Rates and driving forces of the exhumation of plutonic complexes in oceanic intraplate settings (Kerguelen archipelago) : contributions of low and mid temperature thermochronology

• Main Author: Ahadi, Floriane
• Other Authors: Géosciences Paris Sud (GEOPS), Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS), Université Paris Saclay (COmUE), Cécile Gautheron, Sébastien Nomade
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2019
• Subjects: Thermochronology; (U-Th)/He; Oceanic island; Kerguelen; Exhumation; Erosion; Île océanique; Thermochronologie; Érosion; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; [SDU.STU.VO]Sciences of the Universe [physics]/Earth Sciences/Volcanology; [SDU.STU.GM]Sciences of the Universe [physics]/Earth Sciences/Geomorphology; Indian; Kerguelen Islands
• Online Access: https://theses.hal.science/tel-02614387; https://theses.hal.science/tel-02614387/document; https://theses.hal.science/tel-02614387/file/73308_AHADI_2019_archivage.pdf

The main scientific aim of this work is the understanding of driving forces and erosion rates, at the scale of several dozens of millions of years, of an oceanic volcanic island. A low and mid temperature thermochronological approach on intrusive rocks is used, in order to reconstruct exhumation paths in the oceanic crust of the Kerguelen archipelago (southern Indian Ocean). This archipelago was created 30 Ma years ago and is the emerged part of the eponymous oceanic plateau, formed following the activity of the Kerguelen hot spot, which began 120 Ma ago. The singularity of the Kerguelen archipelago, compared to other oceanic islands, is the occurrence of acid plutonic rocks, on which we can perform thermochronology on. Such methods allow reconstructing the thermal cooling paths, and thus, exhumation paths of the plutons since their deep formation to their surface exhumation. In this work, three thermochronometers were used: the ⁴⁰Ar/³⁹Ar on biotite method, and the (U-Th)/He on apatite and zircon methods. The data obtained on Kerguelen Islands indicate a differential erosion over the archipelago, with local erosion pulses within a plutonic complex, contrasting with regional low erosion rates since 25 Ma. This observation points to the predominant role of magmatic activity, and the associated local tectonic activity, on the exhumation of plutonic bodies and surface denudation. La question scientifique principale de ce travail de thèse est la compréhension des moteurs et des taux d’érosion, à l’échelle de plusieurs dizaines de millions d’années, d’un archipel océanique volcanique. Une approche thermochronologique basse et moyenne température sur des roches intrusives est utilisée, afin de contraindre les trajets d’exhumation de roches plutoniques dans la croûte océanique de l’archipel de Kerguelen (sud de l’Océan Indien). Cet archipel, dont la formation a débuté il y a 30 Ma, est la partie émergée du plateau océanique du même nom, formé suite à l’activité du point chaud de Kerguelen, qui commence il y a 120 Ma. ...