The effect of inherited paleotopography on exhumation of the Central Andes of NW Argentina

Abstract

Differential exhumation in the Puna Plateau and Eastern Cordillera of NW Argentina is controlled by inherited paleostructures and resulting paleotopography related to the Cretaceous Salta Rift paleomargins. TheCeno zoic deformation front related to the development of the Andean retro-arc orogenic system is generally associated with >4 km of exhumation, which is recorded by Cenozoic apatite fi ssion-track (AFT) and (U-Th-[Sm])/ He ages (He ages) in the Eastern Cordillera of NW Argentina. New AFT ages from the top of the Nevado de Cachi document Oligocene (ca. 28 Ma) cooling, which, combined with existing data, indicates exhumation of this range between ca. 28 Ma and ca. 14 Ma. However, some of the highest ranges in the Eastern Cordillera preserve Cretaceous ages indicative of limited Cenozoic exhumation. Samples collected from an ~3-km-elevation transect along the northern part of the Sierra de Quilmes paleorift fl ank (Laguna Brava) show AFT ages between ca. 80 and ca. 50 Ma and He ages between ca. 45 and ca. 10 Ma. Another set of samples from an ~1-km-elevation transect farther to the southwest (La Quebrada) shows Cretaceous AFT ages between ca. 116 Ma and ca. 76 Ma, and mainly Cretaceous He ages, in agreement with AFT data. Analysis of existing AFT and He ages from the area once occupied by the Salta Rift reveals a pattern characterized by Cretaceous ages along paleorift highs and Cenozoic ages within paleorift hanging-wall basins and later foreland basin depocenters. This pattern is interrupted by the Sierras Pampeanas at ~28°S, which record mid-Cenozoic ages. Our data are consistent with a complex inherited pattern of pre-Andean paleostructures, likely associated with paleotopography, which was beveled by the Cenozoic regional foreland basin and reactivated during the late Neogene (ca. <10 Ma), strongly controlling the magnitude of Cenozoic uplift and exhumation and thus cooling age distribution. This, combined with variable lithologic erodibility, resulted in an irregular distribution of themochronological ages.

Late Miocene upper-crustal deformation within the interior of the southern Puna Plateau, central Andes

“…3C, section C-C′), apatite fission-track and (U-Th)/He thermochronology indicate rapid exhumation at ca. 21-14 Ma in the Cerro Negro (Carrapa et al, 2014). This exhumation is also recorded by detrital apatite fission-track data in sediments preserved in the Fiambalá basin (Fia, Fig.…”

“…Another recent model characterizes the Eastern Cordillera at ~25°S as a broken foreland, where deformation and relief development took place along steeply dipping inherited faults from the Salta Rift, which do not necessarily show any directional gradients in timing (Hain et al, 2011). Although different authors highlight various specific mechanisms, these irregular basement uplift and deformation models agree on the important role of inversion of preexisting Salta Rift structures (e.g., Carrapa et al, 2014;Cristallini et al, 1997;Deeken et al, 2006;Hongn et al, 2007;Insel et al, 2012;Riller et al, 2012;Riller and Oncken, 2003). However, it is not clear if the southern Puna Plateau inherited any structures from the Salta rifting during the Cretaceous, which is underscored by the lack of Cretaceous sediments or exhumation (Carrapa et al, 2014;Löbens et al, 2013;Marquillas et al, 2005), meaning these models may not be readily applicable to our study area.…”

“…3). We note that several pre-Cenozoic bedrock cooling episodes have been documented in the Puna Plateau and its adjacent Eastern Cordillera (e.g., Carrapa et al, 2014;Deeken et al, 2006;Löbens et al, 2013; and could be related to exhumation associated with extension along the Cretaceous Salta Rift (Carrapa et al, 2014;. However, the pre-Cenozoic history of the central Andes is beyond the scope of this paper and is not included in the following summary.…”

Revised exhumation history of the Wind River Range, WY, and implications for Laramide tectonics

“…Exhumation rates obtained in this study are consistent with rates determined by other studies [ Peyton et al , ] and with erosion rates recorded in other thick‐skinned settings such as the Andes [e.g., Deeken et al , ; Carrapa et al , ]. Modeling of AFT samples from Gannet Peak suggests faster exhumation rates at that location (~0.38 mm/yr) [ Fan and Carrapa , ; Peyton et al , ; Peyton and Carrapa , ], this rate is typical of block‐style uplifts, with large vertical displacement on relatively high angle faults [e.g., Ehlers , ].…”

Late Quaternary Tectonics, Incision, and Landscape Evolution of the Calchaquí River Catchment, Eastern Cordillera, NW Argentina

“…Coupled steepness indices (Figure b) and catchment mean erosion rates (Figure ), high concavity indices (Figure c), and linearly aligned litho‐tectonic knickpoints below ponded Quaternary sediment (Figure a) all point to differential uplift across a band of approximately N‐S trending faults in the western CRC. The orientation of faults within this band reflects preexisting structural anisotropies within the crystalline bedrock and is parallel to nearby Cretaceous rift structures (Carrapa et al, ; Grier et al, ; Hongn et al, ; Santimano & Riller, ). Field investigations in the lower Pucará valley reveal an active reverse fault, an active blind thrust, and locally deeply incised (~100 m) pediment surfaces (Figure S13 and 14).…”