Abstract:

Abstract:  The structural features of the Cenozoic contractional deformation in the transition belt between Kuche depression and southern Tianshan uplift have been revealed by geological outcrop, seismic data, welllog and CEMP(Continuous Electromagnetic Profile)data; it is found that these features are difficult to be interpreted by the typical “Atype” subduction model. This article advances a “nonsubduction” contractional deformation model, i.e., the “delaminating contraction and vertically stacking” model. The “delaminating contraction” means that different structural levels developed their own contractional structural style owing to the detachments caused by the salt rock of PaleoceneEocene and the coalbearing series of Jurassic. The “vertically stacking” means that the stronger deformation zones within various levels were stacked up vertically, and the thinskin contractional deformation of cover detachment was stacked up on the top of the basementinvolved contractional deformation, so that the detachment fault could not develop into a regional detachment fault with great horizontal displacement. Detachment folds were developed in the overlying sequence of PaleoceneEocene salt rock, but a fault system assembled with basementinvolved reverse fault, thrust, and inverse fault or normal fault was developed in the underlying sequence of PaleoceneEocene salt rock or Jurassic coalbearing series. The cover folds show the structural pattern with a closed anticline and an open syncline. The asymmetric anticline was detached within salt rock of PaleoceneEocene or coalbearing series of Jurassic and was cut off by a break thrust in the steep limb. A series of basementinvolved thrust with highangle dipping to southern Tianshan dominate the contractional deformation in the basement. A miniscale imbricate wedge thrust system was developed in the footwall of basementinvolved thrust with a highangle dip, and a basementcored faultedanticline was developed in the hanging wall. Most of fault systems in the lower level probably vanished toward the salt rock of PaleoceneEocene or coalbearing series of Jurassic; the highangle basementinvolved thrust tipped upward to the core of detachment anticline in the shallower level, so that the salt rock or coalbearing series was an important transfer level. The highangle basementinvolved thrust may have been formed by the reverse displacement of a preexisting normal fault and led to the local structural deformations. The occurrence of the highangle thrust or the reverse of the preexisting normal fault may be attributed to the dynamics of vertical shearing caused by the uplift of southern Tianshan.

Key words: Key words: contractional structure; structural style; “nonsubduction” model; Southern Tianshan; Kuche Depression