Quantifying crustal fluid flow and its role in the thermal structure of the Alps

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Thermochronology is a key tool that provides large parts of our knowledge of how orogens have evolved over time. The interpretation of thermochronological data relies on independent estimates of subsurface temperatures. While many processes that control temperature can be modelled with some degree of confidence, the thermal effects of groundwater flow remain highly uncertain. Nonetheless, several studies have demonstrated that in parts of active orogens groundwater can account for up to 50% of the overall heat transport. We propose to quantify the importance of fluid flow on the thermal structure of orogens by quantifying the thermal effects of the most visible outcrop of deep fluid flow: thermal springs. We aim to compile thermal spring data in the Alps and use inverse thermal models to quantify the thermal impact of the fluid flow systems that are associated with these springs. We will combine numerical models and detailed mapping of the hydrogeological structure at outcrop and micro-scale to quantify fluid pressures and flow for a selected number of springs. We will combine models with independent data on changes in recharge and ice cover to quantify the persistence of hydrothermal systems over geological timescales. The results will provide the first image of deep fluid flow and its effect on the thermal field at the scale of an entire orogen. Our results will provide input data and constraints for geophysical models of mountain building processes, and will impact thermochronological studies that rely on estimates of (paleo) geothermal gradients. In addition, fluid pressure plays an important role in seismic activity, but is largely unknown in orogens due to the absence of borehole data. Our results will provide new constraints on fluid pressures and permeability of the crust, and consequently provide input parameters for neo-tectonic models.