Junggar Basin

was found in this area. The Indo-Australian plate collision during Neogene resulted in uplift of the northern Junggar basin. This also resulted in re-activation of Permian thrust faults, produced faults on basement rocks and rifting on basin margin to form Karamay-Urho monocline. This area concentrated abundant hydrocarbons on the anticline part. • East Uplift (Zhangpenggou-Qitai uplift) was formed by deformations in several times. The formation of NE-trend plunging fold in this area activated the faulting of basement rocks. • Tian Shan Foredeep formed during lower-middle Triassic since the Tian Shan has uplifted continuously. During Cretaceous, the basin sank again and thus water depth became shallow due to tectonic deformations. In Paleogene, the size of the lake kept reducing and the eastern basin become a landmass. Also, there was further subsidence of Tian Shan Foredeep because of the formation of Himalayan in Paleogene. == Geology ==

s. The basalts in the basement which indicated trapped late Paleozoic oceanic crust that came from the mantle. == Paleoclimate and environment ==

Throughout Mesozoic, Junggar Basin was mainly in the fluvial and lake depositional environment. From middle to late Jurassic, the climate shifted as a seasonal arid climate that initiated from the northeast and then widespread to the whole basin. == Tectonic evolution ==

. 8. With the influence of Tian Shan collision and anorogenic magmatism from local extensional events, Junggar area subsides to form Junggar basin. Modified from Zhao et al. (2003), Carroll et al. (1990), Buckman et al. (2004), Han et al. (2018). Pre-Permian (before 290 Ma): basement rock evolution Xinjiang paleocraton was pulled apart for a continental rifting episode to form extensional basins in Late Cambrian. The continuous divergence of the continental crust during late Cambrian to Ordovician shaped the West Junggar Ocean. The Ordovician first ocean basin indicated that eastern Junggar was over passive margin. Eventually, the Junggar ocean and Kulumudi Ocean moved towards the north and undergone the subduction from upper Devonian to Late-Carboniferous. Alkali-rich granites with gold deposits intruded the converged plates. The magma underplating during Carboniferous to Permian (330-250 Ma) period heated up the lower crust and thus the crust got hotter. The following cooling crustal episode led to part of the mountain belt sink by thermal subsidence, which ended up forming the Junggar Basin. Permian to Present (From 290 Ma): Junggar Basin evolution With the influence of Variscan orogeny, Early Permian marine facies changed into the terrestrial environment during Late Permian. The collision of the Lhasa block from the south resulted that the delta formed along the margin of the basin. Also, the deeper lake was at the basin centre during Lower Cretaceous. Afterward, the southward lake depression leading the basin centre shift to the south in the Upper Cretaceous period. In Paleogene, braid-delta developed over the basin where sediments entered from the mountains of the surrounding basin. Starting from Neogene, the thrust fault in the Junggar Basin was reactivated. At the same time, there was rapid uplift of Tian Shan since Himalayan orogeny formed by the collision between Indo-plate and Eurasian Plate. This developed an alluvial-rich delta system around shallow lakes with the clastic sediments influx from uplifted Tian Shan and the northern part of the basin. == Geological resources ==

Petroleum system Junggar Basin contains the third-largest petroleum reservoirs in China. For Carboniferous oil and gas deposits in this area, they were moved upward and accumulated in the Permian period and Mesozoic era sandstones. Petroleum is dominant in Karamay, Baikouquan, Urho, Dushanzi, and Qigu. Part of the oil-bearing sedimentary rocks was deposited in the salty oxygen-deficient lake environment during Permian. The followings are the available ore deposits in Junggar Basin: • Porphyry copper-gold deposits found in the west and northeast of the Junggar Basin. • Iron deposits found in the eastern part of the basin due to early subduction events during Lower Carboniferous. • During post-collision extensional events in Permian, gold deposits found on the west side and tin deposits found on the east side. == See also ==