The tectonic evolution of the ancient Asian Ocean lasted until the Late Paleozoic, and closed in the Early Carboniferous and Early Permian along the southern Tianshan-Beishan-Xilinhot region. The ocean basin along the Suorankel-Suolunshan-Xilamulun line closed at the beginning of the Late Permian, ending the evolution history of the ancient Asian ocean. According to its development history and structural location, it can be roughly divided into three structural belts: Altai-Sayan-Mongolia-Okhotsk structural belt, Balkhash-Xing 'an structural belt and Ural-South Tianshan structural belt (Figure 7.9).
Fig. 7.9 Structural Zoning Map of Paleo-Asian Ocean Orogenic Belt and Its Adjacent Areas (according to Chen et al., 2007)
7.2. 1. 1 Opening of ancient ocean basin
Existing data show that the development of Sinian bimodal volcanic rocks in northern Xinjiang and Central Asia (Avdeyev,1984; Bureau of Geology and Mineral Resources of Xinjiang Uygur Autonomous Region,1993; IL, 200 1), isotopic chronology data of ophiolite (Kwon et al.,1989; Xiao Xuchang et al.,1992; Zhang Chi et al.,1992; Huang Jianhua et al.,1995; Parati et al.,1995; Huang Xuan et al.,1997; Yang Haibo et al., 2005), these data show that the ancient ocean basins in northern Xinjiang and Central Asia were opened at least in Sinian. However, in view of the development of early Mesoproterozoic aulacogen in Siberia, China, Korea and India; Khain et al. (2002) reported that 1020Ma ophiolite developed in Sayanling, southeastern China. As far as regional events are concerned, in Proterozoic, Laoya ancient land began to split; By the early CAMBRIAN, the ancient Atlantic Ocean (Iapetus Ocean) appeared between ancient North America and ancient Europe, and the pre-Appalachian Ocean appeared between ancient North America and ancient Africa (Gondwana). Combined with the pre-Atlantic-Paleo-Asian ocean tectonic domain (or the northern hemisphere paleo-ocean tectonic domain), it was formed in Mesoproterozoic and Neoproterozoic, and in the early Paleozoic, the ocean basin was mainly reduced and the continental crust proliferated, forming a middle block; In the Late Paleozoic, there were mainly residual ocean basin closure, arc-arc or arc-continental collision, continental collision and super collision (Winedle,1984; Zhang Yun is equal, 20 10). Therefore, the opening of the ancient Asian ocean basin can be pushed to at least Mesoproterozoic, that is, it was formed on the basis of the second disintegration of columbia supercontinent and Rodinia supercontinent.
7.2. 1.2 subduction and closure of the ancient ocean basin
7.2. 1.2. 1 ancient ocean basin subduction
Paleomagnetic data (Smethurst et al.,1998; Yang Zhenyu et al.,1998; Li Yongan et al., 1999), coral fossils in strata (Wang Baoyu, 198 1, 1986, 1987, 1988,1998. Cai Tuci, 1988a, b, 1989a, b, 199 1a, b, 1993, 1996,/kloc-0. Middle and Late Silurian Tuwabei fauna fossils are only found in East Junggar and its northeast area (Zhang Zixin et al.,1983; Wang Baoyu, 1990), on both sides of the ophiolite belt in South Mongolia (Kurkov, 1993), in the north of Hegenshan ophiolite belt in Northeast China (Su, 198 1), but in the contemporary strata of the northern margin of the Sino-Korean landmass, Tianshan Mountains, West Junggar and Central Asia. The symbiosis of angara and Cathaysian flora, which began to develop in the late Carboniferous in the Asian continent, only appeared in the late Permian strata (Dou et al.,1985; Wu Shaozu, 1993).
Ophiolite is generally regarded as a record of oceanic crust fragments and subduction. In Sayanling area and western Mongolia, besides 1020Ma ophiolite, there are 600~500Ma ophiolite (Bukan et al., 2002), which started to develop from Neoproterozoic active continental margin rocks (Kuzmichev et al., 2001; Salnikova et al., 200 1), but it is the most widely distributed in CAMBRIAN. These ophiolite coexists with the eclogite and blueschist in Sayanling, Altai Mountain, the southern part of western Junggar and the northern margin of southern Tianshan Mountains, in which the Ar-rA age of Tangbale blueschist in western Junggar is 458~470Ma (Zhang, 1997) and that of blueschist in northern southern Tianshan Mountains is 350Ma (Xiao Xuchang et al., 65438).
