Exhumation history and landscape evolution of the Sierra de San Luis (Sierras Pampeanas, Argentina) - new insights from low - temperature thermochronological data

Abstract

ABSTRACT. This paper presents low-temperature thermochronological data and K-Ar fault gouge ages from the Sierra de San Luis in the Eastern Sierras Pampeanas in order to constrain its low-temperature thermal evolution and exhumation history. Thermal modelling based on (U-Th)/He dating of apatite and zircon and apatite fission track dating point to the Middle Permian and the Triassic/Early Jurassic as main cooling/exhumation phases, equivalent to ca. 40-50% of the total exhumation recorded by the applied methods. Cooling rates are generally low to moderate, varying between 2-10 °C/Ma during the Permian and Triassic periods and 0.5-1.5 °C/Ma in post-Triassic times. Slow cooling and, thus, persistent residence of samples in partial retention/partial annealing temperature conditions strongly influenced obtained ages. Thermochronological data indicate no significant exhumation after Cretaceous times, suggesting that sampled rocks were already at or near surface by the Cretaceous or even before. As consequence, Cenozoic cooling rates are low, generally between 0.2-0.5 °C/Ma which is, depending on geothermal gradient used for calculation, equivalent to a total Cenozoic exhumation of 0.6-1.8 km. K-Ar fault gouge data reveal long-term brittle fault activity. Fault gouge ages constrain the end of ductile and onset of brittle deformation in the Sierra de San Luis to the Late Carboniferous/Early Permian. Youngest K-Ar illite ages of 222-172 Ma are interpreted to represent the last illite formation event, although fault activity is recorded up to the Holocene. RESUMEN. Historia de la exhumación y evolución del paisaje de la sierra de San Luis (Sierras Pampeanas, Argentina)-nuevas perspectivas a partir de datos termocronológicos de baja temperatura. Esta contribución presenta datos de termocronología de baja temperatura y edades de illitas generadas en zonas de fallas de la sierra de San Luis, en las Sierras Pampeanas Orientales de Argentina, con el propósito de aportar al conocimiento de la historia de su exhumación y evolución termal de baja temperatura. El modelado termal basado en dataciones de (U-Th)/He, apatita, circón y trazas de fisión sugiere que las principales fases de exhumación y enfriamiento ocurrieron durante el Pérmico medio y Triásico/Jurásico inferior, contribuyendo con aproximadamente 40-50% de la exhumación total registrada por los métodos utilizados. Las tasas de enfriamiento son, en general, bajas a moderadas, variando entre 2-10 °C/Ma durante el Pérmico y Triásico y 0,5-1,5 °C/Ma después del este último período. El lento enfriamiento y la persistente residencia de las muestras analizadas en condiciones térmicas de retención parcial (partial annealing) ha influenciado notoriamente las edades obtenidas. Los datos termocronológicos indican que no ha habido una exhumación 276 Exhumation history and LandscapE EvoLution of thE siErra dE san Luis (siErras pampEanas, argEntina)... significativa después del Cretácico o incluso antes. Consecuentemente, las tasas de enfriamiento durante el Cenozoico, son bajas, ge...

Using a Paleosurface to Constrain Low‐Temperature Thermochronological Data: Tectonic Evolution of the Cuevas Range, Central Andes

“…Our model suggests that no significant relief developed since the Famatinian orogeny until Pliocene time. In contrast, based on low‐temperature thermal modeling, Permo‐Triassic relief development has been suggested for the region south of the Sierras Pampeanas (Bense et al, , ). In the models presented in Bense et al () is not clear how the radiation damage was treated for the ZHe and the AHe systems.…”

“…The Sierras Pampeanas are characterized by Paleozoic to Pliocene ZHe, AFT, and AHe ages (Bense et al, ; Coughlin et al, ; Jordan et al, ; Löbens et al, ; Sobel & Strecker, ; Stevens Goddard et al, ). This thermochronological record has been interpreted to result from several contrasting tectonic and erosional processes including postorogenic cooling and relief reduction, extensive exhumation related to compressional phases, and horst exhumation during several rifting cycles (Bense et al, , ; Coughlin et al, ; Löbens et al, ). These contrasting tectonic settings also imply significant spatial and temporal variations of the geothermal gradient in the Sierras Pampeanas (Dávila & Carter, ; Stevens Goddard et al, ).…”

“…During the Mesozoic, the Sierras Pampeanas province was characterized by the development of several rift basins related to the opening of the South Atlantic Ocean (Horton, 2018;Oncken et al, 2006). Late Triassic to Cretaceous rifting cycles were responsible for extensional magmatism and basement exhumation in local depocenters, such as the Salta, Sierras Chicas, and El Gigante basins ( Figure 1) (Bense et al, 2017;Marquillas et al, 2005;Schmidt et al, 1995;Viramonte et al, 1999). In the Velasco range, Early Cretaceous high thermal gradients (35-50°C/km) related to the rifting phases have been inferred using thermal modeling of low-temperature thermochronologic data .…”

“…Bense et al () have suggested that most of the relief formation and rock exhumation took place during the Permo‐Triassic based on thermal modeling of these old thermochronologic ages. In contrast, several studies have proposed Miocene relief development based on the Miocene stratigraphic record and thermal modeling (Bense et al, ; Davila et al, ; Mortimer et al, ; Sobel & Strecker, ; Zapata et al, ).…”

Tracing Geophysical Indicators of Fluid‐Induced Serpentinization in the Pampean Flat Slab of Central Chile

“…Some authors agree that the Sierras Pampeanas were created by the collision of the ridge with the South American continent through thick‐skinned basement cored uplift (Gans et al, ; Jordan et al, ; Kay et al, ; Ramos et al, ). Other authors propose that the Sierras Pampeanas were created earlier than the latest Cretaceous based on thermochronological data of sediments deposited in the high‐altitude basins (Bense et al, ; Goddard et al, ; Levina et al, ). Arc volcanic activity fully ceased by 7 Ma in the Precordillera and 6 Ma in the Main Cordillera (Kay & Abbruzzi, ).…”