Formation and Evolution of Sanjiang Collision Orogenic Belt

Li, Wenchang; Pan, Guitang; Hou, Zengqian; Mo, Xuanxue; Wang, Liquan; Zhang, Xiangfei

doi:10.1007/978-981-99-3652-6_3

Wenchang Li¹²,
Guitang Pan¹²,
Zengqian Hou¹³,
Xuanxue Mo¹⁴,
Liquan Wang¹² &
…
Xiangfei Zhang¹²

Part of the book series: The China Geological Survey Series ((CGSS))

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Abstract

In terms of collision, Suess (Die Entstehung der Alpen. Wien (Braumüller), p 168, 1875) divided orogenic belts into Pacific type and Tethyan type according to collision types of orogenic belts and took Alpine and Himalayan orogenic belts as typical examples of collision orogeny. Sengor (Earth Sci Rev 27:1–201, 1992) divided collision orogenic belts into Alps type, Himalayan type and Altai type according to the collisional type and different internal tectonics of the orogenic belt. Based on the various tectonic units involved in the collision, Li et al. (Chin J Geol 34:129–138, 1999) pointed out that collision may occur in various geological bodies (such as land-land, land-frontal arc, land-residual arc, land-accretionary arc, arc-arc, land-arc-land), which is the most complete description of collision behavior between collision objects and various geological bodies so far.

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3.1 Definition and Classification of Collision Orogenic Belt

3.1.1 Definition of Collision

In terms of collision, Suess (1875) divided orogenic belts into Pacific type and Tethyan type according to collision types of orogenic belts and took Alpine and Himalayan orogenic belts as typical examples of collision orogeny. Sengor (1992) divided collision orogenic belts into Alps type, Himalayan type and Altai type according to the collisional type and different internal tectonics of the orogenic belt. Based on the various tectonic units involved in the collision, Li et al. (1999) pointed out that collision may occur in various geological bodies (such as land-land, land-frontal arc, land-residual arc, land-accretionary arc, arc-arc, land-arc-land), which is the most complete description of collision behavior between collision objects and various geological bodies so far.

In terms of collision modes, Ren et al. (1999) called the collision between micro-landmasses soft collision and the collision between macro-landmasses hard collision based on the scale and size of landmasses and considered that the landmasses were not connected yet and were in a state of “linked but not joined” after the soft collision; different macro-landmasses were finally joined into a whole and entered a unified dynamic evolution model only after the hard collision. In terms of collision stage, Harris et al. (1988) divided the collision into three stages: syn-collision, late-collision or post-collision and rear-collision; Liégeois et al. (1998) divided the background related to the collision into three tectonic environments: collision, post-collision or rear-collision and intraplate collision; Deng et al. (2002) divided the collision into 3 stages: continental collision between continents, intracontinental collision and post-orogenic collapse.

We believe that the initial collision between the Indian continent and Eurasia was the first collision of moving arc-arc and moving arcs-lands, and the subsequent continuous land-land collision had experienced a long development process, reflecting the interaction of the mesosphere in the earth system. Therefore, the comprehensive convergence collision between Bangong Lake-Nujiang River Junction Zone and Yarlung Zangbo Junction Zone, including Gangdise MABT, can be called the main collision zone of Qinghai-Tibet Plateau. After the comprehensive convergence collision, the sedimentary environment will change radically (e.g., passive margin basin will be transformed into foreland basin, and back-arc-basin will be transformed into back-arc foreland basin), and extensive and intense magmatic activity will occur along the frontal arc in front of the collision zone. Post-collision is marked by the emergence of various significant intracontinental deformations such as molasse, two-mica granite and foreland thrust zone.

3.1.2 Classification of Collision Orogenic Belts

As the main orogenic belts throughout the world were formed at different ages during the evolution of the earth and distributed in different tectonic parts of the global tectonics, their internal tectonics, shapes and formation mechanisms are complex and diverse, even those in different parts of the same orogenic belt are different. Therefore, there are various types of orogenic belts. Different scholars have formulated different classification standards and principles according to time or space, tectonics or composition and formation mechanism from different perspectives, so different classification schemes are obtained (Miyashiro et al. 1984; Sengor 1992; Xu et al. 1992; Li et al. 1999).

The key to the study on collision orogenic belt is to determine the temporal and spatial structure, composition, collision process and nature of collision zone. Based on the discovery and determination of more than 20 collisional melange zones in Qinghai-Tibet Plateau, they are generally divided into three types: arc-arc collision zone, arc-land collision zone and land-land collision zone. In a sense, the type of collision orogenic belt is closely related to the nature of collision zone in the determination. The orogenic belts are divided into three types according to the collision unit, temporal and spatial structure and assemblage relationship of orogenic belts (Table 3.1): circumoceanic continental margin arc (ocean-arc collision) orogenic belts, collision orogenic belts and continental margin orogenic belts. Collision orogenic belts are divided into land-land collision orogenic belt, arc-land collision orogenic belt and arc-arc collision orogenic belt. Arc-land collision orogenic belts are generally divided into three types based on the different properties of the basement (or substratum) of the island arc: magmatic arc with the continental crust (metamorphic basement or old stratum) as the basement, accretionary arc of volcanic magma with the subduction complex as the basement and volcanic arc with the oceanic crust (i.e., frontal intra-oceanic arc) as the basement. After further study on fine temporal and spatial structure and composition, it can be divided into three types: residual arc-land collision type, accretionary arc-land collision type and frontal arc-land collision type.

Table 3.1 Classification framework of collision orogenic belt types

Full size table

Examples of collision orogenic belt classification: ① circumoceanic continental margin arc orogenic belt. This kind of orogenic belt was formed by subduction of oceanic plate before the closure of the ocean basin. It mainly refers to modern Cordilleras and Andes. After the closure of the ocean basin, it can be transformed into a land-land collision orogenic belt or a land-arc collision orogenic belt. ② Land-land collision orogenic belt. This is an orogenic belt formed by collision between two circumoceanic continental plates or blocks, and a mountain system formed by the collision between the passive margin of one continent and the active margin (i.e., the continental margin arc) of the other continent. Although this collision orogeny will be reflected in the arc-shaped mountain chain around the ocean margin formed in the early stage, it has long been combined on the continent as the main body of the arc-shaped mountain chain around the ocean margin, and together with the passive continental margin fold-thrust nappe orogeny, it forms the land-land collision orogenic belt. For example, Gangdise Mountain of the continental margin arc type and the Himalayas of the passive continental margin fold-overthrust nappe type together form a land-land collision composite orogenic belt. ③ Land-arc collisional mountain system. This is an orogenic belt formed by the collision between a mountain chain in the island arc zone and a microcontinent. There is a marginal ocean basin between the island chain and microcontinent, and the core of its mountain system is a back-arc-basin subduction zone. For example, Taiwan Province coastal mountain orogenic belt, North Qilian Mountain and Middle Qilian Mountain of Qilian Mountain belong to this kind of arc-land collision orogenic belt. ④ Arc-arc collision orogenic belt. This refers to the orogenic belt formed by the collision between the island arc mountain chain and the island arc mountain chain due to the closing of the ocean basin and the two arcs of the two-way subduction. These types of mountain systems will be formed after some marginal seas in the western Pacific Ocean disappear. Such mountain systems will be formed by the collision between Mariana Arc and Ryukyu Arc after the Philippine Sea is closed. Maluku Sea is an example of arc-arc collision orogeny in action in modern times. Arc-arc collision orogenic belt is formed by the collision between Cretaceous Gangdise Arc and Bange-Bengcuo Accretionary Arc.

3.2 Types and Spatio-temporal Structure of Orogenic Belt in Sanjiang Area

Our years of research revealed that the spatial and temporal structure of Hengduan Mountain Orogenic Belt is mainly as follows: ① It was based on the evolution of MABT on the northwest side of Paleo-Tethyan Ocean from Late Paleozoic to Triassic, and it had experienced subduction orogeny, arc-arc or arc-land collision orogeny and intracontinental subduction in the middle and late stage of Mesozoic to intracontinental strike-slip contraction orogeny in Cenozoic since Triassic; ② from the perspective of three-dimensional geometry, the four backbone collision junction zones and the landmasss or volcanic arcs sandwiched between them show a reverse s-shaped tectonic framework with the waist in the middle being contracted and two members being scattered from north to south; ③ the sectional structure shows the Lancang River Junction Zone and Taniantaweng Island Arc Orogenic Belt, Jinsha River Junction Zone and Ningjing Mountain-Ailaoshan Arc-land Collision Orogenic Belt are of fan-shaped mountain system, while Qamdo-Markam and Lanping-Pu’er Depression Zones in the southern member between two recoil fan-shaped mountain systems of Jinsha River and Lancang River form a hedged strike-slip fan-shaped mountain system (Fig. 3.1). Although the spatial and temporal structure and evolution process of “Hengduan Mountain” Orogenic Belt are very complicated, the geometry of the orogenic belt located at present is concise and clear.

The Sanjiang area in southwest China has experienced the subduction and closure, collision and orogeny of Proto-Tethys, Paleo-Tethys and Meso-Tethys, especially the Yanshanian-Himalayan orogeny stage due to general intracontinental convergence (or over-collision), which is a complex orogenic belt with various orogenic types. According to the above-mentioned classification scheme of orogenic belt types, the classification of orogenic belt types and its temporal and spatial structure of Hengduan Mountain area in Sanjiang are described as follows from east to west.

