Using 3D Geodynamic Models of Flexure Backed by Seismic Imagery to Constrain the Rheology and Thermal Structure of the Oceanic Lithosphere Under the Hawaiian Islands

Abstract:

The geodynamic modelling code Advanced Solver for Problems in Earth’s ConvecTion (ASPECT) will be used to model the deformation of the Pacific lithosphere in response to loading from the Hawaiian Islands. We have carried out numerous tests of ASPECT’s ability to model lithospheric flexure to ensure the accuracy of solutions for this study. These benchmarks include a uniform-density elastic cantilever fixed at one end flexing under its own weight, a viscoelastic plate over an inviscid substratum, an elastic plate over a viscous substratum, and a viscoelastic half-space. Additionally, we tested ASPECTs Drucker-Prager plasticity for simulating the brittle stress limit of a bending plate. All models were run with an open boundary opposite the load to allow for material to be easily displaced as flexure occurred, improving accuracy and runtime efficiency. All flexure models were compared to an analytic solution, and the error for the point of maximum flexure is always below 1%. Accuracy is maintained across various values of effective elastic thickness and load sizes. Models with Drucker-Prager plasticity produced “yield stress envelopes” of Mohr-Coulomb failure and high-temperature ductile creep that matched analytical solutions for a range of brittle strength properties. The final models will simulate a composite rheology of brittle failure, Peierls creep for low-temperature creep, and high-temperature creep subject to the growth of the Hawaiian chain over 4-5 million years. Model results will be compared to new seismic imagery of the flexed surface of the pre-existing oceanic seafloor, which will provide new information about temporal evolution of flexure. Ultimately this study aims to advance our understanding of lithosphere rheology and thermal structure of hotspot-influenced lithosphere.