Tertiary evolution of the Intra-Carpathian area: A model

Abstract The Outer Carpathian flysch nappes encircle an Intra-Carpathian domain which can be divided into two megatectonic units (North Pannonian and Tisza) mostly on the basis of contrasting Mesozoic and Palaeogene facies development. We see two major kinematic problems to be solved: 1. (1) The present distribution of the Mesozoic and Palaeogene facies is mosaic-like, and some belts form exotic bodies within realms of Austroalpine affinity. 2. (2) Late Eocene palinspastic reconstruction of the Outer Carpathian flysch nappes suggest, that the entire Intra-Carpathian area must have been located several hundreds of kilometres to the south and to the west of its present position. Neogene extension can account for shortening in the external Carpathian nappes, but is unable to explain Mesozoic facies anomalies and offsets of Palaeogene formations. We suggest that evolution of the Intra-Carpathian area involved first Late Palaeogene-Early Miocene juxtaposition of the North-Pannonian and Tisza megatectonic units, accompanied by the closure of the external Carpathian flysch troughs; thereafter extension of this amalgamated unit occurred, which was compensated by thrusting of flysch nappes onto the European foreland and formation of molasse foredeeps. Eastward escape of the North-Pannonian unit from the Alpine collisional belt involved left lateral shear along the Pieniny Klippen belt and right lateral shear along the Mid-Hungarian zone. Parts of the Late Palaeogene basin and an Early Miocene volcanic edifice were dissected, offset and elongated by several 100 kms. The driving mechanism of the eastward escape of the Intra-Carpathian area can be related to the collision of Apulia and Europe and the subduction of the external Carpathian crust under the Pannonian units. The escape ceased gradually in the Early Miocene, when oblique collision between the North-Pannonian unit and European continent occurred. Neogene extension of the Pannonian region was an areal deformation. The extension at locally variable rate resulted in the break-up of the heterogenous floor of the Neogene basin. The driving mechanism of basin extension and contemporaneous compressional deformation of the external Carpathians is thought to be related to ongoing subduction, involving the marginal part of the attenuated European continental crust. Tectonic activity in the Carpathians and basin subsidence and volcanism shifted in time and in unison from the west toward the east-southeast.