3.2.1 Continental Margin Orogenic Belt of Bayankala (Longmen Mountain and Jinping Mountain) in the Western Margin of Yangtze Landmass

The mountain system was transformed from Late Triassic passive continental margin system on the western margin of Yangtze Landmass to the fold-overthrust nappe-type mountain chain of foreland basin. The whole land-arc collision orogenic belt was formed the period from the end of Triassic to Cretaceous, which was further developed in Paleogene, as evidenced by the development of a large number of Yanshanian and Himalayan crustal melting granites and the formation of Western Sichuan Foreland Basin. The overall shape is an asymmetric mountain zone with a noncoaxial shear and eastward thrust nappe stack.

3.2.2 Shaluli Mountain Arc-Arc Collision Orogenic Belt

The main body of this orogenic belt is the island arc orogenic belt, which is a composite orogenic belt formed by the westward subduction, destruction and closing of Ganzi-Litang Back-arc Ocean Basin at the end of Late Triassic, subduction and shrinkage of the continental margin on the western margin of Yangtze Landmass and Changtai-Xiangcheng intra-arc rift basin and collision between Que’er Mountain-Haizi Mountain Magmatic Arc and Yidun Volcanic Arc Mountain Chain and between Que’er Mountain-Haizi Mountain Magmatic Arc and Zhongza-Shangri-La Block. As rock strata and island arc mountain chain on the west side of Zhongza-Shangri-La Block generally thrust eastward, the orogenic type is an asymmetric mountain zone with noncoaxial shear. However, due to the westward thrust of Haba Snow Mountain and Yulong Snow Mountain on the east side and the eastward thrust of Shangri-La Block, the hedged mountain chain type is formed in its southern member (Fig. 3.2). During the Late Cretaceous-Eocene, a sequence of transitional alkaline granites invaded from the post-orogenic belt to the nonorogenic belt.

3.2.3 Ningjing Mountain-Ailaoshan Land-Land and Land-Arc Collision Orogenic Belt

This is a complex orogenic belt, showing different types in different zones. In the middle-south member of Jinsha River, namely Zhubalong-Pantiange area, due to the development of an Early Permian intra-oceanic arc, a Late Permian continental margin arc is developed in Jiangda-Weixi on the west side. Therefore, the land-arc collision orogenic belt formed by the collision of Zhongza-Shangri-La Landmass and Zhubalong-Pantiange intra-oceanic arc and the land-arc collision mountain belt formed by the collision of intra-oceanic arc and continental margin arc in the west side were formed after the closure of the ocean basin in the middle-south member. In addition, a mountain chain formed after the closure of Late Triassic rift basin was developed in the Xuzhong-Luchun-Cuiyibi area, which forms the Yunling Mountain Range together with the continental margin arc mountain chain. Therefore, the middle-south member of Jinsha River is a composite orogenic belt.

No intra-oceanic arc was found in the northern member of Jinsha River Zone, and Zhongza-Shangri-La Landmass directly collided with Qamdo Landmass, forming Ningjing Mountain land-land collision orogenic belt. The mountain zone was formed earlier than the middle-south member; for Early Triassic Pushuiqiao Formation had unconformably overlaid on Jiangda collision crustal melting granite body.

Like the northern member of Jinsha River Zone, no intra-oceanic arc was found in Ailaoshan Zone, which forms Ailaoshan land-land collision orogenic belt. That said, the passive margin overthrust nappe-type mountain chain of Yangtze Continent and Taizhong-Lixianjiang continental margin arc-type mountain chain constitute the land-land collision orogenic belt.

The outstanding features of Ningjing-Ailaoshan Orogenic Belt are as follows: ① The crust on the subduction plate, melange in the junction zone and the volcanic-sedimentary strata on the volcanic arc overthrusts backward in the direction of the superimposed plate in turn, forming a wedge-shaped mountain chain with subduction in the lower part and obduction in the upper part. For example, in the south-central member south of Batang in Jinsha River Zone, Cambrian-Ordovician strata and Devonian-Carboniferous strata on the subducted Zhongza-Shangri-La Landmass thrust westward on the passive margin rock stratum of Jinsha River Zone, or even on the melange zone in the junction zone, showing reverse polarity orogeny (Figs. 3.3 and 3.4). The strata in Permian–Triassic arc volcanic zone in the west thrust westward on Mesozoic red beds in Qamdo-Pu’er Basin (Figs. 3.2 and 3.5). In Southern Diancang Mountain-Ailaoshan Zone, Cangshan Group and Ailaoshan Group in the crystalline basement of Yangtze Landmass thrust westward (or southwestward) on the melange (Fig. 3.6) and volcanic arc zone of the junction zone and cover the junction zone and volcanic arc zone in Yangbi-Midu area. However, in Xiongsong of Eastern Tibet and Tuoding-Tacheng of Western Yunnan, the folds and thrusts on the passive continental margin, which thrusted eastward, were formed in the early subduction and collision stage, were not reworked due to the later deformation but preserved and can still be found at the lower part and the frontal margin the east nappe. ② A sequence of calc-alkaline volcanic rock series was developed, and intermediate-acid magmatic rocks were invaded in the post-orogenic stage of Late Triassic.

The main mountain ranges of this collision orogenic belt include Aila Mountain, Chali Snow Mountain, Yunling Mountain and Xuelong Mountain of Eastern Tibet and Western Yunnan in its west, Baiyu-Batang-Derong (such as Gajin Snow Mountain) of Western Sichuan and Western Yunnan in its east, the snow mountains on the west side of Shangri-La and Diancang Mountain and Ailaoshan in its south.

The Jinsha River-Ailaoshan Ocean subducted westward in the Late Permian and closed in the Early and Middle Triassic, and the volcanic arc mountain chain on the continental margin was formed in the period from Late Permian to Triassic. Collisional orogeny occurred in Mesozoic. The thrust zone composed of crystalline basement rock series in Diancang Mountain and Ailaoshan was mainly formed in Paleogene-Neogene; that is, the primary peaks of the two mountains were formed in Paleogene-Neogene.

3.2.4 Taniantaweng Residual Arc-Land Collision Orogenic Belt

The orogenic belt was formed by the eastward subduction of back-arc oceanic crust and closure of ocean basin of Paleo-Tethys Lancang River, continental-arc collision between Qamdo-Pu’er Block and Dongda Mountain-Lincang Magmatic Arc. This orogenic belt was not only formed at the same time as Jinsha River-Ailaoshan Orogenic Belt, but also had the same tectonic deformation and mountain chain shape (wedge-shaped), while they had opposite direction. That said, the upper crust of the subduction plate on the west side reversely obducted eastward on the Qamdo-Pu’er Block of the superimposed plate.

A back-thrust spreading foreland basin is also formed at the front margin of the thrust zone, that is, Qamdo-Pu’er back-thrust spreading foreland basin shared with Jinsha River-Ailaoshan Orogenic Belt (Figs. 3.2, 3.5, 3.7, 3.8 and 3.9). At the same time, their magmatic activities are similar. A sequence of calc-alkaline volcanic rock series was developed outside the original volcanic arc zone in the post-orogenic stage and high-potassium shoshonite was found.

It is worth mentioning that an abyssal sedimentary basin was developed in the period from Carboniferous to Permian in Xiaohei River in the west of Yunxian-Puer-Zhendong of Yunnan. The southern extension member of the basin is likely to be connected with the small ocean basin represented by the ophiolite zone in the Nan River Area in the north of Thailand. If so, this small ocean basin may have been a back-arc-basin formed by the eastward subduction of the Lancang River Ocean in Permian. Therefore, the Southern Lancang River Zone may have been a land-arc collision orogenic belt, while the Northern Lancang River-Ulaan-Uul Lake zone is a land-land collision orogenic belt. This orogenic belt experienced orogeny again in the Yanshanian-Himalayan super-collision stage. The main mountains include Ulaan-Uul Mountain, Taniantaweng Mountain and part of Nu Mountain.

3.2.5 Meri Snow Mountain-Biluo Snow Mountain Arc-Land Collision Orogenic Belt

The orogenic belt was formed by the eastward subduction of the oceanic crust in Mali-Bitu and Changning-Menglian Zone in its south as well as the closure and collision of the ocean basin, that is, the collision between Jiayuqiao residual island arc and Zuogong-Baoshan Block. Due to large-scale eastward thrust and coverage of Gaoligong Mountain, there are different opinions on whether there are ocean basins between Bitu Ophiolitic Melange Zone and Changning-Menglian Zone, but the sea areas are connected between them, that is, there is an abyssal trough between them. The time of oceanic crust subduction and collision orogeny is roughly the same as that of Ulaan-Uul Lake-Lancang River Zone, namely the period from Late Permian to Triassic, and the subduction and collision orogeny was intensified in the Paleogene.

