Concordia Diagrams If a system has been closed to uranium and lead and a correction is made for initial lead then the isotope ratios will plot on the concordia – an ideal plot of 206 Pb/ 238 U vs 207 Pb/ 235 U If lead or uranium are lost or gained then the ratios will lie along a straight line that intersects the concordia at the time the rock crystallized (t) and when it was disturbed (t).
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