3.2.4. The Bohemian Massif
Starting in the Late Turonian and culminating during the Paleocene, basement blocks forming the Bohemian Massif were upthrusted in response to the build-up of pre- and syn-collisional intraplate stresses originating at the front of the evolving Alpine-Carpathian Orogen (Malkovsky, 1987; Ziegler, 1990; Ziegler and Dèzes, 2007). Subsequently, the Bohemian Massif was subjected to profound weathering and erosion, resulting in the development of a regional peneplain on which only locally thin late Eocene-early Oligocene fluvial and lacustrine clastics were deposited, whilst its southern flank was overstepped by late Eocene and Oligocene marine series of the evolving Alpine-Carpathian flexural foreland basin (Ziegler, 1990).
During Early Oligocene to Early Miocene times volcanic activity preceded the main subsidence phase of the Eger Graben (Malkovsky, 1987). During the latest Oligocene to Burdigalian, when volcanic activity gradually abated, a northerly-directed drainage system developed on the Bohemian Massif and up to 500 m of lacustrine and fluvial clastics accumulated under a mildly tensional setting in the Eger volcano-tectonic zone (Malkovsky, 1975; Malkovsky, 1979). After sedimentation in the Eger Graben had ended around 18 Ma, extension intensified and the northern parts of the Bohemian Massif, including the Eger Graben were uplifted and subjected to erosion during the Middle and Late Miocene, presumably in response to lithospheric folding. During the early Middle Miocene, marine transgressions advanced from the Alpine-Carpathian foreland basin along valleys into the southern and eastern parts of the Bohemian Massif, indicating that they were located close to sea level, and that the intra-Bohemian watershed had shifted northward (Malkovsky, 1979; Suk, 1984). During the late Middle Miocene, compressional reactivation of the Bohemian Massif fault systems commenced and persisted into the Quaternary, causing disruption of the pre-existing peneplain, and by uplift of its marginal fault blocks the gradual development of its present physiographic relief that peaks at 1452 m above MSL. In the process of this, Middle Miocene marine deposits were locally uplifted to 600 m above MSL.
During the Late Miocene and Pliocene volcanic activity resumed in the Eger Graben area that, after deposition of Pliocene fluvial clastics, was affected by uplift and minor extension (Malkovsky, 1979).
Pliocene and Quaternary uplift of the Bohemian Massif exerted a strong control on the development and deep incision of its present-day mainly north-directed drainage system that, as compared to its middle Miocene drainage system, entailed an important south-eastward shift of the watershed between the Danube and North German-Polish drainage systems (Ziegler and Dèzes, 2007).
End-Paleocene relaxation of compressional intraplate stresses controlling deformation of the Bohemian Massif can be related to post-collisional mechanical decoupling of the foreland and the Alpine-Carpathian orogenic wedge owing to sediment subduction. Mid-Miocene to recent uplift of the Bohemian Massif is attributed to a renewed build-up of intraplate compressional stresses, inducing lithospheric buckling and later transpressional reactivation of pre-existing crustal discontinuities in response the onset of northward subduction of Adriatic lithosphere beneath the European foreland (Ziegler et al., 2002; Schmid et al., 2004).
Close dating of terrace systems, supported by geodetic data will help to constrain the rate of neotectonic and ongoing topographic uplift of the Bohemian Massif that had severe repercussions on the evolution of the Central European drainage system, which is prone to repeated catastrophic flooding.
TOPO-EUROPE will address Late Miocene to Quaternary uplift, deformation and denudation history of the Bohemian Massif and related magmatic activity and analyze it in terms of controlling mechanisms. Astronomical dating of terrace systems, supported by geodetic data and seismotectonic analyses are required to constrain the pattern, dynamics and rates of Pliocene-Quaternary and ongoing uplift and topography development of the Bohemian Massif and their repercussions on the development of the Central European drainage system.