This collision orogenic belt is connected to Chongshan Metamorphic Zone in its south, and Chongshan Metamorphic Zone is characterized by a significant strike-slip ductile shear zone, and the melange zone which may be a tectonic pattern of the composition of Changning-Menglian Zone and the subzone of Lancang River Zone. Baoshan Block on the west side of Changning-Menglian Zone collided with Lincang Island Arc on the east side, forming a noncoaxial asymmetric fold-overthrust nappe orogenic belt on the eastern passive margin of Baoshan Block. Its basic characteristics are similar to those of the passive continental margin orogenic belt on the west side of Yangtze Landmass. Its foreland zone is composed of Shuizhai-Muchang Mesozoic Foreland Basin, while Ximeng Metamorphic Core Complex is outcropped in its rear margin due to spreading and splitting (Liu et al. 1993). The mountains formed include Laobei Mountain, Bangma Mountain and Ximeng Mountain. Due to the eastward thrust nappe in the east, a fan-shaped pattern will be formed when jointing with the mountains in the Lincang-Menghai area in the east. This fan-shaped pattern can also be found in the Wayao-Caojian-Liuku area at the north end of Baoshan Block and Chongshan area in the east. Its magmatic activity is characterized by the development of a sequence of Cretaceous boron-rich granite zone in the passive margin orogenic belt on the east side of Baoshan Landmass, which may be mainly formed in period from Triassic to Paleogene, and the mountain chain shape is generally asymmetric due to noncoaxial extrusion, that is, the super-posed mountain system with eastward thrust nappe is formed.

3.2.6 Boshula Ridge-Gaoligong Mountain Frontal Arc-Land Collision Orogenic Belt

Dingqing-Basu-Santaishan Ocean Basin (i.e., Bangong Lake-Nujiang River Ocean) subducted and closed toward the south and west, causing the Gangdise island arc to collide with Zuogong-Baoshan Landmass and then forming an arc-land collision mountain system. The member in this area refers to the area east and south of Dingqing. The famous Tanggula Mountain and Boshula Ridge are formed in the north member, and Gaoligong Mountain Range is formed in the south member, which were mainly formed in the Late Cretaceous-Paleogene.

The shape of the mountain chain varies in different areas. As mentioned above, Gaoligong Mountain is an asymmetric mountain chain, and Liuku-Mengga foreland basin was formed in its foreland-Baoshan Landmass (Liu et al. 1993), and Zuogong Late Triassic Foreland Basin was formed in Jitang Landmass, showing a passive continental margin fold-overthrust nappe orogenic belt. In the Basu area, the upper crust of the subduction plate on the north side reversely obducts southward to form a wedge shape on the superimposed plate, and Boshula Ridge and Gaoligong Mountain on the south and west sides are the frontal arcs on the south side of Tethyan Ocean, in which a sequence of tin-bearing crust-melting granite is developed to constitute the main tin ore zone in western Yunnan. Calc-alkaline volcanic activity occurred in the Tengchong area during the Neogene post-orogenic stage.

3.3 Sanjiang and “Hengduan Mountain” Orogenic Process and Dynamics

Due to the spreading of the Indian Ocean, the Indian plate continuously pushed toward the north, thus the collisional deformation pattern of Qinghai-Tibet Plateau since 50–60 Ma varies in terms of material movement states, kinematics and dynamics characteristics in different time periods, different parts of the crust and different levels of three-dimensional transformation process of lithosphere. Qinghai-Tibet Plateau is dominated by intracontinental strike-slip orogenic belt of Cenozoic Hengduan Mountain in the southeast part, borders the “Namjagbarwa Mountain Tectonic Junction Zone” at the northeast end of Indian plate in the west, connects to the western margin of Yangtze Landmass in the east and finally rotates clockwise in the north–south direction to form a strike-slip and is longitudinally faulted in the east–west Tethyan orogenic belt. The topography, tectonic deformation pattern and geodynamics are obviously different from those in the interior, the west and the north of the plateau. It is of special significance to study the collisional deformation, kinematics, collision dynamic mechanism of Qinghai-Tibet Plateau on its lateral collision effect and spatial and temporal difference, continental collision process, crustal spreading process and the coupling relationship between the deep development process and the dynamic change of the crust surface.

3.3.1 Global Plate Tectonic Setting of “Hengduan Mountain” Orogenic Process

From the perspective of global tectonics, the large-scale Alps-Himalayan Tethyan orogenic belt runs from east to west and then bends eastward and connects Cenozoic MABT in South Asia through Sanjiang Hengduan Mountain-indosinian peninsula arc. By taking Hengduan Mountain-Taima intracontinental north–south orogenic belt as the hub, completely different orogenic processes are shown in both the east and west sides. The southeast side is characterized by the evolution of the Cenozoic MABT in South Asia, which is controlled by the northward subduction of the Indian Ocean. Indonesia frontal arc is distributed in an arc shape and near E-W direction. Subduction, volcanic arc uplift, back-arc spreading, micro-landmass splitting, back-arc and foreland thrust, strike-slip, arc-land and arc-arc collision and other geological events occurred in Cenozoic.

The west side of Hengduan Mountain and the northern margin of India Landmass connecting Indian Ocean created the Cenozoic Himalayan orogenic belt after Gangdise arc-arc collision orogeny in the early stage of Late Cretaceous, subsequent collision with the Asian Continent and continuous intracontinental subduction. As a north–south transform fault, Ninety East Ridge of the Indian Ocean may play a role in regulating the different subduction collisions of the east and west sides, while it is characterized by different types of intracontinental deformation in the part extending into the interior of the continent, such as Hengduan Mountain strike-slip transition, rotational extrusion and extensional detachment, which are widely deformed in the north–south direction. The continuous northward extrusion of Indian Plate caused significant shortening and thickening of Himalayan-Gangdise crust; in addition, the passive impedance of lithosphere of Yangtze Landmass caused the dynamic imbalance between them, forming special strike-slip transformation form of Hengduan Mountain intracontinental orogeny. This transformation and convergence strain includes the westward overthrust nappe of India-Myanmar Naga Mountain in the west of Hengduan Mountain in Sanjiang, which extends to Longmen Mountain-Jinping Mountain area in the east.

3.3.2 Basic Characteristics of “Hengduan Mountain” Orogeny

“Hengduan Mountain” Orogenic Belt is one of the most complex orogenic belts in the world. Since the 1990s, many achievements have been obtained in the study of strike-slip transformation deformation of Hengduan Mountain zone caused by the collision between India Plate and Asiatic plate at home and abroad (1995). Hengduan Mountain Zone is characterized by tectonic patterns due to the oblique collision between the Indian Plate and Yangtze Landmass, such as significant thrust, overthrust nappe and strike-slip rotation; in addition, the associated pull-apart basin tectonics was formed in this zone.

3.3.2.1 Thrust Tectonics

After the collision between continents, the tectonic pattern was superimposed and Sanjiang Hengduan Mountain Zone was dominated by an asymmetric strike-slip thrust tectonic pattern with Qamdo-Markam-Lanping-Pu’er Basin as the central axis under the action of continuous shortening and extrusion of the crust (Fig. 3.8). According to the main marginal oblique overthrust zone and its fold-thrust sheet, the characteristics of both sides of the thrust tectonic are briefly described as follows.

3.3.2.1.1 Thrust Sheet with Westward Overthrust Nappe in the East

3.3.2.1.1.1 Haba Snow Mountain-Diancang Mountain-Ailaoshan Thrust Sheet

Cangshan Group and Ailaoshan Group in Yangtze Basement and Paleozoic strata overlaid on it thrust westward and southwest on Mesozoic and Cenozoic strata in Lanping-Pu’er Basin. This overthrust event mainly occurred at the end of Paleogene, showing that Yangtze Triassic limestone overthrust to the southwest on Paleogene red bed in Jinding Lead–Zinc Deposit. This event also caused the tectonic stratigraphic units in Yidun Island Arc Zone, especially in the southern end of Ganzi-Litang Junction Zone, to be covered and pinched out.

The eastern part of Lanping Basin is located in Weixi-Lanping-Yunlong, and Mesozoic strata in the basin overthrust westward on Paleogene red beds. Li et al. (1999) divided it into two thrust nappe schists: Huachang Mountain thrust schist and Tongdian-Madeng (and its southern area) thrust schist. ① Huachang Mountain thrust schist system was formed by Huachang Mountain thrust fault thrusting Upper Triassic limestone on the east side westward on Paleogene and Neogene strata. In the east and northwest of Hexi Township, Lanping County, limestone (T₃) of Sanhedong Formation covers Yunlong Formation of Paleogene and Neogene and Cretaceous strata. The northward extension of Changshan Fault is cut by the NW-trending Weixi-Qiaohou fault or covered under the thrust schist of the volcanic-sedimentary rock zone on the west side of Jinsha River tectonic zone and connects with Bijiang River fault to the south. ② Tongdian-Madeng Thrust Schist. This thrust schist is on the west side of Tongdian-Madeng and its southern area and is mainly composed of rock strata of Upper Triassic Sanhedong Formation and Maichuqing Formation, which thrust westward on Middle Jurassic to Cretaceous strata. A sequence of detached blocks mainly composed of Upper Triassic strata is developed in Tongdian-Longtang-Wenshuimiao-Jinding Deposit, which is covered on Jurassic, Cretaceous, Paleogene and Neogene strata. Drilling in Jinding Lead–Zinc Deposit revealed that the stratigraphic sequence in the detached block composed of Mesozoic strata are inverted, indicating that they were once an inverted limb of an inverted or flat fold and suggesting that there are folds and thrusts inverted from east to west. The thrust zone is also cut by Weixi-Qiaohou Fault to the north.

3.3.2.1.1.2 Zhongza-Shangri-La Thrust Sheet

The sedimentary facies and biological features of Paleozoic strata of Zhongza-Shangri-La Landmass are similar to those of Yangtze Landmass, so it is a micro-landmass split from Yangtze Plate. In the Triassic, the back-arc oceanic crust of Jinsha River subducted westward and collided with the Qamdo Landmass. Influenced by the collision between Indian and the Asian continents, the Paleogene stratum is dominated by a large-scale thrust sheet that thrusts westward from Zhongza to Shangri-La.

