Capabilities and constraints of the Pb-Pb dating of metamorphogenic minerals using the step-leaching method

Abstract

Based on particular examples, this paper considers the capabilities and constraints of the step-leaching Pb-Pb dating (PbSL) of metamorphogenic minerals. It was shown that stepwise leaching allows the separation of fractions enriched in uranogenic and thorogenic Pb isotopes, which can be used for the determination of mineral ages and the time of crystallization of coexisting equilibrium and, occasionally, disequilibrium monazites. The presence of monazite in a mineral is indicated by a high Th/U ratio similar to that of monazite. The main limitation of the method is related to the presence in minerals of both disequilibrium domains of the mineral matrix and disequilibrium monazite microinclusions. By the example of minerals studied, we discussed three scenarios for the development of the U-Th-Pb isotopic systems of metamorphogenic minerals.