Multiple postorogenic denudation events: An example from the eastern Lachlan fold belt, Australia

Abstract

Fission-track results from 40 surface samples from the eastern part of the Lachlan fold belt, Australia, suggest that two distinct episodes of rapid kilometre-scale denudation have occurred since the middle Carboniferous, when deformation within the fold belt is believed to have ceased. The first episode, during the Early Triassic, was possibly in response to the Hunter-Bowen orogeny, which affected the New England fold belt and the Sydney-Bowen basin, but the effects of which have previously not been recognized within the Lachlan fold belt. The second episode occurred during the middle Cretaceous, possibly in response to the onset of continental extension in the Tasman Sea ca. 96 Ma. Uplift at this time resulted in kilometre-scale denudation over much of the southeastern highlands of Australia and may have been caused by underplating inward of the rift. These results indicate that the Lachlan fold belt has remained tectonically active long after the last recognized deformational event in the region, and highlight the importance of fission-track data in elucidating the posttectonic histories of orogens previously undetected due to a lack of stratigraphic and structural crosscutting relationships.