Preprints
https://doi.org/10.5194/egusphere-2022-629
https://doi.org/10.5194/egusphere-2022-629
 
14 Jul 2022
14 Jul 2022

The western Andes at ~20–22° S: A contribution to the quantification of crustal shortening and kinematics of deformation

Tania Habel1, Martine Simoes1, Robin Lacassin1, Daniel Carrizo2,a, and German Aguilar2 Tania Habel et al.
  • 1Université Paris Cité, Institut de physique du globe de Paris, CNRS, F-75005 Paris, France
  • 2Advanced Mining Technology Center, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Avenida Tupper 2007, Santiago, Chile
  • anow at: GeoEkun SpA, Santiago 7500593, Chile

Abstract. The Andes are an emblematic active Cordilleran orogen. Mountain-building in the Central Andes (~20° S) started by Late Cretaceous to Early Cenozoic along the subduction margin, and propagated eastward. In general, the structures sustaining the uplift of the western flank of the Andes are dismissed, and their contribution to mountain-building remains poorly constrained. Here, we focus on two sites along the western Andes at ~20–22° S, in the Atacama Desert, where structures are well exposed. We combine mapping from high-resolution satellite images with field observations and numerical trishear forward modeling to provide quantitative constraints on the kinematic evolution of the western Andes. Our results confirm the existence of two main structures, once our field observations are combined with regional data: (1) the Andean Basement Thrust, a west-vergent thrust system placing Andean Paleozoic basement over Mesozoic strata; and (2) a series of west-vergent thrusts pertaining to the West Andean Thrust System, deforming primarily Mesozoic units. Once restored, we estimate that both structures accommodate together at least ~6–9 km of shortening across the sole investigated ~7–17 km-wide field sites. This multi-kilometric shortening represents only a fraction of the total shortening accommodated along the whole western Andes. The timing of the main deformation recorded in the folded Mesozoic series can be bracketed between ~68 and ~29 Ma – and possibly between ~68 and ~44 Ma – from dated deformed geological layers, with a subsequent significant slowing-down of shortening rates. Even though negligible when compared to total shortening across the whole orogen, the contribution of the structures forming the West Andes has been relatively significant at the earliest stages of Andean mountain-building before deformation was transferred eastward.

Tania Habel et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-629', Benjamin Gérard, 08 Aug 2022
    • AC1: 'Reply on RC1', Martine Simoes, 23 Sep 2022
  • RC2: 'Comment on egusphere-2022-629', Patrice Baby, 15 Sep 2022
    • AC2: 'Reply on RC2', Martine Simoes, 29 Sep 2022

Tania Habel et al.

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Short summary
The Central Andes are one of the emblematic reliefs on Earth, but their western flank where mountain-building initiated, remains understudied. Here we explore two rare key sites in the hostile conditions of the Atacama desert to build cross-sections, quantify crustal shortening and discuss the timing of this deformation at ~20–22° S. We propose that the structures of the western Andes accomodated here significant crustal shortening, however during the earliest stages of mountain-building.