In the early Paleozoic, on the unified "Pan-Yangtze" landmass, there were "Sinian and later sedimentary caprocks" in western Sichuan, western Yunnan and eastern Tibet. At the end of Early Paleozoic, except for some areas of Jinsha River belt, most of the land blocks on both sides of Jinsha River belt were uplifted into land. At the same time, the Caledonian movement at the end of early Paleozoic caused extensive and intense deformation and metamorphism of the pre-Devonian strata, and the Devonian system was unconformity or pseudo-conformity on the underlying strata. In the late Paleozoic, the Jinshajiang arc-basin system took Qiangtang-Tangji-Chongshan-Lancang residual arc on the west side of Changdu-Lanping landmass as the forearc, and entered a new development period on the basis of metamorphic "soft basement" in the late Silurian and early Paleozoic, and began the generation, development and evolution of the Paleotethys Jinshajiang arc-basin system. It has gone through the following stages (Figure 3-9).

Figure 3-9 Geological Evolution of Jinsha River Structural Belt

I. Rift basin stage (D)

During Devonian, western Sichuan, western Yunnan and eastern Tibet were platform deposits on the interconnected "Pan-Yangtze Block", and seawater entered the Sanjiang area from the north and south of the Jinsha River belt. Except for the Tangji-Chongshan-Lancang ancient island arc belt, which exists in Lincang ancient land and Zhunquqi ancient land (island arc mountain system) at the north and south ends respectively, both sides of the Jinsha River belt generally refuse to accept deposits, forming alluvial facies and alluvial facies. In the Jinsha River belt, Devonian may be continuously deposited on the underlying Silurian strata, and it is a shallow shelf carbonate-clastic rock formation.

The transgression area in the Middle Devonian was enlarged, and local extension and rifting occurred on the background of the open shallow continental shelf in Devonian. In Yangla-Benzhilan-Xiaruo-Tacheng area, shallow-sea facies-sub-deep-sea facies carbonate rocks and siliceous-sandy argillaceous flysch formation were formed in the rift basin, and intermediate-basic volcanic rocks erupted. During the late Devonian, the extension and rifting of the basin increased. In the rift basin with Yangla-Dongzhulin-Shigu as the central axis, semi-deep-sea deposits, represented by radiolarian chert-thick limestone-sandstone-mudstone combination, accompanied by the eruption of extensional continental tholeiite and intermediate-basic volcanic rocks, indicate that extension and rifting have deepened the seawater in the rift basin, and volcanic activities have developed, marking the formation of thinning and cracking of the landing shell.

On the west side of Jinsha River rift basin and the west edge of Changdu landmass, with the expansion of middle and late Devonian rift basin, subactive shallow-sea carbonate rocks and clastic rocks sandwiched with basic and intermediate-acid volcanic rocks were formed in Jiangda-Deqin-Weixi area. The stable landmasses on both sides of Jinsha River (Changdu landmass in the west and Zhongzan-Zhongdian landmass in the east) are platform carbonate-clastic rocks in shallow sea basin.

Second, the formation stage of ocean basin and its mineralization

Carboniferous-Early Permian is an important period for the expansion of the back-arc ocean basin of Jinsha River. On the basis of the late Devonian rift basin, the Carboniferous-Early Permian further expanded to form an ocean basin, and the evolution and development of the Jinshajiang ocean basin began. With the formation of Jinshajiang ocean basin from Carboniferous to Early Permian, Changdu landmass broke away from Pan-Yangtze landmass and formed an independent micro-landmass. In the early and middle Carboniferous and late Devonian, the rift basin continued to expand and the continental crust cracked, forming the early and middle Carboniferous Jinshajiang initial ocean basin. Volcanic, endogenous and terrigenous low-density turbidite series, represented by radiolarian chert-thick layered limestone-black mudstone-tuff combination, as well as the eruption of ridgeline basalt, are deposited in the basin, which are sub-deep-deep-sea carbonate rocks, volcanic rocks and sandy argillaceous-siliceous flysch formation.