The active continental margin complexes in northern Xinjiang and Central Asia began from Ordovician to Carboniferous (Avdeyev,1984; Li et al., 2003; Li Jinyi, 0204a). The pre-arc accretion complex is a direct record of the existence and contraction and subduction of the ancient ocean basin. In northern Xinjiang, such geological bodies can be found in the linear orogenic system in southern Tianshan, Bayingou in northern Tianshan, salto Sea in western Junggar, Karamaili Mountain in eastern Junggar, Xibedu to Qiaoxia Hala in front of Altai Mountain. In these areas, marine lithospheric fragments are structurally wrapped in Devonian and early Carboniferous forearc sedimentary rock series. The northeastern margin of Junggar basin, south of Karamaili ophiolite belt, has been continuously deposited from Middle Silurian to the lower part of Lower Carboniferous. The lithology is mainly continental clastic rocks, with a small amount of carbonate rocks, among which the fossils are rich and the thickness is not large, which has the characteristics of passive continental sedimentary rock series. The lower Carboniferous Liang Shan gravel layer above it is a set of conglomerate with a thickness of 1600 m (regional stratigraphic table compilation group of Xinjiang Uygur Autonomous Region Bureau of Geology and Mineral Resources, 19866, 1993, 1999), which has the characteristics of syngenetic molasses.
Boanite is a rock of great significance for determining the tectonic environment of ophiolite and its associated rocks, the corresponding arc basin evolution process and understanding the early history of crust-mantle evolution (Sun S et al.,1989; Fan j et al.1997; Kerrich R et al.,1998; Puchtel Z S et al., 1999), as long as Boantite is found in ophiolite, it can be determined that the ophiolite is affected by attenuation (Zhang Qi et al., 2000). At present, it is found that almost all Boan rocks occur in the pre-arc environment (Hickey R L et al.,1982; Crawford A J et al., 1989), which mainly appeared in the early stage of island arc or back-arc basin evolution (Cameron W E et al.,1979; Hickey R L et al.,1982; Beccaluva L et al.,1988; Crawford A J et al.,1989; Zhang Qi, 1990), the typical rock assemblage is often Hartz (harzburgite) -IAT (island arc tholeiite)-Bonite (high magnesium andesite), which often represents the immature intracontinental island arc formed during the initial subduction.
Volcanic rocks of ishak Group (Yuan Chao et al., 2002) and Dacha Daban ophiolite (Zhang Qi,1998; Feng Yimin, 1995). According to geochemical evidence (Samuel Kwok, 2009), Silurian basalts in Dashizhai Town, Inner Mongolia can be divided into two groups: the first group is relatively high in TiO _ 2, MgO and compatible elements, and low in Sr and Th, which may come from the mantle source area of the ocean lithosphere, and the isotopic composition is extremely poor after subduction fluid transformation; In the second group, the contents of TiO _ 2, MgO and compatible elements are low, but the contents of Sr and Th are high, and the melting source region is obviously helpful for subduction deposition. Reported in northern Xinjiang, Inner Mongolia and adjacent areas (Liu Dequan, etc.,1993; Dobret sov et al., 2004; Zhao Zhenhua, 2007), a set of magnesium-rich volcanic rocks (Niu Cai He, 1999) was found in the marine volcanic rocks of the Ashele Formation of the Middle Devonian in the Ashele copper mine area in western Altai, Xinjiang. The pyroxene andesite of the Middle Devonian Beitashan Formation in Shaerbulak, Fuyun County, northern Xinjiang has the geochemical characteristics of boehmite (Zhang et al., 2003). In addition, Middle Devonian and Carboniferous magnesium-rich andesite have also been found in Ashele (magnesium-rich dacite), Alatao Mountain, Dabate, Axi, Guozigou, Tuwu-Cave, Weiya, Penguin Mountain and the east of 3 12 National Highway (Zhao Zhenhua, 2007); Magnesium-rich andesite has also been found in some ophiolite distribution areas, such as Bayingou ophiolite area in the western Tianshan Mountains (Wang Qiang et al., 2006). The above data show that in the early Paleozoic and late Paleozoic (Middle Devonian and Carboniferous), the ancient Asian Ocean had at least two subductions. The magnesium-rich andesite, magnesium-rich dacite and magnesium-rich diorite in northern Xinjiang gradually become younger from north to south. The Altai region is Devonian and the east and west Tianshan Mountains are Carboniferous (Zhao Zhenhua, 2007). Most of the deep-water sedimentary rocks associated with ophiolite in northern Xinjiang contain radiolarians or conodont fossils, among which the red jasper associated with ophiolite in Karamaili, Bayingou and Kule Lake in northern Tianshan contains Carboniferous radiolarians (Xiao Xuchang et al.,1992; Liu Yu et al.,1994; Shu et al., 2003), Kramer (2005). According to Rb-Sr and 40Ar/39Ar dating of muscovite in high-pressure metamorphic rocks, the metamorphic peak age is determined to be 3 10~3 1 1Ma. From early Carboniferous to late Permian, there are different flora in the north and south of the Xilamulun River-Changchun-Yanji line, namely Angara flora and Cathaysian flora. This shows that the two subductions of the ancient Asian ocean in the early Paleozoic (Silurian) and the late Paleozoic (Middle Devonian and Carboniferous) were intracontinental subductions, and the ocean basin was not closed.
