What controls mountain width? Evaluating geometry, rate of deformation, exhumation, and landscape response in the central and southern Peruvian Andes

The kinematics, magnitude of shortening, rate of shortening, and controls on topography in the central and southern Peruvian Andes are evaluated through the use of geologic mapping, balanced cross-sections, low-temperature thermochronology, thermo-kinematic modeling, and landscape modeling. The Tarma section, north of 13°S and the Marcapata section, south of 13°S were chosen to evaluate the controls on mountain width as the Tarma section has a high-elevation (>3 km) width of ~150km, whereas the Marcapata section has a high-elevation (>3 km) width of ~300 km. The northern Tarma section is situated above the Peruvian flat-slab subduction zone and the southern Marcapata section is above a normal subduction geometry. Both sections were found to have similar magnitudes of shortening over the region between the eastern boundary of the Western Cordillera to the Sub-Andean Zone, with 125 km of shortening in the Tarma section and 147.5 km of shortening in the Marcapata section. The ~25 km greater shortening in the Marcapata section is accommodated by the basement ramp located under the Eastern Cordillera. The youngest ages in both sections are controlled by the active basement fault ramps in the Eastern Cordillera. Unlike the Marcapata section, the Tarma section has a broken foreland basin, with basement uplifts within the foreland. The Tarma section also has a less severe precipitation gradient with less overall precipitation when compared to the Marcapata section. We find that the topography is largely controlled by active tectonic uplift in both sections, with a smaller influence due to changing climate scenarios over the Miocene, Pliocene, and Modern day. Linking surface process models to cross section kinematics highlights that surface uplift and the resulting high topography is concentrated over active basement ramps in both sections. High precipitation alone cannot erode away the uplift signal, but can change the location of the plateau edge and allow greater incision. Conversely, a low magnitude of precipitation over areas with little to no active uplift does not preserve previously uplifted topography.