ICE 2022


The 3D geometry of fold-and-thrust belts is strongly controlled by both syn-tectonic sedimentation and décollement rheology. Its influence has been extensively tested through analogue models. However, the influence of syn-tectonic sedimentation in fold-and-thrust systems with two décollements has rarely been tested although it is a common scenario in the outer parts of fold-and-thrust belts such the Apennines, the Appalachians, the Pyrenees, the Zagros or the Sub-Andean and Kuqa fold-and-thrust belts. The Kuqa fold-and-thrust belt, in the southern foreland of the central Tian Shan Range (NW China), is a oil-bearing fold-and-thrust system that was contractionally deformed during Late Mesozoic and Cenozoic times as recorded by well-preserved syntectonic continental sequences. Its structural evolution was strongly controlled by synorogenic salt (Eocene-Oligocene in age) and presalt décollements (Upper Triassic-Lower Jurassic coals and lacustrine mudstones) with varying spatial distribution. In this context, the present study aims to understand how the rate of syn-contractional sedimentation influences the deformational style in the foreland of fold-and-thrust belts involving multiple décollements. To achieve this purpose we designed an analogue experimental program with a set-up inspired in the Kuqa fold-and-thrust belt. It is based on compressional wedges involving two interlayered weak décollements. The upper décollement is made of pure silicone polymer (simulating salt), it is syn-compressional and its length varies along-strike. The lower décollement is constant thickness and consists of a mixture of sand and silicone polymer (simulating coals and lacustrine mudstones) that changes its mechanical properties laterally. Using this set-up, three syn-tectonic sedimentary rates were tested and results were compared to a baseline model without syn-tectonic sedimentation. Experiments yield results that are consistent with the deformation pattern observed in nature. It provides valuable insights on how the rate of syn-kinematic sedimentation and décollement rheology influences the deformation style in the foreland areas of a fold-and-thrust belt involving multiple rheological different décollements. It also contributes to a better understanding of the previous poorly characterized structure of the Mesozoic units underlying the salt in the Kuqa fold-and-thrust belt, where the main oil reservoirs are found.