Tectonic Evolution And Trap Characteristics Of The Western Qaidam Basin

In this paper, based on structural geology, sedimentology, geophysics and petrology and basin analysis theory, combined with basin tectonic evolution and sedimentary features, using the way of surficial and underground geological and geophysical exploration what can study structures and sedimentary facies and seismic flattening technology, the outcrops and seismic profiles in west margin of Qaidam Basin were studied in detail. Fracture development and distribution characteristics of main tectonic faults were studied, and the tectonic evolutions were builded. Based on the above results, the empfhasis trap characteristics and the causes of effective traps in studying area are described and analyzed, what can lay the foundation for further geological exploration deployment.Combined with regional tectonic background information, choose13main seismic skeleton seismic profiles were chosen to analyze the dynamics characteristics of the study area. It showed that tectonic deformation in west margin of Qaidam Basin occurred mainly in the Eocene, Miocene and Pliocene-Quaternary. Strong tectonic deformation caused serious uplift and erosion in the area influenced by Arkin and Kunlun Mountains. In the middle to east direction, deformations decreased significantly, and the east-west deformations in the middle of basin are strongest.Based on these geological characteristics of the Qaidam Basin, the study area can be divided into3different zones, namely Arkin foreland zone, the west of Qaidam Basin and the western part of northern edge of Qaidam basin. Arkin foreland zone influenced by multi-phase slips of Arkin mountain uplift and fracture zone, have experienced many tectonic movements, with the general features of high in the West and low in the East, and several internal fault nose and nose structure towards the basin. Influenced by SW-NE compressive stress and the Arkin fault sinistral strike slip, the anticline was en echelon arrangement, with the curved, S and reverse S shape axis in the west of Qaidam Basin, what can be divided into Shizigou-Youshashan and Youquanzi-Kaitemilike anticline belts. In the western part of northern edge of Qaidam basin, with compression torsion slip effect, the anticline was broken, because the axis was partially cut by a small strike-slip faults, including many reverse "S" type vortex structure system, like Eboliang, Lenghu, and Mahai-Beijixing reverse "S" structure belt.According to the regional tectonic background and evolution, combined with the balanced seismic profile, the ancient structure was restored. There were three major ectonic evolution period in Qaidam Basin since Cenozoic era, first one in Eocene, second one in Miocene, the third from late Pliocene to quaternary. Himalayan movement played an important role in the structure evolution of Qaidam Basin.The reverse and strike slip faults were dominant while small fault were developed locally. The basement involved and cap rock detachment were the main features of the fault. According to the properties and relationship between evolution history and stratigraphic deposition, faults were divided into three categories, the early fault, synsedimentary fault and post fault. In the profiles, according to the fault assemblage characteristics, faults were divided into five kinds of combination patterns:imbricate thrust fault, hedge fault, back thrusting fault, flower fault and extensional fault. There were three kinds of modes of the formation and evolution of faults. Firstly, some faults had been fully developed and finalized the design in Oligocene (Ni), what controled the formation and evolution of ancient structure and deep strata. Secondly, during Miocene (N21) and Quaternary (Q), some faults formed with strong tectonic enhancement and reconstruction and also had an impact on the later deposition. The last faults were long-term active in the process of basin evolution with large scale and multi stage activity and also had an important influence on the regional tectonic and sedimentary filling.There are various traps in the study area, mainly including anticline, fault nose and fault block types. The trap distribution has the following characteristics:㏕he peripheral orogenic belt and foreland area have a great development of traps, the formation of what have great influence by the tectonic deformation and extrusion strike.(2) The trap distribution is obviously controlled by distribution of tectonic belt, with NW trending.㏕here are a deep relationship between the distribution of faults and traps.瓯he number of traps in different layers have different distribution.㏕he same trap in different layers have similar morphological characteristics. The main factors affecting the development of structure traps should be the stress status, the strength of tectonic deformation and the development status of fracture.The main controlling factors for the formation of the effective trap are the match of trap formation and hydrocarbon migration period and the distant between traps and hydrocarbon sags, that cause a favorable trap for the accumulation of oil and gas. The next step should focus on the ancient and synsedimentary tectonic traps near the generating sag, like Yingxiongling, Saishiteng and Gaqiu.