CRETACEOUS ALTERATION OF JURASSIC VOLCANIC-ROCKS, PAIN-MESA, NORTHERNVICTORIA-LAND, ANTARCTICA

The Kirkpatrick basalt (Jurassic) of Pain Mesa in the Mesa Range of no rthern Victoria Land consists of low-Ti tholeiite basalt overlain by u p to six flows of hypocrystalline, high-Ti tholeiite. The Rb and Sr co ncentrations and Sr-87/Sr-86. 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 tholeiites which s catter above and below a 175-Ma reference isochron. The apparent lower ing of the Rb-Sr date of the high-Ti flows is attributed to aqueous al teration of the rocks and coincides with the separation of Australia f rom Antarctica during the Cretaceous Period.