From the late Carboniferous to the early Early Permian, with the increase of crustal detachment intensity, the Jinshajiang ocean basin expanded rapidly with asymmetric structural pattern, forming a mature ocean. The lithofacies in the ocean basin is composed of mafic-ultramafic rocks in the ocean and oceanic ridge-oceanic island tholeiite, which together with radiolarian cherts form ophiolite suite in Gajin Snow Mountain, Gongka and Jiyidu, accompanied by the formation of late Carboniferous-early Permian iron-rich manganese rocks in Gajin Snow Mountain, Yangla, Gongka, Jiyidu-Xiaruo and Xinzhong areas.

The Changdu block area on the west side of Jinsha River ocean basin is mainly composed of metastable platform deposits of basic volcanic rocks sandwiched between carbonate rocks and clastic rocks in offshore basins. The eastern margin of Changdu landmass is close to the sea basin and located in the area of Jiangda-Deqin-Asbestos Factory. With the strong expansion of Jinsha River ocean basin from middle and late Carboniferous to early Permian, marginal rift (valley) basin was formed, and extended basic and intermediate basic volcanic rocks such as carbonate slump deposit, submarine turbidite fan deposit, turbidite, radiolarian chert, isobath and shelf margin slope facies were developed. The Zhongzan-Zhongdian block on the east side of the Jinsha River ocean basin is mainly composed of stable carbonate rocks and clastic platform deposits in offshore basins, and the shelf marginal facies near the basin are metastable carbonate rocks and clastic rocks sandwiched with intermediate-basic volcanic rocks.

With the transformation of Jinshajiang basin from continental lithosphere to oceanic lithosphere, not only the Jinshajiang ocean basin has been formed, but also new oceanic crust, large-scale oceanic ridge volcanic activity and its corresponding deep-sea sedimentary assemblage have emerged, and at the same time, a series of deep ore-forming materials, such as gold, have been brought in, forming a regional metallogenic geochemical anomaly field, which provides a rich material source for the re-enriched integrated ore in the later stage of tectonism. Wang Dalong gold mine, Xiazuo gold mine and the famous Ailaoshan gold mine all occur in ophiolite melange. The ore-bearing rock series include ultrabasic rocks, basic volcanic rocks, pyroclastic rocks, gabbro, siliceous rocks, slate and carbonate rocks. There are various types of rocks, and the metallogenic age is Yanshanian-Himalayan (28.2 ~ 178 Ma, Li Dingmou, etc. Mo Metaphysics et al., 1998).

Thirdly, the subduction and subduction stage of oceanic crust and the formation of Yangla copper series.

From the late Early Permian to the late Permian, the structure and geological background of Jinsha River belt changed greatly. On the basis of the expansion of Jinshajiang Basin into an ocean basin from the early Carboniferous to the early Permian, a large-scale westward subduction occurred in the late early Permian, and the ocean lithosphere began to transform into a continental lithosphere structure system, which was marked by the development of island arc volcanic rocks and the formation of back-arc basins.

In the middle axis of Jinshajiang ocean basin, due to subduction and subduction between oceanic crust (its formation mechanism is related to subduction of oceanic crust plate), the late Early Permian-late Permian ZhuBa Long-Yangla-Dongzhulin ocean volcanic arc and its West Canal River-Xueyangyongkou-Dongzhulin-Jiyidu-Gongnong back-arc basin (oceanic crust basement) were formed respectively. In the arc environment of Zhubalong-Yangla-Dongzhulin Ocean, shallow-sea carbonate rocks-clastic rocks and sub-deep-sea sandy siliceous flysch formation are deposited, and a series of timely tholeiite-basaltic andesite-andesite-dacite (a little) island arc volcanoes are developed in the volcanic arc from morning till night. On the west side of the continental volcanic arc is the West Canal-Xueya Yangkou-Dongzhulin-Jiyidu-workers and peasants back-arc basin (oceanic crust basement). In the back-arc spreading basin, a set of underwater-deep-sea siliceous-sandy argillaceous flysch formation is formed, accompanied by the development of diabase dikes in the back-arc spreading environment and the combination of uplifted porphyritic basalt and basaltic tuff.

