GEOMETRIC AND KINEMATIC EVOLUTION OF THE FORELAND THRUST AND FOLD BELT IN THE SOUTHERN URALS

The first balanced and restored cross section through the foreland thr ust and fold belt of the southern Urals along the Belaya River of Bash kortostan is presented. This cross section is used to discuss the Pale ozoic structure and kinematic evolution of the area and to provide qua ntitative estimates of fault displacement and shortening. The Belaya R iver thrust stack can be divided into a late imbricate thrust system ( Nygush thrust system), the Burzyan thrust sheet, and an early duplex s ystem (Timirovo thrust system). Overprinting relationships indicate tw o deformation events during which the foreland thrust and fold belt ev olved by a forward propagating thrust sequence. The first deformation event involved emplacement of the low metamorphic grade Timirovo thrus t system and the overlying Zilair Nappe during accretion of the Magnit ogorsk volcanic are with the East European Craton at the end of the De vonian. A deformational hiatus followed until the end of the Carbonife rous, at which time a second deformation event related to final closur e of the Uralian ocean resulted in development of the Nygush thrust sy stem. The calculated shortening in the Belaya River area (16.7 km or 1 7%) 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 ge ometry, instead of following an easy glide horizon.