Late Cenozoic tectonic evolution of the western Eger Rift

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The Eger Rift and Cheb basin in northwestern Bohemia are associated with earthquake swarms, voluminous CO2 outgassing and Quaternary mantle-derived volcanism. First-order structural relationships indicate that the NNW-striking Marianske Lazne Fault (MLF), the master fault of the Cheb basin, has cross-cut the Eger rift at right angles and offset it with dominantly normal sense of motion. These relationships suggest that activity on the MLF was accentuated late in the history of the rift - around early Pliocene time -, reflecting a fundamental change of the governing stress field. We propose to constrain the tectonic evolution of the two basins, and in particular of the Krusne Hory (Erzgebirge) and Marianske Lazne bounding faults over Late Cenozoic time. This will be done by modelling the subsidence of the basins from stratigraphic data. Rift shoulder uplift, exhumation and fault offsets will be constrained by low-T thermochronology, especially (U-Th)/He on apatite (AHe). Subsidence and exhumation data must be matched by a 3D, restorable structural model of the Eger Rift-Cheb basin junction, thus constraining the deep architecture of the large faults. Tectonic geomorphologic analysis based on high-resolution digital elevation models (DEMs) and complemented by ground truthing and fault-slip analysis will be used to detect smaller-scale, distributed faulting. These data as well as those derived from distributed seismicity in our Czech companion project are to be compared to strain patterns predicted by the structure model under varying movement directions. Such kinematic variations for the MLF will be deciphered by detailed geomorphological and paleoseismological investigations that are also part of the Czech project. The results of both projects will be combined in a detailed tectonic model of the evolution in Miocene through Recent time. This model will also help to understand the present-day localisation of fluid ascent and earthquake swarms.