Main evolutionary stages of the ancient Asian Ocean

The time period of the ancient Asian Ocean region during the tectonic evolution of Central Asia can be roughly divided into 8 stages:

(1) Archaean Eon (Ar): the formation period of the ancient continental core (3600 ~2500Ma).

(2) Paleoproterozoic (Pt): The crust around the core of the ancient continent continued to grow to form the primitive ancient continent. The primitive ancient continent split and merged to form a unified crystalline basement. ("Columbia Supercontinent", formed between 1990 and 1500 Ma Rogers et al., 2002).

(3) In the Mesozoic-early Neoproterozoic (Pt2-3), the "Colombia Supercontinent" broke up and converged to form the "Rodinia" Supercontinent (1800~850Ma). In Kazakhstan-Kyrgyzstan, the Isedon Movement represented by the 1050 Ma granite intrusion, the Altyn Mountain Movement in Xinjiang, and the unmetamorphosed Qingbaikou System continental sea sediments are unconformably located on the underlying metamorphic rock system, which is roughly equivalent to the Green Mountains in North America. Will movement. It is a symbol of the aggregation of the supercontinent "Rodinia".

(4) Middle to late Neoproterozoic (Cryogenian-Ediacaran): The "Rodinia" supercontinent broke up and developed from a rift into the ancient Asian Ocean (850-542ma) . Moraine rocks, moraine-like rocks, alkaline volcanic rocks, bimodal volcanic rocks, etc., which are widely developed in Central Asia, are signs of the breakup of ancient continents.

There have always been different opinions on the understanding of the Ancient Asian Ocean. The Ancient Asian Ocean defined by Sanianshan et al. (1990) refers to the ancient continent that once developed between Siberia, North China, Tarim and Kazakhstan. The ancient ocean; Dobrezov et al.’s opinion is that the ancient Pacific Ocean and the ancient Asian ocean belong to two branches of the trifurcated rift system, both of which were born during the breakup of the Neoproterozoic supercontinent; Ren Jishun et al. (2002) The ancient ocean between Gondwana and North America, Russia, Siberia and other land masses is called the Laurasian Ocean, and its eastern section, that is, the ancient ocean between East Gondwana and Siberia is called the Paleo-Asian Ocean, and it is considered that the Paleo-Asian Ocean It is a large ocean basin with a very complex structure, including a series of ocean basins and microcontinental blocks. The main ocean basins include the Paleo-Atlantic Ocean, the Appalachian-Central European Ocean, the Ural-Southern Tianshan Ocean, the Sayan-Ergun Ocean, Tianshan Xinganyang Ocean, Kunqi Qinyang Ocean, and the Tibet-Malay-South China Trident Rift, etc.; In the Manual of the Central Eurasian Lithofacies Paleogeography, Tectonic, Restoration, and Geological Ecology Atlas (2002), which was completed during the joint map compilation of the eight Central Eurasian countries. It is believed that the ancient Asian Ocean was formed due to the disintegration of the ancient Rodinia continent and the disintegration and separation of Siberia and Laurasia. In short, most scholars believe that the formation of the ancient Asian Ocean was related to the disintegration of the ancient Rodinia continent. However, many scholars (Pan Guitang et al. 2009) believe that the Paleo-Asian Ocean was limited to the north of the Tarim continent, and that the south, including the Qin-Qin-Kun orogenic system, belonged to the Tethys range and pushed the evolution of the Tethys Ocean to the early Paleozoic. However, the author believes that the Qinqi-Kunming orogenic system is an accretionary orogenic system surrounding the southern edge of the Tarim continental area. It is the transition zone between the Paleo-Asian tectonic domain and the Tethys tectonic domain, and has the same characteristics as the two.

(5) Cambrian-Ordovician-Silurian: In the Early Paleozoic, the Paleo-Asian Ocean developed to the end of the initial collision (542~416Ma). In some areas, ocean basins began to appear at the end of the Late Proterozoic.

Liegeois (1998) divided the continental collision process into two stages: initial major impact and post-collision, and pointed out that post-collision refers to the occurrence of two or more collisions. A stage of orogeny evolution that follows the initial main collision of continental plates but is still related to the collision. When the converging continental plates are completely welded together and begin to move around a unified axis of rotation, they enter the intraplate tectonic system, marking the end of the post-collision stage.

Xu Xin et al. (2005) believed that the closure of the ancient Asian Ocean and the convergence and collision of the Asian continents were a long-term evolutionary process. It is more in line with the reality in Xinjiang to separate the initial collision and the main collision as two independent stages and the post-collision into three stages. The author believes that every major tectonic evolution stage (the opening and closing of the ocean) is divided into main collision and post-collision.

