Central Asian Orogenic Belt

[1][3] It is also considered a relatively distinctive collisional orogenic belt because widespread subduction-accretion complexes and arc magmatic rocks can be found in the region, but collision-related foreland basins are not common.

[11] In Precambrian time, the major terrane of the Kazakhstan orocline was mainly Mesoproterozoic metamorphic rocks, which potentially had Gondwana affinity.

[11] During Devonian to early Carboniferous, several unconformities were formed, together with the thrusting in the back of the Balkhash-Yili volcanic belt, documenting the event of lateral accretion of the continental crust.

[11] The south-verging thrusts in the northern part of the South Tienshan consist of ophiolites, accreted high-grade metamorphic rocks, basalts and cherts formed in deep sea environments.

[13] For both portions in the Tuva-Mongolia Orocline, intrusions of granites occurred after the mountain building events and were covered by the volcanic and sedimentary rocks which formed during Jurassic to Cretaceous.

[13] Ophiolites, which are uplifted and exposed fragments of oceanic crusts with pieces of upper mantle, are considered to be able to provide important information regarding the history of formation and evolution of the orogenic belt.

[3] One of the hypotheses posits that oceanic arcs and possible continental blocks derived from Gondwana were added to the Siberian, Russian, and North China cratons via accretion.

[3] Another hypothesis suggests that the Central Asian collage is made of accumulated Paleozoic materials that were derived from subduction, accretion, and deformation of a single magmatic arc.

[3] This hypothesis states that the Central Asian Orogenic Belt involved numerous subduction, collision in parallel orientation, accretion, amalgamation of microcontinents and bending of oroclines.

[3] The second hypothesis proposed by geologist Celal Sengor in 1993 suggested that the Central Asian Orogenic Belt was formed due to the accumulation of Paleozoic subduction-accretion materials against a single magmatic arc.

[28] During the Late Carboniferous (318-303 Myr), Baltica and Siberia experienced right-lateral shearing, combined with compressional force, the entire Kazakhstan orocline became more tightly packed.

[28] Until the Early Permian (269-260 Myr), the Nurol basin, which is a stretched continental crust, was formed and alkaline magmatism occurred at its basement.

[28] With this final act during the Late Permian, Sengor's hypothesis on the Central Asian Orogenic Belt evolution was completed.

They include: The Central Asian Orogenic Belt is rich in natural resources and more extensive study of the region would yield more benefits to society.

[3] The Central Asian Orogenic Belt is rich in mineral ores, including platinum, gold, silver[3] and copper.

[3] For platinum, its associated minerals can be found in the dunite, a type of ultramafic intrusive igneous rock, from the Xiadong Alaskan complex.

[1] The Laoshankou Iron Oxide-Cu-Au deposit, which is located at the southwest of the Qinhe City, Xinjian, Northwest China, is considered as one of the most important high-quality copper and gold reserve in the Central Asian Orogenic Belt, with the deposit being hosted by the volcanic rocks formed during Middle Devonian.

[30] Since Central Asian Orogenic Belt has a complex tectonic setting, it is often being associated with different kinds of energy production in the world.

[32] It is important to note that some of the richest hydrocarbon reserves in the world can be found in the region near Central Asian Orogenic Belt.

[32] The Yinggen-Ejinaqi Basin, which is located at the southern portion of the Central Asian Orogenic Belt has been suggested to have a high potential of having a hydrocarbon reserve.

Figure 1 Location map of the CAOB. Adapted from Han and Zhau 2017. [ 6 ] The map shows that the Central Asian Orogenic Belt is located at the northern portion of Asia, and can be divided into two major parts, which are Kazakhstan orocline and Tuva-Mongolia orocline. It is bounded by the East Europe Craton, Siberia Craton , Karakum Craton, Tarim Craton, and North China Craton . [ 7 ] The Central Asian Orogenic Belt is made up of the fragments of continental crust , magmatic arc , and subduction-accretion complexes, which are defined as the sediments or oceanic crust added to a continental crust at a subduction zone . [ 6 ]
Figure 2 Cross section of part of the Kazakhstan Orocline. Adapted from Biske 2015. [ 11 ] This figure shows a fold and nappe structure of part of the Kazakhstan Orocline. [ 11 ] It was formed due to compressional tectonic settings. [ 11 ] This part of the orocline is mainly composed of sedimentary rocks and extrusive igneous rocks , meaning that they should follow the law of superposition during formation. Its current syncline folding illustrates that the region experienced compressional tectonic force and the originally horizontal layers were folded later on in the geological history. [ 11 ]
Figure 3 Cross section of part of the Tuva Mongolia Orocline. Adapted from Lehmann et al. 2010. [ 13 ] This cross section indicates that the rocks were folded under compressional force, and were partially melted due to friction , causing crustal melting, and thus the formation of the Tuva-Mongolia Orocline. [ 13 ]
Figure 4 Diagram showing the formation process of Northern Xinjiang of the CAOB in the first hypothesis. Adapted from Xiao et al. 2008. [ 27 ] This hypothesis illustrates that the Central Asian Orogenic Belt was formed accretion of multiple oceanic arcs and continental fragments . [ 27 ]
Figure 5 Diagram showing the evolutionary history of the CAOB proposed by Sengor. Adapted from Sengor 1993. [ 28 ] This hypothesis illustrates that the Central Asian Orogenic Belt was formed due to the accumulation of accretionary complexes against a single magmatic arc. [ 28 ] See more detailed explanations of the evolutionary history of the CAOB in Table 2 .