Late Cenozoic deformation and uplift of the western flank of the Altiplano: Evidence from the depositional, tectonic, and geomorphologic evolution and shallow seismic activity (northern Chile at 19°30′S)

Abstract

We analyze the west vergent thrust system (WTS) along the western flank of the Altiplano in northern Chile (18°S–21°S). In our study area (19°20′S–19°50′S), the WTS consists of three thrust propagation monocline folds (flexures) developing growth strata. The relative uplift accommodated by the flexures is rapid between 26 and 8 Ma (0.1 mm/yr), diminishing to 0.02 mm/yr after 8 Ma. Approximately 2000 m of relative surface uplift was accommodated by the flexures since the late Oligocene. Sedimentological and geomorphological analysis shows that westward tilting of the forearc occurred after 10 Ma, coeval with the shifting of deformation from the Altiplano to the sub‐Andean zone, where the underthrusting of the Brazilian Craton would have resulted in crustal thickening, surface uplift in the orogen, and westward ductile subcrustal flow. Forearc tilting is accommodated by east vergent thrusts (ETS) issued from the Benioff zone beneath the Central Depression emerging into the Western Cordillera, contributing 500–1400 m of surface uplift. The WTS connects the ETS in the brittle‐ductile crustal transition (∼25 km depth), continuing farther east as the Altiplano low‐velocity zone, configuring the western Altiplano as a crustal‐scale fault bend fold. Forearc tilting would be caused by westward ductile flow in the lower crust pushing the rigid forearc in the ETS. Meanwhile, between 19°S and 21°S, the WTS accommodates dextral strike slip, and ∼3 km of N‐S shortening occurred in the Coastal Cordillera. Transcurrence and strain partitioning are probably the result of slight plate convergence obliquity, strong coupling within the interplate zone, westward continental concavity, and high elevation opposing horizontal contraction.

Renewed uplift of the Central Andes Forearc revealed by coastal evolution during the Quaternary

“…In northern Chile, the data compilation by Le Roux et al (2005) indicates that except when the Juan Fernandez Ridge passed into subduction, the Coquimbo area underwent slight subsidence during late Miocene and Pliocene. The Andean forearc uplift was quantified in Northern Chile to ~ 0.1 mm/yr in the precordillera between 26 and 8 Ma, dropping to ~0.02 mm/yr on average for the last 8 Ma (Farías et al, 2005). More accurate dating indicates uplift and canyon incision between ~10 and ~5 Ma (Hoke et al, 2007;Schildgen et al, 2009;Schildgen et al, 2007), with no more than 250 m postdating the 2.0 to 2.3 Ma-old Ocoña basalt in southern Peru (Schildgen et al, 2009;Thouret et al, 2007).…”

Constricción neógena en la Cordillera de la Costa, norte de Chile: neotectónica y datación de superficies con 21Ne cosmogónico

“…Al considerar que las condiciones de oblicuidad y velocidad del vector de convergencia han sido relativamente continuas a lo largo del margen andino, el estilo de deformación de la zona de antearco responde principalmente a condiciones dinámicas de la zona de acoplamiento y a las características de la placa cabalgante. A pesar que en la zona del antearco estudiada existen importantes sistemas de fallas dispuestos paralelos a la fosa (Sistema de Fallas de Domeyko y el Sistema de Fallas de Atacama), no se han reportado movimientos transcurrentes dextrales importantes post-pliocenos en los sistemas (i.e., Tomlinson y Blanco, 1997;Tomlinson et al, 2001 1 ;Farías, et al, 2005;González et al, 2006). Esto indica que el componente paralelo a la fosa del vector de convergencia no ha sido acomodado por transcurrencia paralela al margen.…”

The topographic imprint of a transient climate episode: the western Andean flank between 15·5° and 41·5°S

“…Here, deformation is partitioned in intra-arc strike-slip tectonics along the Liquiñe-Ofqui fault zone and thrust faulting (Cembrano et al, 2000;Thomson, 2002;Rosenau et al, 2006). Surface-uplift rates in the Main Cordillera are poorly constrained and only few studies provide information (Figure 1) (Farias et al, 2005;Charrier et al, 2007;Schildgen et al, 2007). Therefore, we additionally consider Neogene uplift rates derived in the forearc along the coast.…”