The crustal architecture of the Southern and Middle Urals from the URSEIS, ESRU, and Alapaev reflection seismic surveys

Abstract

The Urals Seismic Experiment and Integrated Studies (URSEIS), Europrobe's Seismic Reflection Profiling in the Urals (ESRU), and reprocessed Russian reflection/refraction seismic surveys have shown the known Uralides to be bivergent, with a crustal root along the central volcanic axis of the orogen. In the Southern (URSEIS) and Middle (ESRU and Alapaev) Urals the East European Craton crust thickens eastward from ∼40 km to ∼48 km, and is imaged by sub-horizontal to east-dipping reflectivity that can be related to its Paleozoic and older evolution. The suture zone between the East European Craton and the accreted terranes, the Main Uralian fault, is poorly imaged in the URSEIS section, but in the ESRU and Alapaev sections it is imaged as an abrupt change from a zone of east-dipping reflectivity that extends from the surface into the middle crust. East of the Main Uralian fault, the Magnitogorsk (Southern Urals) and the Tagil (Middle Urals) volcanic arcs display moderate to weak upper crustal reflectivity, and diffuse middle to lower crust reflectivity. The Moho beneath both arc complexes is poorly imaged in the reflection data, but based on refraction data is interpreted to be at 50 to 55 km depth. East of the arc complexes, the Uralide structural architecture is dominated by a wide zone of anastomosing strike-slip faulting into which numerous syntectonic Late Carboniferous and Permian granitoids intruded. This area is imaged in the seismic sections as clouds of diffuse reflectivity interspersed with, or cut by sharp, predominantly west-dipping reflections. In the Southern and Middle Urals, west-dipping reflectivity of the Trans-Uralian zone extends from the middle crust into the lower crust where it appears to mergz with the Moho. The boundaries and internal faults of the strike-slip fault system are well marked by magnetic anomalies, allowing them to be correlated between the seismic sections.