MESOZOIC PRECURSORS OF THE CENOZOIC RIFT STRUCTURES OF CENTRAL-ASIA

The 1 000 km wide and 5 000 km long Central Asian mountain belt, which includes many of the Cenozoic rift basins of East Siberia, was produc ed by Mesozoic orogeny acting on an older folded basement - the Centra l Asian Fold Belt, The orogeny was most active in the eastern segment of the belt with the subsidence and uplift of crustal blocks, the latt er being associated with the initiation of fault-related basins, pluto nic intrusions and volcanism. The orogeny-related rocks within the bel t are essentially sedimentary and volcanogenic molasse in association with granitoid intrusions. The Mesozoic eastern Central Asian Fold Bel t is divided into three provioces (Khangai-Yablonovy, West Baikal and Mongol-Okhotsk) which differ io their geology and structural pattern. The Khangai-Yablonovy province displays the widest range or orogeny-re lated formations in five unconformity-limited groups. The origin and e volution of the belt were controlled by the collision of large blocks of the old China-Korean and Siberian plates. While the mechanism invol ved in the creation of the Central Asian Fold Belt is still disputed, the available geological and geophysical data can be best explained by a plate-motion model with mantle diapirism.