The oceanic crust on the west side of Jinshajiang ocean basin subducted westward to Changdu land, and the continental margin volcanic arc of Jiangda-Deqin-Weixi and the back-arc basin (continental crust basement) on the west side were formed from the late Early Permian to the late Permian respectively. Volcanic-sedimentary rock series on the volcanic arc on the continental margin have various lithofacies and sedimentary types in space, and the topography of the island arc fluctuates greatly. There are terrestrial plants and columnar jointed land exposed on the surface, and carbonate platforms and deep-water valleys lurk underwater. There are many sedimentary facies and types from continental-land-sea transitional facies-shallow sea facies-platform slope-deep-water basin, which is a tectonic paleogeographic pattern of island chain distribution. The volcanic rocks of island arc develop tholeiite series → calc-alkaline series → potash basalt series from morning till night, and the properties of volcanic rocks mark the complete process of island arc generation-development-maturity (Mo Xuanxue et al., 1993). On the west side of the volcanic arc of the Jiangda-Deqin-Weixi continental margin is the Changdu back-arc basin (continental crust basement), where coal-bearing clastic rocks and volcanic rocks, coastal clastic rocks and volcanic rocks, and shallow-sea carbonate rocks, clastic rocks and volcanic rocks are deposited.

The Zhongzha-Zhongdian block on the east side of the Jinsha River ocean basin mainly maintains carbonate deposits of shallow platform facies. The western edge of Zhongzha-Zhongdian block corresponds to the island arc-basin system of the eastern active edge of Changdu block, and the Permian is the evolution and development period of the passive continental margin rift basin, which is used for the passive continental margin rift basin in Fulongqiao-Nishi-Tuoding area. The carbonate slump deposits, submarine turbidite fan deposits and sandy argillaceous-siliceous flysch, as well as extensional basic and intermediate-basic volcanic rocks, volcanic rocks and sandstone in the sub-deep sea basin facies have the characteristics of passive continental margin environment (Mo Xuanxue et al., 1993). The formation of rift basin in the western margin of Sino-Zambia-Zhongdian landmass echoes with the occurrence and development of island arc-back arc basin in the eastern margin of Changdu landmass in the Permian active margin of Jiangda-Deqin-Weixi.

From the late Early Permian to the late Permian, due to the westward subduction and subduction of the Jinshajiang oceanic crust, the spatial configuration structure of the Jinshajiang arc basin system was formed in the oceanic and continental volcanic back-arc basins. This process is not only the transformation from marine lithosphere to continental lithosphere, but also the process of material composition adjustment, reorganization and transformation. The jet sedimentary massive sulfide deposit represented by Yangla copper mine was formed in the oceanic island arc basin of porphyry copper-molybdenum mineralization from Yanshanian to Himalayan, and the ore-bearing rock series are skarn island arc volcanic rocks, pyroclastic rocks, siliceous slate and sandy slate. Structural altered rock-type gold deposits related to arc volcanic rocks have also been discovered, which has a good prospecting prospect. The ore-bearing rock series are basic volcanic rocks, pyroclastic rocks and sand shale in the island arc, such as West Canal and Jiaobaixi Gold Mine. Volcanic-subvolcanic hydrothermal copper-gold-lead-zinc mineralization related to island arc volcanic rocks, represented by Nanren copper-gold deposit, was formed in continental margin volcanic arc. The ore-bearing rock series are basic and intermediate-acid volcanic rocks, pyroclastic rocks, subvolcanic rocks, carbonate rocks and slate in the island arc phase.

Four. Arc-land collision stage (T 1-T2)

In the early and middle Triassic, the tectonic and sedimentary environment of Jinsha River arc basin system and Changdu and Zhongzan-Zhongdian landmasses on the east and west sides changed greatly. At the end of the late Permian, the Jinsha River ocean basin shrank and closed, and the ocean crust disappeared. In the early and middle Triassic, the Jinsha River belt turned into the stage of arc-continental collision, which was marked by the development of the volcanic arc on the continental margin of the Jiangda-Deqin collision, and the formation of the foreland basin behind the Changdu arc and the Jinsha River residual basin (marginal sea).

