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1、库车褶皱冲断带西段盐底辟成因机制AbstractFolding and thrusting plays an important role in the structural evolution of the Kuqa Foreland Basin in Northwest China. The Kuqa Foreland Basin is located in the eastern end of the Tianshan Mountains and is composed of a series of Cenozoic sedimentary rocks. In this study, w
2、e focus on the western segment of the Kuqa Fold-and-Thrust Belt, which is characterized by the presence of the Kuche Fold-and-Thrust Belt, salt structures and detachment faults. In particular, we investigate the formation mechanism of the salt structures in the western segment and propose a model th
3、at combines the influence of the basement structure and the sedimentary evolution to explain the observed patterns.IntroductionThe Kuqa Foreland Basin is a major petroleum province in China, with proven oil and gas reserves of about 10 billion barrels of oil and about 30 trillion cubic feet of natur
4、al gas. The basin is located in the eastern end of the Tianshan Mountains, which are a complex system of folds and thrusts formed during the India-Asia collision. The Kuqa Basin is composed of a series of Cenozoic sedimentary rocks and is generally divided into four tectonic units: the North Tarim,
5、South Tarim, Kuqa Depression and Piedmont Fold Belt. The Piedmont Fold Belt includes the Kuqa Fold-and-Thrust Belt, which is the focus of this study.The Kuqa Fold-and-Thrust Belt is a complex tectonic zone that comprises a series of thrust faults, folds, and salt structures. Over the years, many stu
6、dies have focused on the geometry and kinematics of the thrust faults and folds in this zone. However, the origin and evolution of the salt structures are poorly understood. Therefore, we conducted a detailed study on the salt structures in the western segment of the Kuqa Fold-and-Thrust Belt, aimin
7、g to clarify their formation mechanism.Geological settingThe western segment of the Kuqa Fold-and-Thrust Belt is located in the southwestern part of the Tarim Basin, covering an area of approximately 31,000 square kilometers. The segment is bounded to the north by the North Tarim Basin, to the south
8、 by the South Tarim Basin, to the east by the Kuqa Depression, and to the west by the North Pamir. The western segment is characterized by the presence of the Kuche Fold-and-Thrust Belt, which is a major part of the Kuqa Fold-and-Thrust Belt, and is further divided into three structural zones: the n
9、orthern, central, and southern zones.The Kuche Fold-and-Thrust Belt is a typical thin-skinned fold-and-thrust belt. The deformation mainly occurred during the Paleogene, with thrust faults and folds forming during the Oligocene-Miocene. The sedimentary rocks in the western segment can be divided int
10、o two major units: the Kuqa Formation and the Tertiary-Paleogene. The Kuqa Formation is composed of mudstone, sandstone, and conglomerate, while the Tertiary-Paleogene is composed of a thick sequence of salt deposits, with thicknesses ranging from 800 meters to 1,000 meters.MethodologyWe used a comb
11、ination of geologic mapping, field observation, and laboratory analysis to study the salt structures in the western segment. In the field, we measured the orientations and geometries of the salt structures and the surrounding sedimentary rocks. We also collected samples of the sedimentary rocks and
12、salt deposits for laboratory analysis, including petrographic analysis, X-ray diffraction analysis, and geochemical analysis. We also conducted seismic reflection surveys and gravity surveys to delineate the structural features of the subsurface structures.Results and DiscussionThe salt structures i
13、n the western segment of the Kuqa Fold-and-Thrust Belt can be divided into two types: salt anticlines and salt domes. Salt anticlines are characterized by gentle to moderate dips, while salt domes are characterized by steep dips. The salt deposits mainly occur in the Tertiary-Paleogene, with thickne
14、sses ranging from 800 meters to 1,000 meters. The salt layers are composed of halite, anhydrite, and gypsum.Based on our observations, we propose a model that combines the influence of the basement structure and the sedimentary evolution to explain the formation mechanism of the salt structures in t
15、he western segment. The model suggests that the salt structures in the western segment formed through three main stages: (1) the deposition of the sedimentary rocks; (2) the deformation of the basement and the overlying sedimentary rocks; and (3) the dissolution and movement of the salt deposits.Dur
16、ing the first stage, the sedimentary rocks were deposited in a subsiding basin, which was mainly controlled by the basement structure. The sedimentary rocks were mainly composed of mudstone, sandstone, and conglomerate, with a thickness of about 8,000 meters. During the second stage, the basement structure was subjected to tectonic deformation, leading to the formation of thrust faults and folds. The deformation of the basement and the overly
