New xenotime ages obtained from the Paleoproterozoic Kimberley Group, NW Australia: implications for regional hydrothermal events

Abstract

New xenotime ages are obtained from the Paleoproterozoic King Leopold Sandstone of the Kimberley Group, NW Australia. The concordant age of 1679 ± 13 Ma can be equated with the ca 1.7 Ga xenotime age within errors obtained from the Warton and Pentecost Sandstones of the same group. These ages are much younger than the robust SHRIMP ages (1790 ± 4 Ma) obtained from zircons from the dolerite dyke intrusions, and thus indicate that the xenotime growths recorded in the Kimberley Group are unlikely to be diagenetic in origin but may have resulted from the post-depositional hydrothermal event. The overgrowth of xenotime recorded from these three units of the Kimberley Group was probably caused by the same hydrothermal event that took place ca 1.7 Ga ago in Kimberley. Radiogenic Pb loss occurred at ca 325 Ma, which could have been caused by the 400–300 Ma Alice Springs Orogeny. This Pb loss event was responsible for the discordant U–Pb ages from 1.6 to 1.1 Ga.