Understanding outliers in thermochronological anomalies in the Swiss Subalpine Molasse and how they are linked to geological uncertainty

Abstract

Thermochronological data and kinematic models are often combined to retrace exhumation, cooling or fault activity. However, structural uncertainty is often neglected in thermokinematic models, which can lead to bias when interpreting data. Here we aim to test the influence of structural uncertainty on the interpretation of low-temperature thermochronological data in Mount Rigi in the Subalpine Molasse, a key region in the Swiss foreland fold-thrust belt of the European Alps. The region has been incorporated into the Alpine orogenic wedge in the Miocene, which led to the development of a triangle zone at the leading edge of deformation. An extensive low-temperature thermochronological data set exists, including apatite fission track as well as apatite (U-Th)/He data, which contains outliers not easily to be explained with the existing kinematic models.To diminish bias in the thermokinematic model we first estimated the geological uncertainty by computing and comparing 1000 stochastically generated 3D implicit geometric models, varied within an assigned uncertainty range assigned to geological input parameters. Model generation is performed with the stochastic geological modeling engine implemented in the Python package GemPy. In a second step a kinematic model was created which was altered in areas of high uncertainty found in the first step. With this setup, minimum and maximum values of cooling associated with shortening within the fold-thrust belt can be determined. The remaining cooling signal (if present) must hence be associated with other drivers, such as erosion caused by drainage reorganization, or uplift and erosion due to deep seated processes. Additionally, hydrothermal fluids could be held responsible for explaining individual data points. With this research, we hope to give new insights into the temporal evolution of heat flow in foreland basins and show how including geological uncertainty can lead to better constrained time-temperature histories.