Mesozoic origins and antecedents of Australia's Eastern highlands

Australia's Eastern Highlands are a conspicuous manifestation of a tectonic regime that has been previously shown to go back at least 65 Ma. This review of the Mesozoic stratigraphy of eastern Australia gives evidence of a very different regime before 95 Ma, related to the presence of a plate boundary close to the present east coast of the continent. During the prior regime, cratonic sedimentation in eastern Australia was dominated by labile sediment from an andesitic orogen coincident with the coast north of Brisbane during the Cretaceous, and further offshore in the Jurassic. Whereas the plate boundary north of Brisbane appears to have been simply convergent, that south to Bass Strait may have experienced prolonged oblique-slip, manifested in the Jurassic by alkaline volcanism within the SE Highlands terrain. Following a Cenomanian (95-90 Ma) phase of transition, during which the eastern Australian plate boundary may have resembled that margining western North America at present, the plate boundary migrated away from mainland Australia, as is evidenced by the subsequent dominance of quartzose sedimentation on the craton, and the fission-track and palaeomagnetic evidence of rapidly falling geotherms in the Late Cretaceous. The Eastern Highlands were initiated around 90 Ma ago, and the crestline subsequently migrated west from an initial location at the present coastline. The geography and history of the Eastern Highlands are inconsistent with concepts of continental margin development based on analogues outside the Pacific realm. The Highlands are an intrinsic element of a continent formerly fronting the Pacific Ocean, but now abutting a back-arc basin.