Authors

Kara Matthews (Earthbyte Group, The University of Sydney), Alina Hale ( Earthbyte Group, The University of Sydney), Mike Gurnis (California Institute of Technology), Dietmar Müller (The University of Sydney), and Lydia DiCaprio (Earthbyte Group, The University of Sydney)

Abstract

For billions of years mantle convection and plate tectonics have been sculpting the Earth’s surface. They have driven the amalgamation and dispersal of continents, uplifted mountain ranges and shaped climate. Modelling these processes enables the fundamental drivers of geological evolution to be examined, enabling deeper understanding of how the deep earth and surface environments interact. Improvements to modelling software, coupled with advances in high-performance computing, are facilitating endeavours to reconstruct global surface evolution since the Cretaceous and correlate large-scale topography to mantle convection. The geodynamic modelling software CitcomS 3.0, enables high-resolution regional models to be integrated into a lower-resolution global framework, allowing the influences of global processes to be incorporated into regional studies.

Mantle convection processes profoundly influenced Australia’s Cretaceous paleogeography. Despite global sea-level lows, an inland sea dominated the eastern interior. These seemingly discrepant phenomena are attributed to the eastward passage of the Australian continent over subducted slab material, originating from subduction that spanned its paleo-Pacific margin. Although there exists considerable geological evidence for subduction east of Australia during the Cretaceous, the exact location of the subduction zone remains elusive. We have used CitcomS to model the surface evolution of Australia since 140Ma and subsequently constrain the location of the Cretaceous subduction zone.

Our forward models assimilate data describing mantle rheology, plate motions since 140Ma and evolving plate boundaries. While mantle rheology affects the magnitude of vertical motions, timing of subsidence and uplift depends on plate boundary geometries. Models with subduction adjacent to the reconstructed coast resulted in accelerated subsidence delayed by ~20Myr. This timing offset was reconciled when subduction was translated 23º east. Comparisons with mantle seismic tomography, and the absence of subduction related volcanism along Australia’s east coast in the Cretaceous, further support our conclusion that a back-arc basin existed east of Australia during the Cretaceous.