Markmann, Thorsten Andreas (2024). The geochemical record of metamorphic fluid-rock interaction in subducted terranes. (Thesis). Universität Bern, Bern
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Abstract
Dehydration during metamorphism in subduction zones plays a crucial role in the redistribution of fluids within the subducting oceanic crust. This can can lead to significant fluid-rock interactions during metamorphism, which affects the mineral growth and stability, whereas fluid fluxes play a critical role in mass transfer and element recycling on Earth. This thesis investigates fluid-rock interaction and metamorphic processes in subduction zones, focusing on how fluid release, transport, and mineral growth shape geochemical signatures during prograde metamorphism. Integrating methodological advancements and applications to natural samples from high-pressure terranes, this work provides a detailed perspective on the fluid-mediated geochemical evolution of subducted rocks, particularly within the Cyclades (Greece) and the European Alps. Chapter 2 introduces a novel routine approach for quantitative compositional mapping using LA-ICP-MS, which enables high-resolution, major to trace element analysis of compositionally zoned minerals, such as garnet. The routine stresses the usage of an accurate pixel allocation strategy of square pixels. Implemented within the open-source XMap-Tools software, the mapping approach addresses calibration challenges in inhomogeneous phases and demonstrates accurate calibration across diverse geological contexts, such as garnet-bearing eclogites, feldspar and biotite in migmatites, and rutile in metapelites. Chapter 3 presents a petrochemical model that integrates mechanical and thermodynamic simulations to explore the effects of dehydration reactions on fluid release and pressure fluctuations within subducting rocks. The model results emphasize the link between metamorphic reactions and episodic brittle failure, and highlights the fluid release in pulses. This interplay has implications for transient permeability and fluid flow along shear zones in subduction environments. Applications to the Monviso ophiolite indicate that brittle failure episodes may correlate with observed compositional zoning in garnet from subducted metagabbro. Fluid pressure variations during metamorphism can potentially modify the incorporation of elements into garnet as resolved for chemically zoned garnets in bluecshists from Syros. Chapter 4 examines fluid-rock interaction in subducted oceanic crust on Syros through in-situ oxygen isotope analyses of garnet and phengite. Variations in δ18O across different lithologies reflect hydrothermal alteration during seafloor processes and subsequent interaction with isotopically heavier fluids during high-pressure metamorphism. The isotopic data suggest that fluid infiltration was extensive in certain areas, notably Katergaki, while other sites experienced limited interaction, supporting a model of localized fluid transfer and mineral stabilization. Chapter 5 investigates garnet growth mechanisms and their geochemical implications in blueschist samples from Syros, using 3D micro-computed tomography and 2D compositional mapping. Findings show that garnet growth was influenced by fluid infiltration and mineral breakdown, leading to trace element zoning patterns indicative of interface-controlled growth and episodic fluid pressure changes. Differences in trace element distribution between samples reveal that garnet in the locality Katergaki interacted with externally derived fluids, producing oscillatory zoning not observed in samples from the locality Achladi. Collectively, this thesis illustrates how compositional mapping, petrochemical modelling, and isotopic analysis together provide insights into the geochemical processes at play during subduction. This work underscores the role of fluids in regulating mineral stability, mass transfer, and the overall geochemical evolution of subducted lithologies, with implications for the dynamics of element recycling and metamorphism in Earth’s crust and mantle.
| Item Type: | Thesis |
|---|---|
| Dissertation Type: | Single |
| Date of Defense: | 29 November 2024 |
| Subjects: | 500 Science > 550 Earth sciences & geology |
| Institute / Center: | 08 Faculty of Science > Institute of Geological Sciences |
| Depositing User: | Hammer Igor |
| Date Deposited: | 11 Dec 2025 16:42 |
| Last Modified: | 11 Dec 2025 23:25 |
| URI: | https://boristheses.unibe.ch/id/eprint/6958 |
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