The interplay of hydrothermal and tectonic processes at (ultra)slow-spreading mid-ocean ridges

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The young oceanic lithosphere created at mid-ocean spreading centres is subject to a complex network of magmatic, tectonic and hydrothermal processes. Observations of, among others, bathymetry, fault structures, microearthquake distribution, and locations of high-temperature hydrothermal vent fields reflect the interplay of these processes. At (ultra)slow-spreading ridges, many ridge segments are dominated by a transition from high-angle normal faults to long-lived detachment faults exposing large shear planes of crust and mantle rocks to the seafloor. Channelling of hydrothermal fluids along these permeable fault zones weakens the deforming rocks through thermal, hydraulic, and chemical processes, thereby controlling the fault zone’s evolution and explaining the observed correlation between faulting and hydrothermal activity. Being the result of a dynamic interplay between all involved processes, it is hardly possible to identify and quantify single feedback mechanisms from the observational standpoint alone. This project therefore aims to systematically investigate feedback mechanisms between tectonic and hydrothermal processes together with the influence of fluid-rock-interactions like hydrofracturing and serpentinization using numerical models. The overarching question here is a chicken-or-egg problem: Does tectonic faulting simply provide the geometry for hydrothermal fluid flow or does hydrothermal circulation modify the thermal and mechanical properties of the lithosphere enough to play an important role in initiating faults and/or extending their active lifetime? To address these questions, we will develop a novel hydro-thermo-mechanical model based on the existing codes LaCoDe and HT2_SP. Relevant feedback mechanisms will be investigated and quantified in two parameter studies. We will finally test our numerical model in two case studies to reconstruct the tectonic and hydrothermal evolution of the Logatchev (Mid-Atlantic Ridge) and Longqi (South-West Indian Ridge) hydrothermal fields.