THE MESO-TO NEOPROTEROZOIC EVOLUTION OF THE EAST EUROPEAN CRATON

The East European Craton (ProtoBaltica) displays a diverse evolution between 1.7 and 0.9 Ga. In western ProtoBaltica, several pulses of convergent tectonics and accretion of the crust at ca. 1.7, 1.6, 1.45-1.42 and 1.2 Ga created a complex combination of blocks of different tectonics. These are separated from each other by major shear zones and were mostly juxtaposed at ca.1.2 and 1.03-0.95 Ga in the Sveconorwegian collisional belt. Generally, active continental margin settings can be attributed to the Mesoproterozoic evolution of western ProtoBaltica. Semi-simultaneously with the orogenies in the west, discontinuous sedimentary covers with rare volcanics were repeatedly formed in the central parts of the craton. That development was interrupted by rifting of the crust, and the formation of grabens and aulacogens which were most characteristic of the “anorogenic” periods at ca. 1.4-1.2 and 0.9- 0.7 Ga. The former was a consequence of mantle plume tension of the lithosphere, possible separation, drift and rotation of ProtoBaltica until the final assembly of Rodinia at ca. 1.0 Ga. The later rifting was connected both with the post-Sveconorwegian destruction of the crust and the evolving Rodinia break-up. In contrast to western ProtoBaltica, the eastern edge of the craton developed after ca. 1.65 Ga continuously as a passive continental margin. In northern Scandinavia, Timan and the Polar Urals, such evolution commenced later and continued into the Neoproterozoic. Here, it was marked by transition with time from shallow- to deep-water sedimentation and the formation of an ophiolite suture towards the northeast. It appears that ProtoBaltica was completely surrounded by oceans about 700 Ma, as recorded by the preserved ophiolites and LIP provinces in NW Scandinavia, Poland and Ukraine. The dramatic changes in the evolution of the craton occurred at the end of the Neoproterozoic, between 620 and 540 Ma ago when almost all passive margins of ProtoBaltica were reworked by the Timanian/Cadomian orogenic processes and became active. This is seen best along the northern, northeastern and eastern margins of the craton.. Elsewhere, rifting and the creation of oceans in the Late Cambrian and Early Ordovician have disrupted the evidence.