The western fold-and-thrust-belt of the southern Urals, Russia - review and perspective

The western fold-and-thrust-belt of the southern Urals developed by collisi on of the East European craton with the Magnitogorsk magmatic are and Kazak hstanian terranes. It developed on thick, cold and rigid continental crust and is characterized by thick-skinned tectonics with the involvement of cry stalline basement, by minor tectonic shortening and weak internal deformati on, and by reactivation of Precambrian rift-structures and tectonic inversi on. The kinematic evolution was two-fold with an early continent-magmatic-a rc collision in the Late Devonian and a compressional phase around the Perm ian-Triassic boundary which resulted from the final closure of an East Ural ian ocean. The continent - magmatic-arc collision included the early obduct ion of an accretionary complex in the Middle/Late Devonian (380-370 Ma), an d the formation of an early orogenic wedge which thrusted the accretionary complex and a Cadomian basement block onto the East European craton (EEC) i n the Lower Carboniferous (340 Ma). These two stages mark the main tectonic shortening with partitioning of the deformation mainly in the immediate fo otwall of the suture zone. The late Permian E-W compressional phase resulte d in a W-propagation of the wedge with reactivation of former extensional s tructures and minor shortening. The hinterland experienced out-of-sequence - thrusting and intensive back-thrusting. Along-strike variations of the fo ld-and-thrust-belt can be tentatively correlated with a change from a low-c ompressional to a high-compressional continent - magmatic-arc collisional s etting. The investigated area of the fold-and-thrust-belt along the URSEIS' 95 profile represents a transitional position between both settings. Under these aspects, far-reaching lateral extrapolation of tectonic structure app ears doubtful.