(A) the establishment of Jiamusi-Meng Xing block.
Devonian-Lower Carboniferous in Northeast China is mainly developed in Daxinganling area in the west and Jiamusi area in the east, and their construction characteristics and fossil assemblages are obviously different. Devonian-Lower Carboniferous developed in the west of Xing 'an massif is characterized by marine volcanic-sedimentary formation under the background of active continental margin. In the east, except for the volcanic rock formation of the Upper Carboniferous Yufutun Formation in central Hebei, all other areas are marine carbonate-terrigenous clastic sedimentary formations formed in a stable continental margin environment, directly overlapping with the granite weathering crust in the eastern margin of Jiamusi block. Biofossils from Devonian in the eastern margin of Jiamusi block contain molecules from North America and South China, which are obviously different from those from Europe and Siberia in Devonian in Daxing 'anling area. Early Carboniferous deposits are similar to Devonian, with marine deposits in the west and a set of coastal-shallow marine volcanic-sedimentary formations in the east. The marine life in the early Carboniferous limestone in the eastern region is only found in South China, and there are two kinds of products belonging to the continental margin of the coastal Pacific Ocean, which have never appeared in Inner Mongolia and Xing 'an (geological geography of Heilongjiang Province, 1993), indicating that there is still ancient land separation in the east and west of the early Carboniferous, and it should be Songnen-Jiamusi block. In the Late Carboniferous, the whole northeast of China was uplifted to the land, and river and lake deposits and angara-type plant fossils were widely developed. According to the different biological characteristics of Devonian-Lower Carboniferous on the east and west sides of the early Carboniferous magmatic arc in Daxing 'anling, and the distribution range of late Carboniferous continental deposits has crossed the early Carboniferous magmatic arc in the eastern margin of Daxing 'anling, it shows that the Caledonian consolidated block has completed collision and assembly along the eastern margin of Daxing 'anling before the late Carboniferous. The sedimentary unconformity of the Upper Carboniferous Gegen Aobao Formation in Xiwuzhumuqin Banner, Central Inner Mongolia (Shenyang Geodetic Center, 2006) also supports this understanding.
It can be seen that two relatively independent metamorphic blocks (Jiamusi-Songnen block and Ergon-Xing 'an block) were finally integrated by Caledonian tectonic-magmatic events in the early Carboniferous, and collided and spliced into a unified composite block, on which Devonian-Early Carboniferous and Late Carboniferous-Middle Permian sedimentary caprocks were developed, referred to as "Jiamusi-Meng Xing block" or "Jiameng block". The vast area south of the Mongolia-Okhotsk suture zone and east of the proliferation zone of the Schott-Alin terrane is mainly composed of Ergon-Xing 'an block, Songnen block, Jiamusi block and related blocks on the Russian side.
(B) The evolution of Jiamusi-Meng Xing block.
After the formation of Jiameng block, as a unified structural unit, Paleozoic-Mesozoic experienced three stages of structural evolution. The first stage occurred in the Late Carboniferous-Middle Permian, which was an independent evolution stage of Jiameng block and the whole South China Sea and northern land. The second stage occurred in the Late Permian-Early Triassic, marked by the closure of the ancient Asian Ocean and the collision between the Jiameng block and the North China plate. The third stage occurred from the Middle Jurassic to the early Late Jurassic, marked by the proliferation of the Schott-Alin terrane in the eastern margin of the Jiameng block and the collision between the northern margin and the Siberian plate. The above-mentioned three stages of tectonic evolution not only formed three obvious boundary tectonic belts around the Jiameng block, namely the Xilamulun River-Changchun-Yanji suture belt in the south, the Tongjiang-Mishan terrain collage belt in the east and the Mongolia-Okhotsk suture belt in the north, but also led to two obvious sedimentary discontinuities on the Jiameng block, which generally lost the Middle-Upper Triassic and Upper Jurassic.
(3) The nature of the boundary zone of Jiameng block.
Characteristics of the southern boundary zone of 1. and its tectonic and sedimentary effects
The Xilamulun River-Changchun-Yanji Line has always been considered as the suture zone between the North China Plate and the Northeast Block. However, the continuous marine sediments in the southern Jiameng block from Late Carboniferous to Middle Permian indicate that the southern part of the block has been in a continental margin environment connected with the ocean (ancient Asian Ocean) during this period. Evidence of lithospheric structure shows (Figure 1- 13) that there is an extremely thick lithospheric root with a thickness of over 130km under the northern edge of the North China Plate along the Chifeng-Shenyang line, which spreads in the east-west direction, is wide in the west and narrow in the east, turns to the northeast near the Meihekou, and does not cross the Dunmi fault in the east, reflecting the left-lateral strike-slip of the Dunmi fault. The thickened lithosphere mainly occurs under the North China plate, and the gravity anomaly characteristics also show similar characteristics. The east-west low gravity anomaly zone with a width of nearly 200km extends eastward to the east of Chifeng and is cut off by the northeast structure parallel to the gravity gradient zone in Daxing 'anling.
