Qilian Orogenic Belt

This belt is located between the North China Platform and the Qaidam Block. Its main body lies in the Qilian Mountains at the border between Qinghai and Gansus Provinces. The orogenesis included the Hexi Corridor and the steep eastern margin and northern margin of the Qaidam Basin. From north to south, this belt can roughly be divided into three zones: (a) central Qilian is an uplifted block with exposed metamorphic crystalline basement; (b) northern Qilian was an early Palaeozoic deep sea trench and active continental margin, which includes several ophiolite belts and numerous island-arc volcanic rocks; and (c) southern Qilian was an early Palaeozoic passive continental margin with a large amount of Silurian clastic flysch. After the Caledonian orogeny, the entire belt was uplifted. Devonian molasse sediments were deposited widely across the piedmont depression. A unified North China Craton formed when North China, Qilian and Qaidam merged. In the late stage of the Middle Cenozoic,...