The western Pacific belt is equivalent to Baoshan block. The Yintai Warm Zone (namely, the area around Chiang Mai, Fangxian County) is characterized by the development of metamorphic core complexes in Yintai Warm Mountain, and the basement gneiss is separated from the overlying low-grade or non-metamorphic lower Paleozoic caprock by detachment faults. Silurian-Devonian is a set of deep-water basin sediments. There are graptolites and radiolarians in Devonian siliceous sediments and Carboniferous-Permian siliceous rocks in Fangxian County, northern Chiang Mai (Bunopas and Vera,1978; Sashida et al. (1993) and Sashida et al. (1993) think that it has the characteristics of ocean basin deposition. There are a large number of volcanic rocks representing the late Carboniferous and early Permian rift periods in Chiang Mai, and there are Permian-Triassic S-type granite bedrock on the east side of Chiang Mai. This belt is very similar to the Changning-Menglian granite belt, with the characteristics of Ximeng metamorphic core complex and Devonian-Permian ocean basin deposition, and the Carboniferous-Permian rift volcanic rocks and Lincang-Jinghong granite belt on the east. Lu' an fault is the boundary fault between this belt and Xitai belt, and it is also equivalent to Jack fault between Changning-Menglian belt and Baoshan block.
The Suketai belt is characterized by a set of Paleozoic and Mesozoic sedimentary rocks and volcanic rocks with folds and thrusts, and a small amount of I-type granite intrudes. Bunopas (1983) thinks that this zone belongs to shallow metamorphic limestone, tuffaceous shale, radiolarian chert and limestone deposited before arc. Carboniferous-Middle Permian pyroclastic rocks, limestone, mudstone and limestone are deposited in the crevices of the arc trench, while phyllite, schist and quartzite are deposited in the trench. The Late Permian-Early Triassic is mainly a set of acidic to neutral volcanic rocks and pyroclastic rocks, which are not covered by Triassic molasses. The overall characteristics of this zone can correspond to the volcanic arc zone of the South Lancang River. Barr and Macdonald( 199 1) assume that there is a hidden suture line diving eastward between Sukhothai and Indianapolis. Cain suture zone extends to the south, connecting with Wendong-Labu zone in Malaysia. The northward extension of this concealed suture zone may lurk under the nappe pushed eastward by the Jinghong and Dongdashan magmatic belts in Lincang, eastern China, and the oceanic ridge basalt exposed to the north of Tangji Group in the quasi-Wuqi area is obviously its northward extension and exposure. Phetchabun belt is the western margin of Indosinian landmass, which is mainly composed of Upper Paleozoic sedimentary rocks, Permian and Triassic calc-alkaline volcanic rocks and sporadic I-type granite plutonic rocks. The river between this belt and Sukhothai belt is difficult to sew. Although its counterpart has not been found in the western margin of Simao Basin in China, it is worth noting that the Nanhe belt may be the closed product of the back-arc basin formed by the eastward subduction of the ocean represented by hidden suture lines, and the back-arc basin may extend northward to Longdonghe area in Jingdong County of Simao Basin, where a set of deep-water volcanic-sedimentary rock series from Carboniferous to Permian developed, but the basin has not yet expanded to form an ocean crust. The South River Belt extends southward through Cheng Yi and Shajiao, and may cross the South China Sea to connect with the Lupa River suture belt (C.S.Hutchison, 1975) extending from Danatu Island to Kalimantan, but its closure time may be a little later, from Jurassic to Cretaceous.
Figure 7- 1 Schematic Diagram of Tectonic Stratigraphic Zoning in Thailand
(According to S.M. Barr and A.S. MacDonald, 199 1)
Note: The West Pacific Belt is equivalent to Baoshan Block in China, and the Yumu Fault Zone is equivalent to the Jack Fault. Industrial-western Pacific belt; Ⅱ-because of his warm zone; ⅲ-sukotai zone; Ⅳ —— phetchabun belt. 1- intermediate zone granite (S type); 2- Metamorphic core complex in the middle zone; 3- western granite (S+I type); 4— Eastern Granite (Type I)
Because another warm zone and Sukhothai zone have a development history from early Paleozoic to late Paleozoic, similar to Changning-Menglian and Nanlancang River zone. Therefore, there may be two ocean basins on both sides of the Tangji-Jinghong ancient island arc belt or landmass in the Lancang River structural belt, which developed from the primitive Tethys to the ancient Tethys and communicated with each other to form the primitive Tethys Ocean and the ancient Tethys Ocean.
In the Late Paleozoic, the eastern branch of Shuangyang was connected with Jinshajiang Ocean and Bayan Kara Ocean from the north of Wuqi, and after closure, the heteropoly-Liudongjiang-Nanzuo and Nanlan-Jinghong volcanic arc belt was formed on the eastern edge of Changdu-Simao land block, which was collectively called the heteropoly-Jinghong island arc belt (Li Xingzhen et al., 199 1). The west branch extends westward through Shuanghu and Gangmacuo to Longmucuo (Li Xingzhen et al., 199 1). Recently, blue plagioclase amphibolite schist was discovered in Machuo area of Shuanghugang, and the existence of this suture zone was also revealed by magnetotelluric sounding research (Qin Guoqing et al., 1994).