Uplift, Shortening, and Steady State Topography in Active Mountain Belts

Abstract

We present a tectonic, surface process model used to investigate the role of horizontal shortening in convergent orogens and the effects on steady-state topography. The tectonic model consists of a specified velocity field for the Earth's surface and includes a constant uplift rate and a constant horizontal strain rate which varies to reflect the relative importance of frontal accretion and underplating in an orogenic wedge. The surface process model includes incision of a network of rivers formed by collection of applied precipitation and diffusive hillslope mass transfer. Three non-dimensional parameters describe this model: a ratio of the maximum horizontal velocity to the vertical velocity, a Peclet number expressing the efficiency of the hillslope diffusion relative to the uplift rate, and a fluvial "erosion number" reflecting the fluvial incision efficiency relative to the uplift rate. A series of models are presented demonstrating the resultant steady-state landforms parameterized by these three numbers. A finite velocity ratio results in an asymmetric form to the model mountain range, although the magnitude of the asymmetry also depends on the Peclet number. Topographic steady-state is achieved faster for models with no horizontal component to the velocity field. With finite horizontal velocity, topographic steady state is achieved only at the scale of the entire mountain range; even the first order drainage basins are unstable with time in the presence of horizontal shortening. We compare our model results to topographic profiles from active mountain ranges in Taiwan, New Zealand, and the Olympic Mountains of Washington state. All these examples exhibit asymmetric topographic form with the asymmetry consistent with the polarity of subduction, suggesting that horizontal tectonic motion is affecting the macro-geomorphic form of these ranges.

Analysis of longitudinal profiles along the eastern margin of the Qinghai-Tibetan Plateau

“…Taiwan, South Island of New Zealand). Similar patterns, where heightened rates of incision promote increased uplift, have been predicted by numerical modelling (see Beaumont et al 2000;Willet et al 2001).…”

Drainage reorganization during mountain building in the river system of the Eastern Cordillera of the Colombian Andes

“…Koons, 1995; Kooi and Beaumont, 1996;Willett et al, 2001; Goren et al, 2014). However, 30 during mountain building, active folds and thrusts can deviate rivers from the regional slope 31 (e.g., Van der Beek et al, 2002).…”

Late Pleistocene Climate Change and Erosion in the Santa Maria Basin, NW Argentina

“…The history of many Cenozoic orogens demonstrates how the creation of high relief profoundly influences climate; examples include the uplift of the Tibetan Plateau and its influence on the westerlies and the monsoon system, or the evolution of the PunaAltiplano plateau on the position and seasonal migration of the Intertropical Convergence Zone (ITCZ) (e.g., Molnar et al 1993;Raymo and Ruddiman 1992;Raymo 1994). On the basis of modeling results, feedback among orogenic activity, erosion, isostasy, and climatic change has also been proposed (e.g., Molnar and England 1990;Bull 1991;Mulder and Syvitski 1996;Whipple et al 1999;Willett et al 2001). Molnar and England (1990) initially argued that accelerated rates of Quaternary tectonism might in fact be produced by a more erosive climate and hence an increase in topographic relief.…”