The Permian subduction of Jinshajiang ocean basin decreased to the end of Late Permian, when the oceanic crust closed, and arc-land collision and land-land docking occurred. On the basis of the pre-Permian Jinshajiang ocean basin, the early-middle Triassic turned to the development stage of residual sea basin (marginal sea), and a sub-deep sea fine-grained turbidite composed of cobweb keratophyre, radiolarian chert and marl mixed with endogenous and volcanic sources was formed in the basin, which is a combination of carbonate rock, siliceous argillaceous rock and sandy argillaceous rock. As a continuation of Permian intracontinental arc to Middle Triassic, intermediate-acid volcanic rocks, subvolcanic rocks and intrusive rocks appeared in Shusong-Tongyou area. The main part of the Zhongzan-Zhongdian landmass on the east side of the Jinsha River residual sea basin (marginal sea) was uplifted and denuded, and it was missing in the Middle Triassic. The Lower Triassic is a clastic deposit in the shallow sea basin on the continental surface, and the river conglomerate at the bottom is pseudo-conformity or unconformity in the Permian, and the middle and upper parts are composed of carbonate-clastic rocks in coastal and shallow sea.

On the west side of Jinsha River remnant sea basin (marginal sea), it is located in Jiangda-Gobi Desert-Xu Zhong area on the east edge of Changdu landmass. Due to the arc-land collision and land-land docking, the collision-type continental margin volcanic arc was formed in the Early-Middle Triassic, superimposed with the Permian subduction-type continental margin volcanic arc, and the volcanic rock combination of basaltic andesite-andesite-dacite-rhyolite series with island arc characteristics was developed. Arc volcanic rocks began three years ago. The Middle Triassic changed into the spatial pattern of arc basin system of pre-arc, inter-arc and back-arc basins, and developed semi-deep-sea volcanic rocks, terrigenous rocks and volcanic turbidites (Luo Jianning et al., 1992).

In the early and middle Triassic, the Changdu block on the west side of the volcanic arc of the Jiangda-Gobi Desert-Xu Zhong collision continental margin changed from the Permian back-arc basin to the back-arc foreland basin. Most areas were uplifted due to arc-land collision, and the early and middle Triassic strata were missing. In the early Early Triassic, rivers, coastal clastic rocks and intermediate-acid volcanic rocks were formed in the marginal zone of the back-arc foreland basin only in the Mangkang area near the island arc in the eastern part of the landmass, showing false integration.

Verb (verb's abbreviation) Metallogenesis in extensional basin stage after collision.

At the end of the Middle Triassic, the Jinsha River residual basin (marginal sea) disappeared, and the land-land collision occurred, forming an orogenic belt (tectonic hybrid belt). At the beginning of Late Triassic, the volcanic arc on the continental margin of Jiangda-Deqin-Weixi changed from compression to extension, and the possible transformation mechanism of its mechanical properties was the retraction of subducting plates or the extension of oblique collision (Li Xingzhen et al., 660) or the thinning and extension collapse of continental crust caused by lithospheric disintegration (Nelson,1992; Zhong Dalai et al., 1998), extensional split from the original volcanic arc, forming a post-collision extensional basin dominated by the early Late Triassic. It was formed in time after subduction and subduction of Jinsha River ocean basin, arc-land collision and land-land docking collision, but before the large-scale and large-scale accumulation of molasses in Jinsha River. In space, the main body is superimposed on the volcanic arc on the continental margin of Jiangda-Deqin-Weixi, which belongs to the post-collision extensional tectonic background.

The post-collision extensional basin in the early Late Triassic is characterized by volcanic turbidites, tuffaceous turbidites, tuffaceous siliceous turbidites, sandy argillaceous flysch, bimodal volcanic rocks and diabase walls and dikes composed of basalt-rhyolite. The geochemical characteristics of volcanic rocks show the rift basin environment under the extensional background. The early rift basin consists of basalt, basaltic tuff, sandstone, sandy mudstone, tuffaceous siliceous rock and marl from shallow sea to sub-deep sea, and a large number of diabase walls and dike groups are developed. In the middle period of rift basin, it is composed of sub-deep sea basalt, basaltic tuff, rhyolite, rhyolite tuff, rhyolite volcanic breccia, sandy mudstone, tuffaceous siliceous rock and marl, and a large number of diabase walls and dike groups are developed. The late rift basin is composed of rhyolite, rhyolite tuff, rhyolite volcanic breccia, sandstone, sandy mudstone and marl, with diabase walls and dike groups. At the end of the rift basin (that is, in the middle of the Late Triassic), extension and rifting were transformed into compression, and the basin gradually shrank and disappeared, forming clastic rocks with the characteristics of molasses in coastal and shallow seas, mainly neutral-intermediate acid volcanic rocks and pyroclastic rocks, and developing a large number of gypsum, barite and siderite deposits. The formation of regional post-collision extensional basin is a very distinctive scene in the tectonic evolution of Jinsha River belt, and the deep-sea trough with the nature of volcanic rift basin finally closed and disappeared in the early and late Late Triassic. At this point, the Jinshajiang ocean plate began to subduct westward in the late Early Permian, followed by ocean basin closure, arc-land collision and land-land docking, which was marked by the location of ophiolite in Baimang Snow Mountain and the unconformity coverage of the Shi Zhongshan Formation (T3 s), and the long-term collision process finally ended.