The frontal fracture zone of the western thrust starts from Dongpu, Dege Country in the north, passes through Batang, Zhongza, Derong, Riyu, Nixi, Shangri-La City and Tuoding to Shigu in the south, generally extending over 600 km from north to south in the east boundary zone of Jinsha River Ophiolitic Melange Zone. The thrust zone thrusts westward on Jinsha River Ophiolitic Melange Zone, in which detached block in nappe and slip nappe composed of Paleozoic limestone from Zhongza-Shangri-La Landmass can be found everywhere. Bengzha Village, Batang Country, was once considered as the unconformity between the Upper Permian stratum and the Lower Permian stratum. It is judged that the slide nappe overlaid on Jinsha River Melange Zone based on our observations on sections of three routes. Inclined overturned folds are developed in the nappe zone, and the significant tectonic mylonitization, flow cleavage and dynamic metamorphism can be found in the boundary thrust fault.

3.3.2.1.1.3 Obducted Sheet in Jinsha River Melange Zone

Obducted sheets in Jinsha River Melange Zone significantly thrust westward on Permian–Triassic Jiangda-Weixi Arc Volcanic Zone on the west side, and its frontal inclined fault is Aila Mountain-Xiquhe Bridge-Baima Snow Mountain-Gongnong fault. This sheet includes intra-oceanic arc remnants and back-arc-basin subtraction complex assemblage (Fig. 3.10). A series of thrust faults and secondary shear zones can be found in this zone. Melange contacts with Paleogene red bed thrust fault in Baimang Snow Mountain and other places.

3.3.2.1.1.4 Thrust Sheet in Arc Volcanic Zone in Jiangda-Weixi

The thrust sheet of the arc volcanic zone in Jiangda-Weixi is mainly composed of Permian–Triassic volcanic-sedimentary rock series, under which Paleozoic Ordovician, Devonian, Carboniferous and Precambrian metamorphic rocks are developed and thrust westward on Mesozoic strata in Qamdo-Lanping. It can also be divided into two sub-thrust sheets: one is Jiangda-Mangcuo-Deqin arc volcanic rock thrust sheet in the east, of which the frontal tectonics is Zixiasi-Deqin Thrust Fault and the arc volcanic rock thrust on Paleogene Gongjue red bed; the other is Qingnidong-Haitong Foreland Thrust Zone in the west.

On the basis of Early Qingnidong-Haitong Thrust Zone, the frontal area of the thrust zone in Paleogene had been represented by Ziwei-Xiangdui frontal thrust fault system through the study of regional geological mapping and comprehensive mapping with a scale of 1:200,000 in Qamdo area in the eastern part of Qamdo Back-arc Foreland Basin (as shown in Fig. 3.11). Only in the west of Gongjue Basin, regional oblique thrust zone with an extension member of more than 50 km from northeast to southwest includes: Chesuo-Canggu Oblique Thrust Fracture Zone; thermal oblique thrust fault; Jueyong-Longda Oblique Thrust Fault; Shaxie River Oblique Thrust Fault; Ziduo Oblique Thrust Fracture Zone; and its thermal oblique thrust fault; Babeng Oblique Thrust Fault; Kangba-Jinda Oblique Thrust Fault; Mangzong-Zongbu Oblique Thrust Fault; Juelong Oblique Thrust Fault; Zalong Oblique Thrust Fault; Deri-Gangda Oblique Thrust Fault; Tuoba Oblique Thrust Fault; Lado Oblique Thrust Fault; Wengda Oblique Thrust Fault; Xiama Oblique Thrust Fault; Dama (Lajila) Oblique Thrust Fault; and Ziwei-Xiangdui Frontal Oblique Thrust Fault.

A sequence of strike-slip oblique thrust faults is superimposed to the southwest in a gentle arc shape, and Paleogene anatectic hypabyssal porphyries are developed along the anticline of the oblique fold on the hanging side of the oblique thrust fault. Interfaces from Mesozoic strata in Qamdo Basin conformably overlaid on continuous marine to continental sedimentary stratum, so its tectonic deformation occurred in the Paleogene. It is closely related to the significant subduction and wedging of Indian Plate to Eurasia and the extrusion tectonic system of Qinghai-Tibet Plateau. Due to its special tectonics, the frontal faults of each thrust sheet are characterized by strike-slip and oblique thrust.

3.3.2.1.2 Thrust Sheet with Eastward Overthrust Nappe in the West

3.3.2.1.2.1 Dongda Mountain Thrust Sheet

In Riwoqê-Jitang-Dengba area on the west side of Qamdo Basin, the metamorphic rock series of Jitang Group (An∈) and Dongda Mountain Granite Zone on the west side thrust eastward on Carboniferous-Permian–Triassic strata in the arc volcanic zone. The arc volcanic zone thrusts eastward on Jurassic-Cretaceous strata in Qamdo Basin, with Lancang River Fault as its frontal fault. Accordingly, a sequence of schist which thrusts from west to east is also developed in the basin. From Rongxubing Station to the east of Zhuka, Markam Country, through Dengba, Dongda Mountain granite overthrusts eastward on Carboniferous-Permian strata, which overthrusts eastward on Upper Triassic and Paleogene red beds, and Middle and Upper Triassic strata overthrusts eastward on Jurassic-Cretaceous strata. In Zhuka-Lawu area, folds of Jurassic strata are characterized by inclined folds overturned eastward due to eastward thrust.

3.3.2.1.2.2 Thrust Sheet of Jiayuqiao Metamorphic Terrane

Its eastern margin is the Mali-Bangda-Chawalong Frontal Thrust Fault, and Paleozoic volcanic-sedimentary rock series in Xiyuqiao thrusts eastward on the littoral-neritic and marine-continental coal measure strata of the Late Triassic marginal sea and thrusts on Upper Paleogene red bed in Mali. The southwest side of the thrust sheet is developed with Luolong-Basu Thrust Fault, and Jiayuqiao metamorphic rock series is characterized by fan-shaped extrusion and uplift.

3.3.2.1.2.3 Chongshan-Lincang Thrust Sheet

In the northern member-Biluo Snow Mountain-Chongshan area, the metamorphic rocks of Chongshan Group (An∈-PZ) thrust eastward on Carboniferous-Permian strata in the arc volcanic zone. Similarly, Carboniferous-Permian strata in Lanping Basin in its front margin from west to east thrust eastward on Manghuai Formation and Xiaodixing Formation of Late Triassic. The latter thrust on Jurassic-Cretaceous strata, which thrust on Paleogene and Neogene strata, forming many detached blocks (Fig. 3.12). Finally, in Baiyangping-Yingpan-Yunlong area, Daqing Mountain-Beimang Mountain Gault thrusting eastward stands opposite Huachang Mountain-Bijiang River Fault thrusting westward on the east side of the basin. These two faults are close at hand, forming a thrust belt with Paleogene and Neogene basins as its axis.

In the Yun Country-Jinghong area in the southern member, the metamorphic rocks of Lincang Granite Zone and Lancang Group (An∈) thrust westward on Permian–Triassic arc volcanic zone, and a sequence of thrust sheets is also formed in Lincang Granite Zone. The thrust zone and detached block formed by Upper Triassic NE-treading thrust nappe is developed on the north bank of Lancang River between Yun County and Weishan in Lanping-Pu’er Basin. In Wuliang Mountain area, Wuliang Mountain Group at the basement of the basin is also involved in the thrust nappe tectonics; that is, it thrusts northeastward on Mesozoic strata.

3.3.2.1.2.4 Gaoligong Mountain Thrust Sheet

Its frontal fault is Gaoligong Mountain Thrust Fracture Zone (including Nujiang River Fault, Lushui Fault and Longling-Ruishanyu Fault). The southern member of the fault overthrusts the metamorphic rock zone (An∈) in Gaoligong Mountain Group and the granite zone of Gaoligong Mountain on Paleozoic stratum on the west side of Baoshan Block to the east.

Gaoligong Mountain Fracture Zone is the dividing boundary between Baoshan Block (the northern extension member of Shan Block) and Gangdise continental crust island arc zone in the division of Sanjiang tectonic unit in Southwest China. In the Cenozoic intracontinental deformation, it also acts as the eastern end of continental crust block and significantly thrusts the frontal area of nappe eastward, showing as a large-scale ductile nappe fracture zone. Among them, the ductile shear zone with a width of 3–4 km and the mylonite zone with a width of 1 km on the west side are found, with a dip angle of 30–60. Closed synclinal folds that overturn eastward are often found along Gong Mountain-Fugong-Longling-Luxi area. The NW-treading extension member of the northern member of the fault is connected with Jiali strike-slip fault and may also be connected with the fracture zone in Zhaxi, Basu Country, which is limited by the low degree of study and has not been verified on the spot. The middle-south member of fracture zone extends in near N-S direction, slightly bulges to the east in an arc shape, turns to the SW direction at the place near Longling and is cut by the NS-treading dextral fracture zone.

