Late Miocene–Holocene canyon incision in the western Altiplano, northern Chile: tectonic or climatic forcing?

Abstract

Major fluvial incision (600–1000 m) affecting the Coastal Cordillera and Central Depression of northern Chile is analysed to evaluate supposed coeval uplift of the Altiplano and/or climatic changes in the Atacama Desert. The timing of the beginning of incision is constrained by the age of deposition of the Central Depression top. In the north (18–19°S), this top corresponds to fluvial gravels accumulated between 11.9 ± 0.6 Ma and 8.3 ± 0.5 Ma, which are genetically related to semiarid climate and to an eastward poorly dissected parallel drainage network that developed between 15.0 ± 0.6 and 11.2 ± 0.6 Ma; thus, gravel deposition ended at 11.9–11.2 Ma. To the south (19–20°S), the Central Depression top corresponds to c . 6 Ma alluvial deposits. Stratigraphically determined canyon ages and knickzone locations indicate that southward dissection began later and/or developed under a regime of lower erosion capacity owing to drier climate. Vertical incision rate evolution is compatible with eastward knickzone migration. Dissection required a considerable altitude difference between ancient and present-day river base levels, which was achieved predominantly by basin infill on an already partially elevated bedrock. Therefore subsequent incision would have been triggered by local semiarid climatic periods rather than by contemporaneous surface uplift. Exoreic canyons occur when climatic conditions in the catchments are arid–semiarid whereas endoreism is developed when these conditions in catchments are hyperarid.

Origin and development of theater-headed valleys in the Atacama Desert, northern Chile: Morphological analogs to martian valley networks

“…García et al (2011) attributed these age relationships to less runoff in the southern headwater areas than in the north, thus arguing for the later establishment of exorheic drainage. They concluded that the quebrada incision was more due to periods of semiarid (i.e., wetter) paleoclimate in the headwaters than to uplift during the time of incision.…”

“…The cold Humboldt Current runs northward along the Pacific coast, cooling the near-surface air and creating a stable temperature profile, so moist air is trapped along the coast. In northern Chile, the annual precipitation and resulting fluvial dissection decline rapidly westward, with annual rainfall ranging from $20 cm/a at higher elevations to <0.1 cm/a near the coast (Houston and Hartley, 2003;Houston, 2006;Strecker et al, 2007;García et al, 2011). Long-term semiarid to hyperarid climates, arguably since the late Triassic (Clarke, 2006) or late Jurassic (Hartley et al, 2005), has combined with rapid uplift of the Andes since the Miocene (when the rain shadow and aridity were enhanced) to create a landscape in which tectonic features are unusually well expressed on the surface (Gregory-Wodzicki, 2000;Rech et al, 2006).…”

“…The exorheic quebradas (i.e., draining to the ocean rather than to enclosed continental basins) from 18 to 19.5°S crosscut a parallel drainage network that formed between 15.0 ± 0.6 and 11.2 ± 0.6 Ma, whereas those endorheic quebradas (i.e., draining to enclosed basins) south of 19.5°S have incised alluvial sediments that were deposited about 6 Ma (García et al, 2011). García et al (2011) attributed these age relationships to less runoff in the southern headwater areas than in the north, thus arguing for the later establishment of exorheic drainage.…”

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

“…Coudurier‐Curveur et al (2015) attributed this change to latitudinal precipitation gradients over the WC and Altiplano, which carry monsoonal Atlantic humidity and ultimately drain toward the Pacific. The endorheic/exorheic threshold may thus coincide with a transition from aridity/semiaridity to hyperaridity (García et al, 2011) rather than one based on tectonic controls (e.g., subducted ridges and effects of enhanced subducting plate rigidity in the Arica bend).…”

Cenozoic tectonostratigraphic evolution and architecture of the Central Andes in northern Chile based on the Aquine region, Western Cordillera (19°-19º30’ S).

“…2), with the West-Vergent Thrust System (WTS) located within the Precordillera (Muñoz and Charrier, 1996;Victor et al, 2004;Farías et al, 2005;García and Hérail, 2005;García et al, 2011) and the East-Vergent Thrust System (ETS) located within the Western Cordillera, in the presentday arc Farías et al, 2005;Cortés et al, 2012a). These systems controlled the Neogene structural and depositional evolution of this part of the Andes (Charrier et al, 2007(Charrier et al, , 2013 García et al, 2004García et al, , 2011Charrier et al, 2007Charrier et al, , 2013Cortés et al, 2012a García et al, 2011), exerting a substantial role in the construction of the present-day relief of the region (Muñoz and Sepúlveda, 1992;Muñoz and Charrier, 1996;Pinto et al, 2004;Victor et al, 2004;Charrier et al, 2005;Farías et al, 2005;Jordan et al, 2010;Cortés et al, 2012a, b). Nonetheless, the detailed temporal and geometrical interrelationship of these structural systems has not yet been well established, nor the role they have played in controlling the lithostratigraphy and structure of the region lying between them.…”