Tectonic reconstructions with deforming plates and geodynamic modeling of passive margin systems

The effect of mantle flow on surface topography has been the subject of considerable interest over the last few years. A common approach to the problem is to link plate tectonic reconstructions and global geodynamic models. An important limitation of this approach is that traditional plate tectonic reconstructions do not take the deformation of the lithosphere into account. We introduce quantitative models of surface plate kinematics that include areas of deforming continental crust. We present a series of global reconstructions including deforming plates in key areas, derived using tools developed within the open source plate modeling software GPlates. In traditional plate models, the continents are represented as rigid blocks that overlap in full-fit reconstructions. Models that use topological polygons avoid continental overlaps, but plate velocities are still derived on the basis of the Euler poles for the rigid blocks. To resolve these issues, we use a methodology that requires at minimum two inputs; (1) the relative motions of the major rigid blocks within the continents; (2) a definition of the regions in which continental crust between these blocks deformed. We use geological and geophysical data to interpret the landward limit of significant extension and crustal thinning along both conjugate margins. These boundaries are used to construct polygons along both margins that define the extent of the stretched continental crust on either side of the rift. We derive individual motion histories for each point on the conjugate COBs. Joined together, these COB points form the topological boundaries of deforming domains in which each vertex moves independently. The deforming domains represented by topological meshes extend as the major rigid plates either side diverge. In our tectonic reconstruction with deforming plates, the timing and the intensity of continental extension is imposed by the progressive, diachronous breakup and initiation of seafloor spreading for each major margin system. Our methodology allows us to investigate different models for the full-fit reconstruction of major ocean basins such as the North and South Atlantic and the South East Indian Ocean, and revise them if necessary to yield a better fit to available crustal thickness estimates. Once the kinematic models are constructed, the surface velocities within the deforming regions of our reconstruction are calculated within GPlates by linearly interpolating velocities from adjacent non-deforming areas. Velocities derived from the global reconstruction are used as a time-dependent surface boundary condition in mantle convection models that include compositionally distinct crust and continental lithosphere embedded within the thermal lithosphere. These models are the first step towards investigating the effect of both lithospheric stretching and of mantle flow on the total tectonic subsidence of these margins.