The development of horizontal lineations on the foliation of the ductile shear zone along Gaoligong Mountain Watershed and a large number of noncoaxial rotating tectonics indicate the dextral shear of the fault, with the horizontal displacement of the shear zone above 50 km. The samples of mylonite from the ductile shear zone of Baoshan-Tengchong Highway collected by Zhong Dalai et al. are used to test ⁴⁰Ar/³⁶Ar ages of biotite and muscovite, which are 14.4 Ma, 15.0 Ma, 11.66 Ma and 23.8 Ma, respectively. These deformation ages indicate that Gaoligong strike-slip deformation peak is about 15 Ma in the Miocene and 23.8 Ma in the thrust peak shortened due to collision. Zhong proposed that the forward collision between two blocks shall be shortened to a certain stage. In order to adjust the deformation space, the oblique and tangential convergence collisions should be shortened gradually, and the secondary faults in the block are detached by rotation, being characterized by strike-slip tectonics. It is worth paying attention to the viewpoint that Shan Block slides to the south and east. Since Miocene, Pliocene–Quaternary fluviatile-lacustrine sediments in the extensional basins of Tengchong-Lianghe River-Longchuan-Longchuan River area in Southwestern Yunnan and the basalt interlayer and high-potassium calc-alkaline volcanic groups are the products of strike-slip pull-apart of crustal blocks.

3.3.2.2 Large-Scale Sinistral or Dextral Strike-Slip Tectonics

3.3.2.2.1 Deformation of India-Myanmar Mountains

Xilong protrusion is wedged obliquely from east to north on the west side of the “wasp waist” tectonic knot in Hengduan Mountain. Motuo NE-trending sinistral strike-slip fracture zone is found on the north side, and Daoji dextral strike-slip fracture zone is generally used as the southern sliding interface on the southwest side. In the Indo-Burma Mountains, Paleogene gully slope sedimentary rock series in the western depression overthrust westward, and in the Mugu belt of Myanmar, there are granite, gneiss and migmatite in the middle Oligocene–Miocene, which indicates that a thermal event occurred in the middle Paleogene and Neogene, which may be caused by the westward thrust along the Lochte thrust fault, and the Lochte thrust fault is northwest to Yarlung Zangbo River. Along the Sagaing-Namming fault in central Myanmar, there has been a right-handed translation of about 430 km since Miocene. It is pointed out that the basis of this fault displacement is as follows: ① the northern end of the eastern belt of the Indo-Myanmar mountains (in Naga Mountain) and the junction zone of Dagong-Myitkyina (north of Mandalay) were connected in Mesozoic, but now they are right-handed; ② Mayedeng complex on the west side of the fault belongs to the faulted part of the Precambrian wiped valley belt on the east side; ③ the schist and quartzite of Jiesha-Ganshan Mountain were originally connected with the Mish metamorphic rock body and were staggered. Nanming fault extends from the north into Assam, also called Miyou Fault, and then intermittently extends westward into Himalayan Boundary Fault. Quaternary basalts were found in three sites on the east side of Nanming-Sagaing Fault. Pliocene–Quaternary volcanic-magmatic activities and porphyry copper mineralization occurred in Bopa and Dongtonglong in the south of Naga Mountains. There is a strong pleistoseismic zone in the northern tectonic knot of Myanmar, and the focal depth tends to increase eastward. The above statement fully demonstrates that the tectonic knots are still in the convergence effect today. Indo-Myanmar mountain belt is strongly curved, and the right rotation of the Burma Sage fault for 13 Ma leads to the expansion of the Andaman Sea for 435 km, which may be related to the clockwise rotation of South Asia to the south of the tectonic knot relative to the Indian plate, in addition to the oblique wedging of the west uplift and the westward pushing of Yangtze Landmass.

3.3.2.2.2 X-Type Strike-Slip Fault System

In the wedge of Assam in the northeast corner of India plate to the northeast, the Sanjiang Hengduan Mountain belt shows a large-scale left-handed or right-handed strike-slip structure in addition to the overlapping of crustal blocks caused by hedging and recoil in different parts. For example, Sagaing-Nanming dextral strike-slip fracture on the west side of Sanjiang Hengduan Mountain as mentioned above, with a strike-slip displacement of 430 km. At the same time, the strike-slip fault system with X-type distribution is formed on the two sides of Qamdo-Lanping block in Hengduan Mountain, Sanjiang, which regulates the strain components of the Changdu-Lanping block that are squeezed and contracted and extruded northward and southward, respectively. And the displacement of Jinping displacement body (similar tectonic stratigraphic unit to Haidong of Dali) in Ailaoshan belt, which is left-handed strike-slip by 350 km, reflects the west-to-left movement of the Yangtze Landmass.

In the eastern part of Qamdo block, Jurassic-Cretaceous strata formed a series of axial or NW-trending folds and faults, and the Eocene Gongjue strike-slip pull-apart basin formed, reflecting the right strike-slip characteristics of Zigasi-Deqin fault. The left strike-slip fault and Nangqian strike-slip pull-apart basin are mainly developed on the west side, which is characterized by the left strike-slip. Both of them reflect that Qamdo Block was split to the north due to extrusion (Li et al. 1999).

In Weixi-Qiaohou-Ailaoshan Fracture Zone on the northeast edge of Lanping-Pu’er Block, the left strike-slip fault formed a series of folds in Jurassic-Cretaceous in Lanping and Nanjian areas, which were obviously the product of this left strike-slip movement. The magnetic fabric analysis of 8 mylonite samples taken near the 95 km highway monument of Enle-Shuitang Highway shows that the easy (main) magnetization direction D = 325° and the extrusion pressure direction is 58.2°. According to the obtained anisotropy parameters of magnetic susceptibility E (flatness) = 1.06°, T (shape factor) = 0.33, P (anisotropy) = 1.25, the geometrical shape of the magnetic susceptibility value ellipsoid is a squashed ellipsoid. The easy magnetization direction is nearly horizontal, which is very close to the stretching lineation direction of 327°. Magnetic fabric research also reflects the characteristics of strike-slip deformation. The K–Ar age of the whole felsic mylonite is (18.7 ± 1.9) Ma, which is roughly similar to the ⁴⁰Ar/³⁹Ar age (20 Ma) of biotite, potash feldspar and amphibole provided by Wu et al. (1989).

On the western edge of Pu’er block, a mylonite belt with a width of tens of meters was found at the contact between Lincang granite in Xiaodixing, Yun County and Mesozoic Xiaodixing Formation, showing the right strike-slip characteristics, which corresponds to the southeast slip of Pu’er block. The interior of the block is mainly characterized by the formation of a series of Paleogene and Neogene strike-slip pull-apart basins, such as Yunlong Basin, Zhenyuan Basin, Jiangcheng-Mengla Basin, Weishan Basin and Jingdong Basin. In the Paleogene and Neogene of Zhenyuan Basin, there are folds with axial near east–west and slightly northward inclination, which indicates that strike-slip is still going on after the deposition of Paleogene and Neogene. Paleomagnetic data show that Zhenyuan was in the Cretaceous period about 3 north of today, which further proves that Pu’er block was pushed away from southeast. The mineralization of Jinding Lead–Zinc Deposit in Lanping is closely related to the geological background of this extrusion-detachment and induced surge of ore-forming materials.

3.3.2.2.3 Strike-Slip Tectonics on the East Side of Hengduan Mountain

The eastern edge of Hengduan Mountain is adjacent to the Longmen Mountain-Jinping Mountain Overthrust Zone, connecting with the West Qinling Mountains in the north, curving through Muli in the south and connecting with the Sanjiang belt on the west side of Yulong Snow Mountain. With a total length of nearly 1000 km, it is composed of a series of imbricate thrust sheets, nappes and metamorphic base blocks (Yu 1996; Xu et al. 1992). Longmen Mountain-Jinping overthrust orogenic belt was a continuous complex tectonic belt in the middle and late Mesozoic. Because of the displacement of thrust fault and large-scale strike-slip, two adjacent tectonic units rotate relatively and the development of Daxiangling structural knot, the continuity between them becomes blurred. Among them, the oblique cutting of Xianshuihe strike-slip fracture zone is the main reason that the eastern edge of the plateau is divided into two zones.

As shown in the tectonic map, affected by Xianshui River Fault Zone, the sinistral shear dislocation occurred between Longmen Mountain Thrust Zone and Jinping Mountain Thrust Zone; however, by which we cannot judge that the thrust zone in the eastern plateau was formed first and then was dislocated and split by Xianshuihe Strike-Slip Fault. Both of them were formed at the same time along with the strong uplift of the Qinghai-Tibet Plateau in Cenozoic. They are the Bayankala trough-shaped tectonic unit in the east of the Qinghai-Tibet Plateau and the Sichuan-Yunnan rhombic fault block on the southwest side of the Qinghai-Tibet Plateau, which both slide to the south and converge with Yangtze Block to the west. On the one hand, a huge Longmen Mountain-Jinping Mountain overthrust belt is produced. On the other hand, the sliding rate of Sichuan-Yunnan fault block to the southeast is higher than that of Bayan Har area to the east, resulting in the left-handed sliding nature of its boundary fault. At the same time, the emplacement of Zheduo Mountain-Gongga Mountain syntectonic granite occurred, with the main age of 10–15 Ma (Yu 1996). A series of alkali-rich hypabyssal granite porphyries, monzonitic porphyries and syenite porphyries of Himalayan crust-mantle mixed source are known in Muli-Yanyuan and Ninglang-Binchuan areas where the main boundary fault extends to the south. Their isotopic ages are 35–65 Ma, and rock formations and beds intrude into the Upper Triassic and Paleogene strata, respectively, and some intrude directly into the boundary fracture zone. This kind of magmatic rock formed at the same time as nappe tectonic belt may be closely related to the dynamic process of “up-thrusting and down-thrusting wedge” in which the lower crust in the eastern part of the plateau wedged into the Yangtze continental crust and the upper mantle and the middle and upper crust overthrusted onto the Yangtze Landmass (Yu 1996).

