Eastern Plateau of China: Other Information

Limited by the author's knowledge, I can only say some sporadic materials to prove the existence of the plateau. If we misinterpret the following materials, the author of this book will bear the responsibility.

8. 1.2. 1

Fig. 8. 1 distribution map of adakite in eastern China.

According to the research of Davis and Zheng Yadong (Davis et al., 1996, 1998, 2001; Zheng Yadong, 2000 and its attached references), there are three stages in the north-south shortening deformation of the crust in western Liaoning: pre-middle Jurassic (180 Ma), late Jurassic (16 1 ~ 148ma) and early Cretaceous (/kloc-0). They speculate that the SN-directional shortening of the pre-Middle Jurassic may be related to the merger of the Mongolian arc and the North China plate along the Soren suture zone, while the shortening deformation of the Late Jurassic-Early Cretaceous may be related to the intra-plate response caused by the collision of Siberia and Mongolia-North China plates along the north of the Mongolia-Okhotsk suture zone 1000 ~ 1800 km. We believe that the three-stage shortening deformation developed in the northern margin of the plateau may be the main reason for the crustal thickening and plateau uplift in eastern China (of course, the convergence of Yangtze block and North China block in the south of the plateau should also be considered.

The study shows that the three Mesozoic tectonic changes in Liao Yan area were the most intense in the late Late Jurassic-Tuchengzi period, and obvious nappe and folding occurred (Zheng Jun et al.,1998; Davis et al, 2001; Wang Genhou et al, 200 1). Zheng Yadong and Davis et al. It is considered that the two main shortening events of Yanshan belt occurred in the Late Jurassic (about 16 1 ~ 148 Ma) and the Early Cretaceous (about 143 ~ 127 Ma), which may coincide with the strong compression of the northern margin of the plateau and may lead to the strong uplift of the plateau. They also found that in the middle Cretaceous, the Yanshan belt in western Liaoning and northern Hebei experienced extensive regional extension deformation, marked by the development of normal detachment faults and metamorphic core complexes (Zheng Yadong, 2000; Davidset et al., 1996, 1998). They reported that the youngest Cretaceous rock mass in Chengde-Pingquan area (120 ~10 Ma) contains more potassium than Yunmengshan granodiorite (adakite, author's note). Zircon U-Pb and Ar/Ar geochronology of Waziyu, which may be related to the study of Middle Cretaceous (1 18 ~) by Zhang Xiaohui et al. (2002) and Darby et al. (2004), shows that crustal extension and metamorphic core complexes were formed in the early Cretaceous (about127 ~/kloc-0) According to the research in this book, the eastern plateau of China collapsed on a large scale after 126Ma, which is consistent with the large-scale regional extension deformation in this period. Therefore, the tectonic transition in eastern China should occur around 126 Ma, which is a reflection of a strong tectonic extension event. Zhao Yue et al. (2004b) also believed that the middle and late Jurassic was a period of intense folding, thrust, remarkable shortening of the crust and thickening of the lithosphere in Yanshan area.

The rise of the plateau originates from the thickening of the crust, which is usually related to the horizontal tectonic compression. For example, the collision between the Indian plate and the Eurasian plate leads to the thickening of the Qinghai-Tibet Plateau. The study by Davis et al. (200 1) shows that before the Middle Jurassic (earlier than 180 Ma), the compressive stress in the north-south direction mainly developed in western Liaoning and northern Hebei, and the Archean basement and Proterozoic and Phanerozoic caprocks were related to the low-angle thrust faults moving southward. They speculate that this nappe may be the result of (1) collision between the Mongolian arc and the Andean continental arc along the northern margin of the North China plate in Paleozoic, or (2) the northern landmass was formed by subducting southward under the Archean craton in North China, similar to the Cordillera-style back-arc and foreland fold thrust belts in the United States. After the fold thrust, the upper wall (south) of the nappe fault experienced a large area of erosion, and then the volcanic-sedimentary strata of Tijishan Formation began to deposit. Therefore, the tectonic deformation of Jurassic-Cretaceous Yanshan belt (which may be connected with Yinshan belt in Inner Mongolia to the west) reflects the north-south intraplate shortening in this area.

