To what extent do hydrothermal systems disturb the temperature field of the Molasse Basin?
Final Report Abstract
This project focused on understanding the influence of hydrothermal flow on the temperature field of the northern foreland basin of the European Alps, the Molasse Basin. Quantifying this influence is important for our understanding of temperature-sensitive dating techniques (thermochronology). To estimate the temperature history of a region rates using thermochronological data, some studies assume steady state temperature, whereas others include more complex solutions of the heat equation, and take into account e.g. changes of geothermal gradient through time due to tectonic movements. However, currently none of these models are able to quantify the influence to fluid flow and hydrothermal activity. Our research focused on two aspects, models of hydrothermal activity and structural uncertainty. We developed a new workflow for accounting for structural uncertainty in crosssection balancing, and show how improved structural cross-sections are important for identifying potential flow paths for deep fluid flow in foreland basins. The second main scientific advance is the development of a new open-source model code of heat flow and thermochronology in hydrothermal systems. The main difference is the direct coupling of hydrothermal activity and thermochronology in this code, which is something that is not available in existing model codes of fluid & heat flow. In addition, the code includes realistic land surface heat flux based on current land surface meteorology literature, which turns out to be very important for modeling hot springs and their thermal effects. The development of the model code did delay the model-data comparison that will provide answers to the original research questions on the thermal footprint of the Baden and Schinznach hydrothermal systems and their age. Current work is on the way to complete this part of the project. The somewhat poorer than expected outcrop conditions directly around the springs precluded a very dense thermochronology dataset. However, the combination of subsurface temperature data from nearby boreholes and the thermochronology dataset gathered in the course of this project are still expected to provide broad constraints on the thermal effects of hydrothermal activity that will be publishable. We provided an open-source model code that can be freely used by the scientific community to model hydrothermal systems and to quantify their thermal footprint and age (http://doi.org/10.5281/zenodo.2527845).