Like the Himalayan orogenic belt, Longmen Mountain-Jinping Mountain overthrusts eastward, while a large-scale extensional detachment takes place at the rear edge (western edge). The extensional structure is characterized by the formation of Wenchuan-Maowen ductile shear zone, the bending of intestinal strata with gravity detachment and the development of large recumbent folds. And more than 20 dome-shaped deformations and metamorphism with different sizes have been divided into metamorphic core complex, magmatic core complex and structural dome according to their structure, composition and mechanism. The fission ages of apatite obtained from Pengguan metamorphic complex and Baoxing metamorphic complex in Longmen Mountain are 4.3–18.2 Ma. The ⁴⁰Ar/³⁹Ar sealing temperature age of amphibole and biotite at the upper limit of fast cooling time of Danba gneiss dome is 20 Ma (Xu et al. 1999). The ages of amphiboles around Xuelongbao Metamorphic Core Complex range from 25 to 30 Ma (Xu et al. 1992, 1999), for example, the age of uplift of the Qinghai-Tibet Plateau, exhumation inversion of the metamorphic complex and formation of Longmen Mountain-Jinping Mountain Thrust Zone is between Oligocene to Miocene, which is completely consistent with the syntectonic magmatic activity, the detached block overlying on the omnidirectional anticlinal limb with Paleogene red bed as the core before the formation of Longmen Mountain and geological records of no orogenic unconformity in strata after the formation of Phanerozoic strata in the middle-southern member of Longmen Mountain. However, the shortening range of the earth’s crust is very small, the height difference between the mountain range uplift and the Sichuan Basin is over 4000 m, and the landscape of Hengduan Mountain falls slowly from north to south. The research on the coupling relationship between these geomorphic surface processes and deep tectonic processes will be an important direction for further research in the future.

3.3.2.3 Extensional Detachment Tectonics

It refers to the detachment fault formed by detachment lithosphere extension, including detachment fault in the process of metamorphic core complex formation and anti-slip normal fault caused by gravity potential at the rear edge of large-scale overthrust nappe structural belt. Anti-slip normal fault was often accompanied by the metamorphic core complex. The former is the cause of the latter, while the latter is the consequence of the former. The large extensional detachment faults or anti-slip normal faults in Sanjiang area are mainly formed at the rear edge of large overthrust nappe, such as the anti-slip normal faults and basin-range structures in Tengchong-Yingjiang area of the rear edge of Gaoligong Mountain thrust belt, the anti-slip normal faults at the rear edge of Lincang-Lancang nappe, the extensional detachment faults and basin-range structures in the eastern edge of Ximeng Group metamorphic core complex and Diancang Mountain metamorphic core complex and its detachment faults. This paper focuses on the Ximeng metamorphic core complex.

Ximeng Metamorphic Core Complex is located in the backland area of Gengmadashan fold-thrust zone on the eastern margin of Baoshan Block. Ximeng Group is outcropped in dome shape, ranging from Laojiezi Formation and Pake Formation in the core to Wangya Formation and Yungou Formation in the margin. Its metamorphic grade has changed from amphibolite facies to greenschist facies, and the sericite chlorite zone of greenschist facies is outcropped in the outermost margin and has been subjected to retrogressive metamorphism. There is a detachment fault between the dactylic erosive prism or mica plagioclase gneiss in Laojiezi and the mylonite marble in Pake Formation, and its tension lineation is southeast or east–west, and Ximeng tin deposit is located in this detachment fracture zone. Pake Formation was in contact with Wangya Formation by normal fault, and a sequence of normal faults tilting eastward or southeastward was developed to the east from the interior of the core complex. The larger faults include Wanggong Fault, Kuanghai Fault, Dabannang Fault and Kelai Fault. According to the research of Li et al. (1999), a series of faults with different sizes is also developed in Mengjiao, Cangyuan and the Ordovician-Carboniferous in Taierbu, Lancang.

On the north side of Laochang Mining Area, the basalt was reduced to only a few meters thick due to the stripping fault between the carbonate rocks in Middle and Upper Carboniferous strata and the basalt of lower Carboniferous strata and formed a traction fold together with the underlying Devonian sandstone. The bottom of carbonate rock is obviously broken, and this stripping fault extends southeastward into Laochang mining area, where some ore bodies of Laochang lead–zinc mine are located in the fracture zone between basalt and carbonate rock. Carbonate rocks have been mylonite in the waste slag of the tunnel, and sheath folds can be seen in large mylonite blocks. We measured the fluid inclusion temperature of carbonate mylonite at 350–370 °C, the pressure of 1600 × 10⁵–1400 × 10⁵ Pa and the ore-forming temperature of Laochang lead–zinc mine at 200–520 °C, which are close to each other. The measured temperature and pressure of the fluid inclusions in felsic mylonite in Laojiezi Formation of Ximeng Group are 460–520 °C and 2750 × 10⁵ Pa, respectively, which is obviously much higher than that of carbonate mylonite formation in peripheral Laochang area, indicating that the temperature and pressure decrease outward from the core complex and reflecting the different formation depths or levels of mylonite (Li et al. 1999). The formation of metamorphic core complex was accompanied by acid magma intrusion, resulting in the formation of large and small Sama rock bodies and outcropping of concealed granite porphyries and quartz granitic thin vein containing disseminated chalcopyrite by drilling holes in Laochang lead–zinc mine area. The age of the large and small Samas and granite porphyries is about 50 Ma. The initial strontium isotope ratio of granite porphyry is 0.7113, belonging to crustal melting granite. The general buried depth of rock mass is large in southeast and small in northwest, which is consistent with the western uplift of the metamorphic core complex.

At the same time, the Jurassic extensional faulted basins in the north–south direction are developed on the east and west sides of the Ximeng metamorphic core complex, forming a basin-range tectonic framework with alternating basins and mountains. In the middle basin, there is a sequence of red molasse formations from Middle Jurassic to Lower Cretaceous, and there are coal-bearing formations in Paleogene and Neogene inter-mountain basins in some places. According to the development period of basin-ridge structure, the extensional detachment fault started in Jurassic during the multi-island arc-land collision orogeny, and the emplacement of many Yanshanian crust-melting granite bodies in this area may be related to this action. This effect lasted until Paleogene and eventually led to the structural stripping of Ximeng Group. The absence of crust in this belt may also be the result of this detachment fault. The formation of Ximeng metamorphic core complex was caused by the tensile collapse of the rear edge of nappe belt, that is, the east side of Gengma Mountain. The delamination and detachment of the crust caused by this tensile collapse may further promote the formation and development of the back-edge thrust fault of Lincang-Jinghong Island Arc Zone and Lancang River thrust fault.

Ximeng metamorphic core complex is on the same tectonic belt as the metamorphic core complex on the eastern edge of Shan block discovered in 1997 on the west side of Chiang Mai, Thailand, in the south. There is a large area of granite basement in the metamorphic core complex in Chiang Mai area. From this point of view, there is probably a large granite base lurking under the Ximeng metamorphic core complex, and the large and small Sama rock bodies, the hidden rock bodies in Laochang lead–zinc mine area and the hidden rock bodies implied by Xinchang skarn-type lead–zinc mine are just the rock branches protruding upward from their rock bases. Therefore, the intrusive activities and stripping faults of the latent bedrock and its branches accompanying the formation of metamorphic core complex play an extremely important role in the formation of tin, copper, lead and zinc minerals in Ximeng area. The buried granite (porphyry) rocks in the deep part of the factory should pay attention to looking for copper, molybdenum and other deposits.

3.3.3 Stress Field and Kinematic Model of Intracontinental Deformation After Hengduan Mountain Collision

3.3.3.1 Division of Deformation Zones

The analysis of Cenozoic stress field and kinematics is based on the field data in eastern Sichuan, Tibet and Western Yunnan (Fig. 3.13). The deformation in the late Cenozoic can be divided into four zones, which are separated by weak deformation zones and have obviously different forms of kinematics and stress fields (A, B, C and D in Fig. 3.13). ① The Pailong-Basu-Nujiang River dextral fault system in the northeast of Nanjiabawa structural junction, the principal compressive stress δ₁ is distributed radially around this structural junction. ② The middle part of Jinsha River-Ganzi conjugate fault system is located between Nanjiabawa structural junction and Gongga structural junction at the western end of Longmen Mountain. The principal compressive stress δ1 is east-northeast and the minimum compressive stress δ3 is northwest-southeast. ③ Xianshuihe sinistral fracture zone is on the west side of Longmen Mountain. It is a strike-slip fault extending from Tibet to Yangtze, passing through the end of Longmen Mountain fault and connecting with Xiaojiang fault system. δ1 and δ3 are roughly east and north, respectively. From the strike-slip fault of Xianshuihe in the west to the nappe fracture zone of Longmen Mountain Zone in the east, the stress field also changes clockwise from west to east. ④ Longmen Mountain Nappe Fold Zone, δ1 and δ3 directions are NW and NE, respectively.

In the central part of eastern Tibet, western Sichuan and northern Yunnan, the most obvious feature of neotectonic activity is the NW–SE stretching from eastern Tibet to western Sichuan. (Batang-Litang Fracture Zone, Xianshui River Fracture Zone) is characterized by east–west stretching and north–south nearly horizontal and vertical shortening in the south, resulting in the north–south belt of Sichuan and Yunnan and the north–south strike-slip pull-apart basin in western Yunnan.