The initial collision was the main closure period of the ancient Asian Ocean, which occurred during the Ordovician-Silurian Period.

Roughly equivalent to the "Altai Movement", this movement has strong reflections in the Altai, Junggar, and the northern and southern margins of the Central Tianshan Mountains. As a result, the Siberian continent has expanded to the northern Junggar, and the "Tuvabe Biome" has been distributed to the south of the Karamaili Fault. : In the northern margin of the Central Tianshan Mountains, the Lower Silurian sand-slate containing a large amount of graptolites is unconformably overlain by the Ordovician fine hornbeam porphyry; in many places in the eastern Junggar, the Upper Silurian or Lower Devonian unconformably overlain On top of the Early Paleozoic granodiorite or Ordovician ophiolite, the Lower Devonian and Middle Devonian are generally missing in the Borokonu area, unconformably or overlying the Ordovician or Upper Silurian. , known as the Borokonu movement, in the Balkhash area, the Silurian system is from bottom to top: Landoville Series (S1), with variegated sandstone and siltstone in the lower part, tuff sandstone and tuff layer 350m thick at the bottom; The variegated siltstone and sandstone contain calcareous nodules 450m thick; Wenlock Series (S2), the lower dark red fine clastic rock and calcareous nodules are 60-100m thick; the middle variegated siltstone and sandstone are 200m thick; the upper clastic The rock and fine conglomerate are 500-600m thick; the upper part of the Rodero Series-Pridaoli Series (S3-4), the Tokrawu Formation, siltstone, sandstone, volcanic sandstone, fine conglomerate, and tuff are 800m thick; In the Seager-Bingenghis belt, the layers above the Landowili Series (S1) are mostly denuded. The Landovelli Series (S1) is dominated by red, gray-green, and clastic rocks with nodular limestone lenses. In the Moint-South Junggar belt, the Silurian system is mostly unconformable with the underlying strata. In the Moint block, the Silurian system only retains the layers below the Wenlock Series (S2), which are mostly denuded.

The Silurian system of the Genghis-Tarbach platform belt is in unconformable contact with the underlying strata. The lower part is mainly terrigenous clastic rock intercalated with limestone, and the upper part is andesitic-basalt porphyry, The tuff intercalated with red sandstone is 3000-4000m thick, and the Rodero-Prydocian (S3-4) above it is missing.

In the Altai region, the Silurian system is dominated by greenschist phase metamorphic rocks, with tuff and medium-acid lava in the upper part. In Western Junggar, Xinjiang, the Lower Silurian Chalgaye Formation (S1g) is purple-red, light gray tuffaceous siltstone, fine sandstone containing Monogroptus sedgewiceii and other graptolite fossils intercalated with sandy conglomerate. Blue amphibole mineral fragments in the underlying strata were isolated, and the Upper Ordovician was missing in the area, indicating that the ocean basin was once closed and denuded. The Late Ordovician strata in the and Buxail area are composed of slump deposits and molasses. In Honguleng, the Middle Silurian volcanic flysch structures are unconformable above the Middle Ordovician and are found at its base. The underlying limestone and ophiolite gravels. The Talas-Sonkelly Lake suture zone in Kyrgyzstan represents the existence of the North Tianshan Ocean. Its time limit is Wende-Early Ordovician. This zone exposes the Early Cambrian oceanic crust construction (ultramafic rocks, gabbro Diabase, mafic volcanic rocks, plagioclase granite, etc.), to the north are exposed Middle Cambrian-Early Ordovician arc volcanic rocks, Middle Ordovician acidic volcanic rocks, etc., forming an island arc-type building assembly. By the Middle-Late In the Ordovician, molasse construction during the collisional orogeny period and Late Ordovician collision-type granites were common, such as the Late Ordovician porphyritic granite-granodiorite (Susamel Complex) or the Late Ordovician-Early Ordovician. The remaining gneissic and porphyry granodiorite, diorite (Yildek combination) and granodiorite and granite are often in porphyry, gneissic and quartz diorite (Tabarek combination). Complex II), porphyritic granite, granodiorite (Tabarek Complex III), etc. (According to research by Deng Jinfu et al., the age of co-collision magmatic rocks can be about 20 to 40 Ma later than the age of plate convergence and collision). The leucogranite, leucogranite, and alkaline granite (Jinarachi complex) that appeared in the Early Silurian are post-collision magmatic complexes (located in the syn-collision zone in Peace's Rb-Y-Nb-Ta diagram, but research by Deng Jinfu et al. It is believed that this alkaline granite should be a product of the post-collision period). Therefore, from an overall perspective, the Silurian period generally had sedimentary characteristics similar to those of foreland flysch basins, and some even had double-episode construction with thin lower parts and thick upper parts. Reflects the formation of the early Paleozoic continents. And became the continental area of ??the newly born Kazakhstan-Junggar Plate. On its north and south sides (current location) are the Southern Tianshan Ocean and the Charlesk-Zhaisan-Irtysh Ocean respectively, separated from Tarim and Siberia. This has formed a situation in which the three major plates of Siberia, Kazakhstan-Junggar and Tarim coexist in Central Asia and northern Xinjiang. The author believes that the formation of the unified continent in the Early Paleozoic was the main collision period of the Early Paleozoic in the ancient Asian Ocean in the study area, and the subsequent overlapping structures were products of the post-collision period.

