Quantitative reconstruction of orogenic convergence in the northeast Carpathians

The NE Outer Carpathians form a fold-and-thrust belt of large displacement. This mainly consists of deformed Cretaceous-Tertiary deep-water clastics, and can be divided into an imbricate stack of four major supracrustal nappe s (the Magura, Dukla, Silesian and Skole nappes). An extensive reflection s eismic, surface geological and drillhole database is used to constrain the deformed geometry of the two uppermost and southernmost allochthonous units : the Magura and Dukla nappes. A retro-deformable cross-section shows that the Cretaceous-Tertiary sediment piles are detached along a single, large d ecollement at about 5-7 km depth. The rear and frontal parts of the Magura nappe show steep imbricate fan geometries, while the central part has a dup lex structure with long thrust horses, To the NE, the Dukla nappe is a stac k of imbricate slices and is separated from the subjacent Silesian nappe by a large thrust flat, Reverse modelling of deformation reveals that the Mag ura nappe was horizontally shortened by at least 80 km, and the Dukla nappe by about 20 km in the NE-SW direction. Together with previously published estimates of shortening in the Silesian and Skole nappes, the total orogeni c contraction in the NE Outer Carpathians is at least 260 km. Shortening wa s accumulated between the Middle Oligocene and the Middle Miocene. Almost a ll of the shortening can be balanced against contemporaneous back-are exten sion and eastward extrusion of rock masses from the Eastern Alps. (C) 2000 Elsevier Science B.V. All rights reserved.