Accretionary complex structure and kinematics during Paleozoic arc-continent collision in the southern Urals

The southern Urals contain a well-preserved accretionary complex that has o verthrust the continental margin during are-continent collision between the East European Craton (EEC) and the Magnitogorsk island are in the Late Dev onian. Within the accretionary complex, we study three tectonic units that differ in deformation style, and each provides a unique geodynamic implicat ion. The Zilair Nappe, the largest and best exposed unit, consists of 5-6 k m of syncollisional, are-derived Upper Devonian to Lower Carboniferous poly mictic and graywacke turbidites that were deposited across the continental margin and incorporated by frontal accretion into the accretionary complex. The Zilair Nappe is a bivergent thrust imbricate where the west-vergent th rusts dominate and have associated kilometer-scale ramp anticlines with wel l developed east-dipping axial planar cleavage. Along its eastern contact, however, the cleavage fans until it dips moderately westward and the folds are east-vergent. Following its emplacement, west-vergent, basement-involve d thrusting that breached the whole accretionary complex imbricated the Zil air Nappe. The Timirovo Duplex is structurally beneath the Zilair Nappe, an d outcrops for several tens of kilometers along its northwestern margin. Th e duplex forms a west-vergent thrust stack composed of a highly deformed an d sheared Lower and Middle Devonian reef carbonates of the former EEC margi n platform. These rocks were shallowly underplated at the base of the accre tionary complex during emplacement over the margin. The Suvanyak Complex ou tcrops along the eastern contact of the Zilair Nappe, and consists of polyd eformed greenschist facies metasediments of the former EEC slope that were offscraped, underplated and incorporated at the rear of the accretionary co mplex. (C) 2000 Elsevier Science B.V. All rights reserved.