Cretaceous alteration of Jurassic volcanic rocks, Pain Mesa, northern Victoria Land, Antarctica

The Kirkpatrick basalt (Jurassic) of Pain Mesa in the Mesa Range of northern Victoria Land consists of low-Ti tholeiite basalt overlain by up to six flows of hypocrystalline, high-Ti tholeiite. The Rb and Sr concentrations and 87Sr86Sr ratios of 28 specimens of high-Ti basalt from Pain Mesa yield an anomalously low errorchron date of 100 ± 15 Ma in contrast to whole-rock samples of the low-Ti tholeftes which scatter above and below a 175-Ma reference isochron. The apparent lowering of the RbSr date of the high-Ti flows is attributed to aqueous alteration of the rocks and coincides with the separation of Australia from Antarctica during the Cretaceous Period.