Lithospheric structure of the Bohemian Massif and adjacent Variscan belt in central Europe based on profile S01 from the SUDETES 2003 experiment

Grad, M; Guterch, A; Mazur, S; Keller, GR; Spicak, A; Hrubcova, P; Geissler, WH.

Journal of Geophysical Research: Solid Earth

113(10), 2008, art. B10304, 10.1029/2007JB005497

The SUDETES 2003 seismic experiment investigated the lithospheric structure of the eastern part of the Variscan belt of central Europe. The key profile of this experiment (S01) was 630 km long and extended southwestward from the margin of the East European craton, across the Trans‐European suture zone (TESZ) and Sudetes, and across the Bohemian Massif that contains the active Eger (Ohře) rift, which is an element of the European Cenozoic rift system. Good quality first arrivals and later phases of refracted/reflected P and S waves were interpreted using 2‐D ray‐tracing techniques. The derived seismic model shows large variations in the internal structure of the crust, while the depth to the Moho varies in the relatively narrow depth interval of 28–35 km. Except for the Polish basin on the northeast end of the profile, the sedimentary cover is thin. The crystalline upper and middle crust with velocities of 5.9–6.4 km s−1 is about 20 km thick, and the 7–10 km thick lower crust can be divided into three regions based on P wave velocities: a low‐velocity region (6.5–6.6 km s−1 beneath Eger rift and Sudetes) that is bounded on the southwest and northeast by regions of significantly higher velocity (6.8–7.1 km s−1 beneath the Saxothuringian and Moldanubian in the southwest and Fore‐Sudetic Monocline and Polish Basin in the northeast). High‐velocity bodies (Vp > 6.5 km s−1) were delineated in the upper crust of the Eger rift region. The seismic structure along the S01 profile images a Variscan orogenic wedge resting on the down warped margin of the plate margin containing the TESZ. This situation implies the northerly directed subduction of the Rheic Ocean that existed between the southern margin of the Old Red Continent and the Armorican terranes presently accreted into the Variscan belt. Closure of this ocean produced the Rheic suture between low‐velocity crust of the Variscan orogenic wedge and higher‐velocity crust of the TESZ.