Pressure–temperature–time evolution of subducted crust revealed by complex garnet zoning (Theodul Glacier Unit, Switzerland)

Collisional orogens commonly include mono-metamorphic and poly-metamorphic units, their different evolution can be difficult to recognize reconcile. The Theodul Glacier Unit (TGU) in the Western Alps consists of an association metasedimentary metamafic rocks embedded within Zermatt-Saas tectonic unit. In spite recent petrological studies, it remains unclear whether these underwent one or multiple metamorphic cycles. this study, lithologies from TGU unit (mafic schist, mafic granofels, chloritoid schist) were investigated for petrography, quantitative compositional mapping garnet, thermodynamic modelling, Lu–Hf garnet dating. data reveal a coherent history with ?-shaped pressure–temperature (P–T) path characteristic oceanic subduction. Garnet ages yield restricted crystallization time window between 50.3 48.8 Ma (±0.5%, 2SD). A prograde stage recorded cores yields conditions 490 ± 15? 1.75 0.05 GPa. Maximum pressure 2.65 0.10 GPa 580 reached at 0.3 Ma. Initial exhumation was rapid led isothermal decompression 1.50 1 This associated lawsonite breakdown schist causing intense fluid–rock interaction lithologies. process is textures trace element patterns, major composition K-white mica. followed by re-heating ~30? Perturbation subduction-zone thermal structure may related upwelling hot asthenospheric mantle material transient storage crust–mantle boundary.