Trench migration and slab buckling control the formation of the Central Andes

Abstract

The formation of the Central Andes dates back to ~50 Ma, but its most pronounced phase, including the growth of the Altiplano-Puna Plateau and pulsatile tectonic shortening phases, occurred within the last 25 Ma. The reason for this evolution remains unexplained. Using geodynamic numerical modeling we infer that the primary cause of the pulses of tectonic shortening and growth of Central Andes is the changing geometry of the subducted Nazca plate, and particularly the steepening of the mid-mantle slab segment which results in a slowing down of the trench retreat and subsequent shortening of the advancing South America plate. This steepening first happens after the end of the flat slab episode at ~25 Ma, and later during the buckling and stagnation of the slab in the mantle transition zone. The Intensity of the shortening events is enhanced by the processes that mechanically weaken the lithosphere of the South America plate, which were suggested in previous studies. These processes include delamination of the mantle lithosphere and weakening of the foreland sediments. Our new modeling results are consistent with the timing and amplitude of the deformation from geological data in the Central Andes at the Altiplano latitude.

Flat-slab conveyor effect induces precursory crustal contraction in the Central Andes

“…Since the gradient of the oceanic plate steepening at the North is less important than in the south, we would expect less rotations. The steepening would also be associated with mantle removal, thermal weakening and trench hindering that would contribute to efficiently weaken and then shorten the upper plate (Isacks, 1988;Pons et al, 2022). As a results of the passage of the flat slab the angle of the oceanic plate remains relatively shallow, therefore a buckling instability could formed under the weight of the long oceanic segment in the upper mantle (Ribe et al, 2007) resulting to the trench hindering of the plate (Pons et al, 2022) which would further contribute to the development of the present-day elevation of the Central Andes (Capitanio et al, 2010;Lee & King, 2011;Cerpa et al, 2015;Pons et al, 2022) .…”

Hindered Trench Migration Due To Slab Steepening Controls the Formation of the Central Andes

“…The modified version of ASPECT (version 2.3.0‐pre, dealii 9.2.0), including the implementation of new custom plugins necessary for the model set up and the prostprocessing, is accessible from https://github.com/Minerallo/aspect/tree/Paper_slab_buckling_Andes. The input parameters files and initial temperature and composition are also available from https://doi.org/10.5880/GFZ.2.5.2022.001 (Pons et al., 2022). The FASTSCAPE code is also accessible from https://github.com/fastscape-lem/fastscapelib-fortran.…”