A possible lower crustal flow channel in the Middle Urals based on reflection seismic data

The Europrobe Seismic Reflection Profiling in the Urals Experiments (ESRU) reflection seismic data from the Middle Urals images c. 10-km thick band of strong, subhorizontal lower crustal reflectivity and a thinning of the crust that is associated with the East Uralian Zone, a broad strike-slip fault system containing high-grade metamorphic rocks and syn-orogenic to post-orogenic granitoids. The lower crustal reflectivity consists of discontinuous to continuous, high-amplitude reflections. Reflections are subparallel to slightly oblique and have a layered to oblate appearance. Geometrical relationships indicate that the reflectivity post-dates fault activity, suggesting that late-orogenic processes modified the lower crust. The surface geology indicates that the conditions for lower crustal flow were met in the East Uralian Zone. We suggest that the lower crustal reflectivity imaged by the ESRU data is related to a flow channel that developed at the base of the crust in the interior of the orogen.