Integrating deep Earth dynamics in paleogeographic reconstructions of Australia

Abstract

It is well documented that the Cenozoic progressive flooding of Australia, contemporaneous with a eustatic sea level fall, requires a downward tilting of the Australian Plate towards the SE Asian subduction system. Previously, this large-scale, mantleconvection driven dynamic topography effect has been approximated by computing the time-dependent vertical shifts and tilts of a plane, but the observed subsidence and uplift anomalies indicate a more complex interplay between time-dependent mantle convection and plate motion. We combine plate kinematics with a global mantle backward-advection model based on shear-wave mantle tomography, paleogeographic data, eustatic sea level estimates and basin stratigraphy to reconstruct the Australian flooding history for the last 70 Myrs on a continental scale. We compute time-dependent dynamic surface topography and continental inundation of a digital elevation model adjusted for sediment accumulation. Our model reveals two evolving dynamic topography lows, over which the Australian plate has progressively

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“…Spreading was slow until 45 Ma, with rapid northward movement after this time. According to Heine et al (2010), from 65 to 45 Ma the Australian continent was migrating to the northwest with ϳ36 mm/year northwest absolute motion. This velocity increased to ϳ48 mm/year in the early Eocene, due to Circum-Pacific plate reorganisation: as a result, Australian plate motion changed from north-northwest to northnortheast.…”

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“…Such flooding occurred across large expanses of the continental region east of the cratonic portion of Australia marked by the Tasman Line. The northeastward motion of Australia over a descending Pacific-derived slab induced a strong negative dynamic topography signal that accentuated flooding from the mid-Cretaceous sea level highstand (DiCaprio et al, 2009;Gurnis et al, 1998;Heine et al, 2010;Matthews et al, 2011). Well-constrained models of paleogeography are an important validating mechanism for numerical models of dynamic topography, as demonstrated by Gurnis et al (1998) in the study of the Cretaceous inundation of Australia (Fig.…”

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“…These subsidence anomalies have long been known (Müller et al, 2000;Kennard et al, 2003) and can be ascribed to dynamic topography because both thermal subsidence and flexural effects are minimal (Czarnota et al, 2013). Advancements in computer modeling (DiCaprio et al, 2011) have attributed subsidence anomalies along the NWS to dynamic drawdown of the Earth's surface driven by Australia's rapid northward motion over a generally stationary accumulation of subducted slabs within the mantle beneath southeast Asia (e.g., Lithgow-Bertelloni and Gurnis, 1997;Heine et al, 2010). These models predict that the NWS should be affected by a southward-propagating wave of subsidence related to Australia's northward motion over this stationary cold and dense mantle anomaly.…”

“…WA = Western Australia, NT = Northern Territory, SA = South Australia, QLD = Queensland, NSW = New South Wales. ( Figure F3) (Russell and Gurnis 1994;Gurnis et al, 1998;Veevers, 2000;DiCaprio et al, 2009;Heine et al, 2010). Lateral displacements of continents relative to mantle convection patterns have significant impact on the flooding history of continental platforms and margins (Sleep, 1976;Gurnis, 1990Gurnis, , 1993Russell and Gurnis, 1994).…”

“…The amount of inundation (red line with circles) is computed relative to the present-day 200 m isobath from the ETOPO2 global 2′ topography (NOAA, National Geophysical Data Center, 2006). Adapted from Heine et al (2010). (2) the location of the main outlet, and (3) variable sill depths and locations through time (Kuhnt et al, 2004).…”