INHERITED PB COMPONENTS IN MAGMATIC TITANITE AND THEIR CONSEQUENCE FOR THE INTERPRETATION OF U-PB AGES

Abstract

The occurrence of inherited radiogenic Pb components in 35 Ma old magmatic titanite is reported here for the first time. The about 810 Ma age of the inherited components is identical to that contained in zircon from the same amphibole-bearing syenite sample. In both minerals the Precambrian components were not totally reset during magmatic new growth at 35 Ma. This age pattern substantiates that the U-Pb chronometer in titanite is resistant to temperatures in excess of 712°C, as is already known for zircon and monazite. In consequence, U-Pb ages from crystalline titanites have to be interpreted as the age of mineral formation or re-crystallization, rather than the time of U-Pb system closure during cooling of the rock.