The tectonic palaeogeographic environment of the post-collision extensional basin in the early Late Triassic has undergone great changes in time and space. From the time point of view, the rift basin in the early and middle period was extensional rifting, volcanic activity broke out in deep water, and gabbro walls, dikes and subvolcanic gabbro porphyrite developed under the extensional tectonic background. In the late rift basin, the degree of extension and rifting was small, and it ended with acid volcanic activity. Volcanic rocks were formed in shallow seas, and even continental eruptions occurred, and columnar joints developed. At the end, it became a compressive environment, marked by the appearance of neutral-intermediate acid volcanic rocks, and a large number of gypsum and salt deposits developed. In space, there are both continental-shallow volcanic islands and deep-water sedimentary rift extensional basins, thus forming an alternating paleogeographic structure pattern of "graben and barrier". From north to south, we can roughly distinguish the volcanic sedimentary basins such as Shengda-Chesuo Township, Xu Zhong-Lu Chun (several tops)-Hongpo (cascade), Hetuitang-Cuiyibi-Shanglan.

According to the age standard of geological year, and the comparison diagram of K2 O and rift extension velocity data in basalt of Kenya and Tanzania (Figure 3- 10) (Xia et al., 1998), the extension distances of three volcanic-sedimentary basins are determined. The average value of w(K2O) in six kinds of basalts (1.43%) was adopted in the volcanic sedimentary basin of Shengda-Chesuoxiang in the northern section, and it was cast at point A in the figure, with the tensile fracture velocity (vp)=0.27 cm/a and the tensile fracture distance (D) = 63 km. The average value of w(K2 O) in 10 basalt (0.48%) is used in the middle Xu Zhong-Lu Chun (several roofs)-Hongpo (Yeza) volcanic sedimentary basin, which is cast at point B in the figure, with fracture velocity (vp)=0.43 cm/a and fracture distance (D =1a). The average value of w(K2 O) of four kinds of basalts (0.8 1%) is adopted in the southern section of the Reshuitang-Cuiyibi-Shanglan volcanic sedimentary basin, which is cast at point C in the figure, with the tensile fracture speed (vp)=0.36 cm/a and the tensile fracture distance (d= 1 16 km). Mo Xuanxue et al. (1993) estimated that the distribution width of three volcanic-sedimentary basins was 49.5 km in Chesuo basin, 1 13 km in several top basins and 8 1 km in Cuiibi basin, and the results were close. According to Sleep( 1975) and Kuzmir( 1980), the critical expansion rate (0.5 ~ 0.9 cm/a) that can produce subgingival magma is put forward, and the extension speed of the Chesuo basin in the north section (0.27 cm/a) is lower than that of several top basins in the middle section and the Cuiibi basin in the south section (0.44). Therefore, the tensile strength of the top basins in the middle section and the Cuiibi basin in the south section is relatively high, and there is a "bimodal" volcanic rock assemblage in the basin, while the tensile strength of the Chesuo basin in the north section is relatively low, with only tholeiite and no "bimodal" volcanic rocks in the basin. At the same time, the pull-apart velocity (0.27 cm/a, 0.43 cm/a, 0.36 cm/a) of the northern, central and southern basins are all less than the critical expansion rate (0.5 ~ 0.9 cm/a) of the magma under the ridge, so the spreading ophiolite assemblage cannot be formed.

