Contractional Structure Model of the Transition Belt between Kuche Depression and South Tianshan Uplift

Abstract

The Cenozoic contractional deformation in the transitional belt between Kuche Depression and South Tianshan Uplift can be hardly deciphered by the typical “A-type” subduction model with the structural features like geological outcrop, seismic data, well-log, and CEMP (Continuous Electromagnetic Profile) data. This article advanced a “nonsubduction” contractional deformation model with “delaminate contraction and vertical stack”. The former, “delaminate contraction”, means that the basement and the cover, even multilevel cover, are of their own distinct contractional structural styles. The latter, “vertical stack”, means the strong deformation zones within various levels are stacked up vertically. No regional detachment fault developed. Detachment folds were developed in shallower cover, whereas fault system assembled with reverse fault, thrust, and inverse fault or normal fault developed in the lower cover and basement. The cover folds express structure pattern of a closed anticline combined with an opened syncline. The asymmetric anticline detached within salt rock of Eocene or coal strata 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 South Tianshan Uplift dominate the contractional deformation in the basement. A miniscale imbricate wedge thrust system developed in the footwall of basement-involved thrust with high-angle dip and a faulted-anticline with basement-cored developed in the hang-wall. Most of the fault system in the lower level disappeared toward the salt rock of Eocene or coal strata of Jurassic. The high-angle basement-involved thrust tip in the core of detachment anticline is in the shallower level so that the salt rock of Eocene or coal strata of Jurassic might be an important transfer level. The high-angle basement-involved thrust could be an inverse fault utilizing the preexisting normal fault and leads to the local structure deformation, thus attributing to the dynamics of vertical shearing resulted from the uplift of Southern Tianshan mountains.