Uplift of the western Altiplano plateau: Evidence from the Precordillera between 20° and 21°S (northern Chile)

Abstract

We present a quantitative reconstruction of uplift of the western flank of the Altiplano plateau (central Andes), one of the largest monoclines on the Earth, on the basis of an analysis of tectonic structures, syntectonic deposits, and geophysical data. Uplift occurred on a west vergent, slowly propagating system of high‐angle reverse faults merging into a joint detachment that ramps down to midcrustal levels below the plateau edge. The upper ramps determine local fold geometries while the lower ramp controls large‐scale surface tilting and uplift. At 20°S, this fault system was active between ∼30 Ma and 5–10 Ma, with maximum shortening rates of 0.22 mm/yr between 17 and 10 Ma. It generated some 2600 m of surface uplift with only minor shortening of ∼3000 m. Its activity was largely synchronous to eruption of large‐volume ignimbrites from a midcrustal source. Geophysical data indicate that the fault system localized deformation at the boundary between a cool, strong forearc crust and a presumably fluid‐rich and/or partially molten zone underneath the plateau area. The systematic relation between crustal melting and shortening with uplift at the western plateau margin can be traced along most of the plateau flank, with a stepwise decrease in age of deformation and magmatism toward the south indicating discontinuous addition of plateau segments. Crustal thickening to as much as 70 km from westward underthrusting in the back arc parts of the plateau isostatically compensated the tectonic surface uplift and monocline formation with respect to a stable forearc, which only reacted with minor tilting.

More constraints to determine the seismic structure beneath the Central Andes at 21°S using teleseismic tomography analysis

“…The WF is usually described as a sub-vertical strike-slip fault system integrating the Precordilleran Fault System (e.g. Scheuber and Reutter, 1992;Scheuber et al, 1994;Reutter et al, 1996;Victor et al, 2004). The change in relative velocities west and east of the WF indicates variations in the composition of the rocks and thermal state of the materials across these faults.…”

Slow Long‐Term Exhumation of the West Central Andean Plate Boundary, Chile

“…The CC is crosscut by N‐S striking normal faults, E‐W striking reverse faults, and some NW‐SE striking strike‐slip faults (Figure 2a; Allmendinger et al, 2005; González et al, 2003). Separating the Central Depression from the Coastal Cordillera on the west and the Precordillera on the east are the Atacama Fault Zone and the West Andean Thrust, respectively, accommodating some of the differential uplift between the physiographic domains (Armijo et al, 2015; González et al, 2003; Muñoz & Charrier, 1996; Muñoz & Sepulveda, 1992; Victor et al, 2004). Most of northern Chilean (e.g., Isacks, 1988; Jordan et al, 2010; Wörner et al, 2002) and Peruvian (2.5° northward; e.g., Schildgen et al, 2007) Western Cordilleran uplift, however, is thought to have occurred by way of a crustal‐scale monocline of which the Precordilleran slope constitutes the limb.…”

Migrating deformation in the Central Andes from enhanced orographic rainfall

“…Th e d é collement horizon is not readily evident in subsurface images of the western margin. However, similar to the situation beneath the Altiplano, it is assumed that the d é collement horizon lies within upper crustal units above the Moho, where seismic refl ectors dip at 9 ° -10 ° to the east and extend from the subducting Nazca plate to the ALVZ ca 60 km farther east 32 ( Fig. 1c ).…”

“…Th e chronology of tectonic deformation along this transect has been restored based on tectonic and stratigraphic investigations, and low-temperature thermochronometres 3,[7][8][9][10][11]26,32,33 . Although the rate of cumulative shortening across the entire Central Andes has been constant between the Oligocene and the present ( Fig.…”

“…Pre-7 Ma shortening was accommodated by thrusting along a west-vergent system of steeply dipping reverse faults ( Fig. 1d ) that were kinematically linked with the Altiplano low-S velocity zone (ALVZ) at ca 30 km depth 32 ( Fig. 1c ).…”