3.3.3.2 Stress Field and Kinematics Model

According to the development characteristics of strike-slip fault system and the stress field data obtained from the analysis of epicentral mechanical mechanism and geometric and kinematic data of large-scale faults in the area (Fig. 3.14a), we will discuss two late Cenozoic deformation modes: ① Elastic mode (Fig. 3.14b). Between the flank of Nanjiabawa and Gongga structural junction at the western end of Longmen Mountain, the track of principal stress is similar to the stress field distribution of the compressed rigid plate, and there is an expansion along the unsupported edge of this rigid plate. ② Subsequent rheological model, the kinematics of the southeast Qinghai-Tibet Plateau fault can be explained by convergent streamline. This linear convergence toward the neck between the two tectonic nodes (Fig. 3.14c) reflects that the crustal material flowing out of central Tibet proliferates toward the neck between the Nanjiabawa tectonic node and Gongga Mountain tectonic node and decelerates and radially expands toward the Indosinian block on the south side. This stress field and streamline shows that the material is rotating clockwise from central Tibet to the southeast (Indo-China), but the moving speed is inconsistent, with a decreasing trend from west to east.

3.3.3.3 Regulation of Strike-Slip Transformation in Paleogene and Neogene

Jiali-Pailong fault and Jinsha River right-lateral strike-slip fault have been active since 20 Ma. According to the formation of syntectonic magmatic rocks, the neotectonic activity of Xianshuihe sinistral fracture zone can be traced back to Miocene at least, and they adjust the lateral shortening of the blocks on both sides. Paleogene and Neogene orogenies in Hengduan Mountain between Bangong Lake-Nujiang River Suture Zone and Ganzi-Litang Fracture Zone at 32° N in Eastern Tibet are dominated by dextral compression and twist, accompanied by nappe shortening. The orogenic belt presents a series of spatio-temporal structural patterns with dextral thrust or recoil fault structures. The Paleogene and Neogene kinematic forms of several laterally shortened blocks bounded by conjugate strike-slip faults indicate that apart from the near-vertical stretching, there is also the adjustment effect of strike-slip transformation. In India-Myanmar Mountains adjacent to Hengduan Mountain, Naga Mountain in the west of Shijian Fault overthrusts westward, while Gaoligong Mountain in the east of Sagaing Fault overthrusts eastward, indicating that the dextral strike-slip of Sagaing Fault has a shift and adjustment effect along the strike.

3.3.4 Dynamic Mechanism and Effect of Intracontinental Deformation After Hengduan Mountain Collision

Once the lateral extrusion model of plateau crust was proposed, it has been supported and demonstrated by many scholars, with considerable influence. With a great deal of research on crustal geology and deep geology, especially the GPS survey, paleomagnetism survey, VLBI survey and the appearance of surface geology and deep geology, many new understandings have been obtained (Harrison et al. 1992; Molnar et al. 1993; Li et al. 1995; Zhong and Ding 1996; Lv et al. 1996). Generally speaking, the characteristics of plateau uplift, such as segmentation, multi-stage and multi-factors, and deep dynamic action (gravity equilibrium, mantle plume, large-scale partial melting rheology of lower crust, plate bottom cushion, etc.) are emphasized. Typically, Owens and Zandt (1997) put forward a new understanding on the basis of a large number of geophysical achievements. They believed that the uplift of the plateau was related to these joint influences, such opposite subduction of South India Plate and Eurasian Plate in the north, and the large-scale melting and rising of the lower crust in the plateau and the underpinning of the plate bed. These understandings have had a great impact on the early representative model, the theory of double crust caused by the simple intracontinental subduction of the Indian plate and the theory of horizontal shortening and vertical thickening of the crust caused by the simple extrusion. However, it is worth noting that the above-mentioned model is mainly based on the study of the north–south large section inside the Qinghai-Tibet Plateau, emphasizing the north–south dynamic action between India and Europe and Asia, while little consideration is given to the Cenozoic geological records and deep geological data analysis in the eastern part of the Plateau. Many geological and geophysical data show that the collision deformation and uplift mechanism of the plateau must take into account the northwest subduction or intracontinental obstruction of the east Yangtze Landmass.

3.3.4.1 Deformation Mechanism in the Eastern Part of Qinghai-Tibet Plateau

In recent years, surveys from GPS, paleomagnetism and VLBI have reached similar conclusions. Since the Pleistocene, the movement rate of the Indian plate to Eurasia has been 50 mm/a, only a small part of which is absorbed by compression shortening and most of which is absorbed by the shear component dominated by strike-slip. If the simulation experiments done by Tapponnier and Molnar are correct, as they put forward, the Qinghai-Tibet Plateau will “escape” eastward along a large strike-slip fault due to a large-scale oblique collision, which will inevitably lead to a large-scale eastward migration of Yangtze Landmass, and the uplift of the Qinghai-Tibet Plateau will lose important boundary conditions. The VLBI data show that the migration rate of the Yangtze Landmass to the southeast is only about 8 mm/a. Therefore, Molnar held that the penetration of the Indian plate into Europe and Asia is mostly regulated by the thickening of the Asian crust, and the eastward “escape” is only a small effect. However, he neglected the large-scale intracontinental subduction along the Longmen Mountain-Jinping thrust nappe orogenic belt on the northwest margin of the Yangtze plate. It may be that this subduction prevented the eastward “escape” of the Qinghai-Tibet Plateau material and formed a huge vortex structure in Hengduan Mountain orogenic belt.

The Muli-Yanyuan Cenozoic nappe in Jinping Mountain, southwest China, moved at least about 150 km to Yangtze Block. In the late stage of Longmen Mountain-Jinpingshan orogenic belt, Xianshuihe-Xiaojiang fault, which turned from north to south to northwest, split into two parts. In the early stage (20 Ma), it was a large left-handed ductile shear zone with a translation distance of 80–100 km (Xu et al. 1992). A lot of data show that Xianshuihe and Xiaojiang faults are ancient faults, especially Xiaojiang fault’s activity time can be traced back to Paleozoic. Before the Cenozoic, they were not connected with each other. Since the Cenozoic, they have been connected into one, which has transformed into a sinistral strike-slip extensional property. Four north–south sinistral strike-slip faults in central Yunnan have shifted 45 km, 55 km, 57 km and 60 km from east to west, respectively, which play an important role in controlling crustal deformation and stress distribution in this area. This situation is related to the short-range effect of the Yangtze plate on the intracontinental collision of Qinghai-Tibet Plateau.

3.3.4.2 Formation of Yunnan-Tibet Vortex Tectonics Due to Oblique Collision of Indian Continent

Recent research data show that the collision between India and Eurasia is not a simple forward collision but an oblique collision from west to east, and the oblique collision may be the most obvious in the eastern part of the plateau. According to Koons’s research on the Southern Alps orogenic belt in New Zealand, the frontal collision forms a wide and slow peak-valley mountain range, while the oblique collision forms a narrow and steep peak-valley mountain range. The formation of the steep Hengduan Mountains and the Sanjiang valley in the eastern part of the Qinghai-Tibet Plateau is the important lateral effect of this collision. Several important tectonic thermal events of oblique collision were recorded. Three thermal events of 25–18 Ma, 13–7 Ma and 3 Ma–modern times have been recorded in the mineral fission track ages of granite exposed at different altitudes in several granite belts in Demula-Chayu, east of Gangdise. The peak activity times of Gongrigabu strike-slip fault in Red River in western Yunnan and eastern Tibet are 23 Ma and 24 Ma, respectively. The dextral shear of Sagaing Fault in Myanmar for 13 Ma led to the opening of Andaman Sea for 435 km, and the dextral displacement of Gaoligong fault occurred for about 100 km at 12.7 Ma. The estimated slip distance along Jiali-Pailong dextral strike-slip fault was over 200 km since Miocene (20 Ma), and the strike-slip speed of Quaternary stratum is between 10 and 2 mm/a.

Modern crustal movement in Eastern Tibet-Western Yunnan is controlled by vortex tectonic. From 1991 to 1997, we carried out a GPS survey to obtain the velocity vector direction of the modern crustal movement from eastern Tibet to western Yunnan: eastern Tibet turned east, then turned to nearly north–south direction in northwest Yunnan, and then turned to southwest direction. If Basu, Shangri-La, Lijiang, Lanping and Tengchong are considered as the inner trace of the eddy, Yajiang, Xichang and Chuxiong are considered as the outer trace of the eddy, and Kunming, Tonghai and Gejiu are considered as the periphery of the eddy, the speed of each trace is relatively close, namely the speed of the inner trace ranges from 8.38 to 17.49 mm/a, the speed of the outer trace ranges from 7.7 to 8.61 mm/a, and the peripheral speed ranges from 1.57 to 5.64 mm/a. Due to the difference of rotation speed between the inner and outer circles, there will be dextral strike-slip (such as Jiali-Pailong, Gaoligong Mountain and Jinsha River Zone), conjugate shear (Sichuan-Yunnan block) and sinistral strike-slip (Xianshuihe-Xiaojiang sinistral strike-slip shear zone) from the core to the outer circle, respectively. The core of the vortex structure is the Nanjiabawa structural knot.

Based on the explanation of focal mechanism of natural earthquakes, we analyzed the kinematics and deformation stress field of the East Himalayan tectonic junction and its adjacent areas and concluded that the movement speed of western Sichuan, eastern Tibet and Yunnan was right-handed shear and rotated clockwise relative to that of southern China, and its rotation rate could reach 1.7°/Ma. We also concluded that the Himalayan wedged northward at a speed of (38 ± 12 mm)/a and its P axis distributed around the tectonic junction in a fan shape.

