Geometric and kinematic evolution of the foreland thrust and fold belt in the southern Urals

Abstract

The first balanced and restored cross section through the foreland thrust and fold belt of the southern Urals along the Belaya River of Bashkortostan is presented. This cross section is used to discuss the Paleozoic structure and kinematic evolution of the area and to provide quantitative estimates of fault displacement and shortening. The Belaya River thrust stack can be divided into a late imbricate thrust system (Nygush thrust system), the Burzyan thrust sheet, and an early duplex system (Timirovo thrust system). Overprinting relationships indicate two deformation events during which the foreland thrust and fold belt evolved by a forward propagating thrust sequence. The first deformation event involved emplacement of the low metamorphic grade Timirovo thrust system and the overlying Zilair Nappe during accretion of the Magnitogorsk volcanic arc with the East European Craton at the end of the Devonian. A deformational hiatus followed until the end of the Carboniferous, at which time a second deformation event related to final closure of the Uralian ocean resulted in development of the Nygush thrust system. The calculated shortening in the Belaya River area (16.7 km or 17%) is significantly less than that in other foreland thrust and fold belts. The basal thrust in the Belaya River section is located within the basement and cuts continuously up section with a staircase-like geometry, instead of following an easy glide horizon.