How Australian Plate Interaction With Subducting Slabs and the South Pacific Superswell Drove Multi-Phase Uplift and Paleogeography in Eastern Australia

Abstract

The Eastern Highlands of Australia are a type example of so-called “passive margin mountains”, and their stepwise uplift has had a profound effect on the paleogeography of eastern Australia. Suggested mechanisms for their formation range from flexural rift shoulder uplift, volcanism and underplating to mantle-convection driven dynamic topography, including plumes and small-scale convection. We use a coupled tectonic-geodymamic modeling approach to investigate their origin, including two alternative subduction evolution models. The first model includes a large Early Cretaceous (140–120 Ma) back-arc basin east of the Lord Howe Rise; in the alternative scenario a west-dipping subduction zone is continuous to the East of the Lord Howe Rise between 140–85 Ma, without a large back-arc basin, and the South Loyalty Basin opens as a back arc basin from 85–55 Ma. The best-fit model produces a total uplift up to ~400 m in the interval between 120 and 90–70 Ma, well-matched with recent published estimates from river profile inversion for the Snowy Mountains, New England and the Central Highlands. The driving mechanism is rebound from the eastwards motion of Australia over a sinking slab, first leading to transient subsidence and continental flooding followed by rebound and uplift. Our model predicts cessation of uplift from 70–40 Ma (Snowy Mountains), 90–60 Ma (New England), followed by renewed uplift of up to 200 m. In the Central Highlands we model continuing, but distinctly slower uplift from 90 Ma to the present, also totaling ~200 m. This uplift is due to the gradual motion of Eastern Australia over the edge of the southwest Pacific superswell. The Central Highlands experienced the influence of the perimeter of the superswell first, due to their more northerly location, more proximal to the swell's edge, resulting in a continuous history of uplift since the mid-Cretaceous, whereas the Snowy Mountains started interacting with the superswell edge ~40–50 Myr later, resulting in a distinct break in uplift. The magnitude of the 2nd phase of uplift from river profile inversion versus geodynamic modeling matches well for the Central Highlands, but not further south. We attribute this to the lack of plumes in our current geodynamic models; plumes have clearly played an additional, important role in exacerbating uplift in the Late Cenozoic in the southern highlands, as indicated by the abundant, time-progressive Late Cenozoic volcanism in Eastern Australia.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015