Adakite is another important rock related to subduction magmatism (Defant, M.J. et al., 1990). Its unique rock geochemical characteristics and important geodynamic significance have attracted wide attention of geologists at home and abroad in recent years (Prouteau et al., 2001; Schiano et al.,1995; Yogodzinski et al, 2001; Zhang Qi et al., 2002) has become a very active frontier field in the study of magmatism in subduction zone (such as Yogodzinski et al.,1995; Drummond et al.,1996; Kepezhins-kas et al.,1996; Sajona et al., 2000; Smith and Champion, 2000; Wyman et al., 2000; Aguilon et al, 2001; Polat and Kerrich, 20065438+0; Hollins, 2002; Bourdon et al., 2002; Defant et al., 2002). Recent research shows that under some thermal conditions, such as young, fast, inclined and gentle oceanic crust subduction (Defant et al.,1990; Peacock, etc,1994; Gutscher et al., 2000; Yogodzinski et al., 200 1), diving depth >: 50km (with pressure >: 12× 108Pa, with (16~22)× 108Pa as the best) partial melting. The tectonic position is volcanic arc, and the time is often in the early stage of subduction
It is reported that there are two kinds of adakite in northern Xinjiang (Zhao Zhenhua, 2006). One is subduction type, which was formed from early and middle Devonian to late Early Carboniferous, including adakite, basalt-rich and high-rich andesite; The second type is the underplating type, which was formed in the Middle and Late Permian. The first type adakite is distributed in Alatao Mountain in the west Tianshan, Nushan Mountain in Borocco in the middle Tianshan, Luotuogou, Barentai, Tuwu-Yandong in the east Tianshan, Fuyun-Qinghe South in the southern margin of Altai Mountain, Lvliang in the middle of Junggar Basin, Karamay and other places (Figure 7. 10). In the southern margin of Altai continent, picrite is closely associated with adakite, basalt-rich and high-rich andesite. The second kind of adakite is distributed in Awulale Mountain in the west Tianshan Mountains and Sanchakou in the east Tianshan Mountains, and no combination of rich basalt and rich andesite is found. The second type of intrusive adakite classified by the original author may be related to the denudation of orogenic lithosphere and the upwelling of asthenosphere to melt residual eclogite facies rocks (Qiu et al., 2006), belonging to C-type adakite.
Adakite identified in Northeast China is mainly distributed in Jilin, with sporadic reports in Inner Mongolia and Heilongjiang (Figure 7. 1 1). They are located in the Paleo-Asian Ocean, the Binxi Pacific Ocean and the Binnan Mongolia-Okhotsk Ocean structural belt, respectively, and are related to the mineralization of gold, copper and molybdenum.
Fig. 7. 10 distribution map of two adakites in northern Xinjiang (according to Zhao Zhenhua, 2006)
Fig. 7. 1 1 Distribution map of adakite and adakite in northeast China (according to Fei et al., 2004).