According to the plate tectonic theory, the formation of the extremely thick lithosphere in the northern margin of the North China plate should be related to the southward subduction of the ancient Asian ocean plate and the collision between the north and south continents. There are orogenic belts in the northern margin of North China Plate, and there are many post-collision uplift granites in the vicinity of the collision zone, and the early Triassic continental purplish red coarse clastic deposits are developed on the north and south sides, which proves that the collision between Jiameng Block and North China Plate occurred in the late Permian-early Triassic. The eastern and northern margins of the block are still in the tectonic environment of the continental margin facing the sea, and accepted the marine and land-sea interactive deposits from the late Triassic to the early middle Jurassic.
2. The characteristics of the eastern boundary zone and its tectonic effect.
The eastern boundary refers to Tongjiang-Mishan fault between Jiamusi block and Nadanhada terrane in the east, which belongs to a part of the north-south fault zone between Breya-Jiamusi-Xingkai block and Xihuote-Alin terrane. Before the terrane accretion, two rock assemblages developed in the eastern margin of Jiameng block: first, the early and middle Permian intermediate-basic acidic volcanic rocks were mixed with carbonate rocks containing warm-water animal fossils, and the geochemical characteristics of volcanic rocks showed that they were formed in the active continental margin environment; Second, the late Triassic-early Jurassic sea-land interaction-marine passive continental margin deposition. In the late Middle Jurassic, the Schott-Alin terrane containing oceanic crust-like basic-ultrabasic rocks (gabbro zircon U-Pb age is 166Ma) and radiolarian siliceous rocks proliferated from south to north to the eastern edge of Jiameng block, which collided with Siberian plate along the Mongolia-Okhotsk suture zone, forming a unified Northeast Asia continent.
Geophysical characteristics show that the accretion and collage boundary between the Schott-Alin terrane and Jiamusi massif is located near Baoqing (Figure 1- 14). The M T results show that there is a nearly vertical boundary of electrical structure near Baoqing, and Jiamusi micro-area in the eastern region has the characteristics of high resistance.
Figure 1- 13 Lithospheric Structure and Thickness of Collision Zone between North China Plate and Jiameng Block
(According to Lu Zaoxun and others, 2005)
Figure 1- 14 Electrical structural characteristics of Jiamusi micro-block and Wandashan terrane.
Characteristics, the characteristics of Nadanhada terrane in the west are between low resistance block and high resistance block. The shallow interface of the collage boundary gently inclines to the west, and the deep interface is almost vertical. It is worth noting that the western part is the exposed area of metamorphic rocks and granite in Jiamusi micro-plot, which is called South China Uplift. The electrical structure shows that there is a horizontal low stop band between 7 ~ 15 km in Huanan uplift, and there is a high stop band with uniform structure below it. In Dongnadanhada terrane, the electrical structures are horizontally distributed above 8km, while the electrical structures with alternating high resistance and low resistance are nearly vertically distributed below it. When studying the tectonic evolution of the eastern basin, we should pay full attention to the geological and tectonic significance of this electrical structure.
3. Characteristics and tectonic effects of the northern boundary zone.
The northern boundary of Jia-Meng block is Mongolia-Okhotsk suture zone, and the collision age is Middle Jurassic (Killirova, 2004; 2006)。 The characteristics of the western and eastern sections of the Mongolia-Okhotsk suture zone are obviously different. Wusimeng Basin is developed in the south of the western section, which is connected with Mohe Basin in China. Wusimeng basin is steep in the north and slow in the south, and there are marine clastic rocks mixed with carbonate rocks in the basin from late Triassic to early Jurassic. The Middle Jurassic is mainly composed of continental sandstone and siltstone, mixed with a small amount of marine clastic rocks, and all the Middle Jurassic entering Mohe Basin in China is continental deposits. The sedimentary thickness gradually deepens from south to north (Figure 1- 15). Yoda basin develops on the north side of the eastern section, steep in the south and slow in the north. Foreland basin formed by thrusting from south to north in late Jurassic.
The structural-sedimentary characteristics and basin type characteristics of the western and eastern sections of the Mongolia-Okhotsk suture zone show that the western section closed early and the block north of the collision pushed southward. The eastern section closed late, and the collision showed that the southern block thrust northward. This shows that the dynamic background of the East and the West is different. The western part belongs to Mongolia-Okhotsk tectonic domain, and the eastern part belongs to coastal Pacific tectonic domain. The transitional boundary between these two tectonic domains is shown in the basin, that is, the western boundary of Songliao basin-Amur-Jieya basin.
Figure 1- 15 North-South Gravity and Electrical Profile of Mohe Basin