Spät känozoische tektonische Entwicklung des westlichen Eger-Rifts
Zusammenfassung der Projektergebnisse
This project was aimed at the late-stage evolution of the Eger rift, a branch of the European Cenozoic rift system (ECRIS) that shows several peculiar features. It is rich in volcanics, but subsidence and fault throws are low, except for the main Krušné hory (Erzgebirge) fault (KHF) that has strongly uplifted the NW shoulder. Activation of the KHF post-dates the main phase of Eger rifting and may coincide with an episode of approximately E-W compression. The youngest evolutionary phase is centered on the Cheb Basin at the western end of the rift which originated as a shallow depression during the main phase and, after a hiatus, evolved into a separate half-graben bounded by the Mariánské Lázně (Marienbad) fault (MLF) from Pliocene time to the Present. The MLF crosscuts and displaces older rift features at approximately right angles, indicating another major re-orientation of the stress field. New AHe ages obtained show widespread exhumation in Mesozoic time both north and south of the Eger rift. Cenozoic exhumation associated with rifting was insufficient to expose rocks containing fully reset apatite, implying that the present-day topography can be used as a strain marker for Cenozoic deformation. However, thermal modelling suggests that samples from the Krušné hory/Erzgebirge north of the rift still resided at a depth corresponding to ca. 50° C and were exhumed to the surface only in Cenozoic time, very probably due to motion on the KHF. The AHe modelling does not precisely constrain the age of this event. Topographic profiles across the Erzgebirge show gradually southward increasing slopes until the abrupt break due to the KHF. This geometry is suggestive of an elastic beam flexed upward and can indeed be well reproduced in flexural models containing a break, modelled as a narrow region of very low rigidity. Implementing this feature required a modified formulation of the flexure equation and new program code. The model does not constrain the geometry of the break representing the KHF, but the upward rotation of the Erzgebirge could be most easily achieved by a KHF steepening at depth. The upward-directed force inducing the flexure could in part be due to a low-density upper to middle crust (granites) of the Erzgebirge. However, this negative load must have been counteracted by dense material until activation of the KHF. We tentatively propose a rapid loss of mantle lithosphere and lower crust triggered by the main rifting phase to explain fast unloading of the Erzgebirge. The Cheb Basin is a half-graben with plan-view shape of a half-ellipse truncated in the NE by the MLF. The geometry of its basin floor is well constrained by numerous boreholes. Kinematic modelling suggests the MLF is a WSW-dipping listric, predominantly normal fault soling out into a detachment at around xx km depth. Maximum fault displacement constrained by paleosol remnants on the footwall is around 400 m, decreasing towards the NW and SE. Counter to earlier interpretations we found no geomorphic evidence for active faults within the Cheb Basin controlling CO2 emanations. However, a detailed paleoseismologic (trenching) study in our Czech companion project has demonstrated Holocene activity near the northern end of the MLF itself, in addition to the recent fault plane outlined by the EQ swarms of Novy Kostel. The swarm EQ, despite their epicentres west of the MLF´s surface trace, probably occur in the footwall of the MLF and the fault plane hosting them may be linked to it at depth.
Projektbezogene Publikationen (Auswahl)
- (2017). Tectonic evolution of the Western Eger rift: a tale of two faults. EGU General Assembly Conference Abstracts 19, p. 7876
Tomasek, J., Kley, J., Fischer, T., & Štěpančíková, P.
- (2018). Cenozoic Exhumation and Fault Activity of the Western Eger Rift, Czech Republic, from Low Temperature Thermochronology. GeoBonn2018
Tomasek, J., Szameitat, A., René, M., Dunkl, I., Kley, J.
- (2018). Cenozoic Exhumation and Fault Activity of the Western Eger Rift, Czech Republic, from Low Temperature Thermochronology. THERMO 2018
Szameitat, A., Tomasek, J., René, M., Dunkl, I., Kley, J.
- (2018). Quantifying the Eger Graben and its shoulders: should we consider a 'phantom rift'? GSA2018, Indianapolis
Tomasek, J., Kley, J., Hindle, D.
(Siehe online unter https://doi.org/10.1130/abs/2018AM-323782) - (2018). Tectonics of the Krušné hory Fault (Czech Republic): observations from broken-plate flexure models. GeoBonn 2018
Tomasek, J., Kley, J., Hindle, D.
