Large-scale dynamic surface topography of Australia since 150 million years ago

This animation shows a model for the mantle-convection-driven component of Australian surface topography (Müller et al., Earth Planet. Sci. Lett., 2016). The model was calibrated against four locations in the Eastern Highlands of Australia where surface uplift had been estimated from river profile modelling by Czarnota et al. (J. Geophys. Res. 2014).

 

Between 150-120 Myr Eastern Australia experiences dynamic subsidence, resulting in flooding of the Eromanga Basin, as the continent moves eastwards, overriding subducted slab material sinking in the mantle. This sinking slab, subducted along the East Gondwana subduction zone, acted to draw the surface down through viscous coupling. From 150-100 Ma, the ocean crust subducted along East Gondwana is progressively younging (see related plate tectonic animation that shows the age of ocean crust through time), gradually decreasing the thickness, and thus volume, of the sinking subducted slab. This change, coupled with the progressive sinking of older subducted slabs further into the deep mantle, gradually reduces the downward pull of the slabs on the surface, leading to a reversal from subsidence to uplift of the Eromanga Basin after 120 Myr ago.

The exact timing of the modelled onset of uplift is dependent on the longitudinal component of the absolute plate motion model used. Because this model is based on paleomagnetic data before 100 Myr ago, the longitudinal plate motion component through time is relatively uncertain. After 120 Ma subducted slab volumes are progressively decreasing, Australia stops moving eastward around 100 Ma, and plate convergence slows down and becomes quite oblique (see plate motion animation). This and independent geological observations suggest that a temporary cessation of subduction followed around 100 Myr ago. The combination of these factors led to the first phase of uplift of the Eastern Highlands, reflecting a progressive rebound from the previous downward pull by sinking slab material.

After 80 Myr ago a period of tectonic quiescence followed, lasting to about 60 Ma in the south (Snowy Mountains). Renewed uplift of ~700 m in the Snowy Mountains is propelled by the gradual motion of the margin over the edge of the large Pacific mantle upwelling. In contrast the northernmost portion of the highlands records continuous uplift from 120 Ma to present-day totalling about 800 m. The northern highlands experienced a continuous history of dynamic uplift, first due to the end of subduction to the east of Australia, then due to moving over a large passive mantle upwelling. In contrast, the southern highlands started interacting with the edge of the large Pacific mantle upwelling ~40-50 million years later, resulting in a two-phase uplift history. An interactive globe showing the dynamic topography predicted by this model and allowing to visualise and download the modelled vertical motion history of user-selected locations is available at the GPlates Portal. Video created by Dietmar Müller, based on the geodynamic model published here:

Müller, R.D., Flament, N., Matthews, K.J., Williams, S.E., Gurnis, M., 2016, Formation of Australian continental margin highlands driven by plate–mantle interaction, Earth and Planetary Science Letters, 441, 60-70.

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