KINEMATICS AND MECHANICS OF KUQA FOLD-AND-THRUST BELT, CHINA: INSIGHTS FROM ANALOG AND NUMERICAL MODELS

Kuqa Cenozoic fold-and-thrust belt is located along northern Tarim basin, China. The widely distributed Paleogene rock salt has a significant influence on the deformation in this area, resulting in quite different structural styles above and below the salt. Structures beneath salt are mainly imbricate thrust and passive-roof duplex systems. Structures above salt include thrust faults and a salt nappe complex. In order to investigate the geometric pattern, structural evolution, and deformation mechanism of Kuqa thrust belt, we constructed a series of physical and numerical models. In the physical experiments, the silicone putty and dry quartz sand are used to model the rock salt and sedimentary strata respectively. A computer controlled moving wall induced horizontal compression and deformation in the sand layers. The experimental process was photographed at regular intervals. The sandbox experiments reproduced the major structural patterns observed in the Kuqa fold-and-thrust belt. In the hinterland of the thrust belt, deformation mainly develops in the Mesozoic strata beneath the salt rock, and forms imbricate thrust and passive-roof duplex systems. In the foreland, deformation primarily develops in the Cenozoic strata above the salt layer, and forms low-angle thrusts. Salt prevents the deep structures from being exposed at the surface, and thus generates good oil and gas traps. A series of discrete element models (DEM) were carried out to expand this study, i.e., to investigate the impact of rock competence and compression rate on the kinematics and mechanics of Kuqa and other salt-related fold-and-thrust belts. Preliminary DEM results show that competent strata develop more faults and maintain their bed thicknesses during the deformation, which suggests only minor internal deformation compared to the incompetent strata. In contrast, the incompetent strata develop fewer faults and exhibit obvious changes in bed thickness, suggesting more intense internal deformation. With identical rock competence and shortening magnitude, systems with low rates of horizontal compression tend to develop larger fold-and-thrust belts than systems with high rates of horizontal compression.