Spatial and temporal patterns of Cenozoic dynamic topography around Australia

Abstract

[1] Despite its importance, the spatial and temporal pattern of dynamic topography generated by mantle convective circulation is poorly known. We present accurate estimates of dynamic topography from oceanic basins and continental margins surrounding Australia. Our starting point is measurement of residual depth anomalies on the oldest oceanic floor adjacent to the continental shelf. These anomalies were determined from a combined dataset of~200 seismic reflection and wide-angle images of well-sedimented oceanic crust. They have amplitudes of between À1 km and +0.5 km, and their spatial variation is broadly consistent with long-wavelength free-air gravity and shallow seismic tomographic anomalies. Along the Northwest Shelf, a regional depth anomaly of À300 to À700 m intersects the adjacent continental shelf. The temporal evolution of this anomaly was determined by analyzing the stratigraphic architecture of an extensive carbonate platform, which fringes the shelf and records a dramatic switch from progradation to aggradation during Neogene times. Three-dimensional seismic mapping calibrated by boreholes was used to calculate water-loaded subsidence histories at rollover points of clinoforms along the shelf. At 9 AE 3 Ma, the rate of subsidence increases from 5 to up 75 m Myr À1 , generating a subsidence anomaly of À300 to À700 m. The amplitude of this anomaly varies along the shelf and cannot be generated by glacio-eustatic sea-level variation. Instead, we propose that a regional subsidence episode, which affects both the proximal shelf and the distal oceanic basin, was generated by convective drawdown. By combining our results with other published estimates of uplift and subsidence, a map of Australia, which shows the spatial and temporal pattern of dynamic topography is presented. Most, but not all, of Australia's epeirogeny can be attributed to rapid northward motion of the Australian plate over a pre-existing pattern of convective circulation.

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“…In contrast to the diachronous results suggested by geodynamic modeling, recent backstripping of NWS clinoform rollover positions indicates that margin-wide anomalous subsidence was instead broadly synchronous and commenced at ~10 Ma with a down-tothe-north gradient equal in amplitude to adjacent oceanic floor residual depth anomalies (Czarnota et al, 2013). These data suggest that the mantle anomaly responsible for this subsidence may be transient and coupled to the plate motion.…”

“…Subsidence anomalies along the NWS are ideal targets for investigation of dynamic topography, as the region lies across the gradient of the degree 2 geoid anomaly and on the fastest moving continent since the Eocene (about >35 Ma). 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).…”

“…These data will enable us to decipher the contribution of large-scale geodynamic processes, such as dynamic topography, on the vertical motions of the Earth's surface and associated effects on the NWS sedimentary system (Czarnota et al, 2013).…”

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“…Subsidence anomalies along the NWS are ideal targets for the investigation of dynamic topography because the region lies across the gradient of the degree 2 geoid anomaly and on the fastest moving continent since the Eocene (about >35 Ma). 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).…”

Episodic post‐rift deformation in the south‐eastern Australian passive margin: evidence from the Lapstone Structural Complex

“…Weissel and Karner, 1989), base-level change initiated at a rift margin (e.g. Heine et al, 2010;Czarnota et al, 2013Czarnota et al, , 2014. Braun et al, 2009) and dynamic topography related to northward plate motion over a pre-existing pattern of mantle convective circulation (e.g.…”