The Antrim Plateau Volcanics, Australia's largest Phanerozoic flood-basalt province, originally covered an area of at least 300 000 km(2) across northern Australia. Stratigraphic constraints indicate that the Antrim Plateau Volcanics are of Early Cambrian age (ca 545-509 Ma), although previous attempts to date the Antrim basalts by radiometric methods have been inconclusive. We present an ion microprobe U-Pb zircon age of 513 +/- 12 Ma for the similar to 250 km-long Milliwindi dolerite dyke in the west Kimberley. The dolerite is geochemically identical to basalts of the Antrim Plateau Volcanics, and was probably a feeder dyke for basalts that have since been eroded. It is suggested that the Antrim Plateau Volcanics extended hundreds of kilometres further to the west than recognised previously and may have once covered part of the Kimberley block.