Northern Eurasia, within the limits of the territory of the former Soviet Union (FSU),
has an immensely long and intriguing history, and most of it consists of very ancient
blocks that are cemented by fold belts into a single continent. The most important of
these continental blocks, because of their sheer size, are the East European and Siberian
platforms.
These platforms have shown dramatic movements through geological time. Indeed, although
they both existed 1700 million years ago, in the early Cambrian (c. 540 million years ago)
Eastern Europe and Siberia were both located in the Southern Hemisphere. The former
platform was in a temperate climatic zone and the latter in the tropics! They were
separated from each other, and from the other continents, by wide oceans. The subsequent
closure of oceans and numerous continental collisions account for the predominantly
accretionary tectonics of the area and for the wide distribution of fold belts like the
Urals.
Present plate margins occur mainly on the margins of the territory of the FSU. In the
far east, the Pacific Plate is being subducted under Eurasia at a rate of 10 cm per year.
It is here that one finds the Kuril-Kamchatka island arc with its active volcanism. In the
far north, under the Arctic Ocean, the Gakkel (Arctic Mid-Ocean) Ridge marks both the
boundary between the Eurasian and North American Plates and the spreading axis along which
the Eurasian ocean basin floor is forming. In the south the two great platforms are
bordered by the African-Arabian, Indian, Tarim, and North Chinese continental blocks, and
it is here that the highest mountains, recent volcanic activity and currently intense
seismic activity are concentrated. Great mountain chains, like the Caucasus and the
Pamirs, have been created by the continental collision of broken fragments of Gondwanaland
with the mass of Eurasia. This remarkable history of plate interactions, which is
fundamental for an understanding of the gross relief of Northern Eurasia is described by
Zonenshain et al. (1990a, b).