Adakite in Paleo-Asian Ocean: Su Nite Zuo Qi-Hagenshan suture zone is the suture zone between Siberia plate and North China plate (Tang Kedong et al., 1992). The Baiyinbaolidao pluton was formed in the early Paleozoic island arc tectonic environment on the southern margin of Siberian plate (Xu Bei et al., 1997). According to the single zircon U-Pb age of 439.8±4.3ma (Fei et al., 2004), it is considered that adakite was formed in Ordovician. The early Paleozoic island arc in Duobaoshan area of Heilongjiang Province is located in the northeast extension of Hegenshan suture zone (Cui Ge,1983; Tang Kedong et al.,1992); The Re-Qs isochron age of molybdenite in Duobaoshan copper mine obtained by Zhao Yiming (1997) is 50614ma, indicating that the host rock of Duobaoshan copper mine-granodiorite porphyry was also formed in the early Paleozoic. There are granite belts (Fang Wenchang,1992; Fei et al., 2000); Adakite such as Shichangtun granodiorite and Erdaodianzi tonalite were all formed in the island arc tectonic environment.
The Xilamulun River-Changchun-Yanji suture zone is a very important plate collision splicing zone in the east of Meng Xing orogenic belt, and Dayushan pluton is located in this splicing zone and belongs to high-potassium calc-alkaline type I granite (Sun Deyou et al., 2004). The rock mass has syntectonic properties, and no new metamorphic minerals are generated in the rock, which indicates that the rock mass should be emplaced after the peak of metamorphism. The emplacement age of the rock mass (248Ma) is slightly later than the peak metamorphic age of Hulan Group (Late Permian), which proves that Dayushan rock mass belongs to syncollision granite, and the emplacement time is slightly later than the peak metamorphic age of Hulan Group, which represents the final collision and splicing of the Xilamulun River-Changchun-Yanji suture zone at the end of Permian (Sun Deyou et al., 2004).
Adakite on the west coast of the Pacific Ocean: the eastern part of Jihei belongs to the Mesozoic circum-Pacific tectonic belt (Li Zhitong et al.,1992; Ji Shaoan et al, 2001; Li Jinyi,1998; Fang Wenchang, 1992), adakite has been identified as Miantian, Dong Qing, Zhudundian, Dapuchai River, Daheishan and Tuanjiegou. According to their temporal and spatial distribution, it is generally believed that they were formed in the island arc environment of the Binxi Pacific belt.
Marine adakite in Okhotsk, Binnan: A small amount of adakite, such as Badaka quartz diorite Jiawula and Eryizhan, has been found in the Mongolia-Okhotsk structural belt, and its formation age is 245~ 133Ma.
7.2. 1.2.2 The closed age of the ancient Asian Ocean
Ocean basin is closed, and magmatism is an important symbol. In Xinjiang, Inner Mongolia, China, Mongolia and Central Asia, magmatism is mainly Caledonian and Variscan, of which Variscan is the strongest. In Mesozoic and Cenozoic, magmatism only developed in south-central Mongolia, Russian Far East and northeastern China. According to the statistics of exposed igneous rocks in Xinjiang, according to time, the pre-Sinian system 13.6%, early Paleozoic 7.9%, late Paleozoic 69.5%, Mesozoic 8.9% and Cenozoic 0.000 1%. It can be seen that late Paleozoic granitoids are the main granitoids, of which Carboniferous granitoids account for 46.9%.
Li et al. (2009) analyzed the paleolatitude and latitude migration between North China and Siberia according to the paleomagnetism contrast, and thought that the Siberian landmass began to drift rapidly southward in the early Permian and collided with the North China landmass at the end of Permian (about 250Ma), that is, the ancient Asian ocean between the two landmasses finally closed at the end of Permian. Li Jinyi and others (2006) think that the closing time of the ancient ocean basin in northern Xinjiang and its adjacent areas is different in different regions. The ocean basins in Sayanling and western Mongolia were closed in the early Paleozoic, while those in northern Xinjiang and Central Asia were closed in the late Carboniferous or early Permian.
The new zircon U-Pb age data of Yanbian area in the eastern part of the Paleo-Asian ocean orogenic belt show that these granites were formed in the late Paleozoic to the late Mesozoic (285~ 1 16Ma), and are divided into four periods: the early Permian (285±9Ma) and the early Triassic (224~245Ma). Jurassic (192~ 168Ma) and Cretaceous (119 ~16ma), in which tonalite and central Jilin have COU-in the early Permian (285±9Ma). It may indicate that the paleo-Asian ocean plate subducted under the North China block, and the Triassic syncollisional adamellite reflects the collision age and final closure of the paleo-Asian ocean (Li et al., 2009).
