Crustal structure of the Middle Urals: Results from the (ESRU) Europrobe seismic reflection profiling in the Urals experiments

As a contribution to Europrobe's seismic reflection profiling in the Urals (ESRU) project, three overlapping seismic reflection data sets were acquired in the Middle Urals. A 56 km long profile was registered over the Europe-Asia suture, two 25 km long intersecting profiles were collected over the Urals superdeep borehole (SG4), and an 80 km long profile was recorded eastward extending east toward the West Siberian Basin. Reflections on the seismic sections delineate several major middle to late Paleozoic thrust zones in the upper crust. These thrust zones have a bivergent geometry with westerly vergence west of the Uralian orogenic axis and easterly vergence to the east. The principal terrane boundaries are the Main Uralian Thrust Fault in the west and the Trans-Uralian Thrust Zone in the east. Normal faults are spatially associated with former thrust faults, or they crosscut them. The thrust and normal faults can be confidently correlated with surface geological features. Near-vertical and wide-angle seismic reflection profiling reveals thickening of the crust from about 45 km to approximately 53 km below the central axis of the Urals. East and west of the root zone, the lower crust is reflective, particularly toward the West Siberian Basin. We interpret the reflectivity of the crust below the East European Craton as pre-Uralian, whereas that toward the West Siberian Basin is interpreted as late orogenic. Although the principal tectonic features imaged by the seismic sections are probably of Paleozoic age, a post-Paleozoic origin for the lower crustal reflectivity in the east cannot be ruled out.