STRUCTURAL ARCHITECTURE OF THE SOUTHERN AND MIDDLE URALS FORELAND FROM REFLECTION SEISMIC PROFILES

Abstract

The Urals Seismic Experiment and Integrated Studies (URSEIS), Mikhailovsky, and Europrobe's Seismic Reflection Profiling in the Urals (ESRU) reflection seismic profiles provide constraints for the construction of balanced and restored geological cross sections across the southern and middle Urals foreland. The profiles image the transition from the undeformed foreland basin to the frontal structure of the foreland thrust and fold belt, the location of the basal detachment, and the location of the ramp down into the middle or lower crust. In the URSEIS and ESRU profiles, the transition into the undeformed foreland basin is imaged as an emergent west-vergent thrust that deforms a westward thickening package of reflections related to synorogenic sediments, whereas in the Mikhailovsky profile, it is a buried system of imbricate thrusts. In all three data sets, the western flank of the foreland thrust and fold belt is imaged in the seismic data as an imbricate thrust system developed above a basal detachment located in either the upper part of the Neoproterozoic basement sediments or the lower part of the Paleozoic continental margin sediments. Truncation of reflections related to the undeformed sediments in the footwall to the imbricate thrust system mark the location of the ramp down of the basal detachment into the middle or lower crust beneath the basement-cored anticlines along the eastern flank of the thrust belt. The URSEIS and ESRU profiles image the basement-cored anticlines as predominantly east dipping reflections that extend into the middle and lower crust. Rocks in these anticlines record at least one phase of pre-Uralide deformation and, at least in part, the reflectivity is due to this deformation event. Balanced and restored cross sections constructed along the three profiles indicate that the minimum shortening is about 20-25 km.