Tectonic and Climatic Controls on the Spatial Distribution of Denudation Rates in Northern Chile (18°S to 23°S) Determined From Cosmogenic Nuclides

Abstract

In the arid region of northern Chile the environmental conditions are favorable for measuring tectonic and climatic influences on catchment denudation rates in the absence of vegetation. Previous studies of denudation rates from cosmogenic 10Be and 26Al concentrations are limited to single drainages. In this study, we examine catchment‐ to orogen‐scale spatial variation in denudation rates between 18 and 23°S in the Coastal and Western Cordilleras of northern Chile. 10Be and 26Al data were obtained from 33 catchments to examine the relative roles of tectonics and climate on catchment‐averaged denudation rates. At broader scales, we examine whether denudation rates and orogen topography reflect the 3‐D plate geometry of the region. Cosmogenic nuclide‐derived denudation rates range from 0.4 ± 0.5 to 20.6 ± 1.5 m/Myr in the Coastal Cordillera and from 1.4 ± 0.7 to 168.0 ± 19.8 m/Myr in the Western Cordillera. The controls on the denudation rates are evaluated using a statistical factor analysis of 10 selected catchment parameters. Denudation rates indicate a strong linear relationship with channel steepness indices but insignificant correlations and covariation with mean annual precipitation rates, drainage area, stream order, mean elevation, mean local relief, mean basin slope, and grain size of the sampled sediments. Moreover, denudation rates are better correlated with tectonic controls at catchment scale than orogen‐scale plate tectonics in the Western and Coastal Cordillera.

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

“…While these rates may appear fast compared to other rates from cosmogenic isotopes reported in the west central Andes (e.g., Abbühl et al, 2010, 2011; Carretier et al, 2015; Kober et al, 2007, 2009; Placzek et al, 2010; Starke et al, 2017), we note that the rates reported here are averages over long timescales of 10 7  years and could contain within them punctuated periods of activity with long periods of little exhumation. Also, though 3 χ 2 acceptable maximum values rise to ~0.8 km/Myr in the PC (Figure 10), these changes occur on shorter timescales and earlier in the mineral cooling histories where apparent exhumation is a less trustworthy indicator for mean regional exhumation or erosion.…”

“…More recent, shorter timescale denudation rates (<~10 6  years) based on catchment‐averaged 10 Be, 26 Al, and 21 Ne cosmogenic nuclide concentrations and exposure ages have been reported, as low as <1 m/Myr, up to several orders of magnitude lower than bedrock thermochronometric exhumation rates in the southern Peruvian and northern Chilean fore arc but range up to 300 m/Myr (~0.3 km/Myr) at higher elevations and slopes, particularly in the modern‐day Precordillera (Abbühl et al, 2010, 2011; Carretier, Regard, Vassallo, Aguilar, et al, 2015; Carretier, Regard, Vassallo, Martinod, et al, 2015; Kober et al, 2007, 2009; McPhillips et al, 2013; Placzek et al, 2010; Starke et al, 2017). Generally, higher rates are reported in southern Peru than in northern Chile but correlations with precipitation or hillslope angles are inconsistent (Abbühl et al, 2011; Kober et al, 2009; Reber et al, 2017; Starke et al, 2017) and extreme climatic events (e.g., El Niño) may be important (Abbühl et al, 2010).…”

“…Generally, higher rates are reported in southern Peru than in northern Chile but correlations with precipitation or hillslope angles are inconsistent (Abbühl et al, 2011; Kober et al, 2009; Reber et al, 2017; Starke et al, 2017) and extreme climatic events (e.g., El Niño) may be important (Abbühl et al, 2010). 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.…”

Response of a Rheologically Stratified Lithosphere to Subduction of an Indenter‐Shaped Plate: Insights Into Localized Exhumation at Orogen Syntaxes

“…In contrast, despite thick and mechanically weak crust in the central Andes (Capitanio et al, ; Kley & Monaldi, ; Sobolev & Babeyko, ), no concentric uplift is reported in the South American subduction zone (Figure d), possibly because of a relatively small concavity of the subducting plate (see Figure d) and considerable upper plate advance component due to accelerated westward drift of the South American plate during the past 30 Myr (Russo & Silver, ; Silver et al, ) and finally perhaps due to the limited exhumation magnitudes in the region due to the arid to hyper arid climate in the region. However, despite the lack of localized exhumation observed in the Arica bend of the central Andes due the arid climate, the long‐wavelength topography of the region is highest at the Arica bend, before decreasing slightly to the south, away from the bend (Starke et al, ). This regional trend of decreasing elevations away from the Arica bend that is consistent with the high rock uplift rates predicted here above the bend causes higher elevations (in the absence of erosion).…”

Geomorphology of the coastal alluvial fan complex Guanillos, northern Chile

“…The hyperarid conditions in the Atacama Desert, and the strongly limited denudation related to the climate, favor the preservation of landforms and make the Atacama Desert a key area for studying long-term geomorphological processes (e.g. Evenstar et al, 2017;Haug, Kraal, Sewall, Van Dijk, & Diaz, 2010;Kober et al, 2007;Nishiizumi, Caffee, Finkel, Brimhall, & Mote, 2005;Starke, Ehlers, & Schaller, 2017). However, the climatic conditions of the coastal plain substantially differ from those in the inland desert.…”