THE FOUR DIMENSIONAL DYNAMIC EARTH

Arthur Holmes made fundamental contributions to our understanding of mantle convection before the rise of plate tectonics, including advancing the view that the solid mantle was undergoing thermal convection and that mantle convection was linked to continental evolution and sea floor spreading. These views have stood the test of time and continue to underpin our modern view of mantle dynamics. In this talk, I will focus on how geodynamic models closely linked with a wide variety of surface observations reveal the richness of the connections first uncovered by Holmes. This connection between the surface and interior will be explored through what I will call Dynamic Earth Models, spherical models of mantle convection and plate tectonics. In a first set of models, we predict the motion of plates with individual plate margins resolved down to a scale of 1 km, allowing for the bending of subducting slabs and deformation of plate boundaries and their interiors. The global flow models have been constrained through observations over large and small scales: Euler poles of plates, internal plate deformation, and seismic focal mechanisms. Back-arc extension and slab roll back are emergent consequences of slab descent in the upper mantle. The cold thermal anomalies within the lower mantle are often coupled into oceanic plates through narrow high viscosity slabs, speeding up or slowing down oceanic plates. Models that best fit plateness criteria and plate motion data have strong slabs. Using a lower resolution formulation, time-dependent models are integrated with paleogeography and the evolution of the surface, specifically sea level change, the development of onshore and offshore stratigraphic architecture, and vertical motions inferred from rock uplift. In general, the common-component to sea-level change due to dynamic topography (vertical motions driven by mantle convection) experienced by all continents tends to increase since the Late Cretaceous. This effect partially compensates the sea-level fall driven by the changing age distribution of the sea floor. To match the marine flooding globally, we find that a common component to sea-level change, mostly driven by the age distribution of the sea floor, is required, although for many continents the dynamic topography signal may dominate.