First, the characteristics of neotectonic movement
From Oligocene to now, Tarim Basin has experienced seven stages of tectonic activities, forming seven unconformities or large-scale sedimentary discontinuities, namely:
Meso-Cenozoic intracontinental orogeny and sandstone-type uranium mineralization in the middle subtype orogenic belt in western China.
Among them, the fourth act () has a strong and extensive influence. Cenozoic tectonic movement features mainly include:
1) is high in the west and low in the east, which is a major feature of the two arc mountain systems in Tarim area. Due to the uplift of neotectonic movement, Tianshan system has four levels of planation plane; The gap between the upper reaches of Kaidu River and Yanqi Basin is 1060m, and the exit of the mountain pass forms a six-level terrace. From Kunlun Mountain in the south and Altun Mountain Peak in the north to the basin, it has a stepped landform.
2) Since the Pleistocene, due to the further activities of Himalayan orogenic belt, the surrounding areas of Tarim Basin have been strengthened by the north-south horizontal compression, and two foreland thrust belts, Kuqa and Yecheng, have been formed. The Mesozoic and Cenozoic strata have been folded and deformed, and the old strata have been thrust on the new strata. By the Quaternary, the Tarim subsidence center had moved to the Tarim River area.
3) The nappe structure is the main feature of Cenozoic tectonic activity. Kuqa thrust belt is an arc fold thrust belt protruding southward, and Mesozoic and Cenozoic strata pushed southward along shovel faults, forming three rows of fold thrust structures. The shovel fault is steep in the south of Beiping; The horizontal fault plane is the detachment plane of soft plastic layer, and the main detachment plane has two layers, one is Triassic-Jurassic coal measures stratum, and the other is Paleogene gypsum and salt stratum. Nowadays, the horizontal extrusion is still going on, and the Quaternary system in some areas has been uplifted, and the ground is normal terrain. The angle of Quaternary and Tertiary in Kuqa Depression is unconformity, and the Mesozoic and Tertiary under unconformity have strong fold and fault activities, forming a foreland fold thrust belt, and exposing some of the formed uranium mineralization to the surface, or showing an inverted (reverse) interlayer oxidation zone.
In front of Kunlun Mountain, due to Pamir's northward wedging, not only a strong compression thrust occurred in the piedmont depression, forming a fold thrust belt, but also a large strike-slip component, which made the piedmont fold thrust belt unfold in a wild goose. The strata affected by Yecheng thrust nappe belt range from Proterozoic to Neogene, and from south to north from old to new. Thrust belt consists of nappe system and front belt. The nappe system consists of four rows of thrust faults and thrust rocks clamped by them. The structural strike is NWWNNW, thrusting northeast, and the old strata cover the new strata, such as horizontal fault plane and Feilaifeng. According to the seismic data of Kriya River, the horizontal nappe distance is more than 40 kilometers. The foreland is composed of three rows of folds, located in the piedmont zone north of the nappe system, including Pianman, Sangzhu, Sulaaz, Keriyang and Guma structures. The tectonic strength decreases from south to north, the dip angle of the first row of tectonic strata in front of the mountain is steep, and the dip angle of the northern wing of the anticline is vertical or even inverted. The second and third rows of structures are mostly short-axis anticlines or nose-shaped structures, which reflect the process of compressive stress transmission and release from south to north.
In the southeast, Altun uplift and East Kunlun thrust into the basin strongly, and the Qiele-Luobuzhuang fault zone (Qierqin fault zone) at the front of Qierqin fault uplift is active.
In the abdomen and east of the basin, the neotectonic movement is weak, and it shows a large and gentle syncline structure as a whole.
2. Neotectonic movement zoning and prospecting for in-situ leachable sandstone-type uranium deposits
Through the analysis of the neotectonic movement in Tarim Basin, the neotectonic movement in Tarim Basin can be divided into regions (Figure 2-6-29): Tabei (piedmont of Tianshan Mountain) depression, Awati depression, Southwest Tarim depression, Southeast depression and other structural areas are strong neotectonic movement areas; Bachu uplift, Cherchen uplift, Tadong shallow depression and Tabei uplift are moderately active areas of neotectonic movement. Manjia sag is a relatively stable area of neotectonic movement.
Figure 2-6-29 Zoning Outline of Neotectonic Movement in Tarim Basin
Around the basin, there are almost all areas with strong neotectonic activity, and the overall strong tectonic activity is characterized by orogeny, uplift and large decline of deep depressions, folds and faults, and most of the formed uranium ore bodies have been destroyed. In-situ leaching of sandstone-type uranium deposits should be a relatively stable area with weak neotectonic activity, while the middle-large stable area (Ⅲ) in Tarim Basin is a very thick Neogene and Quaternary shore-shallow lake facies sedimentary area, and there is no ore-forming sand body for research and exploration. Therefore, the structural selection of sandstone-type uranium deposits focuses on the moderate activity area of neotectonic movement and the local relative stability area of strong neotectonic movement in the basin margin.
Three. abstract
According to the analysis of neotectonic movement characteristics, the prospecting for in-situ leaching sandstone-type uranium deposits in Tarim basin is mainly to find a relatively stable local tectonic environment, focusing on finding stable areas in areas with strong tectonic activity on the basin edge, such as the relatively stable area on the northern edge of Kuqa-Baicheng sag, Bachu area in the northwest of the basin and Lop Nur area in the east, and its prospecting prospects are still relatively optimistic.
refer to
Guan Haiyan and Wang Xueyou. 1997. remote sensing geology of Tarim basin. Beijing: Geological Publishing House.
Yang Geng, Qian Xianglin and Guo Hua. 2003. Tectonic evolution and oil and gas prospect evaluation of Kuqa intracontinental flexural basin in the northern margin of Tarim. Beijing: Geological Publishing House.
Ding Daogui, Wang Daoxuan and Liu Weixin. 1996. western Kunlun orogenic belt and basin. Beijing: Geological Publishing House.
(Li Xigen,,,, Chen)