Contrasting Paradigms In Geochronology: The Role Of Fluids, Diffusion And Strain In Modifying Isotopic Compositions

Diplôme Thèse Contrasting Paradigms In Geochronology: The Role Of Fluids, Diffusion And Strain In Modifying Isotopic Compositions eng 2026-07-10 2026-07-13 author Jakobsson Vidar 0009-0000-0495-095X 402332 Services communs du département des sciences de la terre (DETCO) director Spikings Richard Alan 550467 Services communs du département des sciences de la terre (DETCO) 180 10.13097/archive-ouverte/unige:195308 urn:nbn:ch:unige-1953086 Sc. 6021 Mica and apatite are widely used geo/thermochronometers, yet what mechanisms dominate their isotopic records remains unclear. This thesis evaluates how fluids-reactions, temperature-dependent volume diffusion and deformation control chemical and isotopic (re)equilibration in white mica and apatite. Spatially resolved petrochronology from the Black Hills reveals ubiquitous intragrain disequilibrium resulting from pseudomorphic replacement and interface-coupled-dissolution–(re)precipitation. Laboratory heating experiments show that white mica dehydroxylates above 700 °C, modifying the structure, redistributing Na and Ar and invalidating diffusion parameters and plateau dates derived after dehydroxylation. Deformed meta-granites from the Gotthard nappe and Yarrabubba impact crater demonstrate that increasing strain does not increase mineral reactivity and isotopic resetting; requiring direct links between fluid-reactions and deformation. Consequently, chemical mapping is essential for linking isotopic dates to fluid-reactions and geological processes. The kinetics of volume diffusion and deformation are subordinate to fluid-reactions in driving isotopic resetting. Therefore, thermochronological interpretation must demonstrate the absence of fluid-driven reactions. Geochronology Thermochronology White mica dating Ar-Ar dating Rb-Sr dating Mineral reactions Dewey 550 Swiss National Science Foundation Testing key assumptions in thermochronology: the case of Ar isotopes in muscovite 207404 CH 42 Département des sciences de la Terre 154 false 663 Isotope Geochemistry, Geochronology and Thermochronology https://doi.org/10.6084/m9.figshare.32598270 https://doi.org/10.6084/m9.figshare.32598105 https://doi.org/10.6084/m9.figshare.32568669 https://doi.org/10.6084/m9.figshare.31252096 189e8d3f-bc45-4819-94a7-cf2b6c8ec53c Thesis Public Jakobsson_Manuscript.pdf 44195116 application/pdf CC BY-4.0 dedba37c4f5aa85bd9cbb07c198e436ec8e3ff1fb6ce9222c97baa59eb81c90c 263367b3-8c55-4ab3-af86-528493d01359 Imprimatur Public Imprimatur.pdf 314005 application/pdf 0089728621706031f95175c012efc818dc894dc7e4cab182f4881216ad225b62 openAccess Faculté des sciences / Section des sciences de la Terre et de l'Environnement / Département des sciences de la Terre

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Contrasting Paradigms In Geochronology: The Role Of Fluids, Diffusion And Strain In Modifying Isotopic Compositions				2026	1	0

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