EXPLORING THE LINKS BETWEEN VERTICAL UPLIFT, HORIZONTAL TRANSLATION AND HOW TOPOGRAPHY IS CREATED AND MAINTAINED IN CONVERGENT OROGENS

Many models of orogen-scale convergence and landscape evolution typically assume a critically tapered wedge where shortening and rock uplift is occurring everywhere along the wedge. In contrast, mapped and seismically imaged active and inactive structures in fold-thrust belts highlight shortening by horizontal and vertical displacement along discrete fault planes where rock uplift is generated by motion over ramps along the décollement, out-of-sequence thrusting and/or a frontal surface breaking fault. To assess if the proposed/imaged geometry and associated kinematics is viable, the predicted topographic evolution implied by the proposed sequence of deformation can be forward modeled accounting for structural uplift and isostatic subsidence. Both structural uplift and flexural isostasy can be modeled in the kinematic restoration software Move. To do this we model displacement on faults in 10 km increments, employing a simplified, first-order estimation of topography where elevations increase at a specified topographic slope (2°) from the frontal most active fault. Modeled topography increases to the prescribed topographic slope everywhere that has undergone structural uplift during the 10 km increment of deformation and follows pre-existing topography where uplift did not occur. An assumption that is inherent in this modeling process is that topographic elevation is a function of ongoing or former structural uplift. This requires the sequential pattern of uplift to be able to reproduce to the first-order shape of modern topography in the final model step. To produce high topography in the Himalaya or the Andes by rock uplift over discrete structures such as a ramp in the décollement requires that both displacement over the ramp and the resulting uplifted and translated topography are maintained over millions of years. By integrating the proposed kinematics with a landscape evolution model (CASCADE), we can evaluate if this translated topography can be preserved. Our numerical experiments suggest that lateral advection of uplifted topography creates a tapered topography with high-relief, advection-parallel interfluves, and suggests that critical wedge requirement of that all rocks are at Coulomb failure is not necessary to produce the characteristic tapered topography of convergent mountains.