Fig. 2: Proposed stages in the evolution of U–Pb system in dolomite precursor carbonate minerals and dolomite, deposited at 400 Ma and altered at 200 Ma, respectively.
From: Late Paleozoic oxygenation of marine environments supported by dolomite U-Pb dating
Changes to the U–Pb system over time are presented using Tera-Wasserburg concordia diagrams. In each plot, the blue line is the concordia curve with blue dots representing time in Ga. a During deposition of carbonate minerals, the initial 207Pb/206Pb ratio is inherited from seawater. b In burial diagenetic environments, long after deposition and following some isotopic decay within the U–Pb system, Pb is redistributed and isotopically homogenized within the sample in a closed system, and dolomite minerals acquire the system-average 207Pb/206Pb ratio. c Following late-stage diagenetic Pb homogenization, isotopic decay within the dolomite proceeds in a closed system to the present, resulting in a U–Pb date younger than the depositional age and an initial 207Pb/206Pb ratio lower than expected initial seawater composition. Gray rhombs and line represent the isochron that would result if there was no alteration.
