Coupled climatic/tectonic forcing of European topography revealed through thermochronometry (Thermo-Europe)
Final Report Abstract
We used low temperature thermochronology (Apatite fission track and (U-Th-Sm)/He dating on single grains) as well as analogue modelling to explore the combined effect of tectonic and climate-induced variability in exhumation and tectonic activity for orogenic wedges. As a testbed we used the Central European Alps. Initial work has used numerous wells from the North Alpine Foreland Basin, Switzerland, to provide a regional picture of post-5 Ma erosion of the foreland basin and has led to the recognition of major breaks in exhumation close to the Alpine mountain front. PhD Christoph von Hagke has constructed and analyzed in detail four horizontal and two vertical profiles crossing the Alpine front. 47 LA-ICP-MS apatite fission-track ages and 75 (U-Th-Sm)/He single-grain ages have been produced. Modelling of the dataset clearly shows repeated reactivation of the Alpine front in Switzerland as well as in adjoining Bavaria during the past 10 Ma underlining the lateral continuity of these thrusting, uplift and erosion signals. As the key result, we find that erosion and export of the material is exactly balanced by thrusting and thickening of the Alpine wedge for the past 10 Mill. Years indicating kinematic and mass flux steady state since then. A companion analysis was carried out studying the mechanical requirements for reactivation using critical wedge theory. First results show that the present day Alpine decollement is extremely weak beneath the orogenic front, Molasse basin and Jura Mountains but recovers strength as it steps into the basement below the External Massifs of the Central Alps. An associated study explored the mechanical evolution and active deformation using analogue modelling, performed by PhD Fan Ling Wang. 60 analogue models have been carried out to decide upon a suitable fundamental model. 7 different materials have been tested for strength contrast experiments with multiple weak layers as potential decollement levels. Analysing the analogue models qualitatively with particle-image velocimetry and quantitatively by measuring the lateral propagation and uplift rate, it is shown that different model setups and layer thicknesses have a large influence on the results of analogue models. The deformation pattern resulting from multiple weak layers in the incoming sediment sequence leads to activation of multiple decollements, producing a distinctly different pattern from single-decollement experiments. While single layer experiments show cyclical wedge growth with a predictable evolutionary path, multi-level systems exhibit an unpredictable random pattern. Quantitative analysis of time series of wedge taper, internal kinematics and wedge growth show departure from simple cyclic evolution and theoretical predictions of growth of isotropic, cohesionless wedges. Most probably, strain dependent softening and shear localization in combination with mechanical stratification of incoming sediments has a key role. This complexity in response pattern may limit the feasibility of identifying signals in wedge evolution that may be either attributed to tectonic or to climatic forcing in some systems.
Publications
- 2011. Rapid, extensive erosion of the North Alpine foreland basin at 5-4 Ma: Climatic, tectonic and geodynamic forcing on the European Alps. Basin Research
Cederbom, C., Schlunegger, F., Sinclair H., van der Beek P., Oncken, O.
(See online at https://doi.org/10.1111/j.1365-2117.2011.00501.x) - 2012. Linking the Northern Alps with their foreland: the latest uplift and erosion history resolved with low temperature thermochronology. Tectonics 31, TC5010
von Hagke, C., Cederbom, C., Oncken, O., Stöckli, DF., Rahn, MK., Schlunegger, F.
(See online at https://doi.org/10.1029/2011TC003078) - 2014. Critical taper analysis of the Central Alps reveals lithological control of variations in detachment strength - an analysis of the Alpine basal detachment (Swiss Alps). G³ 15
von Hagke, C., Oncken, O. & Evseev, S.
(See online at https://doi.org/10.1002/2013GC005018) - 2014. Late Miocene to present deformation and erosion of the Central Alps – evidence for steady state mountain building from thermokinematic data. Tectonophysics 632: 250-260
von Hagke, C., Oncken, O., Ortner, H., Cederbom, C.E., Aichholzer, S.
(See online at https://doi.org/10.1016/j.tecto.2014.06.021)
