

This method has been most widely used in (i) the °K- °Ar system, (ii) the U-Th-He system, (iii) the U-Pb dating of zircon, and (iv) the U-Th-Pb dating of monazite using electron microprobe measurements. The last is a developing method with large errors because of the low analytical precision and because isotopes are not measured. 

Neymark, L. A., Paces, J. B. Amelin, Y. V. 2003. Reliability of U-Th-Pb dating of secondary silica at Yucca Mountain, Nevada. 10th International High-Level Radioactive Waste Management Conference, March 30 to April 3 2003, Las Vegas, NV, 1-12. 

Ayers J. C., Dunkle S., Gao S., and Miller C. F. (2002) Constraints on timing of peak and retrograde metamorphism in the Dabie Shan ultrahigh-pressure metamorphic belt, east-central China, using U-Th-Pb dating of zircon and monazite. Chem. Geol. 186, 315-331. 

U-Th-Pb Dating of Monazite Using Only Uranium, Thorium, and Lead Concentrations... 

Baadsgaard, H. 1973. U-Th-Pb dates on zircons from the Early Precambrian Amitsoq gneisses. Earth and Planetary Science Letters, 33, 261-267. 

---