According to the above discussion, the evolution of the plateau in eastern China can be divided into three stages: (1) The early Mesozoic (late Indosinian-early Yanshan) may be related to the collision of the North China-Paleo-Asian ocean plate, forming towering mountains in Yanshan-Yinshan area (mountains in northern North China, see Chapter 7 of this book); (2) The uplift of the Late Jurassic-Early Cretaceous Plateau may be related to the closure of the Mongolia-Okhotsk Sea 800 ~ 1000 km away. Davis and others believe that the collision along the Mongolia-Okhotsk Sea may be the main factor leading to intraplate compression deformation in the southern Yanshan belt (and Yinshan belt) far away from it. (3) After the early Cretaceous compression, after 125 Ma, the structural deformation showed a regional extension in NW-SE direction, which was consistent with the end of large-scale magmatism in eastern China, indicating that the overall collapse occurred around 125 Ma.

Structural evidence shows that there is a great difference between Jurassic and Early Cretaceous in northern North China: Jurassic, especially in the late Late Jurassic, is dominated by compressive structures, which is related to plateau uplift; The early Cretaceous was characterized by extensional structures, which formed many fault basins (Zhao Yue et al., 2004a；; Zhang Hong et al., 2005b) reflects the collapse of the plateau.

The evolution of the eastern plateau of China echoes the rise of the Okhotsk (Ergon) mountains, which is related to the closure of the Mongolian-Okhotsk ocean basin. However, the uplift of the Ergon Mountains started earlier in the early Jurassic (about 190 Ma) than the eastern plateau of China, while the plateau did not begin to uplift until the middle Jurassic (about 175 Ma), but both of them were in the late Jurassic-early Cretaceous (Ergon: 150 ~ 65438). The eastern plateau of China: 156 ~ 132 Ma) began to collapse in the middle of early Cretaceous (marked by volcanic rocks of Shangkuli Formation and Yixian Formation, about 125 Ma).

8. 1.2.2 Sedimentary data

Liu Jianzhong et al. (2004) pointed out that the direct result of plateau uplift was the lack of syngenetic deposits, or some sedimentary basins were developed but thin, and many of these basins produced a lot of volcanic materials, indicating that the intense magmatic activity at that time could not reflect the subsidence of the crust. In the middle and late Jurassic, there were few sedimentary basins on the plateau, mainly distributed in the northern foot of Yanshan Mountain and Dabie Mountain, characterized by intermountain and piedmont molasses deposition, accompanied by strong volcanic activity. A large number of upper Cretaceous strata are missing in North China, which can only be seen in some basins. Therefore, the late Jurassic-early Cretaceous sedimentary and denudation conditions in North China generally reflect the uplift of the plateau (Liu Jianzhong et al., 2004). Zhang Hong et al. (2005b) also found that the Cretaceous strata in the western Liaoning-northern Hebei region are well developed, while the Jurassic strata are less preserved, and some places are basically missing, such as Fuxin-Yixian region, suggesting that this region was in a denudation environment (normal terrain) before the formation of Yixian Formation. The development of coarse clastic rock deposits in the lower member of Yixian Formation is usually explained as the result of crustal uplift and denudation, and it can also be explained as the result of crustal subsidence, which is caused by the huge difference in topographic height. Lacustrine deposits widely appeared in the middle and late Yixian Formation, and deep-water lacustrine strata also appeared in Jiufotang period and Shahai period, indicating that the positive landform changed to negative landform in the early Cretaceous (Zhang Hong et al., 2005b), which is consistent with the conclusions of structural and petrological studies.

According to the research of Wang Dongpo et al. (1996), they found ice raft deposits in the early Cretaceous Quantou Formation in Changtu, Liaoning and Xinlicheng, Changchun, Jilin. Ice raft sediments are formed by the melting and falling of ice cubes loaded with sediments when they enter the ocean or lake. They can be formed in low latitudes or high latitudes, and the vertical zoning of climate in high latitudes is obvious. Frakes and Francis( 1988) based on the study of the ice raft deposits in Siberia and Canada in the late Mesozoic and Australia, Alaska and New Zealand in the early Cretaceous, think that the ice raft deposits in the northern hemisphere from the Middle Jurassic to the early Cretaceous are between 65 and 78. The ice raft deposits in Changchun-Changtu area are located in the mid-latitude area (45 ~ 46 north latitude). The sporopollen assemblage of Quantou Formation contains not only the sporopollen of tropical and subtropical plants, but also a small amount of cold-loving mixed molecules, which reflects the great difference in topography around the basin during the period of Quantou Formation, forming an obvious vertical climate zoning phenomenon (Wang Dongpo et al., 1996).

