Geodynamic models of intraplate deformation: Applications to Canada's High-Arctic Eurekan Orogeny

The Phanerozoic tectonic history of Canada's High-Arctic represents a complex history of collision, rifting and intra-plate deformation. Beginning in latest Devonian to earliest Carboniferous times, development of the Palaeozoic Franklinian Basin was terminated by the Ellesmerian Orogeny. Development of the Sverdrup Basin followed the Ellesmerian Orogeny. Subsequently, ~200 km of shortening occurred during the Eocene Eurekan Orogeny that affected parts of the Franklinian and Sverdrup Basins. A problem in distinguishing between Ellesmerian and Eurekan structures is that the Eurekan Orogeny overprinted and reactivated structures initially formed during the Ellesmerian Orogeny. Given that many of the Eurekan structures are reactivated Ellesmerian structures, it is often suggested that pre-existing mechanical weakness, such as faults and/or shear zones, and compositional boundaries likely controlled localization of Eurekan tectonism. Less invoked in the context of the Eurekan Orogeny, though arguably just as important in localizing intra-plate deformation, is strain localization resulting from spatial variations in the thermal state of the lithosphere (thermal refraction). We quantitatively investigate both processes and their importance in localizing deformation during the Eurekan Orogeny using a visco-plastic (thermally-activated power-law creep and Mohr-Coulomb rheologies) finite-element code that solves the governing equations of incompressible fluid flow. The tectonic problem is inherently related to the dynamics of the deep lithosphere where lower crust interacts with the mantle lithosphere, so the models are conducted at an upper mantle depth scale (600 km). The collisional models are evolved to the stage of a young orogen; e.g., ~15 Myr, ~200 km of shortening. The experiments demonstrate the thermal, rheologic, and kinematic conditions that control the reactivation of pre-existing structures and their importance during the Eurekan Orogeny. A free surface and prescribed erosional laws make up the top boundary of the model domain and allow topography to develop self consistently with the underlying geodynamics. We interpret the lithosphere structure and model topography in the context of constraints on the geometry of the Eurekan Orogeny, in addition to available geological/geophysical constraints on internal lithospheric structure.