Eastern European Alpine system and the Carpathian orocline as an example of collision tectonics

Abstract

Although the two mountain belts of the Eastern European Alpine system (the Dinaric—Hellenic and Carpathian—Balkan belts) form two bifurcating but continuous mountain terranes their internal structural development is conspicuously diachronous and is dependent upon the relative motion of at least three fragments of continental crust which lay between the European and African plate. In Late Jurassic time the three fragments of continental crust were separated by narrow zones of oceanic crust and palinspastic reconstructions of the continental fragments indicate they were considerably larger than their present size and had different shapes. Convergence of continental fragments began in the Late Jurassic by subduction of oceanic crust, but upon complete disappearance of oceanic crust, convergence continued with subduction of small(?) amounts of lower continental crust. During continent—continent convergence, the upper 10–15 km of the continental crust were detached forming thrust sheets as the lower crust is thickened and in part(?) subducted. The Carpathian orocline formed by the complex suturing of continental fragments against an irregular European plate boundary and developed during diachronous collision of fragments which began in the Middle Cretaceous and continued to the Recent. Only one narrow fragment of continental crust is oroclinally bent; the European plate to the east and continental fragment to the west of the Eastern Carpathians are not bent. The continental fragments do not behave as rigid plates, but are strongly internally deformed. Thus, the motion of these small continental fragments cannot always be treated in the same way as large plates. During suturing the three primary plates were fragmented into more complex arrays of small fragments whose boundaries cross cut earlier boundaries. Furthermore, it is doubted whether meaningful plate boundaries can be identified between the fragments and the fragments may be more realistically described as continuously deformed fragments of continental crust. The interpretation presented here suggests that the geologic data that remains in the orogenic belts for determining the magnitude of convergence between fragments always yields a minimum value. Much of the evidence for the magnitude of convergence between fragments is lost during subduction and collision processes.