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Belinda Brown

The Influence of Dynamic Mantle Topography & Intra-plate Stress on Tectonic Subsidence along the Australian Southern Margin . Belinda Brown Dietmar Muller School of Geosciences University of Sydney Marine Geophysics and Geodynamics Group. Outline. Introduction Tectonic subsidence

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Belinda Brown

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  1. The Influence of Dynamic Mantle Topography & Intra-plate Stress on Tectonic Subsidence along the Australian Southern Margin Belinda Brown Dietmar MullerSchool of GeosciencesUniversity of SydneyMarine Geophysics and Geodynamics Group

  2. Outline • Introduction • Tectonic subsidence • Dynamic topography • Australian southern margin • Application to exploration…..

  3. Geodynamic model predictions and ground-truth from hydrocarbon exploration wells:Predicted vs. observed dynamic topography in Southeast Asia Modified from Wheeler and White, Geology (2000)

  4. Tectonic Subsidence • Syn-rift (extension & thinning) Post-rift (regain thermal and isostatic equilibrium) • Renewed rifting • Dynamic topography • Tectonic Reactivation

  5. 0 5 km Backstripping Method WellControl Jerboa-1Eyre Sub-basin Backstripping: water loaded tectonic subsidence • Parameters required to compute tectonic subsidence for each lithological unit: 1.age 2.present depth below sea level 3.compaction properties 4.palaeowater depth at time of deposition 5.correction for long-term eustatic sea level variations Potoroo-1 Ceduna Sub-basin

  6. Potential errors in backstripping well data Lithology errors Paleo-water depth errors

  7. Dynamic Mantle Topography • Negative dynamic topography caused by a cold, sinking palaeo-subducted slab in the AAD • Major influence on tectonic basement subsidence during and after rifting

  8. Changes in Cretaceous dynamic topography from eastward motion of Australia over a sinking subducted slab in the mantle (from Gurnis et al., Science, 1998) 90 Ma 60 Ma 120 Ma

  9. Australian Southern Margin

  10. Inconsistency between substantial rifting and lack of thermal subsidence in many wells

  11. Bight Basin Backstripped tectonic subsidence & Synthetic borehole topography from Gurnis’ grid

  12. Duntroon Basin

  13. Otway Basin

  14. Implications for exploration….. • Implications for geothermal gradients used in Geohistory Analysis & Maturation

  15. Strain Rate beta Tectonic Subsidence lithosphere Dynamic Topography mantle

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