THE EVOLUTION OF THE ALTAIDS FROM THE EDIACARAN TO THE EARLIEST CRETACEOUS: MOUNTAIN- AND CONTINENT-MAKING IN ASIA

The Altaids is the super orogenic complex occupying some 12.5 million km² to the west and south of the Siberian Craton and the Baykalides bounded to the west by the Urals, to the south by the 'Intermediate Units' of Asia consisting of the Alay Microcontinent, the Tarim Block and North China carrying also the Manchurides. The Altaids evolved from the Ediacaran to the early Cretaceous along three major arc systems two of which were located on the Tuva-Mongol continent most likely rifted earlier from the Siberian Craton. The other arc, called the Kipchak Arc, also rifted from the Siberian Craton, but during its evolution it added also ensimatic parts to itself. Throughout the evolution of the Altaids there were no arc or continental collisions except when the Kipchak arc bent back onto itself and when the two arms of the Tuva-Mongol fragment finally ended their convergence sometime during the earliest Cretaceous. The entire system was finally sealed by its final collision with the 'Intermediate Units' in the latest Palaeozoic and by the terminal closure of he Khangai-Khantey Ocean during the early Cretaceous (although marine conditions had already ended during Triassic to the earliest Jurassic and further subduction happened in a 'hidden' fashion under accretionary complexes). Available reliable palaeomagnetic data are consistent with the evolution of only three arcs (the Tuva-Mongol is a double arc) and the evolution of magmatic fronts, now fortified by 1090 new, mostly zircon ages collected from the literature, preclude the motion of independent 'terranes' surrounded by oceanic lithosphere. During their evolution, the Altaids generated some 3 million km² of continental crust, but uncertainties under younger cover may increase this to 4 million km². This is about one-third of the average growth rate of the continental crust. The global eustatic sea-level seems to have been dominated by the Altaid evolution only during the latest Carboniferous and the early Permian.