THE OROGENIC BELTS IN CENTRAL ASIA AND THEIR CHARACTERISTICS

The continent of Asia consists of a large number of orogenic belts of Phanerozoic age and cratonic pieces enclosed by them. Those cratonic pieces derived from Gondwana-Land contain pieces of what has been termed the Pan African Orogenic System that stitched together Gondwana-Land. The main Gondwana-Land-Laurasia suture runs south of what has been called the Silk Road arc including the Kuen-Lun and its prolongations east and west. North of the Kuen Lun the intermediate units (Scythides in the west, Tarim in the middle and the Manchurides in the east) have largely terminated the development of the Altaids in the latest Palaeozoic by colliding with them. The Altaids have evolved from three major arc systems that eventually collided with the Siberian craton and its crown of Baykalides (±age equivalent to Pan-Afrcian system): the Kipchak arc, the inner and the outer Tuva-Mongol arcs. The Altaids have been called an accretionary orogen, but this is pleonastic, because all orogens are accretionary: they accrete cover, basement, as well as igneous rocks. In some, sedimentary cover accretion dominates (e.g. Makran, Alaska), in others igneous (e.g. Central Andes; they also accrete sedimentary cover nappes in Bolivia). In some, basement nappes are accreted along with cover nappes for which the Austrian Alps may be given as the prime example. The Altaids in central and northern Asia have been specified as a Turkic-type orogen defined to be one in which subduction-accretion gives rise to immense oceanic cover sediment offscraping and accumulation along the prows of arcs. Into such accumulated cover sedimentary piles arc magmatic axes migrate and consolidate them creating new continental crust. This is the essence of the Turkic-type orogeny. In the Phanerozoic architecture of Asia, Turkic-type orogens dominate the nortern half of the continent and the Himalayan-type the southern half.