| The Qilian Mountains and Qaidam Basin occupy the northeastern quarter of the Qinghai - Tibet Plateau. The tectonic evolution can be broadly divided into 4 stages.; Stage 1 (>1,000 Ma) records the earliest history of the area, which was part of a mobile belt surrounding the Tarim Protoplatform.; Stage 2 (1,000–700 Ma) is characterized by Grenvillian-aged orogens and ∼700 Ma tillites, supporting a hypothetical model that the Tarim - Qilian (TaQi), Qaidam and Yangtze Blocks fit into the gap among East Antarctica, Australia and India in the Rodinia Supercontinent. The North China Craton was a stand-alone plate.; Stage 3 (700–250 Ma), which is the focus of this research, is associated with the formation of the Caledonian Qilian Mountains and the united plates of China (UPC). The Qilian were formed through 3 episodes of orogeny: Tulaian (∼495 Ma), Gulangian (∼460 Ma) and Qilianian (∼410 Ma) and the UPC through collisions between TaQi and Qaidam, North China and Yangtze at ∼490 Ma and TaQi and North China at ∼460 Ma.; Stage 4 (Indosinian - Himalayan) relates to re-uplift of the Qilian Mountains and the formation of the northern part of the plateau.; The Tulaian Orogeny resulted from arc accretion and closure of the North Qilian Sea back-arc basin. The basin opened by rift propagating along (Hongliugou ⇒ Lapei Springs?) ⇒ Tulai ⇒ Qilian while the North Qilian Ocean Plate (earliest Tethys?) was subducting southwards under TaQi. The paleo-geography during this period of time was analogous to that of the present-day western Pacific (between 50°N and 20°N). The Gulangian Orogeny involved the closure of the North Qilian Ocean and collision between TaQi - Qaidam and North China - Yangtze. The rates of the convergence and rift propagation were estimated at 1.57–0.7 cm/yr and 1.97–0.45 cm/yr, respectively. The Qilianian Orogeny refers to the intracontinental uplift of the Qilian Mountains during the Caledonian time.; There are three generations of shear zones. The Caledonian and Hercynian shear zones show, respectively, transpressional and transtensional senses of movement, indicating that the plates collided obliquely and then collapsed at a later stage. The Indosinian shear zones, which are all transpressional, are related to Stage 4 tectonism. The ductile shear zone in the Baiying Mining District shows a slight amount of mass volume gain (1.4% ∼ 3.99%) and hardly any bulk volume change. Paleo-temperature estimated for the first three generations of deformation are as follows: D1: 400°C ∼ 370°C, D2: ≈ 340°C and D3: 300°C ∼ 290°C. Paleo-pressure/differential stress ranged between 81.5 ± 9.6 and 100.7 ± 9.6 MPa. The P-T-t-d paths are clockwise. |
