THERMAL EVOLUTION OF RIFTED CONTINENTAL MARGINS - NEW EVIDENCE FROM FISSION TRACKS IN BASEMENT APATITES FROM SOUTHEASTERN AUSTRALIA

Abstract

The Palaeozoic granitic basement of southeastern Australia shows a regular pattern of apatite fission track ages which is dominated by a rapid decrease in apparent age towards the rifted continental margin. Apparent ages away from the margin vary between about 230 and 360 Myr but drop sharply to minimum values of around 80 Myr near the coast just south of the Sydney Basin and 150-175 Myr elsewhere along the coast. Fission track length information allows the age pattern to be interpreted as the result of partial to complete resetting of the older ages by a widespread thermal event at about 80-100 Myr. This event accompanied the rift phase of passive margin development and peaked just before t..