Authors / CoAuthors
Czarnota, K. | Roberts, G.G. | White, N.
Abstract
The mechanism and uplift history of Australia's southeastern highlands has long been debated. End member models account for the topography as a down warped relict of an ancient plateau or a consequence of uplift associated with either rifting along the eastern margin or Cenozoic volcanism. All of these models assume present-day elevation is a consequence of isostatic equilibrium at the base of the crust. An analysis of the relationship between gravity and topography in the spectral domain shows the admittance at wavelengths longer than those controlled by flexure is ~50 mgal km-1. This value is characteristic of dynamic support arising from thermal anomalies beneath the plate predicted by multiple mantle convection simulations and observed over Africa, Antarctic and the Pacific Ocean. Division of long-wavelength filtered gravity by this admittance value suggests the southeastern highlands are supported by 400-900 m. The morphological expressions of this support are the Great Escarpment and major knick zones on rivers such as the Snowy. The temporal evolution of this support can be determined by exploiting longitudinal river profiles since their shape is controlled by uplift and modulated by erosion. By applying the well-known detachment limited stream power law to model erosion uplift histories can be extracted provided erosional parameters can be constrained. By calibrating the erosional parameters using incision rates along the Tumut River and Tumbarumba Creek as well as palaeoelevations of basalt flows the uplift history of the southeastern highlands can ascertained directly from the landscape. Our results show uplift of the southeastern highlands occurred in two phases associated with Cretaceous age rifting resulting in Tasman Sea floor spreading and Cenozoic volcanism. The latter event accounts for the observed amplitude of present-day dynamic topography thereby suggesting Cenozoic uplift occurred from an unperturbed isotactic elevation. Since Cretaceous rifting along the southeastern margin occurred over a cool mantle given the oldest oceanic floor is thinner than the global average it is unlikely that rift related uplift is a consequence of mafic underplating. The most likely driver for this earlier phase of uplift is emergence of eastern Australia from a dynamically drawdown position which has been inferred to explain the widespread mid-Cretaceous marine inundation of Eastern Australia. Therefore it is likely that both uplift events are controlled by changes in the thermal state of the mantle as opposed to changes in crustal thickness and density. This history of vertical motions is consistent with long-term river incision rates, basin sequence stratigraphy and thermochronological studies.
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nonGeographicDataset
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78537
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- External Publication
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
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2014-01-01T00:00:00
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