Shoutian Cheng et al. (2002) reported the discovery of early Cretaceous glacial debris flow deposits in Zuoyun area, northeast of Ordos. Glacier debris flow is a debris gravity flow deposit formed by mixing moraine and snowmelt water. According to the existence of scratches, freezing marks, giant glacier boulders and giant erosion troughs and valleys, they think that the early Cretaceous debris flow deposits in the northeastern margin of Ordos are the causes of glacial debris flow, suggesting that there were valley glaciers in the northern part of Shanxi in the early Cretaceous.

According to our retrieval of relevant data, the early Cretaceous ice raft deposits in the middle latitudes of the world were only found in the northeast, and the above-mentioned ice raft and glacier debris flow deposits were just distributed in the north and northwest of the plateau, and their ages were all in the early Cretaceous, which may be related to the uplift of the plateau. Today's snow line is about 4000 meters above sea level. In Cretaceous, because the temperature may be higher than today, the snow line may be higher. It is speculated that the plateau (at least the northern edge of the plateau) may have been above the snow line in the early Cretaceous, and there may have been an east-west mountain range across the northern edge of the eastern plateau of China, which is comparable to the modern Himalayas.

8. 1.2.3 clay mineral data

Xu Baoliang et al. (2007) and Li Xianghui et al. (2008) studied the relationship between the mineral composition of plateau clay and paleoclimate, and obtained interesting conclusions. A large number of studies at home and abroad show that clay mineral composition is an important indicator of paleoenvironment and paleoclimate change. For example, warm and humid climate is beneficial to the formation of kaolinite, montmorillonite mainly reflects the characteristics of cold climate, dry climate and weak leaching are beneficial to the formation and preservation of illite, and chlorite represents dry climate conditions. It seems that only kaolinite represents hot and humid climate, and the other three are related to dry and cold climate (according to Li Xianghui and others, 2008).

The combination and change of clay minerals in eastern China show that in the middle and late Mesozoic (J2-K), the dry and cold climate dominated in the southeast of Northeast China and the central and eastern parts of North China, and some areas were dry and hot. It shows that there may indeed be a landform highland in the eastern part of China during this period. According to the distribution characteristics and climate of clay minerals, the eastern plateau may have started from the Middle Jurassic or even earlier and lasted until the end of Cretaceous or even Paleogene. Because the Cretaceous in Liaodong, Luxi, Henan and Anhui was in a dry and cold environment. In the early and middle Jurassic, the climate in Luxi and Jiyang basins was hot and humid, and did not enter the plateau uplift period. Bohai Bay Basin and Subei Basin contained coal in the early and middle Jurassic, and the climate was warm and humid. The eastern plateau in this period was limited to the south-central part of North China, that is, the south of Bohai Bay Basin (author's note: it may be in the west rather than the south of Bohai Sea, see later). From Late Jurassic to Cretaceous, the study area was basically in a dry and cold state, when the eastern plateau extended to the southeast of Northeast China and most of North China. Paleontological and sedimentological evidence shows that most areas in Northeast China, including the Songliao Basin and its surrounding areas in Cretaceous, were in a warm and humid climate state in the middle and late Mesozoic, indicating that Wusuli and Jixi areas are low-lying and connected with the ocean, which may be mainly the result of the Pacific climate. In Xixia Basin in the west and southwest of Henan Province (Zhou Shiquan et al., 1997), the climate in the Late Cretaceous turned dry and hot, and dinosaur eggs were preserved, indicating that the terrain height decreased during this period and became the main place for the foehn effect (according to Li Xianghui et al., 2008).

8. 1.2.4 strontium isotope data of seawater

Richer et al. (1992)' s 87Sr/86Sr isotope evolution data is very interesting (Figure 8.2), which shows that the initial value of seawater Sr has increased sharply since 40 Ma (Richer et al.,1992; Howarth and McArthur, 1997), which shows that a large number of substances with high initial Sr value were added during this period, and it is speculated that it may be the influence of the uplift of the Qinghai-Tibet Plateau (Richter et al., 1992). We noticed that the initial value curve of Sr during 155 ~ 123 Ma (middle of late Jurassic-early Cretaceous) also had obvious steepening section, which was consistent with the strong uplift event of the eastern plateau of China in 156 ~ 125Ma, and perhaps reflected the uplift event of the eastern plateau of China. If our speculation is possible, then, according to the indication in the figure, the curve has a sudden change during 60 ~ 90 Ma, which indicates that there may have been a plateau somewhere in the world during this period, and interested scholars can try to find it.

Fig. 8.2 Evolution curve of global average Sr initial value with time since 206 Ma (modified by Howarth and McArthur, 1997)