A problem of rigidity of the Eurasian lithospheric plate in the light of data on age and dynamics of the Cenozoic intraplate deformations in different regions of the Northwestern Eurasia

Now it became obvious that Cenozoic intraplate deformations of the Northwestern Eurasia were connected with the Alpine plate collision. However, areas of dynamic influence of plate-indenters, such as the Periapulian, Periarabian and Periindian “collisional areas”, as well as relations of the Cenozoic intraplate deformations with the contemporary spreading in the north and transcontinental shears along the Tornquist line and Urals must be determined more exactly. Besides, some paleomagnetic data does not correlate well with an uniform rigidity of the Eurasian lithospheric plate. These questions are discussed here in terms of evolution and dynamics of the Cenozoic intraplate deformations in different regions of Northwestern Eurasia. In West Europe, the aulacogen covers were crumbled in the Paleocene (the Laramic orogeny) simultaneously with the plate collision in the Alps. A spreading axis propagated from the Northern Atlantic into the Arctic at the same time, which allows suggestion on interrelation of these events. On the contrary, in East Europe the moderate Laramic compression took place in the southernmost areas only whereas major activity went on much later, in the terminal Early Miocene-Quaternary, periods of the activity being coincident with those in the Caucasus and the phases of the Red Sea opening. In addition, an evidence that the southern East European craton belongs to the Periarabian collisional area is provided by the orientation of stresses which is the same in the intraplate structures and the Caucasus (e.g., submeridional compression) as well as by similarity of structural patterns. A character of the post-Cretaceous deformations in the northern East Europe is less clear. First, their upper age limits are still unknown. Second, a compression axis orientation was sublatitudinal there. This allows suggestion that the deformations were originated under pressure of the adjacent Urals. The recent Uralian orogen began to grow at the Eocene-Oligocene boundary, i.e., much earlier than the formation of the East European intraplate deformations during the Arabia/Eurasia collision. Accordingly, it could not be related to the Periarabian collisional area. On the other hand, the beginning of its growth coincided with a reinforcement of the India/Eurasia collision. Hence, the Urals may be considered to be a peripheral part of the Periindian collisional area. From the dynamic aspect, the Recent Urals was formed as a result of sublatitudinal shortening caused by an underthrust of lithosphere of the West Siberian platform. The uplift of the Uralian Mountains was accompanied by thrustfold deformations and strike-slips, which were predominantly sinistral. So, compressional intraplate deformations occurred in the northern periphery of a collisional power area of every plate-indenter simultaneously with its northward movement. In addition, the essential changes of the collision zone regime in the south coincided with those of the spreading system in the north. The data generalized allow reconstructing the following scenario of the events. After the West European part of the Eurasian plate and corresponding segment of the spreading zone were blocked by the Paleocene collision in the Alps-Dinarides, the spreading propagated into the Arctic. As a result, East Europe together with Siberia moved southeastward, to the relic Neo-Tethyan subduction zone. They were separated from West Europe by the dextral shear along the Tornquist line. The East European platform was separated from Siberia by sinistral shear along the Urals only in the Oligocene, most likely due to interlock of the Asia movement by Indostan. In the Pliocene, the independent East Europe movement was ceased by the Arabia-Eurasia collision, and since that time Northwestern Eurasia was entirely in compression. Thus, the present view of unity and rigidity of the Cenozoic Eurasian plate is correct only at the first approximation. In reality, the Eurasian plate represented a timevarying kaleidoscope of subplates that moved at different velocities from the Atlantic-Arctic spreading axis. The greatest acceleration was experienced by the Eurasian fragments whose general southeastward motion was in the least degree restrained by the Gondwanian relics colliding with Eurasia.