Analogue modeling on thickness and property differences of shallow décollement along the strike: insights into the Wushi and Kuqa fold and thrust belts
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    Abstract:

    Décollement is one of the main controlling factors affecting structural deformation of fold and thrust belts. The structural deformation of the Wushi and Kuqa fold and thrust belts in the northern margin of the Tarim Basin was mainly controlled by two sets of basal and shallow décollement, between which are differences in thickness and property along the strike. In this paper, with the objective of studying the influence of these "along the strike differences" on the structural deformation of the Wushi and Kuqa fold and thrust belts, four sets of experimental models were designed based on the analogue modeling method and the geological background of these belts. In the sandbox models, glass microbeads are used to simulate brittle décollement such as in shales and mudstones, and silicone gel is used to simulate the ductile décollement such as in salt rocks and gypsum salt rocks. There are two sets of décollements in the experimental models, in which the basal one is a uniformly distributed brittle décollement, and the shallow one has differences in thickness and property along the strike. The experimental results show that in the sandbox model with double décollements, thickness and property differences of the shallow décollement along the strike play a very important role in controlling the structural deformation and wedge taper of the fold and thrust belts. The specific results are as follows: ① when the thickness of the shallow décollement is variable along the strike, deformation on the thinner side of the shallow décollement restricts the deformation transfer to the thicker side. This results in a relatively short transfer distance of the deformation front of the model and the extension range of the deformation front on both sides of the model is basically the same. The number of faults on the thinner side is obviously larger than that on the thicker side, and the interval between them is smaller. The wedge taper gradually decreases from the thinner to the thicker side. ② When there is a difference in the property of the shallow décollement along the strike, the brittle side shows up-and-down deformation, while ductile side shows up-and-down layered deformation. Under the condition that both sides of the shallow décollement have the same thickness, the propagation speed of the ductile side is generally faster than the brittle side, but the extension range of deformation front on both sides of the final model is basically the same, and the wedge taper decreases gradually from the side of the brittle décollement to the side of the ductile décollement. When the thickness of the shallow brittle décollement decreases, the transfer distance of the deformation front on both sides of the model still tends to be consistent with the continuous increase of the shortening distance, and the overall wedge taper is larger, but the wedge taper on the brittle side is always larger than the one on the ductile side. In addition, the analogue modelling results verify that in the Wushi and Kuqa fold and thrust belts, the difference in the property of the shallow décollement along the strike is the main controlling factor that causes the structural style differences, but it is not the primary reason for the large-scale deflection of the deformation front of the fold and thrust belts.

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LONG Yi, CHEN Hanlin, CHENG Xiaogan, LIN Xiubin, ZHANG Yao, CHENG Ya.2020. Analogue modeling on thickness and property differences of shallow décollement along the strike: insights into the Wushi and Kuqa fold and thrust belts[J]. Acta Geologica Sinica,94(6):1763-1779

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History
  • Received:March 31,2020
  • Revised:May 05,2020
  • Adopted:May 06,2020
  • Online: May 19,2020
  • Published: