Sichuan Basin

The Sichuan Basin (in Chinese四川盆地, Pinyin Szechuan Pendi ), which because of its red or purple soils under the name Red Basin (红色 盆地/红色 盆地, Hongse Pendi or赤色 盆地, Chise Pendi ) is known, is a sink on the upper reaches of the Yangtze River in the east of Sichuan Province in the west of Chongqing Municipality in southwest China.

• 2.1 Geological construction 2.1.1 Longmenshan fault zone
• 2.1.2 Northwest Valley
• 2.1.3 Central Sichuan Basin
• 2.1.4 Southeast ply region

Geography

The basin is approximately rectangular in shape and extends in the southwest-northeast direction for about 600 km and 380 km wide. It thus has an area of ​​about 200,000 square kilometers and is almost completely bordered by mountains: the Wu Shan in the east, and Daliang Shan Shan Dalou in the south, the Qionglai Shan and Min Shan in the west, the Daba Shan and Micang Shan in the north. These mountains were once the reason for the seclusion of the area which was accessible only through a river in the north and one in the south.

The ground surface in the basin is 400 to 800 meters above sea level. It is crossed by numerous rivers. The largest rivers are Min Jiang, Tuo Jiang, Jialing Jiang and Wu Jiang, all of them originating in the mountainous western part of Sichuan province. In it the Chinese name of Sichuan Province is - " Four Rivers " - back. You flow through the basin from northeast to southwest and flow into the Yangtze River. In the western part of the area the Chengdu Plain lies with its fertile soil.

The basin is an important agricultural production area and holds rich mineral resources.

Climate

The climate in the Sichuan Basin is balanced. It has hot, humid summers and mild, damp winters also. Rain falls throughout the year, the annual rainfall averages 1,000 mm. Three quarters of the rainfall occurs in the months of May to September. The mountains in the north and east shield the pelvis against continental cold air, while the lower mountain ranges in the south warmer subtropical air masses from entering the pelvis can not deny. Therefore, the average temperature in January is 5 to 11 ° C and in July it reaches almost 30 ° C. The climatic conditions permit almost all year round agricultural activities, the growth period is 11 months. These favorable conditions have meant that since 2000 years in the Sichuan Basin agriculture is intensive.

Geology

The Sichuan Basin is part of the Yangtze Craton or micro- continent that formed in the late Proterozoic ( 850-700 Ma). Until the middle Triassic of micro continent was surrounded by open sea, while were deposited on him sediments of the shallow sea. The Sichuan Basin took first in outline shape as the Yangtze craton initially collided in the early Mesozoic orogeny during the Indosinischen on its northwest side with the Songpan - Ganzi block. After these two microplate collided with the Northern Chinese -Korean block in the north and Tibet in the west, so that the Yangtze craton was an integral part of the Eurasian plate.

Today, the pool is at the southeastern end of the Tibet -collision orogen, which is produced by the collision of India with the Asian continental plate. Eroded While from the Proterozoic almost continuously was depositional environment, especially in the north-west and up to 12 km sediments recorded, it is in the last 10 million years, especially in the center and has been raised to its southeast side, so that in places up to 5 km of sediment re- were. Only in its northwestern part show massive deposits of the Pliocene and Pleistocene continued to decrease.

Geological construction

The Sichuan Basin is geologically divided into three parts. In the northwest, the north-western valley ( Northwestern depression) takes as foredeep of Longmenshan - fold belt on thick sediment series. The central Sichuan Basin (Central uplift) has flat-lying or only gently undulating on layers, while the southeastern third ( Southeastern Fold Belt ) is characterized by a number of long aushaltender wrinkles trains.

The basin is surrounded on all sides by fold-and- thrust belts. The northwest side of the basin is of the elusive prior to the collision of India with Asia to southeast rocks of the Longmenshan fold-and- thrust belt (龙门山 褶皱 冲 断 带/龙门山 褶皱 冲 断 带, Longmen Shān zhězhòu Chong duàndài, English Longmenshan fold and thrust belt ) run over on a thrust fault zone. The fold-and- thrust belt of the Min Shan and Daba Shan in the northeast are transverse to the other geological structures of the Sichuan Basin. Similar to the Longmenshan - fold belt Proterozoic and Paleozoic here, some metamorphic rocks are pushed onto the mighty series of the Triassic and Jurassic. The southeast side is affected by the folds and thrust of Qiaoshan - fold belt, which always brings older strata to the southeast outside the basin by thrust faults and Verschuppungen to the surface. In the southwest of the basin is bounded by the Xichang - Yunnan fold belt, a complex built area that extends over 1,400 km from Qinghai to southern Yunnan. At their significant left-sided horizontal displacements have occurred. Its western side is formed by the still active Anninghe warp and the warp Xianshuihe.

Longmenshan fault zone

Named after the mountain Longmen Shan seismically active Longmenshan fault zone, which is considered the cause of the disaster of the earthquake of 12 May 2008, is located at the northwestern edge of the basin. It is part of Longmenshan fold-and- thrust belt. The Wenchuan, the location of the earthquake's epicenter, located in Longmenshan Earthquake Belt (龙门山 地震 带, Longmen Shan dizhendai ).

The fault zone is usually the place of smaller and larger earthquakes. The occurrence of a stronger earthquake in the approximate range of the earthquake of 2008 was predicted by Chinese scientists in 2006.

Northwest Valley

The northwestern valley is filled by an up to 12 km thick wedge-shaped sediment stack, which considerably thins toward the central basin to the southeast. Due to the constant and still ongoing deposition of weathering debris from the western mountains a substantially flat plane were created, this mainly in the southwestern part of the basin in the plane to Chengdu. Geological profiles that the valley of the northwest is here crossed by the complicated structure Longmenshan fold-and- thrust belt. It is constructed from thick overthrust bodies of granitic rocks of Proterozoic and Paleozoic sedimentary rocks. In the front part of the thrust belt, adjacent to the Sichuan Basin, the lowest Abscherungsfläche lies in the level of Proterozoic or Cambrian. It rises to the southeast up in Mesozoic rocks. Here also rocks are affected, who have listened to the Sichuan Basin, this extends geologically So another piece under the thrust belt.

The orogenic movements that have affected the lower Paleozoic of the frontal Longmenshan - fold belt and the Mesozoic the northwest valley dates back to the collision of India with Asia.

Central Sichuan Basin

The central Sichuan Basin at the surface is underlain by rocks of the Jura that come flat to the northwest towards the northwestern valley. The layers are only moderately affected by bending or folding. Typical of the architectural style of this region are broad anticlines that comprise the whole sequence and its edge are affected locally by normal faults. Rocks of Silurian to Carboniferous and the Cretaceous were removed due to repeated uplift and erosion, so that the whole sequence here is about 6 km powerful.

Southeast ply region

The southeastern wrinkle area is characterized by elongated, pointed saddles, which are also visible on the surface, and extend as a narrow ridge over many kilometers. They consist of sandstones of the Triassic and Jurassic, while the wide and shallow troughs between them consist of shales of the Jurassic. The shape and arrangement of folds is an indication of a Abscherungshorizont under the entire area of ​​folding. The construction of geological profiles has shown that this level in the Cambrian slate must be at about 7 km depth. From it branch off thrust faults, which terminate blindly in the core of the saddles. The folding area is the frontal part of the Qiaoshan - fold belt.

Layer sequence

The Sichuan Basin is characterized by long stretches flat-lying layers of the Neoproterozoic, Paleozoic and early Mesozoic, which are overlain by massive sedimentary series of the Triassic to Cretaceous.

Mineral resources

The rocks of the Silurian, Permian and Triassic have the properties of petroleum source rocks, which have led to the emergence of extensive natural gas reserves. The deposits are primarily bound to the fold structures of the central and southeastern basin. Other mineral resources in the Sichuan Basin are coal, ores, salt and phosphorus.