Interactions between geodynamical process, regional tectonics and climate : example of the Southern Andes during the Neogene

• Main Author: Salze, Méline
• Other Authors: Laboratoire Chrono-environnement (UMR 6249) (LCE), Centre National de la Recherche Scientifique (CNRS)-Université de Franche-Comté (UFC), Université Bourgogne Franche-Comté COMUE (UBFC)-Université Bourgogne Franche-Comté COMUE (UBFC), Université Bourgogne Franche-Comté, Philippe Goncalves, Joseph Martinod
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2019
• Subjects: Southern Andes; Low temperature thermochronology; Analog modelling; Tectonics; Uplift; Glaciations; Andes australes; Thermochronologie basse température; Modélisation analogique; Tectonique; Soulèvement; [SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics; [SDU.STU.GL]Sciences of the Universe [physics]/Earth Sciences/Glaciology; Antarctic; Argentina; Fitz Roy; Fitz-Roy; Patagonia; Antarc*; Ice Sheet
• Online Access: https://theses.hal.science/tel-02555073; https://theses.hal.science/tel-02555073/document; https://theses.hal.science/tel-02555073/file/these_A_SALZE_Meline_2019.pdf

The aim of this thesis is to better understand the processes at the origin of the evolution and present-day topography of the Fitz Roy region, located in the Southern Andes, at the border between Chile and Argentina (49°S). This region is characterized by a particular geodynamic context that may play a major role on surface processes. Indeed, the Chile Ridge separating the Nazca and Antarctic oceanic plates, is being subducted beneath the South American plate since 14 My. The obliquity between the ridge and the subduction trench is responsible for a continuous northward migration of the triple junction that is located today at 46°30’S. Furthermore, the Southern Andes is covered by the 3rd largest ice sheet, that constitutes the relict of a much broader glacier formed during the late Miocene. Nowadays, Patagonia is affected by a strong climatic contrast, with a semi-arid climate on the eastern side chain, while the core and the western side of the chain are covered by glaciers and subject to strong precipitations. The tectonic/climatic setting is unique in the world and constitutes a natural laboratory to study of the interactions between ridge subduction, regional tectonics and climatic conditions on topographic evolution through time.To explore the impact of spreading ridge subduction on the overlying continental plate, analogue modeling of subduction of a ridge were conducted. The models highlight direct effects on the geometry of the slab et thus on the position of the magmatic arc. The arrival of the spreading ridge at trench, when the overriding plate moves rapidly trenchwards, induces a decrease of the superficial dip of the slab. This flattening results in an increase of the distance between the trench and the magmatic arc, prior to the ridge subduction. The eastwards migration of the magmatic arc is consistent with the observed magmatic activity migration in Patagonia during the early Miocene, a few million years before the arrival of the Chile Ridge at trench around 14 My. These models also suggest that ...