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 U rals (ESRU) project, three overlapping seismic reflection data sets we re acquired in the Middle Urals. A 56 km long profile was registered o ver the Europe-Asia suture, two 25 km long intersecting profiles were collected over the Urals superdeep borehole (SG4), and an 80 km long p rofile was recorded eastward extending east toward the West Siberian B asin. Reflections on the seismic sections delineate several major midd le to late Paleozoic thrust zones in the upper crust. These thrust zon es have a bivergent geometry with westerly vergence west of the Uralia n orogenic axis and easterly vergence to the east. The principal terra ne boundaries are the Main Uralian Thrust Fault in the west and the Tr ans-Uralian Thrust Zone in the east. Normal faults are spatially assoc iated with former thrust faults, or they crosscut them. The thrust and normal faults can be confidently correlated with surface geological f eatures. Near-vertical and wide-angle seismic reflection profiling rev eals thickening of the crust from about 45 km to approximately 53 km b elow the central axis of the Urals. East and west of the root zone, th e lower crust is reflective, particularly toward the West Siberian Bas in. 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 feature s imaged by the seismic sections are probably of Paleozoic age, a post -Paleozoic origin for the lower crustal reflectivity in the east canno t be ruled out.