Uplift of the Altiplano-Puna plateau: A view from the west

Abstract

[1] The western flank of the Central Andean Plateau is a crustal-scale monoclinal fold, expressed in the geomorphology and in the westward tilt of fore-arc basin strata. Data from three fore-arc basins quantify the magnitude and time of displacement of the plateau system relative to the fore arc. From 18°30′S to 22°S there is a single monocline strand. There, other authors documented ∼2000 m (±500 m) of early and middle Miocene structural relief growth across small-scale monoclines, and our data reveal 810 m (±640 m) of ∼11-5 Ma relief growth and 400 m (±170 m) relief growth since ∼5 Ma across a long-wavelength monoclinal fold limb. This structural relief growth since ∼11 Ma approximates the topographic relief growth between the fore arc and the Altiplano plateau. From 22°S to 24°S there are two subparallel long-wavelength monoclines. Structural relief on the east side of the fore arc increased by 2840 m (±2510 m) during ∼17-10 Ma and by 2320 m (±1050 m) since ∼10 Ma.

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

“…While local erosion rates on hyperarid surfaces in the Central Depression of northern Chile may be negligible on millennial and even million‐year timescales (Dunai et al, 2005; Kober et al, 2007), intermittent hyperaridity (e.g., Jordan et al, 2014) and the wide range of local and catchment‐averaged erosion rates in the fore arc indicated by these methods is consistent with long‐term semiaridity to aridity suggested by mean exhumation rates on low‐temperature thermochronometry timescales. We further note that rates derived from samples in the Central Depression (Pampa de Tamurgal in our field area) represent values in a depositional basin where up to ~1,500 m of Miocene sediments (Jordan et al, 2010) would be stripped away at exhumation rates prescribed by our thermochronometric models. Thus, it is important to emphasize that our results cannot be extrapolated across the entire Atacama region and apply specifically to the two physographic areas where they are sampled (CC and PC).…”

“…On the contrary, in the CC, sample 15CL013, sampled at the base of the Camarones canyon in the exorheic section of our field area shows the alternative possibility of increasing local rates in the north of the field area since the Miocene. Inhomogeneity in space and time is expected, however, as long‐term low erosion on a regional scale is driven locally by river incision while arid climates with little overland flow can yield negligible erosion elsewhere during these times (Jordan et al, 2010). Additional AFT data where it lacks would be necessary to further resolve the possible higher rates earlier in the sample cooling histories.…”

“…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.…”

“…Present‐day precipitation rates are recorded as low as <1 mm/yr in the coastal cities of northern Chile (e.g., Schulz et al, 2012). The implication of arid climate in Andean mountain building mechanisms is critical as it is associated with the absence of significant and widespread erosion, and removal of surface material can compensate for tectonically induced rock uplift, weaken the thermal integrity of the crust, or initiate an isostatic response (Gregory‐Wodzicki, 2000; Jordan et al, 2010; Schildgen et al, 2009; Zeitler et al, 2001). Additionally, the lack of sediment supply to lubricate subduction in the trench has been suggested to act as a roughening mechanism, enhancing the transfer of compressional forces from the subducting plate to the overlying crust (Lamb & Davis, 2003).…”

“…Only the increase in exhumation rate of the northernmost CC sample, 15CL013, demonstrates the possibility of a spatial variation in exhumation. This trend, however, while hypothetically attributable to tectonic factors (e.g., location near plate syntaxis) may just as well be a result of proximity to an incised canyon, which could have formed in the last ~10 Myr (Jordan et al, 2010; Lease & Ehlers, 2013; Schildgen et al, 2009). …”