Models of mantle convection incorporating plate tectonics: The Australian region since the Cretaceous

Abstract

We propose that the anomalous Cretaceous vertical motion of Australia and distinctive geochemistry and geophysics of the Australian-Antarctic Discordance (AAD) were caused by a subducted slab which migrated beneath the continent during the Cretaceous, stalled within the mantle transition zone, and is presently being drawn up by the Southeast Indian Ridge. During the Early Cretaceous the eastern interior of the Australian continent rapidly subsided, but must have later uplifted on a regional scale. Beneath the AAD the mantle is cooler than normal, as indicated by a variety of observations. Seismic tomography shows an oblong, slab-like structure orientated N-S in the transition zone and lower mantle, consistent with an old subducted slab. Using a three-dimensional model of mantle convection with imposed plate tectonics, we show that both of t hese well documented features are related. The models start with slabs dipping toward the restored eastern Australian margin. As Australia moves east in a hot spot reference frame from 130-90 Ma, a broad dynamic topography depression of decreasing amplitude migrates west across the continent causing the continent to subside and then uplift. Most of the slab descends into the deeper mantle, but the models show part of the cooler mantle becomes trapped within the transition zone. From 40 Ma to the present, wisps of this cool mantle are drawn up by the northwardly migrating ridge between Australia and Antarctica. This causes a circular dynamic topography depression and thinner crust to develop at the present position of the AAD. The AAD is unique within the ocean basins because it is the only place where a modern ridge has migrated over the position of long term Mesozoic subduction. Our study demonstrates the predictive power of mantle convection models when they incorporate plate tectonics.

Mesozoic-Cenozoic evolution of Australia's New Guinea margin in a west Pacific context

“…Late Cretaceous-Paleocene rifting is inferred to have led to formation of marginal basins, including opening of the Coral Sea(Figure 1). Regional uplift may be associated with rifting(Home et al 1990) or with dynamic topographic rebound related to movement over a Cretaceous subducted slab(Gurnis et al 2000). 3D sketch of the New Guinea margin in the Palaeogene(after Hall 2002)…”

“…Alternatively, this may have been associated with dynamic topographic rebound associated with the movement of Australia over a Cretaceous subducted slab as suggested for the eastern Australia margin by Gurnis et al (2000). Widespread Paleocene and Eocene sandstones in western Irian Jaya probably resulted from the uplift and denudation of Papua New Guinea and eastern Australia.…”

“…An important coeval event is the widespread uplift and erosion of the southern Papuan Basin, inferred by Home et al (1990) to be due to uplift of the rift-shoulder. However, similar uplift of the whole eastern margin of Australia occurred in the mid to Late Cretaceous, interpreted by Gurnis et al (2000) to be due to rebound associated with the breaking off of a long-lived subducted slab. Francis (1990) argued that rifting occurred along the northeastern Australian margin in the Campanian-Maastrichtian, citing as evidence the alkaline basaltic volcanism along the outer shelf and upper slope and common tuffs in the Upper Cretaceous mudstone section.…”

Two layer model of lithospheric compression and uplift/exhumation in an intracratonic setting: an example from the Cooper–Eromanga Basins, Australia

“…The opening of the Tasman Sea would have been accompanied by a major change in both the stress and thermal regimes of the region, and may have led to regional uplift of the eastern margin as the deeper convection pattern adjusted. This model can be invoked as a possible explanation of the uplift in the Eromanga Basin which is some 1,000 km from the former subduction zone at the eastern margin (Gallagher et al 1994;Russell and Gurnis 1994;Gurnis et al 1998Gurnis et al , 2000. However, the model does not explain the uplift in Tertiary times as the subduction zone in eastern Australia that was potentially close enough to affect the basins, according to the model, had drastically moved far off by then.…”

Mantle structure and tectonic evolution of the region north and east of Australia

“…We have a number of hypotheses for this anomaly. Gurnis et al (2000) have suggested that an approximately north-south seismic anomaly beneath the Australian-Antarctic Discordance south of Australia may be the result of a slab in the mantle subducted east of Australia during the Cretaceous and subsequently overridden by Australia as it has moved east. Our anomaly 8 is at a similar depth and along strike from the Gurnis et al (2000) Australian-Antarctic Discordance anomaly and may have the same explanation if this subduction zone had continued north with a similar orientation.…”