Zircon SHRIMP U-Pb age of the Paleoproterozoic high-pressure granulites from the Sanggan area,the North China Craton and its geologic implications

Zircons extracted from high-pressure granulite and strongly peraluminous granites from the Sanggan area of the North China Craton,have been investigated by integrating petrogenesis with U-Pb ages.The isometric internal structure and round shape of the zircons as revealed by cathodoluminescence,in combination with low Th/U ratios(0.01～0.93),indicate that they crystallized or recrystallized under metamorphic conditions and the ages obtained must be representative of the metamorphic age.Concordant U-Pb ages of((1 792±12) Ma)(8 points) and (1 891±46) Ma(19 points) were obtained from zircons of the sample DST02 and XYS01,respectively.Zircons U-Pb ages of 1 900~1 850 Ma obtained from unmetamorphosed strongly peraluminous granites,indicate that the upper limit of the peak metamorphic age could not be younger than(1 900) or(1 850) Ma.Therefore,the U-Pb ages of(1 792±12) Ma and(1 891±46) Ma are proposed to represents the time of retrograde and peak granulite metamorphic ages,respectively.