Paper No. 79-2
Presentation Time: 8:20 AM
DECIPHERING THE LANDSCAPE HISTORY IN SOUTHWESTERN NORTH AMERICA SINCE THE LATE EOCENE USING THE COUPLED INFLUENCE OF TECTONICS, CLIMATE, AND SURFACE PROCESSES
The plate tectonic paradigm enables us to understand how mass is transported horizontally and vertically, both internally and on the Earth’s surface, based on principles of physics, such as conservation of momentum, energy, and mass. The Basin and Range Province of southwestern North America (SWNA) is the result of shear and extension following a protracted phase of crustal shortening and mountain building (155–60 Ma). Since ~40 Ma the tectonic history of SWNA involves a complex transition from early shallow- to flat-subduction of the east dipping Farallon slab along the western margin to its present transtensional environment. Through this evolution of changing boundary forces, topography and crustal thicknesses were dramatically altered from high elevations of orogenic plateaus and corresponding thick crustal welts to the current Basin and Range system. This landscape evolution has been attributed to crustal isostasy, dynamic topography, or lithosphere tectonics, but their relative contributions remain controversial. We reconstruct the landscape history since the late Eocene using fully coupled four-dimensional models of mantle convection, lithosphere dynamics, climate, and surface processes to address the interplay between these processes. Our geodynamic model quantifies the depth-dependent strain rate and stress history within the lithosphere under the influence of gravitational collapse and sub-lithospheric mantle flow. Our results show that high gravitational potential energy of a mountain belt relative to a lower Colorado Plateau is required to match the extension directions and stress magnitudes in the belt of core complexes in Arizona and Nevada during topographic collapse. Through the coupling of lithosphere with climate we show that topographic collapse and surface uplift guided three major phases of drainage evolution that include northeast drainage onto the Colorado Plateau during the late Eocene to late Oligocene, south-southwest drainage reversal during the late Oligocene to middle Miocene, and southwest drainage following the late Miocene. The three predicted phases of drainage evolution that our time-dependent simulations show appear to match, in time and space, the major sedimentological and drainage features from the late Eocene to present-day in SWNA.