Slow Cenozoic uplift of the western Andean Cordillera indicated by cosmogenic ³ He in alluvial boulders from the Pacific Planation Surface

Abstract

To determine the mechanisms responsible for mountain belt growth, it is important to accurately establish the timing of surface uplift. Here we exploit the altitude control on the production rate of in situ cosmogenic nuclides to test the hypothesis that the Andes was uplifted in the late Miocene. High concentrations of in situ cosmogenic 3He (3Hecos) have previously been measured in alluvial boulders on the western flank of the Central Andes, northern Chile (Evenstar et al. 2009). These are consistent with deposition soon after formation of the surface (13–14 Ma). We have modeled the accumulation of cosmogenic 3He in several different surface uplift scenarios and compared them to the measured concentrations. The measured 3Hecos concentrations are too high to be produced by late Miocene uplift and imply that the western flank of the Andean Cordillera attained a substantial part of its current elevation prior to 14 Myr ago.

87Sr/86Sr of calcium sulfate in ancient soils of hyperarid settings as a paleoaltitude proxy: Pliocene to Quaternary constraints for northern Chile (19.5–21.7°S)

“…This is consistent with the findings of Evenstar et al . [] based on the concentration of cosmogenic 3 He in alluvial boulders located in the piedmont, that most of the current elevation in the area was achieved before 13.4 Ma.…”

“…Also, Evenstar et al . [] quantified uplift by using cosmogenic nuclide data for two sites at which some of our samples are co‐located. They showed that all but a small fraction of the current site elevations (1690 m and 1900 m) must have existed at the end of the Middle Miocene.…”

“…East of the fore arc, two competing histories for the Neogene surface elevation evolution of the adjacent Altiplano Plateau have been put forward: (i) slow uplift since the early Miocene or before [e.g., Hartley et al ., ; Barnes and Ehlers , ] and (ii) rapid ~2.5 km uplift between 11 and 6 Ma [e.g., Garzione et al ., ; Ghosh et al ., ]. Other studies that looked at the relief growth of the easternmost Central Depression and Precordillera in the eastern fore arc are more consistent with the slow Altiplano Plateau uplift hypothesis [ Victor et al ., ; Farías et al , ; Hoke et al ., ; Jordan et al ., ; Evenstar et al ., ]. Nonetheless, the fore arc is a separate tectonic regime and may have experienced a different uplift history than the Andean region.…”

“…Evenstar et al . [] used the altitude control on the production rate of in situ cosmogenic nuclides to constrain the absolute uplift history of the easternmost margin of the Central Depression, located in the Andean fore arc. Based on the concentration of 3 He in alluvial boulders at two sites, they argue that most of the current elevation of the eastern Central Depression at 19.6°S was achieved prior to 13.4 Ma [ Evenstar et al ., ].…”

Contrasting patterns of Andean diversification among three diverse clades of Neotropical clearwing butterflies

“…The formation of the Andean cordillera that extends from northern Venezuela to southern Chile has been proposed as the main driver of diversification in the Neotropical region (Hoorn et al., ). However, the timing and magnitude of surface uplift along the Andean cordilleras is highly controversial (see, e.g., Evenstar, Stuart, Hartley, & Tattitch, and references therein). Despite such uncertainty, it is undeniable that the formation of the Andes provided new ecological conditions along the slopes of the cordillera, modified the climate of the Neotropical region and deeply affected the formation of the Amazonian basin by depositing large quantities of sediment and modifying water drainage patterns (Hoorn et al., ).…”