The Interplay of Hydrothermal and Tectonic Processes at (Ultra)Slow-Spreading Mid-Ocean Ridges ; Das Wechselspiel Hydrothermaler und Tektonischer Prozesse an (Ultra)Langsam Spreizenden Mittelozeanischen Rücken

Mid-ocean ridges mark the boundary between divergent tectonic plates, where only a relatively thin brittle lithosphere separates the hot, ductile mantle from the overlying ocean. This unique environment fosters complex interactions among magmatism, tectonic faulting, and hydrothermal circulation within the newly formed seafloor. At slow- and ultraslow-spreading ridges with limited melt supply from the mantle, large, long-lived detachment faults are common, often associated with diverse hydrothermal activity. These systems, which have become a focus of recent research, are the expression of intricate hydro-tectono-magmatic feedbacks. In this thesis, numerical models, ideally suited for unraveling such complex systems, are employed to address unresolved questions about detachment faulting: What governs the subsurface thermal structure, and how does it influence the initiation and persistence of detachment faults? Do these faults merely provide a geometric framework for hydrothermal circulation, or do thermal, hydraulic, and chemical feedbacks actively shape fault evolution? Building on existing codes, this work presents a refined model to simulate lithosphere faulting, melt emplacement and hydrothermal activity around active fault zones. Two case studies highlight detachment fault dynamics: (1) the magma-poor section of the Southwest Indian Ridge at 64°E, where alternating "flip-flop" detachment faults create large axis-parallel ridges, and (2) the oceanic core complex at 13°30'N on the Mid-Atlantic Ridge, where the domed shear plane of a detachment fault hosts a series of hydrothermal ore deposits. In the first study, hydrothermal cooling within the fault zone is parametrized to investigate the interplay with magmatic sill intrusions and how thermal and rheological effects control flip‐flop detachment faulting. The second study examines fluid circulation patterns and high-temperature hydrothermal venting around an active detachment to understand the location of large seafloor sulfide deposits at oceanic core ...