The tomography study on the natural earthquakes reveals that the subducted plate of Namcha Barwa-Assam is inserted in the “horn” shape in a NNE direction, forming a high-speed anomalous body in the lower crust and the upper mantle and a NNE-trending “horn” shape within the depth of 90–300 km, which extends to the north or affects the north of 32° N. That is, the plastic vortex of material occurs between the deep high-speed body and the low-speed body, resulting in a new deep process. When the deep vortex is not in harmony with the upper crustal structure, it will be detached from the upper crustal structure, resulting in the disharmony of structure and landform and promoting the segmentation of active structures. Under the push of deep plastic rheology and the transmission of tectonic stress, corresponding geological structures will be produced, resulting in the coupling of the deep process and the upper crustal structure. Driven by the plastic rheology of deep material, the corresponding convoluted structure will be produced in the upper crust. The Yunnan-Tibet vortex is the material flow around this structural junction driven by the down-inserted subduction plate of Nanga Bawa-Assam, from the high-speed (high-density) area to the low-speed (low-density) area.

3.3.4.3 Intracontinental Subduction and Blocking of Yangtze Plate and Comprehensive Effect of the Oblique Collision of Indian Plate

The blocking effect of the Yangtze plate and the oblique collision of the Indian plate have obvious short-range effects on the eastern Qinghai-Tibet Plateau. Traces can be found from magmatic activity, mineralization, tectonic deformation and sedimentary records in this area.

3.3.4.3.1 Magmatic Activity and Mineralization

Magmatic activity is an important link to understanding the abyssal dynamic mechanism. Cenozoic magmatic activities in Qinghai-Tibet Plateau are mainly distributed in the west and southeast, corresponding to the two low-speed mantle zones in Qinghai-Tibet Plateau. The western part is mainly volcanic, with little intrusive activity; in the east, on the contrary, intrusion is the main activity. Volcanic rocks in the west are studied in detail, with obvious time–space zoning from south to north, which can be divided into three active periods: Eocene–Oligocene are mainly concentrated in Gangdise belt, and only Nangqian and Basu are distributed in the east; the Miocene was concentrated in a large area of northern Tibet, and only Jianchuan had a small amount of activities in the east; The Pliocene–Pleistocene was concentrated in Qiangtang-Kunlun and Yumen, Qilian, with only a small amount of activities in Tengchong on the south side in the east. In recent years, it has been found that Yulong, Markam and Xiaojiang fault in Xianshui River in Sanjiang area have a large number of small intrusive rock masses, which were formed in 10–50 Ma, which are consistent with the distribution of Cenozoic strike-slip pull-apart basins, accompanied by large-scale mineralization and have an inevitable relationship with the unique stress release of the intracontinental collision of Qinghai-Tibet Plateau in the eastern arc structural belt. Further research also shows that these intrusions in the eastern margin of the Qinghai-Tibet Plateau can be divided into three categories: the first category is alkali-rich porphyry of crust-mantle mixed source, which was formed in the compression environment of 35–65 Ma; the second type is mantle-derived potassium lamprophyre, which was formed in the local extensional environment during 30–40 Ma. The third type is crust-derived granite, which was formed in the compression strike-slip environment in 10–15 Ma period. Tint granite in Zheduo Mountain-Gongga Mountain (Xu et al. 1992), Chayu-Bowo Himalayan Zone may be the product of partial melting of crust caused by ductile shear.

In a word, the relationship and difference between the eastern and western magmatic activities in time and space, the change of activity nature, provenance type and the coupling relationship between the main fracture stress states in time and space all reflect the characteristics of multi-block, multi-stage and multi-factor control of intracontinental collision in Qinghai-Tibet Plateau, which is also an important part of studying the interaction and dynamic mechanism between the eastern plateau and the Yangtze plate in different stages of Cenozoic.

3.3.4.3.2 Tectonic Deformation

Tectonic deformation is the most direct dynamic manifestation of continental collision. The eastern part of Qinghai-Tibet Plateau is adjacent to the famous eastern tectonic knot in the west, the eastern boundary of Yunnan-Tibet orogeny in the east and located in the eastern arc tectonic belt of Qinghai-Tibet Plateau. It is an important member for studying the east–west tectonic transformation and the release of continental lateral collision stress to the east. The data show that the core, margin and interior and east part of Qinghai-Tibet Plateau are dominated by the north–south extrusion, the thrust nappe and the east–west strike-slip, respectively. A series of east–west depressed basins and extensional basins were formed by compression and local extensional action in the interior of the Qinghai-Tibet Plateau and the central and western regions, but they were all transformed into strike-slip pull-apart basins arranged in a geese-like manner from the east to the arc. Many data also prove that the fault system in the eastern plateau may have undergone different nature changes since Cenozoic. With Xianshuihe-Xiaojiang fault as the boundary, the NW-trending fault (such as Red River fault) on the west side has been left-handed since about 20 Ma and right-handed since Quaternary (Royden et al. 1997); in addition, the NW-trending fault of the fault to the east of Xianshui River shows that it may be right in the early stage and left since Quaternary (Molaner et al. l996). The whole active fault in the east has been restricted by clockwise vortex structure since Quaternary. Earthquakes along the Jianchuan and Lijiang-Dali lines often take place in the changing zones of crustal movement velocity. Measurements show that the movement velocities of Shangri-La, Lijiang, Lanping and Xiaguan stations relative to Chengdu railway station are 8.6 mm/a, 17.0 mm/a, 12.9 mm/a and 7.2 mm/a, respectively, and their orientations are 176°, 223°, 218° and 216°, respectively. In addition, the Xianshuihe-Xiaojiang fault cut the Longmen Mountain-Qinghe Cenozoic thrust fracture zone on the western boundary of Yangtze Block at about 20 Ma, which was just coupled with the east–west lateral deformation of this fault and the internal deformation of the Cenozoic nappe structure in Longmen Mountain experienced several important changes (Xu et al. 1992). On the one hand, these problems illustrate the characteristics of tectonic deformation in the eastern part of the plateau, and on the other hand, they also reflect the obvious short-range effect of continental collision on the eastern part of the Qinghai-Tibet Plateau. From this, we know more about the role of the intracontinental subduction of the Yangtze Plate to the northwest on the uplift of the plateau.

3.3.4.3.3 Sedimention Records

Sedimention record is an important part of understanding geodynamics. There are a series of different types of Cenozoic sedimentary basins in the eastern Qinghai-Tibet Plateau and western Yunnan, among which the foreland basin in the front of Youmenshan-Qinghe nappe and the strike-slip pull-apart basin in the north–south direction of eastern Tibet-western Yunnan are the most important ones. According to Wang Guozhi’s research on sedimentary sequence interface, sedimentation rate and sedimentation flux of Cenozoic Longchuan Basin, Gengma Basin, Baoshan Basin and Yinggehai Basin at the outlet of Red River in western Yunnan, it is found that there is an excellent correspondence with the uplift history of Qinghai-Tibet Plateau. The uplift history can be divided into five stages: the initial stage of 23–19 Ma, the rapid uplift stage of 16.2–11 Ma, the denudation and leveling stage of 11–5.3 Ma, the sharp uplift stage of 5.3–1.6 Ma and the acceleration stage of denudation and uplift of 1.6–0 Ma. This understanding is similar to the conclusion obtained by Ding et al. (1995) on the fission track of granite in Bowo, Chayu. The research on the filling sequence of sedimentary basins in eastern Tibet-western Sichuan region, especially in the western region where the mechanical properties are controlled by Xianshuihe-Xiaojiang fault, and the response of plateau uplift is rarely involved, but this problem is very important for studying the outward expansion and deformation history of Qinghai-Tibet Plateau crust.

It is worth noting that the data of petrology, geological thermometer and geological chronology of the core complex in Nanga Bawa show that the average stripping rate is (4.5 ± 1.1) mm/a since 10 Ma, and at least 14 km of material has been denuded since 1 Ma. Strengthening the study of the coupling relationship between the deep process and the crust surface action is a very important subject for the collision deformation and dynamic analysis of the Qinghai-Tibet Plateau.

To sum up, the crustal deformation in Hengduan Mountain and its adjacent areas is influenced by the intracontinental collision of India plate, Eurasian plate and Yangtze Landmass (even the influence of the Pacific plate), with a very complicated evolution process. Hengduan Mountain is the best place to study the oblique collision between India and Eurasia and the blocking effect of Yangtze Plate.

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Chengdu Center, China Geological Survey, Chengdu, Sichuan, China
Wenchang Li, Guitang Pan, Liquan Wang & Xiangfei Zhang
Institute of Geology, Chinese Academy of Geological Sciences, Beijing, China
Zengqian Hou
China University of Geosciences, Beijing, China
Xuanxue Mo

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Wenchang Li
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Li, W., Pan, G., Hou, Z., Mo, X., Wang, L., Zhang, X. (2023). Formation and Evolution of Sanjiang Collision Orogenic Belt. In: Metallogenic Theory and Exploration Technology of Multi-Arc-Basin-Terrane Collision Orogeny in “Sanjiang” Region, Southwest China. The China Geological Survey Series. Springer, Singapore. https://doi.org/10.1007/978-981-99-3652-6_3

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DOI: https://doi.org/10.1007/978-981-99-3652-6_3
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