On the method of age estimation of open U-Pb isotopic systems

The method of calculation of the age and time of the superposition process for uranium-lead systems, subjected to uranium fractionation as to lead is suggested. It is shown that in three-dimensional space lead and uranium isotopic ratios are located in one plane described with the equation: 207Pb/204Pb=a1206Pb/204Pb+a2238U/204Pb+a3. Application of the method of the least squares according to three parameters permits to calculate coefficient values of the plane equation. Numerical examples of the above method application are presented. The method suggested permits to derive additional geochronological information from non-isochronic dependences and to extend the number of geological objects, which can be dated by lead-isochronic method according to the rock on the whole