In the Late Permian (255 ~ 250 Ma, Figure 7. 12), the right-lateral strike-slip between the Russian and Angolan landmasses was transformed into the left-lateral strike-slip (Seng? R et al., 1993b,1994; Allen, 1995), strike-slip dislocation is mainly concentrated in the Gornostaev shear zone, but it not only affects the whole Altai collage, but also affects the Manzhouli orogenic belt (fig. 7. 12).
7.2. 1.2.3 Opening and closing of Mongolia-Okhotsk Sea
The late Paleozoic depressions in Jiamusi-Xiaoxing 'anling and Han Kai blocks (Figure 7. 13) are divided into Oulmi (урмий) and Malinoff (малинов). Among them, the lower Permian terrigenous carbonate strata (organic matter development) developed in Oulmi sag, while the upper Permian-Middle Triassic terrigenous carbonate strata and terrigenous marine strata may be the record of the reopening of the ancient Asian Ocean after the closure of the late Permian.
Xiaojinguo Caledonian volcanic belt extends 600km north-south and is 30 ~100 km wide, and is located in Jerry-Changbao-Xiaojinguo area. The Binton Hercynian volcanic belt is located in the east of Harbin, covering Emeibo sag and Xiaojinguo volcanic rock. The volcanic belt extends along the north-south normal fault. Volcanic activity occurred in the Early-Middle Devonian, but continental volcanic accumulation began in the Middle Carboniferous, with an isotopic age of 305Ma(Rb-Sr). The offshore carbonate rocks deposited in the early Permian contain intermediate-acid volcanic rocks with a thickness of 3000 meters, which is the characteristic of volcanic rocks on the continental margin. Late Permian and early Triassic were invaded by granitoids (quartz monzonite, granodiorite, syenite and alkaline granite), forming north-south bedrock. According to the above data, combined with the formation age of Okhotsk adakite 245~ 133Ma, it can be inferred that the Mongolian-Okhotsk Ocean was closed in Triassic (also known as the final closure of the ancient Asian Ocean), and it can also be considered as the embodiment of the Indosinian movement in this area.
Zhang Yunping (20 10) thinks that in the evolution of the paleo-Asian oceanic tectonic cycle, the Baikal cycle, the Sarayier cycle and the Caledonian cycle mainly reflect the process of the continuous outward growth of the ancient continental crust and the formation of intermediate blocks; The Variscan cycle is mainly a process of further disappearance of the residual ocean basin and arc-land and land-land collision. Late Paleozoic-early Mesozoic tectonic magmatism was widely superimposed on pre-existing continental margins, intermediate blocks and orogenic belts; The late Triassic-Middle Jurassic structure is related to the collision process between the North American plate and the Asian plate.
During the Mesozoic era, the western Siberian basin experienced an important extension stage, which was characterized by the appearance of Lower-Middle Triassic basalts (Surkov and Jero,1981; Surkov,1986; Ap Lonov, 1988). These extensional structures can usually be compared with classical rift systems, such as Surkov, 1986. The abnormal magnetic field shows that there is a symmetrical magnetic anomaly between the Yamal Peninsula and the estuary, which is related to the scale of the geomagnetic field (Aplonov, 1988). Although there is no particularly convincing evidence to support the formation of a normal ocean basin in the basin (Aplonov, 65488), in fact, it is not difficult to distinguish the classical rift in the mid-ocean ridge from the extensional structure of the western Siberian basin. The former is mainly concentrated in one band, interrupted by frequent transform fault. In the western Siberian basin, the Triassic rift spans a lot, and the largest Cotello Gore-Urango rift extends at least 2000 kilometers in a straight line, and the rift chain presents unusual geometric characteristics (Seng? r， 1995a).
Fig. 7. 12 Late Permian paleostructural reconstruction of Altai orogenic belt and Manzhouli orogenic belt (255~250Ma) (modified according to Seng R, 1993).
Fig. 7. 13 geotectonic schematic diagram of the intersection area between the ancient Asian ocean orogenic belt and the Pacific orogenic belt (the base map is quoted from the copywriter: Snu Yayun, 2008, modified) regional sedimentary structures (basins, depressions, depression groups, depressions).