(6) Devonian-Early Carboniferous Period: It is the main collision stage (416~326Ma) in the late Paleozoic when the Paleo-Asian Ocean finally disappeared. This stage is the final disappearance of the oceanic crust and the latest emplacement of the ophiolite suite, and is usually accompanied by penetrating regional deformation and metamorphism, the emplacement of gneissic syncollisional granite and extensive regional uplift. It constitutes a set of tectonic-construction combinations representing the main collision period of the Late Paleozoic Era (belonging to the main collision period of the demise of the Late Paleozoic ocean basin). The biggest feature of this period was the final demise of the Southern Tianshan Ocean and the Charlesk-Zhaisan-Irtysh Ocean in the ancient Asian Ocean, and the three major plates in Central Asia and northern Xinjiang (Siberia, Kazakhstan-Junggar, and Tarim ) to complete the final convergence collision and complete closure of the ocean basin. Han Baofu et al.'s research on the South Tianshan found that a very important tectonic deformation event occurred in the region between 380 and 350 Ma, and its scope of influence involved various tectonic units. Large-scale ductile shear zones appear in granite, eclogite, blueschist, and basic volcanic rocks, leading to the formation of mylonite. New minerals produced during metamorphic deformation and minerals greatly affected by metamorphism have 40Ar/39Ar Ages are concentrated in this period.

The latest ophiolite suite in northern Xinjiang determined based on conodonts and radiolarians is the Late Devonian-Early Carboniferous (South and North Tianshan), with the upper part being the Weixian Period (Nanmingshui Formation) or the early Late Carboniferous (Qirgis Formation) is unconformably covered or interspersed by unmetamorphosed 316Ma granite; in Central Asia and northern Xinjiang, D3-C1 are mostly continuous volcanic rock series, which are covered by The Weixian-age strata are unconformable; in the Nalati Mountains and the East Junggar Dome River Bar area, it can be seen that the calc-alkaline granite during the main collision period of the Late Paleozoic breaks through the Dunai-age strata and is covered by the Weixian-age strata.

This movement was once called the Saul Movement (Xini Village, 1954). Xinjiang was once called the Ili "Movement". Huang Jiqing and others called it the "Tianshan Movement". Occurred between the early Early Carboniferous (Duneian Period) and the middle and late Wei Xian Period.

(7) Post-collision stage: Early Carboniferous - Early and middle Permian (345~260Ma). This stage is the period when the initially unified new continental crust transforms from collisional compression to post-collision extension. It uses the "movement" main scene as the main symbol to divide the main collision period and the post-collision period.

The Constitutional Period of the Early Carboniferous was the period when the surface sea in northern Xinjiang developed the most, and it also symbolized the beginning of the post-collision stage. This stage is the most intense and frequent period of crust-mantle material transformation in the deep part of the new continental crust. It is one of the most intense periods of magmatic activity in the entire orogenic stage. It is also the period of cratonization in which the new continental crust gradually matures. He Guoqi et al. (2002) called the transition of the continental lithosphere from activity to stability the "cratonization" stage, which is the post-collision stage. It is characterized by strong crust-mantle deep interactions and large-scale extension processes. It is manifested by extensive crustal rifting, intraplate alkaline magma activity, mantle-derived magma intrusion, formation of large shear zones, and large-scale metal mineralization (Xu Xin et al., 2005). Such as volcanic-sedimentary iron (copper) deposits, porphyry copper (molybdenum) deposits, magmatic copper-nickel deposits, ductile shear zone-type gold deposits, and rare and rare earth deposits related to alkaline magma activity, etc.

(8) New continental crust consolidation period: The middle and late Permian period (260-251Ma) is roughly the period when the new continental crust has been consolidated. It marks the end of large-scale magma activity and small-scale alkaline magma activity in the post-collision stage. It is characterized by the basic consolidation of the new continental crust and the entry into the tectonic evolution stage of intracontinental basins and mountains. However, some people believe that the post-collision stage may have continued into the Triassic, but the magmatic activity during this period may be related to the remote effects of activity in the southern (current location) Tethys Ocean.