40Ar/39Ar constraints on the timing and origin of Miocene leucitite volcanism in southeastern Australia

Laser incremental-heating Ar-40/Ar-39 geochronology of seven leucitites from southeastern Australia indicates that leucite-bearing lavas in individual geographic clusters were erupted in one million years or less. The eruption ages range from 17.9 +/- 0.3 Ma (2 sigma) at El Capitan in northern-central New South Wales to 8.9 +/- 0.2 Ma (2 sigma) at Cosgrove in northern Victoria, The 40Ar/39Ar results demonstrate that the southward migration of leucite-bearing lavas was near-contemporaneous with age-progressive central-volcano magmatism in southeastern Australia. As such, the 40Ar/39Ar results are consistent with a hotspot-related origin for the leucitites. However, the question of whether single or multiple hotspots are required to explain these volcanic chains, which are separated by a distance of about 300 km, awaits a more complete geochronological picture of the onset, duration and migration of leucitite and central-volcano magmatism in eastern Australia