BUILDING AND MOVING MOUNTAINS: SUBDUCTION ZONE IMPRINTS ON THE HEIGHTS AND ASYMMETRIES OF CORDILLERAN MOUNTAINS

One of the fundamental questions in geoscience which has cross disciplinary implications is: what processes govern the creation, maintenance, and removal of high mountain topography above subduction zones? At the core of this question is a central hypothesis: if a given climatic regime can drive surface processes to erode the surface faster than tectonics can uplift it over the timescale of mountain building, then highly efficient erosional processes which may be modulated by climate can limit mountain heights and induce orogenic asymmetry via orographic rainfall.

Here, we present a bottom-up, tectonic control of mountain range altitudes and positions in arc-continent convergent zones. We analysed the Cordilleran mountain heights from Patagonia to Alaska as well as the orogenic asymmetry of the Andes. Spanning a wide range of tectonic and climatic regimes, these orogens are ideal to evaluate the competition between climate and tectonics in controlling mountain masses and positions during active mountain building in oceanic-continent subduction zones. Assuming convergence rates (Vc) are a proxy for rock uplift and that its control on orogen heights is regulated by erosional efficiency (Ee), we observe that the maximum mean mountain heights and mountain peaks of most Cordilleran orogens fall within ± 25% Ee of each other and are linearly dependent on Vc. Through this approach, Alaska and the Andes between 35°S and 45°S have a high Ee while the Altiplano has a low Ee. Patagonia, Central America, British Columbia, and the northern Andes fall within a similar trend, indicating that convergence rates set the primary limits for mountain heights.

Across-strike asymmetry of the Andes orogen is also decoupled from climatic effects. We observe a link between the orogenic asymmetry (measured as trench to peak distance normalised by trench to back arc deformation front distance) and the age and geometry of the Nazca plate, both of which are properties expected to affect the distribution of compressive forces in the Andes.

Together, these analyses reveal that the properties of the subduction zone, including slab dynamics, have important imprints in the heights and position of Cordilleran orogens. These effects need to be accounted for when investigating the role of climate in shaping landscapes above subduction zones.