Multi-Decollement Structure Modelling of Kuqa Fold-Thrust Belt in Tarim Basin

Abstract

Abstract The structure model of Kuqa fold-thrust belt in Tarim basin is very complex and special. The Paleogene gypsum-salt strata and Jurassic-Triassic coal measure strata are two detachment layers developed in Kuqa area, and both of them have a large thickness. The shallow structure is salt-related structure which developed above the Paleogene gypsum-salt stratum, there is a large difference with typical salt-related structure because this structure was seriously affected by overthrusting but not by gravity action. The structure style mainly contains salt-loss syncline, salt diaper, piggy-back basin and salt fold. The structures between the two detachment layers developed double detachment structure with a special structure style. The double detachment structure has obvious differences with typical fault-related fold, analyzing from kinetics, we can see that the deformation of fault-related fold was driven by bearing stress which was produced by the contact of different fault blocks, but the deformation of double detachment structure was driven by plastic flowing of the detachment layers; analyzing from geometry, we can see that double detachment structure developed the "suspended structure", this is the obviously different with fault-related fold. Analyzing from the structure characteristics, the Kuqa fold-thrust belt have been developed a whole thrust system from the mountain front to foreland. In order to make a deeply research of the structure style in Kuqa fold-thrust belt, we use the 3D model building technique, structure restoring technique and 4D physical modeling technique, and these techniques has been made a very important role in the research. 1 Introduction The Kuqa fold-thrust belt located on the north of Tarim basin, also on the south of southern Tianshan mountains. It is a huge thrust system was driven by overthrusting which produced when the Tianshan orogenic belt were pushed toward Tarim basin in himalayan period. Affected by the complex structure and poor surface condition, the seismic data have very low S/N, and complex wavefield, it makes the research very hard. In these years, along with the progress of seismic exploration, the quality of seismic data was improved obviously, at the same time, a series new techniques and method were used in the research, all of this makes us have a more deeply recognize of this area. Though a deeply research for the structure style of Kuqa fold-thrust belt, we recognize that a special structure style was developed in this area because the distribution of two detachment strata. The thin-skinned and thick-skinned structure developed in this area at the same time. There are two different structure style distribute at each sides of Paleogene gypsum-salt strata in thin-skinned structure, all of this composed a very complex thrust system. 2 Research of the structure style Characteristics 2.1 Strata The Kuqa Fold-Thrust Belt special structural styles with its special strata very close relationship. According to outcrops and drillings, we can classify the Mesozoic and Cenozoic strata in Kuqa area to a strata system which is shown in figure2, the characteristic of each stratum will be described as below: Early Mesozoic strata: the Mesozoic strata were mainly composed with Mesozoic magmatic rocks, Paleozoic marine clastic rocks and carbonate rocks which suffering a strong deformation and metamorphism.