Hindered Trench Migration Due To Slab Steepening Controls 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 rst happens after the end of the at 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.

Slab buckling as a driver for rapid oscillations in plate motion and subduction rate

“…In our slab-pull-driven subduction models with a freely moving upper plate we also observe oscillating motion of the trench and upper plate 53 . In our simple experiments, the rigid upper plate is not able to deform, and it thus moves along with the trench where naturally this would lead to changes in stress state, reflected by episodic back-arc spreading 54 , extensional or contractional upper plate deformation 35,39,[55][56][57][58][59][60] and even changes in topography 61 . Such variations may be of interest to the understanding of fluid and magmatic processes affecting the upper plate.…”

“…Therefore, for subduction zones where slab buckling leads to oscillating trench motion and upper plate deformation, enhanced resolution in marine magnetic anomalies and accompanying reconstructions could lead to a better predictive power in the timing of these magmatic and ore-genesis related upper plate processes. In the Andes, alternations on a timescale of ~10 Ma between shortening and trench retreat were recently postulated to result from slab buckling 60 . For Tibet, the only high-resolution deformation records in the relevant time interval of 60-50 Ma are from the Qiangtang terrane of northern Tibet, far from the trench 65,66 , which on a first order appear to record shortening pulses that coincide with the oscillations 19 .…”

Localization of Deformation in a Non‐Collisional Subduction Orogen: The Roles of Dip Geometry and Plate Strength on the Evolution of the Broken Andean Foreland, Sierras Pampeanas, Argentina

“…More recent studies, however, have emphasized that the stress regime of the overriding plate is probably more influenced by the velocity difference between the overriding plate and the trench rather than by the subduction angle (Faccenna et al., 2017, 2021; Lallemand et al., 2008). The velocity of trench retreat can be perturbed by a rapid change in the subduction angle, which can be caused by the interaction between the slab and the mantle transition zone (Briaud et al., 2020; Cerpa et al., 2015; Čížková & Bina, 2013; Pons et al., 2022). The absolute motion of the South American plate prescribed in model S1 is considered to be the driving force of the Andean orogeny (Husson et al., 2008; Martinod et al., 2010; Sobolev & Babeyko, 2005); nevertheless, when viewed at shorter geological timescales, model variants such as model S5b–d, illustrate that a similar strain rate as in model S1 can be achieved with a different redistribution of plate velocities while maintaining a similar convergence rate (Figures 6 and 7).…”

“…In the Central Andes (∼24°S), the presence of thick, mechanically weak Palaeozoic sediments in the foreland spatially correlates with a southward change of deformational style from thin-skinned to thick-skinned deformation, which marks the transition between the Subandean FTB and the broken foreland province of the Santa Barbara System of northwestern Argentina (Allmendinger et al, 1983;McGroder et al, 2015;Pearson et al, 2013). The results of numerical models addressing the tectonic style in that region have shown that a low friction coefficient of the sediments (<0.05) promotes asymmetric deformation, a simple-shear and thin-skinned deformation style, which may constitute a necessary condition to initiate foreland underthrusting of the Brazilian Shield (Liu et al, 2022;Pons et al, 2022;Sobolev et al, 2006). Additionally, Ibarra et al (2019) proposed that deformation tends to localize within the areas with large lateral variations of crustal strength, such as the foreland where a thick sedimentary layer is present.…”

Subduction and Hydrogen Release: The Case of Bolivian Altiplano

“…Most authors agree that crustal shortening alone cannot explain the uplift of the Altiplano high plateau basin. On the basis of the deep seismic data and the presence of the late Miocene-Pliocene anomalous back-arc volcanism, they suggest that the Altiplano uplift is mainly related to an orogen-wide lithosphere thinning, whose mechanism, related to the abnormal hot mantle, is still under debate [43][44][45][46][47].…”