49-5 Slab-mantle interactions and erosional controls on crustal thickening of the Central and Southern Andes: coupling numerical modeling with geophysical and geological observations

Session: Exploring Feedbacks Between Tectonics and Climate on Lithospheric Evolution Using Multidisciplinary Approaches

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Abstract:

The  Central Andes (16-32°S) constitutes the sector of the Andes with the thickest crust, reaching 65-75 km under the Altiplano-Puna Plateau, mainly due to extensive crustal shortening (up to 400 km). The drastic change from a highly shortened orogenic wedge to the almost negligible (<50 km) shortening observed in the Southern Andes (32-42°S) has raised questions about the tectonic deep and surface processes controlling crustal thickening and topographic growth for decades, motivating the TANGO NSF Project to perform a seismic deployment and geological observations along the strike of the Central Andes. With the goal of coupling the geophysical observations of the deep tectonic setting with the geological observations at the surface of the Andes, we perform thermo-mechanical numerical modeling of subduction dynamic processes coupled with surface processes such as orographic erosion. Our systematic parametric study examines the effects of different slab temperatures – aiming to test the difference in the Nazca slab age along the Central and Southern Andes – and different degrees of surface erosion, as precipitation and long-term erosion rates change in magnitude and location along the strike of the orogen. Our results for a warm (16.3 °C/km mean geothermal gradient) vs. a cold slab (10.8 °C/km) show that a cold slab generally subduct at a normal (30°) dip angle, and generates episodes of crustal thickening and shortening, followed by subduction erosion of the upper continent. Warm slabs subduct at a lower dip angle and crustal thickening and subduction erosion occur at slower rates and magnitudes. For models with and without surface erosion, high rates of erosion not only consume the crust faster, but also maintain the orogenic wedge at a subcritical state, inhibiting crustal thickening. In contrast, when erosion is absent, the orogenic wedge becomes supercritical and more strain is distributed near the surface. These results suggest that the older, and thus colder, slab in the Central Andes with the lower erosion rates since at least the Miocene might be important factors contributing to the higher crustal shortening in the central Andes as compared to the Southern Andes.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9255

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