Figure 3- 10 Relationship between K2 O of Basalt and Fracture Velocity of Rift Valley Basin

It is worth mentioning that the formation of the post-collision extensional basin on the continental margin arc is not only an important turning point in the structural evolution of the Jinsha River belt, but more importantly, the post-collision extensional basin has become an important metallogenic basin for Mesozoic copper, gold, silver, lead and zinc polymetallic deposits in the Jinsha River belt. Volcanic activity in the basin leads to submarine jet hydrothermal activity system. In the secondary depression of rift basin, a "brine pool" was formed under semi-closed and closed conditions, and a jet sedimentary massive sulfide deposit was formed by deposition. Mineralization was formed in the middle period of basin extension and detachment. Such as Zuna lead-zinc mine in Chesuo basin, the ore-bearing rock series is carbonate rock-clastic rock-barite formation; Lu Chun Cu-Pb-Zn deposit, Hongpo Cu-Au polymetallic deposit in several major basins and Laojunshan Pb-Zn deposit in Cuiyibi basin are composed of acid volcanic tuff-sedimentary rock-siliceous rock. At the end of the basin, volcanic-subvolcanic hydrothermal-sedimentary siderite-type gold-silver polymetallic deposits related to intermediate-acid volcanic rocks were formed under the background of compressional structure, such as Zhaokalong siderite-type silver-rich polymetallic deposit in Chesuo basin, Dingqinnong copper-gold deposit and Chugezha siderite deposit in Cuiibi basin, and the ore-bearing rocks are composed of intermediate-acid pyroclastic rocks, sedimentary rocks and siderite. Gypsum deposit is formed in Yurirenka area in the middle of Lu Chun Basin.

Six, foreland basin stage

In the middle and late Late Triassic, the Jinsha River belt entered the stage of all-round intracontinental collision orogeny. Clastic molasses and coal-bearing formations are accumulated in the marginal foreland basin of Jinsha River orogenic belt and its trailing edge, and do not overlap with Jinsha River structural melange. In the Changdu block area on the west side of the Jinsha River junction zone, the river-lake facies-coastal facies clastic molasses formation was formed in the back-arc foreland basin in the early Late Triassic, and the unconformity covered the underlying strata in different eras. In the middle and late Late Triassic, its back-arc foreland basin continued to develop and evolve, forming shallow-sea carbonate rocks to land-sea coal-bearing clastic rocks. In the late Cretaceous, the foreland basin gradually shrank and disappeared.

Seven. The stage of intracontinental convergence and its mineralization

Cenozoic is the formation and uplift period of Sanjiang area and even Qinghai-Tibet Plateau. The final orogeny led to large-scale thrust nappe, large-scale strike-slip and detachment of the surface and lithosphere formed by thrust nappe and extension. On the one hand, some fault basins, strike-slip basins and extensional basins have been formed; On the other hand, it superimposed and transformed the early mountain system, strengthened the crust, and was accompanied by strong magmatic activity, metamorphism, tectonism and mineralization of non-ferrous and precious metal minerals. The deposits formed in Jinsha River belt in different periods were all formed in the process of intracontinental orogeny, and were superimposed and reformed by tectonic action and magmatic activity to varying degrees, showing the characteristics of one mine with many minerals and complex deposit types.

Tectonic altered rock deposits and supergene stratabound deposits in different tectonic units in Jinsha River belt are the products of tectonism in intracontinental orogeny. Tectonic altered rock type gold deposits occurring in structural ophiolite melange, such as Xiaruo gold deposit, Wang Dalong gold deposit and Ailaoshan gold deposit, are controlled by thrust nappe and ductile shear structure. Tectonic altered rock-type gold deposits occurring in volcanic rocks, such as Xiyunhe gold deposit and Azhong gold deposit, are controlled by shear tectonic altered fracture zone. Supergene stratabound Cu-Pb-Zn deposits, such as Jiao Na Pb-Zn mine, Tuoding copper mine, Sancun Pb-Zn mine and Gelan copper mine, occur in the nappe-detachment structural belt on the western edge of Zhongzan-Zhongdian block and are controlled by extensional detachment structure or the combination of thrust nappe and extensional detachment structure.